EB1943

Donald P. Hanley and David M. Baumgartner

Forest Ecologyin Washington

EB1943

Developed by

Donald P. HanleyPh.D., CF, Department of Natural Resource Sciences and

Extension, Washington State University

David M. BaumgartnerPh.D., CF, Department of Natural Resource Sciences and

Extension, Washington State University

Contributions from

Jay Berube, USDA-Forest ServiceThomas Brannon, Washington State University

Ann Camp, Yale UniversityJanean Creighton, Washington State UniversityDonna Decker-Robinson, USDA-Forest Service

Peter Griessmann, Washington State UniversityOle Helgerson, Washington State University

Chadwick Oliver, Yale UniversityMichael Pidwirny, Okanagan University College

Roger Ward, USDA Forest Service (retired)

Contents

Introduction .....................................................................................................1Structure, Function, and Change .....................................................................1Scale ..................................................................................................................2Landscapes ........................................................................................................3Energy Flows and Photosynthesis ....................................................................4Cycles ................................................................................................................5

Water Cycle ................................................................................................5Nutrient Cycle ...........................................................................................6

Ecosystem Productivity ....................................................................................6Site Quality .......................................................................................................8Characterizing Site Quality ............................................................................10

Four steps to determine site index ..........................................................11Forest Health ...................................................................................................11Vegetation Patterns .........................................................................................12Vegetation Development ................................................................................13

Role of Disturbance .................................................................................15Dynamic Processes and Stand Development ..........................................18

Forest Development Phases ............................................................................19Stand Initiation or “Open” Phase............................................................19Stem Exclusion or “Dense” Phase ...........................................................20Understory Reinitiation Phase.................................................................21Old Growth or “Complex” Phase ............................................................22Natural and Human-Caused Disturbances Alter Development Phases .. 22

Forests and Trees in Washington ....................................................................22West Side Forest Types .............................................................................22

Coastal Douglas-fir ...........................................................................22Douglas-fir–Western Hemlock ..........................................................22Red Alder ...........................................................................................24Sitka Spruce .......................................................................................24

East Side Forest Types ..............................................................................24Inland Douglas-fir .............................................................................24Grand Fir–Western Hemlock ............................................................25Western Larch ...................................................................................25Lodgepole Pine .................................................................................25Ponderosa Pine .................................................................................25

Forest Ecology Glossary ..................................................................................26

Introduction

A forest ecosystem is not just a collection oftrees. Forests contain living, or biotic compo-nents, and nonliving, or abiotic components.Besides trees, the living portion of the forestincludes herbs, shrubs, other plants, animals,and microorganisms like bacteria and fungi.Nonliving parts of the forest include snags,logs (also known as large organic debris orLOD), the underlying rocks from which soilis formed, and the soil itself, which provideswater, nutrients, and support for the plants.The atmosphere and climate have an effectas well. Fires, frost, drought, windstorms,and other disturbances regularly influenceforest growth and development.

Together, the living and nonliving pieces thatmake up the forests often are referred to as aforest ecosystem. Forest ecologists study howall the parts of a forest are related. The wordecology comes from the ancient Greek word“oikos” meaning “house” and the suffix“ology” meaning “study of.” Just as membersof a household influence each other, changesthat happen in one part of a forest ecosysteminfluence other parts. Timber harvesting andnatural disturbances also change the forest. Itis important to learn to recognize the changesthat occur and how they influence the totalforest ecosystem.

Because forests are so complex, scientistsdo not completely understand how forestecosystems work. As a field of study, forestecology is very broad and theoretical, butalso exciting and useful. From explaininghow one population of soil bacteria relatesto another, to describing why ponderosa

pine will grow well on some sites and noton others, forest ecology deals with virtuallyeverything relating to the forest as a whole.Foresters and landowners know differentorganisms in an ecosystem depend on eachother and that changes to one organism canhave an impact on others. This understand-ing has made people think about how theymanage forested lands and realize that man-agement practices must be based on soundprinciples of forest ecology.

Forest ecology is one of the most importantcourses forestry schools offer. It forms thebasis of silviculture—the art and science oftending forests to achieve management goals.Forest ecology is complex. This publicationpresents key concepts as an aid to good for-est management.

Structure, Function,and Change

Forest ecosystems have three major proper-ties: structure, function, and change. Struc-ture includes the underlying rock and soil, theliving and dead tree and plant material, andthe atmosphere. Function refers to the move-ment and exchange of matter and energy.This occurs between the physical environmentand the living community and between liv-ing community components within andbetween ecosystems. For instance, the foodchain or web represents the flow of energyfrom the producer level (green plants) throughvarious consumer levels (plant-eating ani-mals, carnivores, insects) and decomposer lev-

Forest Ecology in WashingtonForest ecology is the foundation on which good forest management is built.

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els (bacteria, fungi) (Figure 1.) Many functionsare described in terms of cycles—the energycycle, the carbon cycle, the water cycle, andthe nutrient cycle. Ecosystem structure andfunction also interact and change over time.This is why we say forests are dynamic.

Changes in structure and function may influ-ence additional ecosystems. Effects becomeapparent at different scales. An event thatoccurs at one scale may not produce notice-able results at a greater scale, or may causeeffects that magnify at increasingly largerscales. Interactions among lichen popula-tions on the bark of an individual Douglas-fir may not be apparent at the scale of theforest stand. If insects defoliate a few needles,the effect will not be visible at the scale ofthe entire tree, which will survive and con-tinue to grow. If insects eat many needles,they can seriously weaken or even kill thetree. While the death of an individual treeis usually not serious at the stand and land-scape levels, the death of trees in an entirestand or landscape is serious because of thescale. Similarly, the effect on forest floor tem-perature and light will be different if manytrees die or if only a few trees die. If a firedisturbs a small area, the effects on soil ero-sion and water quality will likely be less thanif an entire drainage burns.

If a lightning bolt strikes a lodgepole pine ineastern Washington, the initial impact occursat the scale of the cells and of the individualtree. Cells beneath the bark become so hotthat many die. Cell death causes a stress reac-tion within the tree, since the tree cannotobtain adequate water or nutrients withoutthese cells. One way a coniferous tree reactsto stress is by producing chemicals called ter-penes. The chemicals attract insects such asbark beetles. The beetles colonize the stressedtree, eventually killing it. The effects of asingle lightning-struck tree can spread tothe stand level if other trees in the stand aresufficiently large and crowded. An outbreakof bark beetles may occur, originating at thelightning struck tree. If many trees in thestand are attacked, most will die. The buildupof dead trees in the stand can increase theamount of fuels. If lightning were to strikewithin this stand again, the result might befurther magnified as a large fire that destroysmany stands across the landscape. Distur-

GREENPLANTS

GRAZERS

PREDATORSDECOMPOSERS

Figure 1—The Food chain. Green plants take upnutrients decomposers have returned to the soil. Inturn, grazers, their predators, and other predators eatthe plants. The bodies of grazers, predators, and greenplants are decomposed and returned to the soil.

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Scale

Scale is the frame of reference we use to definean ecosystem. The term “ecosystem” does notimply any particular size. Ecosystems rangefrom quite tiny to very large. (Figure 2). Thepopulation of lichens on the bark of a Dou-glas-fir forms an ecosystem. All the plants andanimals in a particular watershed also forman ecosystem. Both are ecosystems having adifferent scale. If we start by thinking aboutone scale, that of the individual tree, smallerscales would include a leaf on that tree, oreven a single cell within that leaf. We canthink about and observe larger scales: a recog-nizable unit of the forest, called a stand, oreven an entire drainage or landscape madeup of many interacting ecosystems.

bances such as this lightning strike examplealso might result in biodiversity changes thatcould be beneficial. As such, the increase inbark beetles attracts insect-eating birds, whichin turn may increase cavity excavation in thedead and dying trees. Cavity increase mayinfluence small mammal numbers, whichmay influence the number of predatory birds,such as owls.

In the past, forest ecology concentrated onstudying interactions at the scale of individualstands. Now, landscape-scale interactions alsoare considered important. Think of a forestlandscape as a mosaic or collage of many for-

Figure 2. Small ecosystems exist within largerecosystems.

Stand/Site(<500 acres)

Watershed(5–20M acres)

Landscape(<2MM acres)

Region(>2MM acres)

World(<Universe)

est stands. Landscapes can be fairly homog-enous—all stands can be similar in age andspecies composition. Heterogeneous, or mixedlandscapes are made up of stands that differfrom each other in age, composition, or both.Diverse landscapes usually result from pastdisturbances (fire, weather, insects, diseases)and topographic features.

Landscapes

A landscape-scale ecosystem is made up ofgroups of smaller interacting ecosystems. Likeall ecosystems, landscapes have the attributesof structure, function, and change. Land-scape structure refers to the sizes, number,kinds, and configurations of ecosystems thatmake up the landscape. Landscape functionrefers to the flows of energy, materials, nutri-ents, and species among ecosystems. Land-scape change refers to alterations in the struc-ture and function of the mosaic of ecosystemsover time.

Historically, landscape patterns were createdand maintained by natural disturbance. Inmanaged landscapes, political boundaries andmanagement decisions affect these patternsand often the character of disturbances. Eco-systems and landscapes change over timeas a result of vegetation development anddisturbances.

In western Washington, large, infrequent firescreated and maintained relatively homoge-neous landscapes. Urban development andtimber harvesting have fragmented this land-scape, altering these ecosystems. EasternWashington landscapes were historicallypatchy because frequent, low to moderatelysevere fires created a mosaic of different-agedforests across the landscape. During the pastcentury, fire suppression has allowed densefire-prone stands to establish and grow acrossthe landscapes. This, coupled with poor

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selective logging or “high grade” loggingpractices earlier in this century, has createdmuch more uniform landscapes than existedhistorically. These landscapes are more sus-ceptible to outbreaks of insects, diseases, andcatastrophic fires.

Energy Flows andPhotosynthesis

Forest ecosystems are driven by solar energythrough the process of photosynthesis (Figure3). Trees and other green plants convert lightenergy from the sun into chemical energy.The leaves or needles capture solar energy(light) and convert carbon, hydrogen, andoxygen to simple sugars. These are then con-verted into more complex compounds suchas cellulose, the main component of wood

fiber. A mature forest produces many tonsof sugars and other compounds per acre eachyear. Of these compounds, the leaves useapproximately 70%; about 5% is convertedto wood, branches, and fine roots, and 25%maintains tree functions. This maintenanceis referred to as respiration. As forests age,more energy captured each year goes intorespiration instead of into the productionof wood, branches, roots, or leaves.

Although a complete understanding of pho-tosynthesis is beyond the scope of this publi-cation, the faster and more efficiently a treecarries on photosynthesis, the faster it willgrow and the less vulnerable it will be toinsects and disease. This is primarily a func-tion of the size of the live crown, actually thetotal leaf area (to capture light), and availablesoil nutrients and water. When a tree or partsof a tree die, it begins to decompose. Themicrobes and other organisms that decom-pose the twigs, leaves, and wood use someof the energy stored in the tree parts. Muchof it remains in organic material that accu-mulates on the forest floor. Following a dis-turbance that removes most of the vegetationfrom an area, the increased light and tempera-ture at the forest floor increase the rate ofdecomposition—that is, the rate at which theenergy stored in the organic matter is released.Recovery of ecosystem structure and func-tion following a disturbance is powered bysolar energy stored in the forest floor.

Some of this stored energy is lost throughgrazing and browsing by herbivores, suchas squirrels, rabbits, grouse, deer, and elk. Asthese animals eat, they use the energy theyconsume to build tissue, such as muscle, fat,and bone. In turn, these herbivores becomefood for forest carnivores and the energy istransformed again, used in the developmentof body mass for these species. When an ani-mal dies, the energy once again is transformedinto food for decomposers and soil microbes.This transformation of energy from plant toanimal tissues also contributes to the dynamicnature of the forest ecosystem. Through

Figure 3. Trees and other green plants convert lightenergy from the sun into chemical energy throughphotosynthesis. The leaves or needles of trees capturesolar energy (light) and convert it to complex sugarsand starches made up of carbon, hydrogen, andoxygen.

Photosynthesis Cycle

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photosynthesis, forests accumulate biomassand stored energy, which cannot build up for-ever. Ultimately, this energy will be releasedthrough microorganisms, fire, or humanactivity.

Cycles

Ecosystem function—the exchange of energyand material within and between ecosystems—can be characterized as the interaction ofseveral cycles, such as water and nutrientcycles. Cycle rates vary. Some cycles operateat regional or global scales and over longperiods of time, so that material movementat smaller scales appears to go only in one

direction. Soil movement is a good example.Soil moves down slope. It can move rapidlyand in great quantities, as in a landslide, orgradually, as gravity moves particles slowlyfrom ridge top to valley bottom. All cyclesare powered by solar energy.

Water CycleThe water cycle also is referred to as the hydro-logic cycle. Rain or snow falling through theatmosphere first strikes the forest canopy(Figure 4). Some is intercepted by needlesor leaves and may evaporate back into theatmosphere or be delayed before reachingthe ground. Some water directly reaches theground. In areas where vegetation is sparseand the soil is compacted, the soil cannotabsorb much of the water, and the water

Hydrologic Cycle

Figure 4. Water or hydrologic cycle.

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flows over the soil surface, picking up soilparticles. Eventually, this overland flowmay reach a stream channel and transfer toanother ecosystem, along with the soil par-ticles and nutrients dissolved in it. If the for-est floor is intact, most precipitation reachingthe ground will move into the soil. The rootsof trees and other vegetation usually take upwater in the soil before the water reaches astream channel. The trees will store someof this water, while some will return to theatmosphere through transpiration. Basically,transpiration is the process by which water ispulled first from the soil by tree roots, thenpulled up the tree through xylem tissue andinto the leaves or needles. The leaves containsmall openings called stomata that continuethe pull of moisture, allowing it to escapeback into the atmosphere. [You can see thestomata as the thin white lines (termedstomatal bands) on the bottom of noble firand subalpine fir needles.]

Nutrient CycleA properly functioning forest ecosystem isable to acquire, store, and recycle nutrients.(Figure 5).

Energy flows power the interconnected waterand nutrient cycles. Through transpiration,the water cycle drives much of the circulationof nutrients within the ecosystem. Many dis-solved nutrients are held within the soil water.These nutrients are lifted into the canopy bytranspirational pull and eventually returnedto the soil through needle fall and decompo-sition. Transpiration also controls photosyn-thesis. When not enough moisture is availablein the soil for trees to transpire effectively,plants close their stomata to reduce transpi-ration. Photosynthesis also is reduced. Thisis why trees do not grow as fast when mois-ture is limiting.

A forest ecosystem, burned so severely thatlittle organic matter remains in the soil, couldlose much of its nutrient capital througherosion and streamflow. If no present vegeta-

tion is available to take up nutrients, and iffew soil organisms are present to store thenutrients, they frequently are washed intostreams and flow out of the area. In somecases, replacing these lost nutrients can takehundreds of years.

The woody parts of trees tie up only smallamounts of nutrients. Traditional harvestingmethods remove only minor amounts of asite’s nutrient capital. Most nutrients occurin the needles, leaves, or fine roots of trees.Whenever possible, leave these tree parts onthe ground after logging so the nutrients willbe available to be cycled.

Ecosystem Productivity

The measurement of productivity providesus with an indication of the rate of photo-synthesis and biomass accumulation in acommunity. Although all biological activityin plants ultimately depends on receivedsolar radiation, solar radiation alone doesnot determine gross primary productivity.All plants require sunlight, carbon dioxide,water, and soil nutrients for photosynthesis.Photosynthesis also depends on temperature,moisture, and nutrient availability. Tempera-ture (heat) controls the rate of plant metabo-lism, which in turn determines the amountof photosynthesis that can take place. Mostbiological metabolic activity takes placewithin the range 0°C to 50°C. There is littleactivity above or below this range. The opti-mal temperatures for productivity coincidewith 15°C to 25°C (59°F–77°F) optimal rangeof photosynthesis. The graph in Figure 6illustrates the relationship between the netprimary productivity of forests and annualair temperature.

The general relationship between net pri-mary productivity and precipitation for for-ests is shown in Figure 7. Water is a principalrequirement for photosynthesis and the main

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Figure 5. Nutrient cycle.

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chemical component of most plant cells. Indry regions, there is a linear increase in netprimary productivity with increased wateravailability. In the more humid forest climatesof the world, plant productivity begins to leveloff at higher levels of precipitation. The pro-ductivity of plants, especially at the localscale, also can be controlled by the availabil-

Temperature ° C

Dry

-Mat

ter

Pro

duc

tivi

ty(g

m-2

yr-

1 )

3000

2500

2000

1500

1000

500

0-10 -5 0 5 10 15 20 25 30

Precipitation (mm)

Dry

-Mat

ter

Pro

duc

tivi

ty(g

m-2

yr-

1 )

3000

2500

2000

1500

1000

500

00 1000 2000 3000 4000

Figure 6. Relationship between forest net primaryproductivity and annual temperature. (Adapted fromLieth, H. 1973. Primary production: terrestrialecosystems. Human Ecology 1: 303–332).

Figure 7. Relationship between forest net primaryproductivity and annual precipitation. (Adapted fromLieth, H. 1973. Primary production: terrestrialecosystems. Human Ecology 1: 303–332).

ity of nutrients. About 20 to 30 elements gen-erally are considered essential for plant metab-olism and growth. These essential nutrientsare sometimes grouped into two categories:macronutrients and micronutrients. Plantsuse the macronutrients for the constructionof structural molecules and for building a vari-ety of organic molecules used in metabolicprocesses. Only two of the macronutrientsused by plants normally occur in limitingconcentration for plant uptake: nitrogen andphosphorus. When limiting, these two nutri-ents control the amount of plant productivitythat can occur. Plants require micronutrientsin extremely small quantities for the creationof less common organic molecules or as ionsto catalyze specific metabolic reactions. Ingeneral, micronutrients are common in abun-dance and do not limit plant production.

Site Quality

Foresters refer to the sum of all the naturalfactors that influence forest vigor, health,and growth as the site. Additionally, forest-ers frequently talk about site index, or referto relative productivity of sites. What theyreally are talking about is the combinationof environmental influences such as climate,soil texture, soil nutrients, slope, aspect, andelevation. These factors affect where treespecies grow, how rapidly they grow, howhealthy they are, and their form at maturity.

Slope, aspect, and elevation combine withlocal climate conditions to determine themicroclimate of a site. For example, gentlysloped, northeast-facing slopes tend to becool and moist, while steep, southwest slopes,which face the sun in the afternoon, tendto be warm and dry. High elevation sites arecolder and more exposed to wind than sitesdeep within a valley. However, frost pocketsmay exist in low-lying areas where air drain-age is restricted. The orientation of a valleydetermines its exposure to prevailing winds.

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Just by knowing the aspect, elevation, andslope of a site (and whether it is east or westof the Cascades Mountains), one can makesome predictions about its potential produc-tivity and which species will grow well there.For example, in western Washington onnortheast slopes below 1000 feet elevation,Douglas-fir—western hemlock forests domi-nate. Northern aspects often result in Douglas-fir—western hemlock—western white pineforests. In eastern Washington, ponderosapine forests usually grow at lower elevationsthat have hot and dry southern aspects. Slopeposition is also important. On wet or poorlydrained riparian areas, western redcedar, redalder, Oregon ash, or black cottonwood maydominate on the west side. On the east side,western redcedar, black cottonwood, Engel-mann spruce, or subalpine fir may dominate.

One of the most important things to knowabout a site is the nature and condition ofthe soil. Forest soils are made up of four mainingredients: mineral particles, organic mat-ter, water, and air. The minerals it containslargely determine soil fertility. Soils derivedfrom basalt or volcanic ash tend to be morefertile than those derived from granite orsandstone, because basalt has a greater con-centration of nutrient-bearing minerals thaneither granite or sandstone.

The physical properties of a soil—whetherit is fine or coarse—depend on the type ofminerals present and on the size of the soilparticles. The three basic soil particle sizesare sand, silt, and clay. Sand is the coarsestsize; clay is the finest. Sand is very porousand normally does not contain many nutri-ents. Clay is very nutrient-rich but drainspoorly and is easily compacted. Soil texturerefers to the proportions of sand, silt, andclay particles in a particular soil. Soils thatcontain a large proportion of clay and silthave a fine texture. Finer soils are usuallymore productive than coarse soils, but finesoils do not drain as quickly, are very suscep-tible to damage from compaction, and aremore easily eroded than coarse soils. A soil

made up of roughly equal amounts of sand,silt, and clay is referred to as a loam. Loamstend to be fertile and hold water, withoutbecoming overly wet.

Organic matter—rotting debris such as needles,leaves, and twigs—strongly influences thephysical and chemical properties of a soil.Soils having large amounts of organic matterhave better structure and greater fertility.Organic matter also helps forest soils holdwater. However, too much organic matter,such as in a poorly drained bog, can tie upnutrients, making them unavailable to livingvegetation, including trees. Thick layers oforganic matter on the forest floor can hinderseed germination for some tree species, suchas ponderosa pine, Douglas-fir, and westernlarch.

More than half the volume in the upper layersof an undisturbed forest soil can be made upof air and water. The proportion of air andwater is both affected and determined bythe physical properties of the soil. Since rootsneed air to respire and water to supply therest of the tree, the air and water componentsof a soil are very important. More than halfthe “feeder” roots in a forest occur in the top6 inches of soil. Soil compaction reduces theamount of space available for air and water,and lowers site productivity. This is why it isso important for rubber-tired skidders to stayon established trails, especially on sites havingwet or fine-textured soils that tend to com-pact easily.

Soils contain living matter too. Fungi, bacte-ria, insects, and a host of tiny creatures liveon organic matter produced by trees andshrubs. Even though we cannot see most ofthem without a microscope, these organismsare absolutely essential to the growth anddevelopment of forests. Although some occa-sionally cause disease in trees, most soil organ-isms feed on fallen leaves and woody debris.Their main role is to recycle nutrients likephosphorous, potassium, and calcium tiedup in dead vegetation and animals. During

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the process of decomposition, nutrients lockedup in dead vegetation and animal carcassesare ingested by soil microorganisms andreturned to the soil upon the death of thesedecomposers. Without them, the forest floorwould be littered with debris accumulatedover thousands of years, and trees would bestarved for the nutrients locked up in thismaterial.

A group of soil organisms known as mycor-rhizae-forming fungi actually colonize theroots of some trees and greatly improve theirability to take up water and nutrients. Thetree and the fungus depend on each other;the tree provides food to the fungus whilethe fungus transfers water and nutrients tothe tree and provides protection againstharmful soil organisms. Mycorrhizal fungiare highly susceptible to changes in environ-mental conditions, especially those causedby soil compaction. Forestry operationsmust take into consideration these unseen,but very important components of forestecosystems.

Characterizing SiteQuality

Site quality refers to the productive capacityof a forest stand. Site quality knowledge isuseful for predicting potential growth anddetermining management priorities. Sitequality is affected by factors such as soildepth, soil texture and composition, slope,elevation, and aspect. Forests on the east sideof the Cascades, on gentle slopes, north ornortheast aspects, and cool, moist areas areusually the most productive. In west side for-ests, the best sites are those having deep non-glaciated soils at lower elevations. Erosionor soil compaction can degrade site quality.

Site quality can be measured by many meth-ods. Foresters often estimate site quality bythe approximation called site index. Site

index is based on dominant tree height, theaspect of tree growth least affected by com-petition from surrounding trees. Dominanttree height is compared with an expected treeheight (from a site index table) to estimaterelative productivity (Figure 8). For example,a site index of 120 for ponderosa pine meansthe site is capable of producing trees 120 feettall when the stand is 100 years old—an aver-age for a good site in east side forests. A siteindex of 80 for the same species is a less pro-ductive site. Because growth is more rapidwest of the Cascades, tables generally use 50years as the index age. Excellent Douglas-firsites in western Washington range from 140to 180 feet with a 50-year base. Sometimessite index is described in relative terms, ona scale of I to V (Roman numerals) with siteI being the best and site V the poorest.

If a stand site index is known and if goodyield tables exist for the species in the region,the volume of wood a stand will produce overtime can be predicted with reasonable accu-racy. However, site index is rarely used topredict yield; rather, it is commonly used todetermine the relative productivity of standson a tract of forest land.

Many foresters learn how to visually estimatesite index and will do measurements occasion-ally as a check. How do they do this? Throughexperience, the same way a seasoned loggercan “sight cruise” a stand of timber and arriveat a remarkably accurate estimate of volume.Experience is aided by visual clues from thestand. Size and form of trees, the height andcondition of their crowns, bark characteris-tics, and the presence or absence of certainindicator plants all factor into the equation.Stem taper, bark appearance, and species com-position of the stand are three good indica-tors of site quality. Although straight stemswith tall, full crowns may be inherent geneticcharacteristics of a species, they are more aptto be a full expression of the capabilities ofthe tree on a favorable site. The same tree ona poor site will be shorter and have a sparsecrown and tapered bole.

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Use the following four steps todetermine site index:1. Select six to eight trees to measure. They

should be trees that have been dominantthroughout their lives, relatively free ofdisease or injury, sound enough to deter-mine age, and without visible crowndamage or height growth interruption.

2. Measure the height of the selected treesand calculate their average height.

3. Determine the age of these trees. Incre-ment borings are generally taken atdiameter at breast height (DBH) (4-1/2')above the ground. Average the ages ofthe selected trees.

4. Determine site index using site indextables or curves for the species and region.

Forest Health

Forest health has been defined as the condi-tion of a forest when it is

• resilient to change, it can recover froma disturbance.

• biologically diverse over a large area(landscape diversity), and

• able to provide a sustained habitat forvegetation, fish, wildlife, and humans.

A healthy forest is made up of trees and otherorganisms all dependent on each other.The presence of single or a small group ofunhealthy trees does not necessarily indicatean unhealthy forest. For example, bark beetlescan actually promote forest structural diver-

Figure 8. Site Index Table for Ponderosa Pine, 100-year Basis.

AGE (Years)0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360

TOTA

L H

EIG

HT

(Fee

t)

0

20

40

60

80

100

120

140

160

180

200

220

240

260

40

60

80

100

120

140

160

SITE INDEX

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sity. A professional forester can help youdetermine the severity of a forest healthconcern.

Just as humans need a certain combinationof food, water, and exercise to maintain physi-cal health, forests and the trees require certaininputs to maintain their health and growth.If one or more of these inputs is missing orinsufficient, trees experience stress. Forestmanagers can influence these inputs throughsilvicultural practices.

One of the major health concerns in Wash-ington forests is stress caused by having toomany trees per acre, or overstocking. Over-stocking causes tree stress because it forcestrees to compete with surrounding trees forlimited light, water, and nutrients. Many sil-vicultural practices are effective because theyreduce the number of trees per acre and, thus,the competition for these essential elements.Other stress factors may include air pollution,soil compaction, and climate changes.

The first requirement for healthy tree growthis light. Through photosynthesis, plantsmanufacture their own food by using thesun’s energy to convert carbon dioxide andwater to a usable food source. Heavy shade,found underneath the closed canopy of aforest, provides insufficient energy for thesmaller, less dominant trees to grow. Shade-intolerant species have great difficulty grow-ing under these circumstances. These includepines and larches. Other species, such as Dou-glas-fir, Engelmann spruce, and most hard-woods, are considered moderately shadetolerant. They can grow in partial shade.The tolerant species—grand fir, hemlock, andwestern redcedar—can grow under conditionsof heavy shade, although not very fast. Athinning operation can release slow-growing(suppressed) trees by providing them morelight and space in which to grow.

The second requirement for healthy treegrowth is water. Tree species vary consider-ably in their water needs and drought toler-

ance. Shade-intolerant species commonlygrow in hot, sunny areas and are moredrought resistant. Shade-tolerant speciesgrow naturally in the cool, moist forest.When drought occurs, which happensfrequently in all western states, these shade-tolerant species are more stressed than theshade-intolerant species. Thinning reducesthe total number of trees competing forwater and can relieve drought stress. How-ever, overthinning (the removal of too manytrees) may increase the amount of sunlightreaching the ground and dry out the areamore rapidly. This is especially true on steepterrain.

The third requirement is a good nutrientsupply. Trees take up minerals through theirroots and incorporate them into developingcells. One of the basic determinants of poten-tial tree growth is the level of nutrients avail-able in the soil. Nutrient-poor soils will neverproduce large trees, and even rich soils can-not produce large trees if they are overstocked.A forest manager may thin a stand to reducecompetition for nutrients. Although it is notalways cost effective, using a fertilizer on for-est soils can provide needed tree nutrients.

Vegetation Patterns

Northwest ecosystems contain many differ-ent vegetation patterns, ranging from brushfields to old growth forests, and includingevery successional stage in between. Collec-tively, the types, amounts, and distributionof vegetation patterns define water quantityand quality, timber resources, wildlife habitat,and many other important ecosystem char-acteristics. Vegetation patterns also impactforest processes such as streamflow, erosion,and succession.

Northwest forest landscapes are created andmaintained through a balance of disturbanceand recovery processes. Disturbance alters a

12

portion of the current forest stand. A newforest grows, declines, and is again replaced.Ultimately, all living biomass is recycled.Disturbance and restoration processes createa sustainable cycle that conserves both bio-logical capacity and options for future forests.Disturbance requirements within ecosystemsvary greatly in intensity and frequency. Themost common forms of disturbance that haveinfluenced Northwest forest ecosystems inthe past are fire, wind, ice, insects, and dis-ease. We have altered historical forest ecosys-tems by creating unnatural disturbances, suchas excessive logging, urbanization, and over-grazing, while suppressing fire. Consequently,these forests have different fire, insect, dis-ease, and hydrologic disturbance cycles andprocesses. Fires in some areas are larger andmore severe than in the past. Insect attackslast longer and spread wider. Sites favorablefor tree disease are expanding. Vegetationcover in riparian areas has been diminishedand stream structure has grown less complex,reducing fisheries habitat.

Human-caused disturbances can be used inmanagement to proactively mimic naturaldisturbances (anthropogenic or human dis-turbances such as fires set by Native Ameri-cans have been a part of many landscapesfor centuries) and to help with restorationactivities.

Vegetation Development

Vegetation development refers to the pro-cesses of change that occur in forest standsand landscapes over time. In the absenceof past disturbances, changes in the speciescomposition of a forest are slow but con-tinuous. The process of continual change isreferred to as succession. Forest managementis based on the fact that the direction of forestsuccession is both predictable and control-lable. “Direction” refers to the gradual orderof species replacement from intolerant to

tolerant—or the scaling back of succession asa result of natural disturbances or silviculturalmanipulation. If forest succession progressesto a more-or-less stable vegetative state overtime, we define this vegetative association asa Habitat Type. Thus, Habitat Types reflectthe climax vegetation in a location. HabitatTypes often are defined by the dominantoverstory tree species and the understory forforest floor complex. One common HabitatType in eastern Washington is the Douglas-fir/ninebark Habitat Type.

The rate at which succession proceeds canbe increased or decreased by altering the spe-cies composition and density of species inthe forest. Disturbances influence rate anddirection of succession, while forestry prac-tices mimic natural disturbances. Thinningsmall trees in the understory mimics groundfires or natural mortality in a stand. Harvest-ing the dominant and co-dominant trees ina stand can have results similar to those fol-lowing a windstorm that removes the over-story. (Figure 9).

A key concept to understanding why succes-sion occurs is tolerance. Though tolerance isreally the degree to which a species can suc-cessfully compete for site resources (light,moisture, and nutrients), it is most often usedwith respect to light and, thus, is referred toas shade tolerance (Table 1). Pioneer or earlysuccessional species such as red alder, westernlarch, and ponderosa pine are often extremelyintolerant of shade. They are not able to growor reproduce in shaded conditions. Mid-tol-erant or intermediate species can grow inpartial shade, and late-successional speciesare able to grow and reproduce in heavyshade. As a result, unless interrupted bydisturbances that remove all or part of thecanopy, forest succession usually proceedstoward more shade-tolerant species.

For example, in western Washington, Dou-glas-fir, western hemlock, and western red-cedar occur together in many forest stands.Of the three, Douglas-fir is the least tolerant

13

Figure 9. Forest Succession is the Gradual Change in the Species of a Forest Stand over Time.

2000

2010

2020

2030

2040

of shade and will almost always be foundonly in the overstory. Western hemlock andwestern redcedar, both very tolerant of shade,can exist in either the overstory or in theunderstory. As overstory trees die, cedars andhemlocks in the understory will grow into

the overstory. If many centuries pass with-out fires or logging, the stand will increas-ingly be composed of western redcedar andwestern hemlock. In eastern Washington,western larch is a very shade-intolerant speciesthat grows rapidly and may quickly dominate

14

some forest stands following fires. Moreshade-tolerant species such as grand fir orsubalpine fir are able to grow beneath thelarch; however, because of its intolerance forshade, larch only appears in the overstory.

Two additional concepts provide a frame-work for understanding vegetation develop-ment patterns. These concepts are growingspace and disturbance. Growing space refersto the availability of all the requirementsa plant needs to grow. The most importantrequirements—or growth factors—are light(for photosynthesis), water, and nutrients.Each tree in a forest uses these growth fac-tors until one or more becomes unavailable.When that occurs, the growing space is essen-tially filled. No new plants can establish,and the ones already there must competewith each other to gain more growing space.Plants that compete the best get more grow-ing space and continue to grow. The losersoften die. This competition ultimately causesforest succession.

The amount of growing space varies in timeand in space. Light is most generally abun-dant for trees in the upper canopy but maybe extremely limited at the forest floor. Some-times light reduction at the forest floor canbe as much as 97% of that in open conditions!Some species are able to tolerate growingconditions (such as low light levels) that arenot adequate for other species. Differencesamong species are not great, but can givesome species a competitive advantage on aparticular site. For instance, ponderosa pine

needs more light to grow than does Douglas-fir. In the understory, Douglas-fir seedlingshave a competitive advantage over ponde-rosa pine. Growing space also can changeover time. In much of the Pacific Northwest,moisture is limited during the dry summermonths but seldom during the fall, winter,and spring. As a young stand matures, somenutrients may become tied up within the veg-etation, limiting further growth, especiallyon coarse-textured soils.

Each tree species has a unique collection ofsilvical characteristics, or how the individualtree interacts with the environment. Thesecharacteristics are summarized for youngtrees growing in both eastern and westernWashington in Tables 2 and 3.

Role of DisturbanceDisturbances play an important role in deter-mining forest structure and species composi-tion. Natural disturbances are quite commonin all regions of the world. Every area hascharacteristic types of disturbances that occurat relatively predictable frequencies. CoastalWashington is subject to periodic windstormsor “blows” that knock down overstory trees,allowing seedlings in the understory to grow.On the western slopes of the Cascades, large,infrequent fires have provided conditionsfavorable for Douglas-fir to germinate andgrow. East of the crest, many areas had his-toric fire regimes consisting of frequent, lowintensity ground fires that killed competingseedlings, but spared, or only scarred, thick-

Table 1. Shade Tolerance of Commercially Important Conifers in Washington

Extremely Intermediate ExtremelyTolerant Tolerant Tolerance Intolerant Intolerant

Western Hemlock Grand Fir Inland Douglas-fir Coastal Douglas-fir Lodgepole PineWestern Redcedar Subalpine Fir Western White Pine Noble Fir Western Larch

Pacific Silver Fir Engelmann Spruce Ponderosa Pine Alaska Yellow Cedar Sitka SpruceMountain Hemlock

15

Tab

le 2. Eastern

Wash

ington

Species C

haracterization

—A

Sum

mary for You

ng Trees*

Western

Western

Do

uglas-

Gran

dW

esternW

esternEn

gelm

ann

Lod

gep

ole

Black

Subalp

ine

Pon

dero

saLarch

Wh

ite Pine

fir Fir

Hem

lock

Red

cedar

Spruce

Pine

Cottonw

oodFir

Pine

Where is Species Found?

Hot—

Dry Environm

entN

oN

oM

aybeN

oN

oN

oN

oN

oN

oN

oYes

Cool—

Wet Environm

entYes

YesYes

YesYes

YesYes

YesYes

Maybe

No

Cold—

Wet Environm

entYes

Maybe

No

Maybe

Maybe

YesYes

YesN

oYes

No

Cold—

Dry Environm

entN

oN

oN

oN

oN

oN

oN

oYes

No

YesN

o

What species to Plant?

Ponderosa Pine Habitats

No

No

No

No

No

No

No

No

No

No

YesD

ouglas-fir Habitats

YesN

oYes

No

No

No

No

Maybe

Maybe

No

YesG

rand Fir Habitats

YesYes

YesM

aybeN

oN

oM

aybeYes

Maybe

No

YesW

estern Redcedar Habitats

YesYes

YesYes

Maybe

YesYes

YesYes

No

YesW

estern Hem

lock Habitats

YesYes

YesYes

YesYes

YesYes

Maybe

No

No

High Elevation H

abitatsYes

Mayb

eN

oN

oN

oN

oYes

YesN

oYes

No

Frost Pocket Habitats

YesYes

No

No

No

No

YesYes

No

YesN

oRip

arian Habitats

Maybe

YesYes

No

YesYes

YesYes

YesM

aybeM

aybe

Time of Year to Plant

Spring

Spring

Spring

Spring

?Sp

ringSp

ringSp

ringSp

ringFall

Spring

or Fallor Fall

or Fallor Fall

What is Expected?

Early SurvivalFair

ExcellentG

oodFair

FairG

oodG

oodExcellent

Good

Good

Good

Early Grow

thExcellent

ExcellentFair

FairFair

PoorFair

ExcellentExcellent

FairG

ood

Is Genetically Im

proved Stock Available?

?Yes

YesYes

??

?N

oYes**

No

Yes

Species Characteristics

Shade ToleranceVery Low

Medium

Medium

High

Very High

High

High

LowLow

High

LowW

et Ground Tolerance

FairFair

PoorFair

Medium

High

FairM

ediumVery H

ighLow

PoorTolerates Rocky or Sandy Soils

PoorPoor

Medium

Medium

Medium

PoorM

ediumH

ighLow

High

High

Rebounds from Physical

Dam

agePoor

PoorM

ediumM

ediumPoor

High

Medium

High

PoorPoor

High

Vulnerable toW

eed Com

petition

Maybe

Maybe

YesYes

YesYes

Maybe

Maybe

Maybe

Medium

YesSnow

BreakageN

oN

oM

aybeM

aybeN

oN

oM

aybeN

oYes

No

Maybe

Drought

No

YesM

aybeM

aybeYes

YesYes

No

YesM

aybeN

oH

eatN

oM

aybeYes

YesYes

YesYes

No

YesYes

No

Late Spring Frost

Maybe

Maybe

YesYes

Maybe

No

No

No

YesN

oN

oA

nimal D

amage

YesYes

YesYes

Maybe

LowLow

YesYes

No

YesG

razing (eaten)Yes

YesYes

YesYes

YesYes

Maybe

YesN

oM

aybeRoot D

iseasesYes

YesM

aybeYes

YesN

oM

aybeN

oIm

mune

YesN

oStem

Diseases

No

YesYes

YesYes

YesYes

YesYes

YesN

oInsects

YesN

oYes

YesYes

No

Maybe

Maybe

YesYes

Maybe

Yearly Frequency of Good

Seed Crops

4–85+

3–63–6

3–62–4

4–83–5

13–6

4–8

* Adap

ted by Don H

anley from num

erous sources and personal exp

erience. Use as a general guide only.

** Do not use hybrids in native ecosystem

s.

16

Western Douglas-fir Grand Fir Western Western Sitka Red Alder Noble FirWhite Pine Hemlock Redcedar Spruce

Where is Species Found?Hot—Dry Environment Maybe Yes No No No No No NoCool—Wet Environment Yes Maybe Yes Yes Yes Yes Yes YesCold—Wet Environment Maybe No No Yes Yes No No Yes

What species to Plant?Douglas-fir Habitats Yes Yes Yes Yes Yes No Yes MaybeGrand Fir Habitats Yes No Yes Yes No No Yes YesWestern Redcedar Habitats No Yes Maybe Yes Yes Maybe Yes NoWestern Hemlock Habitats No No No Yes Yes Maybe Yes NoHigh Elevation Habitats Maybe No No No No No No YesCoastal Habitats Maybe No No Yes Yes Yes Yes No

Time of Year to Plant Fall Fall Fall Fall Fall Fall Fall Fallor Winter or Winter or Winter or Winter or Winter or Winter or Winter or Winter

What is Expected?Early Survival Excellent Excellent Fair Fair Fair Fair Good FairEarly Growth Excellent Excellent Fair Fair Fair Good Good Fair

Is Genetically Improved Stock Available? Yes Yes ? ? ? ? No ?

Species CharacteristicsShade Tolerance Medium Low High Very High High Low Very Low LowWet Ground Tolerance Fair-Low Poor Fair Medium High High High MediumTolerates Rocky or Sandy Soils Medium Medium Medium Poor Poor Poor Poor MediumRebounds from Physical Damage Poor Poor Poor Poor High Medium Poor Poor

Vulnerable toWeed Competition Maybe Yes Yes Yes Yes Maybe Low YesSnow Breakage No Maybe Maybe No No Maybe High NoDrought Maybe Yes Maybe Yes Yes Yes High YesHeat Maybe Maybe Yes Yes Yes Yes High YesAnimal Damage Yes Maybe Yes Maybe No No High YesGrazing (eaten) No Yes Yes Yes Yes No Low YesRoot Diseases Yes Yes Yes Yes No Maybe Immune YesStem Diseases Yes Maybe Yes Yes Yes Yes Yes YesInsects No Yes No No No Yes Low No

Yearly Frequency ofGood Seed Crops 5+ 5–7 3–6 3–6 2–4 4–8 1 4–8

* Adapted by Don Hanley from numerous sources and personal experience. Use as a general guide only.

Table 3. Western Washington Species Characterization—A Summary for Young Trees*

barked mature ponderosa pine or westernlarch. Lodgepole pine stands often had a lifecycle featuring outbreaks of mountain pinebeetles followed by catastrophic fires thatperpetuated the species. Insects and diseaseskilled some trees, creating snags and logsthat provided important habitat for wildlife.The type of wildlife using these structuresdepended on the disturbance that createdthem. For instance, stem decay fungi often

produced soft snags useful for cavity nestingbirds and animals. Douglas-fir mistletoe cre-ates large witches-brooms used as nesting andhiding sites for some birds. But the broomsalso can allow wildfires to move from theground into the crowns of infested trees.

To create sustainable forest ecosystems, con-serving disturbance processes is as importantas conserving individual species. Timber har-

17

vests and prescribed fires can mimic manyeffects of wildfire and other disturbances.However, we need to balance such naturaldisturbances with needs for wildlife, aquaticresources, and sustainable commodity pro-duction. Ultimately, these goals may dependon sustaining the broader ecosystem throughmanaged disturbance.

Disturbances change the availability of grow-ing space. Disturbances that remove the over-story—for example windstorms or timberharvesting—change the amount of light thatreaches the forest floor. Disturbances thatremove organic matter and soil—some fires,landslides, and site preparation techniques—reduce the amount of nutrients and, thus, thetotal amount of growing space on a particu-lar site. Disturbances that remove most of thevegetation on a site increase the amount oflight, moisture, and nutrients available fornew plants to utilize.

Following a disturbance, surviving plantsand new ones expand into the now-availablenew growing space. The plants that grow thefastest and capture the most growing spacecan dominate the stand for decades; such isthe role of red alder on the west side of theCascades. Trees in the open grow more quicklythan those in the understory. In managedstands, thinning and harvesting can controlthe amount of light available to trees. Remov-ing part of the stand allows more availablelight for the remaining trees. In a youngstand, it may be only a matter of a few yearsbefore the crowns of residual trees grow intothe spaces left by those removed.

Dynamic Processes and StandDevelopmentForests are dynamic. Changing vegetationpatterns caused by disturbance or successionalter forest benefits and values. Ecosystemmanagement anticipates and plans for changerather than simply responding to undesirableevents.

Understanding succession is an importantcriterion when actively managing forests tocreate desired future conditions. Nature willcontinue to provide disturbances. Insight intopotential vegetation patterns across adjoiningland should help landowners, managers, andother ecosystem management cooperatorsplan how to better interact for their own needs.

Not all disturbances are stand replacing.Vegetation responses can be described bycategorizing disturbances according to low,moderate, or high severity. Forest ecologistsdefine high severity disturbances as thosekilling 70% or more of the trees in a stand.Moderate severity disturbances kill between20% and 70% of the stand, and low severitydisturbances kill less than 20%.

Succession depends on both the severity andtype of disturbance. After a high severity fire,pioneer species such as grasses, forbs, brush,and tree species such as western larch andlodgepole pine, are usually favored. After ahigh severity windstorm, shade-tolerantadvanced regeneration, such as western hem-lock or western redcedar, is more likely tobe favored.

Moderate severity disturbances favor distur-bance-tolerant species. For example, in east-ern Washington, moderate severity fires instands containing a mixture of lodgepolepine, western larch, and grand fir will favorthick-barked, fire-tolerant western larch. Theother two species have thin bark and usuallyare killed by moderately severe fires. The resultof moderate severity disturbances often isa stand in which two or three age classes(cohorts) are represented. The oldest treeswere able to survive the disturbances. Treeskilled by the disturbances freed resourcesfor the surviving trees and allowed new treesto establish.

Low severity disturbances kill individual treesor small groups of trees. Ground fires, smallpockets of root rot, and small-scale insect

18

attacks are examples of low severity distur-bances. A classic example of the effects ofperiodic low severity disturbances are ponde-rosa pine forests subject to frequent, low sever-ity fires, and small-scale outbreaks of westernbark beetles. These low severity disturbancesmaintain open, parklike stands of pine.

Forest DevelopmentPhases

Following stand-replacing or catastrophic dis-turbances, forest development can be definedby four phases:1 1) Stand initiation or “open,”2) Stem exclusion or “dense,” 3) Understoryreinitiation or “understory,” and (4) Old-growth or “complex.” Each phase is charac-terized by different structures, providing dif-ferent wildlife habitats and forest products(Figure 10).

While these four phases are useful to under-stand stand development over time, thereare no absolute boundaries between them.Residual trees and shrubs are not often com-pletely killed, resulting in “islands” of anolder successional stage. “Legacy areas” actas “refugia” for later successional dependentplants and animals. As the new forest matures,these plants and animals are able to colonizethat new forest area. These legacies oftenprovide significant biological diversity tothe forest site over time and provide wildlifehabitats that differ from the adjacent areasby providing more vertical structural diver-sity. This can be very important to wildlife,especially birds. It was once thought that allforests developed from seral stages to stableold-growth stages in a predictable fashion.We now know that site conditions changeover time, influencing the rate and directionof forest development.

Stand Initiation or “Open”PhaseDeath or removal of most trees from a site,whether by wind, fire, logging, or someother disturbance, greatly changes the envi-ronment at the forest floor. More sunlightreaches the ground, so temperature increases.Grasses, forbs, and shrubs are the dominantvegetation. Decomposition increases theavailability of many nutrients that werebound up in living vegetation. Availablewater also may increase since trees are nolonger taking it up from the soil and tran-spiring it through the leaves.

The soil and forest floor are very important.Energy and nutrients stored in the forestfloor are released as the ecosystem adjustsfrom the disturbance. New plants grow, cap-turing and cycling the nutrients. The standinitiation phase ends when trees, shrubs,and other plants capture all the availablegrowing space on a site. The many species ofplants that grow on the site during the standinitiation phase include not only trees butshrubs, grasses, and other herbaceous plants.The diversity of plant life encourages a greatdiversity of animal species. The many flow-ering and fruiting plants near the groundprovide habitats for a wide range of ani-mals—from butterflies to bears. Shrubs andherbaceous plants provide browse for deer,elk, and rabbits. These animals provide foodfor cougars and bears. Seed-eating and in-sect-eating birds forage in these open areas.Some of the plant and animal species foundin this phase are generalists; that is, speciesadapted to a wide range of conditions. Oth-ers, such as butterflies, are specialists andcannot survive in other conditions.

The coastal Douglas-fir forests owe theirexistence, in part, to severe fires that infre-quently burned west of the Cascades. Thelarge size of some of these fires would havemade it difficult for the seed of trees andshrubs in adjacent stands to rapidly colonizethe interiors of the burned areas. The stand1 Defined by Professor C.D. Oliver, Yale University.

19

initiation phase probably lasted for manydecades before trees filled all the availablegrowing space. An exception to this generali-zation occurs when red alder seed is available.Red alder has the ability to disperse seedgreat distances and colonize disturbed sitesrapidly. Stand development following theeruption of Mount St. Helens is a goodexample of red alder’s colonization ability.

Stem Exclusion or “Dense”PhaseWhen the trees on a site have captured mostof the available growing space, their crownstouch. This point, called crown closure, marksthe end of rapid and successful establishmentof new shade-intolerant trees in the stand.Trees must compete with other trees for lim-ited sunlight, water, and nutrients to survive,so they must grow larger than their neighbors.Larger trees or those having a competitive

advantage are able to grow into the spaceoccupied by less competitive individuals andreduce their growth rate or even kill them.The process by which dominant trees main-tain their dominance is by out-competingtheir neighbors for site resources. This pro-cess results in crown differentiation. The treesthat compete most successfully develop largecrowns above the general level of the canopy.These trees are the dominants. Trees a littlesmaller, but still having large crowns, are thecodominants. Intermediate trees have crownsquite crowded on all sides, and suppressedtrees have crowns that fall below the generallevel of the canopy.

During the stem exclusion phase, the standbegins to accumulate both living and deadmatter. The trees in the stand have capturedthe available growing space, so nutrients arenot readily washed out of the ecosystem.Smaller, weaker trees continue to die during

Figure 10. Stand Development Phases as Defined by C.D. Oliver are Useful to Describe Stand Development.

SAVANNA

COMPLEX

OPEN

DENSE

UNDERSTORY

20

this phase, while surviving trees grow tallerand increase in diameter. In western Wash-ington, the overstory casts a deep shade onthe forest floor, and little or no vegetationmay grow there. In parts of eastern Washing-ton, moisture is more limiting than light.Stands may appear open, but beneath thesurface, roots utilize all available growingspace. During this phase, intense competi-tion between trees often reduces the amountof shrubs and other plants in the ecosystem.Plant and animal diversity is frequently quitelow. However, snowshoe hares and lynx fre-quently use dense, pole-sized stands of lodge-pole pine and subalpine fir for hiding andto avoid intense heat and cold, while eatingplants and prey in nearby stand initiationareas. Many managed forests are harvestedsometime during the stem exclusion phaseand, consequently, the last two phases ofvegetation development are rarely achievedin traditional management of forests.

If trees are able to establish in a stand repro-duced over a period of many decades, theywill vary in size and ability to compete forgrowing space. If little difference exists intree size and age, there may not be clear win-ners and losers in the competition for grow-ing space. As a result, the stand may stagnate,with all trees developing small crowns. Thesize of the tree crowns will greatly influencethe amount of energy produced in photosyn-thesis. Trees first allocate their energy to grow-ing taller. If taller trees grow larger crowns,they capture more sunlight energy and growlarge in diameter. In a stagnated stand, manytrees continue to grow uniformly taller, sotheir crowns become small. Consequently,they grow slowly in diameter. Eventually, thetrees become so tall and thin that they fallover. This occasionally happens in naturalstands of lodgepole pine and also has occurredin managed plantations—especially duringwind or snow storms. When trees are talland thin, they also are vulnerable to insectattacks, and so become infested, die, andcreate fire hazards.

Understory Reinitiation PhaseThis phase marks the beginning of the end forthe original trees that established followinga major disturbance. Weather related distur-bances such as wind and ice storms often startthe reinitiation phase by killing or breakingup less dominant overstory trees, allowingsome light to reach the forest floor. Shade-tolerant plants, including shrubs and trees,are able to establish, survive, and grow inthe partial sunlight reaching the understory.Given little sunlight, these trees do not growvery tall. When a tree in the overstory diesand falls, it often leaves a large opening hav-ing more sunlight. A new age class of treesoften establishes in the opening, and thesetrees grow more rapidly upward. During thisphase, plant and animal diversity again increaseswith the addition of new age classes and struc-tures, such as multiple canopy layers, snags,logs, and trees with forked or broken tops.Birds and animals that use large snags or bro-ken-topped trees for nesting often thrive inthe understory reinitiation and old growthphases of stand development. Several speciesof woodpeckers, including the pileated; Vaux’sswifts, northern goshawks, spotted owls,marbled murrelets, flying squirrels, pinemartens, lynx, fisher, and wolverines choosethese stages. Many beneficial insects suchas carpenter ants need snags and down logsalso. Deer and elk find winter shelter in thesemulti-canopied forests. In the extreme north-eastern part of Washington, woodland cari-bou are associated with stands in the under-story reinitiation phase. Many of the birdsand animals are habitat specialists that pre-fer older forests where overstory trees arebeginning to die and multiple canopy layersare starting to form. Unlike generalist speciesthat can adapt to a wide range of conditions,these specialists require specific forest struc-tures or compositions. For instance, Vaux’sswifts use snags hollow at the top since theyenter these snags from above. Marbled mur-relets build their nests in living old treeswhose gnarled broken tops provide suitablenesting platforms.

21

Many forests, such as Douglas-fir and west-ern larch, on the west and east sides of theCascades, respectively, are referred to as old-growth. However, they are actually in theunderstory reinitiation phase, since the Dou-glas-fir trees established following fire stillmake up a large proportion of the overstory.Stands in the stem exclusion phase can bemanipulated silviculturally to bring aboutthe understory reinitiation phase soonerthan in unmanaged stands. (Figure 10).

Old-Growth or “Complex”PhaseIn many forests, some sort of disturbancegenerally resets the biological clock beforethe old-growth phase of forest developmentis achieved. In a true old-growth forest, themulti-aged stand is composed of trees thatestablished beneath the original overstoryand eventually replaced it. Many plants andanimals found in these forests are specialists.An interesting question is “how old does aforest have to be before it functions as old-growth”? Scientists are interested in findingif plants and animals believed to require oldforest habitat can successfully live and repro-duce in younger stands if they have someof the structures and compositions usuallyoccurring only in older forests. These oldgrowth complexes are also commonly knownas habitat types.

Natural and Human-CausedDisturbances Alter DevelopmentPhasesThe stand development theory describedabove is under further study by ecologists andsilviculturists, who now think, given peri-odic disturbances (fire, wind, floods, insectinfestations, clearcut or partial cut logging),stand structures are much more dynamic asdescribed in Figures 11 and 12. Both naturaland human-caused disturbances create amosaic of diversity across the landscape asdescribed below.

Forests and Trees inWashington

Washington has diverse forest types, fromcoastal forests where western redcedar, Dou-glas-fir, western hemlock, and Sitka sprucedominate, to inland forests of ponderosa,lodgepole and western white pine, Douglas-fir, and western larch. Descriptions of someof the major forest types occurring withinthe state follow:

West Side Forest TypesCoastal Douglas-firCoastal Douglas-fir forests are among the mostproductive forests in the world. These standsare composed of at least 80% Douglas-fir andlesser amounts of other species, includingwestern hemlock, grand fir, Pacific silver fir,noble fir, western redcedar, Sitka spruce, redalder, bigleaf maple, and Pacific madrone.Forests of this type are widespread west ofthe Cascade Range at elevations from sealevel to approximately 1,500 feet. Douglas-fir forests regenerate naturally following firewith seed provided by scattered survivingtrees. Planting following harvest also regen-erates Douglas-fir forests. Mature stands mayremain healthy for decades. When death ofsome of these trees creates gaps in the canopy,shade-tolerant species such as western hem-lock, western redcedar, and grand fir becomeestablished. Unless another disturbancerenews the cycle, these shade-tolerant spe-cies will eventually take over the site. Mostcoastal Douglas-fir forests are essentially even-aged; not until many centuries pass andshade-tolerant species become establisheddo these forests become more diverse in ageclass structure.

Douglas-fir/Western HemlockThese forests are similar to coastal Douglas-fir forests except that together, Douglas-firand western hemlock make up 80% of the

22

SAVANNA

COMPLEX

OPEN

DENSE

UNDERSTORY

Figures 11 & 12. Both natural and human-caused disturbances create a mosaic of diversity across the landscape.

SAVANNA

COMPLEX

OPEN

DENSE

UNDERSTORY

Traditional Stand Development Theory:Forests grow into stable “old-growth” over time

Modern Stand Development Theory:Forests are dynamic and change by growth and disturbance resulting in many structures.

23

species. These are mixed species stands.Douglas-fir is usually the most commonspecies but on less fertile or very moist sites,hemlock may dominate. The most commonassociated species is western redcedar. Otherassociated species include grand fir and west-ern white pine. At low elevations, Sitka spruceis often present. Noble fir may be present athigher elevations in the Cascades. This foresttype thrives in mild, humid climates. Follow-ing fire, these mixed stands may convert tonearly pure stands of red alder. Hemlock oftenseeds in, recreating the mixed species type.Sometimes hemlock forms a substantial por-tion of the main canopy. When stressed byhigh temperatures or low soil moisture, hem-lock remains in the understory as otherspecies grow over the hemlock to form theoverstory.

Red AlderThese forests occur west of the Cascades,usually as pure stands. Stands of red aldertypically grow below 1500-foot elevation,in riparian areas, in moist coves, or in earlystages of succession following soil distur-bance. Elsewhere in western Washington,red alder grows mixed with other short-livedhardwoods such as bigleaf maple, black cot-tonwood, and Pacific willow; or with coni-fers, including Douglas-fir, Sitka spruce, west-ern hemlock, western redcedar, and grandfir. Forests dominated by red alder are alwayseven-aged. Because red alder is very shadeintolerant, only dominant or codominanttrees survive. Starting at an early age, redalder produces abundant annual seed. Thisgives it a competitive advantage over mostconifers. Since red alder has no serious insector disease problems, it will grow readily onmany sites infected by conifer root-rots. Redalder improves soil fertility through nitrogenfixing and produces large quantities of litterthat decompose rapidly, adding nutrientsand organic matter to forest soils. Shrubsare generally an important component ofred alder forests. Common shrubs associated

with red alder include Pacific red elder, blue-berry elder, salmonberry, thimbleberry, anddevils club.

Sitka SpruceSitka spruce occurs primarily along the PacificCoast. It is a shade-intolerant species unlikeother spruce species found in the west. It oftenforms pure stands within 3 to 4 miles of saltwater. The white pine weevil (Pissodes strobi),a native insect, often limits Sitka spruce range.On better sites Sitka spruce often grows withwestern redcedar and western hemlock. Redalder occurs where light reaches the forestfloor.

East Side Forest TypesInland Douglas-firIn some parts of eastern Washington, inlandDouglas-fir forests consist of pure or nearlypure stands of Douglas-fir, but this speciesoccurs primarily in various combinations withgrand fir, subalpine fir, western larch, lodge-pole pine, ponderosa pine, and western whitepine. Douglas-fir generally occurs as an over-story species on moist sites with more shade-tolerant grand fir and western hemlock inthe understory in northeastern Washington.On drier sites, ponderosa pine may dominate,relegating Douglas-fir to an understory posi-tion, especially in younger stands. Severalinsects and pathogens can seriously affectinland Douglas-fir forests. Dwarf mistletoesaffect nearly all species growing in inlandDouglas-fir forest types and can reduce growthand kill severely infested trees. The “witchesbrooms” caused by mistletoe infestations arehighly flammable and may cause ground firesto climb into the crowns of infested trees.Outbreaks of bark beetles, triggered by wind,ice, or other physical damage, or sometimesroot diseases, kill mature and old individuals.Defoliation by western spruce budworm andDouglas-fir tussock moth may retard growth,damage tree form, reduce seed production,

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and even kill trees. These two insects prefer-entially feed on shade-tolerant species, suchas grand fir, and are especially damaging instands with more than one canopy layer.

Grand Fir/Western HemlockForests in which grand fir makes up a signifi-cant portion of the stands, occur as the Dou-glas-fir forests age and grand fir replaces theDouglas-fir. Grand fir associates primarily withponderosa pine, inland Douglas-fir, westernhemlock, western redcedar, western whitepine, lodgepole pine, and western larch.Grand fir forests are common in northeasternWashington, in the Blue Mountains of south-eastern Washington, and on the eastern slopesof the Cascades. Decades of fire suppressionand poorly done “selective logging” haveallowed grand fir forests to occupy areas pre-viously dominated by ponderosa pine andwestern larch. Grand fir is extremely suscep-tible to root and stem rots, especially follow-ing logging damage or other injury. Indianpaint fungus (Echinodontium tinctorium) is themost common stem and root disease in grandfir. Annosus root and butt rot, caused by thefungus Heterobasidion annosum (formerlyFomes annosus), commonly enters throughfreshly cut stumps, wounds, fire scars, anddead or broken tops. The fungus can spreadfrom one tree to another by root contact.Grand fir is also highly susceptible to armil-laria root disease caused by the Armillariaostoyae fungus. Grand fir is a preferred foodof several defoliating insects including thewestern spruce budworm. Because of itsvulnerability to these diseases and insects,harvest grand fir whenever possible in selec-tive logging.

Western LarchWestern larch forests rarely occur as purestands in Washington. Larch, a deciduousconifer, usually occurs in various combina-tions with Douglas-fir, grand fir, ponderosapine, lodgepole pine, western white pine,and subalpine fir. Western larches most fre-

quently occur in northeastern Washingtonwith Douglas-fir as the most common associ-ate. Western larch also grows in the easternCascades and in the Okanogan Highlands,where it associates with grand fir and lodge-pole pine. Western larch is the most shade-intolerant conifer in the inland northwest.Historically, its presence on the landscape wasmaintained by stand replacement wildfires.In the absence of intense fires or logging,more shade-tolerant conifers replace westernlarch: Douglas-fir on drier sites, grand fir onwarm, moist sites, and subalpine fir on cool,moist sites. Infestations of dwarf mistletoe(Arceuthobium laricis) and the larch casebearer(Coleophora laricella) can seriously reducewestern larch growth. Western larch is veryfire resistant due to its thick bark.

Lodgepole PineLodgepole pine forests frequently occur aspure stands in Washington State. Lodgepolepine has one of the broadest ranges of tem-perature and moisture tolerances of any coni-fer. Most natural stands of lodgepole pinedevelop after catastrophic fires or reseed onfrost-prone locations after a killing frost orclear-cut logging. Repeated fires aid perpetu-ation of this forest type. In the absence ofdisturbances, lodgepole pine forests may con-vert to interior Douglas-fir on warm dry sites,or to grand fir, western redcedar, or westernhemlock on warm, moist sites. At higher ele-vations, subalpine fir and Engelmann sprucereplace lodgepole pine. Lodgepole pine olderthan 100 years becomes increasingly suscep-tible to outbreaks of mountain pine beetle(Dendroctonus ponderosae), which can hastenforest conversion to more shade-tolerant coni-fer species. Historically, mortality from beetleoutbreaks created fuel loads that predisposedthese stands to catastrophic fires.

Ponderosa PineThis forest type covers extensive areas of theWest. This type may consist of pure standsor mixed species stands that also include

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some combination of Douglas-fir, grand fir,lodgepole pine, or western larch. As a resultof fire suppression, some formerly purestands of ponderosa pine are developingunderstories of Douglas-fir and grand fir. Themountain pine beetle threatens unthinned

AbioticNonliving components of the environment suchas air, rocks, soil particles, and plant litter.

Adaptive managementA process for ecosystem management that allowsfor continual change as more information becomesavailable on resource conditions and the effects ofmanagement actions on resources.

Age classAll trees in a stand within a given age interval,usually 10 or 20 years.

Age structureThe number and ratio of age classes within a stand.

AnadromousMigratory behavior of fish, such as salmon, thatmature in the sea but return to fresh water to spawn.

Annual growthThe yearly increase in wood volume, usuallyexpressed in terms of board feet or cubic feet peracre.

Annual ringBands, which show tree growth for one year, asviewed on the cross section of a stem, branch, orroot, or on a trunk core sample. Can be counted todetermine a tree’s age. Variation in width of ringsrecords how the tree responded to growing condi-tions in different years.

Aquatic ecosystemA water-based system of living organisms interact-ing with their environment.

AquiferA stratum of earth or permeable rock that storessignificant quantities of water. A confined aquiferis sealed above and underlain below by imperme-able material.

AspectThe compass direction that a slope faces.

AutecologyEcology dealing with biological relations betweena species or individual organism and its environment.

BacteriaOne-celled (or single-celled) organisms that live insoil and water.

Basal areaA key descriptive measure of trees and stands. Fora tree, it is the cross-sectional area of the trunk atbreast height (4.5 feet above ground). The basalarea of a tree 14 inches in diameter at breast height(DBH) is approximately 1 square foot. Basal areaper acre is the sum of basal areas of the individualtrees on an acre. A stand of 100 14-inch DBH treeswould contain about 100 square feet of basal areaper acre.

Biological controlControlling plants, diseases, and animal pestsby the use of natural enemies; or inhibiting thereproduction of pests by methods that result in thelaying of infertile eggs.

Biological diversityRichness and abundance of species and variety ofnatural communities in a forest environment. Boththe number of species and the number of individu-als of each species are important in considering theextent of biological diversity in an area. Alsoreferred to as biodiversity.

Forest Ecology Glossary2

2Adapted from Terminology for Forest Landowners, WSUCooperative Extension, EB1353.

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stands of pole-size trees, especially on poorsites. Western pine beetle plays a lesser rolebecause many of the large, old trees that arethe primary target have been felled. Dwarfmistletoe can become a problem, especiallywhen two or more canopy layers exist.

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Biological propertiesIn soils, this refers to the living organisms in thesoils that assist with decomposition and nutrientcycling (bacteria, insects, and fungi).

BiomassThe total quantity (weight) of biological matter ina unit area, including all living organisms aboveand below ground; or the total quantity of one ormore species in a unit area. Tree biomass compo-nents include wood, bark, foliage, and roots, of asingle tree or of all the trees in a specified area.

BiotaThe plants and animals of a given region or period,considered collectively.

BioticHaving to do with the living components of anecosystem.

BoleThe main tree trunk.

Breast heightFour and one-half (4.5) feet above the ground onthe uphill side. Diameter is usually measured andbasal area calculated at this point on the tree.

BrushCommonly refers to undesirable shrubs and smalltrees.

BufferA protective strip of land or timber adjacent to anarea requiring attention or protection. For example,a protective strip of unharvested timber along astream.

CambiumThe growing layer of cells beneath the bark of atree.

Candidate speciesPlants and animals being considered for listing asfederally endangered or threatened species in theUnited States.

CanopyThe uppermost layer in a forest, formed collectivelyby tree crowns.

Canopy layersForests with varying age classes may have severalheight classes. For example, an overstory canopylayer of trees may overtop a lower canopy of othertrees or shrubs.

Climax communityA relatively stable plant community that hasevolved through stages and has a dominant plantpopulation suited to the environment.

Codominant treesTrees whose crowns form the general level of thestand, receiving full light from above but compara-tively little from the sides. See also Crown class.

CommunityA natural assemblage of different organisms livingand functioning together in a particular area.Usually named for the dominant plants, animals,or major physical components of the area.

ConiferA cone-bearing tree with needles, such as pine,spruce, fir, and larch.

ConnectivityCondition of ecosystem integrity allowing naturalprocesses to work across a landscape withoutdiscontinuity. See also Corridors; Fragmentation.

ConservationThe protection, improvement, and wise use of thenatural environment (such as the forests, soils, andwater systems) to prevent destruction and exploi-tation while still producing goods and services forthe human population.

Conservation biologyThe science of diversity, scarcity, and survival ofspecies. Deals with active management to protectand maintain genetic variety within species. Dealsalso with the concept of sustainability and rela-tionships between biotic and abiotic resources. Seealso Sustainability.

CorridorsGenerally, linear strips of habitat linking isolatedpatches of natural habitat in the landscape. Estab-lishment and maintenance may be actively pro-moted at the state and regional levels. See alsoConnectivity; Fragmentation.

CoverVegetation or other natural shelter serving toconceal wildlife from predators. Also refers to theprotective shade vegetation provides to wildlife,fish, and the forest floor.

Critical habitatSpecific areas within the geographic range occu-pied by a species listed by the federal governmentas endangered or threatened. The physical andbiological features considered necessary for thesurvival and recovery of the species.

CrownThe branches and foliage of a tree.

Crown classA relative designation of tree crowns. Dominant treesare those whose crowns grow above the generallevel of the canopy. Codominant trees are those hav-ing crowns forming the general level of the canopy.Intermediate trees have crowns growing below thegeneral level of the canopy. Suppressed trees aremuch shorter than trees in the general level ofthe canopy.

Crown closureThe point when, in a young stand, the crowns ofthe trees begin to touch each other.

Crown differentiationThe process whereby some trees grow faster anddevelop large, full crowns, while others fall behindin height and have smaller, sparser crowns.

Crown ratioA measure of the length of a tree’s crown relativeto total tree height.

DBHThe tree diameter at breast height (4.5 feet abovethe ground on the uphill side).

Deciduous treeA tree that loses its leaves or needles during the falland winter.

DecompositionThe breaking down of dead matter by decayorganisms.

DefectThat portion of a tree or log that makes it unusablefor the intended product. Defects include rot,

crookedness, cavities, and cracks. Severe defectscause the log to be classified as a cull.

DefoliatorsInsects that feed on foliage.

DendrologyThe study of tree identification.

DesertificationThe process of desert expansion caused by loss ofsoil and vegetative cover through climate change,overgrazing, or other influences.

Diameter tapeA measuring tape used to directly determine treediameter when stretched around the circumferenceof the tree stem.

DiebackAny condition where portions of a tree’s crown diedue to conditions other than shading.

DisturbanceA natural or human-caused event, such as a forestfire, disruptive wind storm, or insect infestationthat alters the structure and composition of anecosystem.

Disturbance managementManaging disturbance events and effects, such asinsects and fire, to approximate natural conditions.

Dominant treesSee Crown class.

DormancyA biological process in which a plant ceases mostgrowth activities and simply maintains existingtissue.

DrainageAn area of land above a given point on a waterwaythat contributes runoff water.

DuffVarious stages of decaying organic matter foundon the soil surface.

Dysgenic selectionRemoving the best trees in the stand while permit-ting the worst trees to occupy the site and reseedthe new stand. Over time, the stand becomes filledwith individuals of undesirable species or poor form.

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Early-successionalThe first species to occupy an area after a majordisturbance, often known as “pioneers.” Typically,an association of plants and animals capable ofsurviving and reproducing under harsh environ-mental conditions.

Ecological approachA type of natural resource management that indeveloping management strategies considers therelationships among all organisms, includinghumans, and their environment.

EcologyThe science that studies the interaction of plantsand animals with their environment.

EcosystemEcological system. An interacting system of livingorganisms and their environment. The dynamicrelationships of living (biotic) and nonliving (abi-otic) components of a region, as well as the forces,such as weather and wildfire, that affect them.

Ecosystem healthA measure of the overall capacity of an ecosystemto maintain biological diversity, normal produc-tivity, sustainability, and resilience to disturbance.

Ecosystem managementA long-term approach to managing a forest, usingecological principles and considering biological,physical, economic, and societal needs, while sus-taining or restoring ecosystem integrity. See alsoAdaptive management.

Ecosystem structureThe horizontal and vertical distribution of livingand dead vegetation.

Ecosystem sustainabilitySee Sustainability.

EcotoneA transitional area between two forest or range-land communities containing the characteristicspecies of each as well as characteristics of its own.A point of abrupt change, such as a prairie-forestjunction or a land-water interface.

EdaphicOf the soil or influenced by the soil rather thanby climatic factors, especially pertaining to livingorganisms.

Edge effectThe tendency toward greater species variety andgreater density of animal and plant life in themargin where two ecological communities meet.See also Ecotone.

ElementsThose basic substances such as carbon, calcium,nitrogen, hydrogen, and phosphorus required fortree growth. Some come from the weathering ofbedrock, while others such as nitrogen come fromthe air. An element is the same as a nutrient.

Endangered speciesA plant or animal vulnerable to extinction in all ora significant portion of its range. Identified by theSecretary of the Interior in accordance with theEndangered Species Act (1973).

Endemic population levelA normal (insect) population level.

EntomologyThe study of insects and their environments. Seealso Forest entomology.

EnvironmentThe external conditions, both physical and biologi-cal in which an organism lives. Includes climate,soil, topography, food supply, and all other influ-ences affecting development.

Ephemeral streamA stream that flows only sporadically, such as afterstorms.

EpidemicWidespread insect or disease incidence beyondnormal proportions.

Exotic speciesA nonnative plant or animal species introduced byhumans, either deliberately or accidentally.

ExtinctSaid of a species or other taxonomic group havingno living members.

Feeder rootsFine roots of trees and other vegetation used toabsorb water and nutrients from the soil.

ForestA plant community dominated by trees and otherwoody plants.

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Forest entomologyThe science that deals with insects in forest treesor products.

Forest ecologyThe study of life in areas where the dominant veg-etation is trees. This includes both the biology oforganisms and how they interact with each otherand their environment.

ForesterA professional who has been educated in forestryat a college or university.

Forest managementThe application of scientific, economic, and socialprinciples to managing a forest property for spe-cific objectives.

Forest pathologyThe science that deals with diseases of forest trees.

Forest PlanA document that guides all natural resource man-agement activity and establishes managementstandards and guidelines for a National Forest,embodying the provisions of the National ForestManagement Act (1976).

Forest Practices ActWashington State legislation designed to protectpublic resources such as water and wildlife fromeffects of indiscriminate management practices.All forest operations on private lands must com-ply with regulations administered by state forestrypersonnel.

ForestryThe science, art, and practice of managing and pro-tecting tree and forest resources for human benefit.

Forest typeA group of tree species that, because of their envi-ronmental requirements, commonly grow together.Examples of forest types are the Douglas-fir/hem-lock type or the spruce/fir type. In addition, adescriptive term used to group stands with similarcomposition and development characteristics.

Form classA measure of bole taper derived by dividing diam-eter inside bark at a given height (usually 17.3 or33.6 feet) by DBH, times 100. These values oftenare entered when using tree-volume tables.

FragmentationThe breaking up of a large forest area into patcheseither by natural processes or through managementor conversion to other land uses. Natural habitatsmay become separated into isolated segments or“islands.” See also Connectivity.

Free-grown treeA tree that has always grown in the open with nocompetition from adjacent trees.

FungiAny group of organisms that live in the soil anddecompose dead organic matter.

Growing spaceThe availability of all the requirements a plantneeds in order to grow, including soil, light, water,nutrients, CO2.

Growing stockAll the trees growing in a stand, generally expressedin terms of number, basal area, or volume.

HabitatThe local environment in which a plant or animalnaturally lives and develops.

Habitat typeClassification of a land area according to dominantplant forms (usually trees and shrubs) and physi-cal characteristics. Can help to indicate the bio-logical potential of a site.

HardwoodA term describing broadleaf trees, usually decidu-ous, such as oaks, maples, cottonwood, ashes, andelms.

HarvestRemoving trees on an area to obtain an income orusable product.

HerbicideAny chemical used to kills plants.

IncrementSee Annual growth.

Increment borerA hollow, augerlike instrument used to bore intothe tree trunk to remove a cylindrical cross section(core sample) of wood. It is used to expose annualgrowth rings.

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Indicator speciesA plant or animal species whose presence in anarea indicates that certain specific habitat condi-tions prevail throughout the area.

InsecticideAny chemical used to kill insects. The term oftenis used interchangeably with pesticide.

Integrated pest management (IPM)A method that evaluates alternatives for manag-ing forest pest populations on the basis of pest-host relationships.

Integrated resource managementA term used to indicate the simultaneous consid-eration of ecological, physical, economic, andsocial aspects of lands, waters, and resources indeveloping and carrying out multiple-use, sus-tained-yield management.

Intermediate treesSee Crown class.

Intolerant speciesTree species that are incapable of establishing orgrowing in the shade of other trees.

LandscapeA large land area composed of interacting groupsof ecosystems, including all the physical andbiological aspects of such an area, regardless ofownership.

Landscape configurationThe pattern of forest stands, meadows, lakes, andother features within a large area.

Landscape connectivitySee Connectivity.

Landscape ecologyThe study of biological interactions across a largeland area, or watershed.

LitterThe uppermost layer of the soil, made up of freshlyfallen or slightly decomposed organic materials.See Duff.

Live crown ratioThe percentage of the length of a tree stem sup-porting living branches.

Low firesFires with a low flame height and low temperaturethat burn duff, seedlings, saplings, and trees thatare not fire-resistant. Mature fire-resistant trees arescorched but generally not killed by low fires.

MacroclimateThe climate of a large region as a whole, consid-ered apart from modifying irregularities of land andvegetation. See also Microclimate.

Management planA written plan for the organized handling andoperation of a forest property. It usually includesdata and practices designed to provide optimumuse of forest resources according to the landowner’sobjectives.

Mature forestA term generally applied in an economic sense toindicate a forest that has attained harvest age.

Mature treeA tree in a managed forest that has reached thesize or age for its intended use.

MBFAbbreviation for thousand board feet.

Mean annual increment (MAI)The annual increase in size (volume) of a tree. Orthe increase in size (volume) of a stand at a certainage, divided by that age in years.

MensurationThat phase of forestry dealing with the measure-ment of volume, growth, and development ofindividual trees and stands.

MicroclimateThe climate of a small, specific area reflecting suchlocal differences as soil surfaces, vegetation, andatmospheric characteristics.

MicrositeAn environmental feature that is small in scale butunique in character. Microsites often have a sig-nificant impact on natural regeneration.

Mid-successionalAn association of plant and animal species thatreplaces early successional species, but is eventu-ally replaced by climax species in the absence ofdisturbance.

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Mixed conifersTimber stands characterized by a mixture of coni-fer species, including ponderosa pine, lodgepolepine, Douglas-fir, grand fir, western white pine, andwestern larch. A mixture of forest types.

Mixed-species standForest stands made up of more than one type oftree.

MMBFAbbreviation for million board feet.

Montane forestsForests that are mid-elevation and generally moisterthan foothill forests, but not as cold as subalpineforests.

MortalityDeath of forest trees as a result of competition, dis-ease, insect damage, drought, wind, fire, and otherfactors.

Multiple useForest land management for more than one pur-pose, such as wood production, water, wildlife,recreation, forage, and aesthetics.

Multi-storiedForest stands containing trees of different heights.

Mycorrhizal fungiFungi, which form a symbiotic relationship withthe roots of certain trees, enabling those trees toextract more water and nutrients from the soil.

NutrientsChemical substances necessary for plant and treegrowth.

Nutrient cyclingThe biological, geological, and chemical circulationof inorganic elements such as nitrogen, phospho-rus, and potassium through the soil, living organ-isms, water, and air, thus providing nutrients toanimals and vegetation in the process.

Obligate speciesA species restricted to a particular environment ora particular mode of life, such as a plant or animalfound only in a narrowly defined habitat, e.g., atree cavity.

Old growthA forest ecosystem containing old trees, usuallyover 125 years old, and associated plants andwildlife.

Organic matterMaterial produced by plants and animals, such asleaves, branches, bark, wood, hair, fur, and bones.

OvermatureA stand of trees that is older than normal rotationage for the forest type.

OverstockedA stand or forest condition, indicating more treesthan desired.

OverstoryThat portion of the trees in a stand forming theupper crown cover.

Overstory retentionLeaving some of the bigger trees in the stand toserve as seed trees or shelterwoods for instance.

PathologyThe science that deals with diseases of forest trees,forest stands, and products.

PhotosynthesisThe process in trees and other plants changing airand water into food using the sun’s energy.

PioneersShade-intolerant species that are the first trees toinvade freshly disturbed sites.

Plant associationA vegetation community, in which the dominantspecies forms the highest level in the hierarchy ofplant species. See also Climax community.

PlantationA reforested area established by planting trees.

Planting stockSeedling trees ready for planting.

PopulationOrganisms (trees, shrubs, herbs, animals, insects)of common ancestry that occupy a particularforest area.

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PrescriptionA management action to cause orderly change ina forest.

PreservationAs applied to wood—Treating wood products withchemicals to prevent damage by insects or decay.In reference to land and resources—Maintaininga natural environment undisturbed by humaninfluence.

ProductivityGrowth per unit time.

ProvenanceThe geographical source or place of origin of treeseed.

Pure standA stand of trees of all one species.

ReforestationReestablishing a forest on an area where forestvegetation has been removed.

RegenerationThe natural or artificial renewal of trees in a stand.

ReproductionYoung trees. The process of forest replacement orrenewal that may be introduced artificially byplanting or naturally by sprouting or self-seeding.

ResidualTrees left in a stand, after cutting, to grow until thenext harvest.

ResilienceThe ability of a forest ecosystem to recover from adisturbance.

RiparianPertaining to the area along the banks of a river,stream, or lake.

Riparian ecosystemAn ecosystem that is transitional between land andwater ecosystems. The soils, plants, animals, andother organisms found in such an area.

RotationThe number of years required to establish and growtrees to a specified size, product, or condition ofmaturity.

Second growthYoung forests that originated naturally or wereplanted on the site of a previous stand that wasremoved by cutting, fire, or other cause.

Seed yearA year in which a given species produces a largeseed crop. Used in reference to trees that produceseed irregularly or infrequently.

Seed zoneAreas that have similar climate and elevationconditions. Used to specify where tree seed wascollected and where trees from such seed willprobably grow successfully.

Seral stageA phase of ecological development toward a moremature or climax community. See Climax commu-nity; Successional stage.

Serotinous conesCones that remain closed after maturity. Lodgepolepine cones open after being exposed to intenseheat. This mechanism ensures seed productionfollowing a fire.

Shade intolerantA term applied to tree species that grow better indirect sunlight than in the shade of other trees.The opposite of shade tolerant. Examples includecoastal Douglas-fir, western larch, lodgepole pine,and red alder.

Shade toleranceA tree’s capacity to develop and grow in the shadeof, and in competition with, other trees. Examplesof highly shade-tolerant species are western hem-lock, western redcedar, and Pacific yew.

Shade tolerantA term applied to tree species that grow betterin the shade. The opposite of shade intolerant.Examples include western hemlock, western red-cedar, and pacific yew.

ShrubA low growing perennial plant with a woody stemand low branching habit.

Single-layered canopyWhen the codominant trees in the stand are allabout the same height (an even-aged stand), theforest has a more or less continuous single-layered

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canopy. Trees in the understory usually are notnumerous enough to make additional layers ofcanopy.

SiteAn area evaluated for its capacity to produce forestproducts. Evaluation is based on combined biologi-cal, climatic, and soil factors.

Site classA grouping of similar sites that indicates relativeproductivity. The common system for the Douglas-fir region includes five site classes, in which SiteI is the most productive and Site V is the leastproductive.

Site indexAn expression of forest site quality based on theheight of the dominant and codominant trees inthe stand at a specified age, usually 50 or 100 years.

Site productivityGrowth per unit time on a given site, determinedby geologic and climatic conditions.

SlopeThe incline of the terrain usually expressed as theamount of incline in feet over a hundred feet ofhorizontal distance.

SocioeconomicCombining social and economic considerations.

Soil textureProportion of clay, silt, and sand in soil.

SpecialistsPlants or animals that require specific conditionsto grow and reproduce.

SpeciesA group of organisms (plants or animals) very simi-lar in appearance, which can interbreed freely witheach other but not with other groups.

Species compositionThe mixture of tree species in a stand within aforest.

StandA recognizable area of the forest that is relativelyhomogeneous and can be managed as a single unit.Stands are the basic management units of theforest. Stand types include:

All-agedA stand that supports trees of all ages and usu-ally all sizes. This stand type is rare. Contrast itwith an even-aged stand.

Even-agedA stand in which trees are essentially the sameage (within 10 to 20 years).

Fully stockedA stand where trees effectively occupy all grow-ing space, yet ample room exists for developingcrop trees.

MixedA stand that has more than one species in themain tree canopy.

OverstockedA stand that is overcrowded, thus reducing treevigor.

PoleA stand in which most trees are 5 to 9 inches indiameter.

PureA stand in which at least 80% of the treesbelong to a single species.

ResidualThe stand that remains after cutting.

SawtimberMost trees in the stand are large enough indiameter (usually 10 to 12 inches DBH or larger)to be sawn into lumber.

UnderstockedA stand in which crop trees do not effectivelyoccupy the growing space.

Uneven-agedA stand that supports trees of several age classes(technically, more than two age classes).

Stand conditionA silvicultural classification used to describe thepresent overall health of the stand, particularly inrelation to its need for treatment.

Stand densityA quantitative measure of stand stocking, or thenumber of trees for a given area.

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Stand initiation phaseFollowing a disturbance, plants regenerate thedisturbed site.

Stand-replacement fireA large fire that burns duff, seedlings, saplings, andmature trees, leaving the site unoccupied by veg-etation and at the start of a successional cycle.

Stand structureStages in the natural development of a forest stand,which often include distinct phases such as standinitiation, stem exclusion, understory reinitiation,and old growth.

Stand tableA table by diameter classes of volume, basal area,or trees per acre existing in a stand or expected toexist at a certain time.

Stem exclusion phaseAfter several years, new individuals are not able toregenerate within the stand. Some of the existingtrees die. Survivors grow larger and express differ-ences in height and diameter.

SuccessionThe replacement of one plant community byanother until ecological stability is achieved. SeeClimax community; Plant association.

Successional developmentWhere a stand lies in the successional cycle betweenpioneer and climax conditions.

Successional stageA phase in the natural development of forest com-munities. Over time, favorable conditions arereached for the establishment of the next stage.See Stand structure.

Suppressed treesTrees much shorter than the general level of thecanopy. These trees exhibit reduced growth rateand vigor.

SuppressionWhen a larger tree overtops a smaller tree, permit-ting little or no sunshine to reach the crown ofthe smaller tree and retarding its growth.

SustainabilityForest development that incorporates the meansto maintain biological diversity, resilience to stress,

and ecosystem health and integrity, in the contextof the ability to meet future as well as presenthuman needs.

Sustained yieldManagement of forest land to produce a relativelycontinuous flow of timber or revenue.

Terrestrial ecosystemA land-based ecosystem.

Timber stand improvement (TSI)Applying cultural practices to a young foreststand to improve the growth and form of trees andto achieve the desired stocking and species com-position.

ToleranceThe ability of a tree to grow satisfactorily in theshade of or in competition with other trees. Treesclassified as tolerant can survive and grow undercontinuous shade.

TranspirationWater loss from leaves during growth and respi-ration.

TransplantA very young tree or seedling lifted from a nurseryseedbed and replanted at the nursery.

TreatmentAny action in forest stands controlled by a silvi-cultural prescription.

TreeA woody plant having a well-defined stem, usuallystanding over 30 feet high at maturity.

Tree farmA privately owned woodland in which producingtimber is a major management goal. It may berecognized as a “Certified Tree Farm” by theAmerican Tree Farm System.

UnderstoryThat portion of the trees or other vegetationbelow the canopy in a forest stand.

Understory reinitiation phaseA later stage in stand development when forestfloor trees and shrubs again regenerate and survivein the understory.

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Uneven-aged managementManaging a forest by periodically harvesting treesof all ages to maintain a broad age (or size) classdistribution. The forester maintains a greater num-ber of trees in each smaller age class than in thenext older or larger class, up to some maximumage. This type of management is not common inthe West. See Selection harvest.

View shedThe landscape seen from a particular viewpoint oralong a transportation corridor.

Virgin forestA forest essentially uninfluenced by humanactivity.

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WatershedAn area of land that collects and discharges waterinto a single stream or other outlet. Also called acatchment or drainage basin.

Watershed analysisThe study of how a particular drainage networkfunctions. An aspect of ecosystem managementplanning.

WetlandsMarshes, swamps, and other water-saturated soils.These areas offer important habitat for wildlife,significant support of nutrient cycling in ecosystems,and protection against the severity of storms andfloods. Wetlands are among the lands most vul-nerable to destruction and conversion to other uses.

College of Agricultural, Human, and Natural Resource Sciences

Copyright 2002 Washington State University

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Issued by Washington State University Extension and the U.S. Department of Agriculture in furtherance ofthe Acts of May 8 and June 30, 1914. Extension programs and policies are consistent with federal and statelaws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, national or ethnicorigin; physical, mental or sensory disability; marital status, sexual orientation, and status as a Vietnam-eraor disabled veteran. Evidence of noncompliance may be reported through your local Extension office. Tradenames have been used to simplify information; no endorsement is intended. Published September 2002.Reprinted November 2003. G. Subject codes 500, 400. EB1943