Lily Castle TidwellDr. TorreanoForestry 31227 April 2015

Ecological Forestry in Douglas-Fir (Pseudotsuga menziesii) Forests of the Pacific Northwestern United States

Ecological Forestry

Ecological forestry is an emerging concept in the field of forest management

based on silvicultural techniques that emulate natural disturbance regimes, thus

preserving a relatively natural functioning forest ecosystem. Although its goal of

blending environmental stewardship with production of goods for human use has

been around for some time, reputable studies and a growing qualitative understanding

of the concrete practice of ecological forestry are in their relative infancy. The

potential behind ecological forestry seems to be a harmony between profitable forest

products and healthy forest ecosystems, both of which are heavily weighted with

ideological and practical importance. With an ever-growing global human population,

the essential question behind the development of the ecological forestry approach is

how these emerging land management strategies are to contribute to the challenging

balance of ecosystem services, forest products, and preservation of intrinsically

valued natural spaces. Studies exploring the data behind ecological forestry in

comparison with natural disturbance regimes and with traditional silvicultural

methods allow land managers, the scientific community, governing bodies, and the

general public the opportunity to understand the vast benefits and real drawbacks of

a new method of tending forested lands.

According to a report from the U.S. Forest Service, “incorporating an

understanding of natural disturbance and stand development processes more fully

into silvicultural practice is the basis for an ecological forestry approach,” (Franklin et

al 2007). This necessarily involves an exploration of environmental and economic

priorities, each of which often comes at some cost to the other. In the development

of forestry in both Europe and in North America, there occurred a transition towards

working with forests, rather than against them, as the limited availability of trees

became clear, though this was as different points in history in these two places

(Seymour and Hunter 1999). Understanding the limits of how much wood a forest or

tree can produce, rather than simply stripping land of all timber and moving to new

areas, has its roots in the concept of playing by the rules of an ecosystem. As

silvicultural technologies have advanced, foresters have become able to produce vast

quantities of timber by stretching these limits; breeding, chemicals, and heavy

machinery have meant that foresters can use water, sunlight, and chlorophyll to their

full advantage without respect to other elements of a forest ecosystem. This

imbalance is where ecological forestry comes into play.

As a part of the environmentalist movement, public demand for more

sustainable land management has grown substantially in the last several decades, even

at the cost of decreased production or profit. Seymour and Hunter (1999) explain

that “what distinguishes ecological forestry […] is the emphasis placed on natural

patterns and processes: understanding them, working in harmony with them, and

maintaining their integrity, even when it becomes financially difficult or inconvenient

to do so.” In practice, this means evaluating the ecological integrity of a silvicultural

system in terms of how true it is to natural disturbance regimes, whether it is at the

scale of single trees, groups of trees, entire stands, or whole landscapes with regards

to intensity and frequency of disturbance (Seymour et al 2002). Ideally, these

ecologically-minded goals can be balanced with social and economic demands to

create diverse and sustainable management systems.

Silvics of Douglas-Fir

Douglas-fir trees (Pseudotsuga menziesii) are generally found along the Pacific

coast from southern British Columbia to northern California, as well as in much of

the Rocky Mountain range. Their range is limited to the north by low temperatures

and to the south by insufficient moisture. Douglas-fir generally does not grow

successfully without well-aerated, slightly acidic soils, which are found both along the

Pacific coast and throughout much of the Rocky Mountains. They exhibit

intermediate shade tolerance, regenerating well in open or mostly open conditions

such as under a clearcut, canopy gap, or shelterwood system. This report focuses on

the Pacific Northwestern region of the Douglas-fir range, characterized by mild, wet

winters and cool, dry summers (Hermann and Lavender 1990). More specifically, the

Western hemlock zone of the Douglas-fir range will be discussed. This zone is

characterized by a Douglas-fir-dominated forest resulting from a history of fires,

clearcuts, and Douglas-fir planting. Other important species in this zone include

western hemlock, western redcedar, and red alder (Curtis et al 2007).

Douglas-fir is the most popular timber production species in the Pacific

Northwestern United States. Since the 1950s, the typical method of growing

Douglas-fir for quick regeneration and maximum timber production has been to

“clearcut, burn, and plant,” (Curtis et al 2007). In commercial settings, the current

rotation length is generally 40 to 60 years, while rotations on National Forest lands

are usually 80 to 120 years (Kohm and Franklin 1997). Common alternatives to

clearcuts include patch cuts and seed-tree cuts, both of which result in greater

retention of structural and biological features than clearcuts. To achieve successful

natural regeneration, either 50% or more of the overstory must be removed, or

patches of 0.4 hectares or greater must be created, though no part of the interior of a

cut patch should be more than 400 meters from standing timber. If planted seedlings

are used to supplement regeneration, the greatest success will result from cutting east-

west strips, making small patch cuts, or using a seed-tree cut with 6 to 10 trees

retained per acre (Curtis et al 2007).

Even-Aged Management

Stand-scale disturbances in the form of even-age management have been the

backbone of harvesting practices through most of the history of forest management,

be they clearcuts, thinning, shelterwood cuts, or seed cuts. The idea behind these

strategies, in addition to timber production, has been that all forests are periodically

impacted by large disturbances and that emulating these disturbances allows these

losses to be captured, so to speak. Disturbances of this scale can be referred to as

stand-replacing events (Seymour et all 2002). In Douglas-fir forests of the Pacific

Northwest, naturally occurring stand-replacing events in the form of catastrophic fire,

large beetle outbreaks, wind storms, or geologic activity occur as infrequently as every

few thousand years (Orians and Schoen 2013). Studies of succession in these forests

have shown that it takes at least 120 to 240 years for Douglas-fir stands to begin to

develop the high structural and biological diversity of old-growth stands (Kohm and

Franklin 1997). The common commercial rotation length of 40 to 60 years, or even

the more modest National Forest rotation length of 80 to 120 years, is clearly not an

accurate emulation of natural disturbance patterns (Fig 2).

Another significant departure of even-age management from organic stand-

replacement events is the removal of nutrients and structures from the site. Even

shelterwood and seed cuts leave far fewer biological legacies in the form of snags,

downed dead timber, and live trees than natural large-scale disturbances (Franklin et

al 2007). This dramatic change in physical and nutritional forest composition can

have significant effects on wildlife and on recolonization of disturbed areas, especially

with the removal of snags and downed boles.

An ecological forestry approach to stand-replacement disturbances means

designing harvests at a scale and frequency that more accurately reflects natural

patterns, which in most cases means smaller and less frequent even-age cuts than are

currently practiced (Seymour et al 2002). For ecological benefits, a return interval

ought to be “long enough that structural complexity, particularly as a result of

noncompetitive mortality processes, can develop,” though this development forms at

different time scales in different forest types (Franklin et al 2007; Fig 3). In a Pacific

Northwestern Douglas-fir forest, the implementation of even-age ecological forestry

tends to focus on retaining biological legacies after harvest, employing variable

density thinning, and allowing at least 120 years for recovery of dominant species

between harvests (North 2008).

While an ecological forestry system is more balanced than a typical clearcut,

there is strong evidence that commercial clearcuts are simply not appropriate for

wildlife, biodiversity, and aesthetic values in Douglas-fir forests. Even when natural

large disturbances occur, it has been shown that Douglas-fir exhibits “multi-decadal

single cohort establishment,” meaning that a naturally regenerated single-cohort stand

can have trees as much as 60 years apart in age (Freund et al 2014). The authors of

this regeneration study explicitly state that “managers seeking to mimic natural

processes will need to consider alternatives to dense plantations,” meaning stands

that are “less dense or more heterogeneous or both,” (Freund et al 2014). Indeed, an

extensive study of natural Douglas-fir forests concludes that “it is more realistic to

think of Douglas-fir stands in terms of a mosaic of eco-units rather than of one large,

even-aged unit,” (Kuiper 1988; Fig 4).

Uneven-Aged Management

Group selection and single tree selection methods of uneven-aged, or multi-

cohort, stands are meant to emulate a pattern of few stand-replacing events but

somewhat frequent disturbances that create small canopy gaps (Seymour and Hunter

1999), often caused by root rot diseases in the Pacific Northwest (Orians and Schoen

2013). In practice, these systems generally involve thinning other areas of the stand in

addition to harvesting groups or individual trees. This method has aesthetic,

economic, and wildlife values, in that a group selection harvest only affects a small

portion of a stand while still accomplishing regeneration.

In Douglas-fir forests, ecological forestry methods generally agree about the

importance of habitat continuity, structural diversity, and biological legacies, but

disagree about how to achieve these characteristics. For example, the “New Forestry”

system, as it is called by Prudham (2005) is designed specifically for the Douglas-fir

region and “draws on the concept of adaptive management and thus embraces a sort

of experimental, management-based learning by doing.” It supports the use of a

multi-aged system that leaves behind biological legacies that benefit wildlife, such as

large overmature trees, snags, and coarse woody debris, but argues against clearcuts

or even group selection (Prudham 2005). Other foresters have suggested that

mixtures of extended-rotation clearcuts, shelterwood cuts, seed-tree cuts, and group

selection can create healthy structural diversity and habitat continuity, so long as

biological legacies are retained, while producing high volumes of timber (Orians and

Schoen 2013, Kohm and Franklin 1997). North (2008) argues that a group selection

system with biological legacies and underplanting can produce a variety of aesthetic,

ecological, and economic benefits, as well.

Applications and Implications of Ecological Forestry

As understanding of ecosystem needs and their relationship to economically-

oriented land management grows, the question of what comes next becomes

important. As stated by Franklin et al (2007), “the challenge many foresters and forest

management organizations now face is the need to develop silvicultural systems that

result in stand conditions that incorporate ecological complexity and heterogeneity in

much greater degrees than have been considered before.” For Douglas-fir forests of

the Pacific Northwest, an important obstacle to ecological forestry lay in economic

considerations. For instance, clearcut logging not only generates large financial

returns, but deer and elk prefer browsing in freshly cut stands, potentially bringing in

major revenue from hunting permits. Additionally, Kohm and Franklin (1997) explain

that, while extended rotations and other considerations for biodiversity are likely to

be more economically sound in the long run than clearcut or group selection systems,

high up-front costs are required to convert traditional Douglas-fir plantations to

more complex stands. Another intriguing and controversial element to consider is the

recent increased return intervals of devastating wildfires and beetle outbreaks

occurring in the region, likely as a result of climate change (Seidl et al 2014). The

impacts of these stand-replacing disturbances can be lessened somewhat by more

frequent prescribed burns and destruction or removal of dead wood (Seidl et al 2014),

suggesting that perhaps traditional clearcut systems may become better suited to

climatic conditions in the near future than ecological forestry systems.

Examining the possibilities of new forest management throughout the world,

some may suggest that all forests should be managed under ecological forestry.

However, this concept is neither economically nor environmentally practical given

that management of any kind is impractical on some lands and that intensive

production undoubtedly allocates energy into fiber production more efficiently than

natural processes. It seems that, instead, a “landscape triad” could balance

preservation, ecological forestry, and intensive management. Some forested lands

would be left alone out of practical necessity and for intrinsic aesthetic value, some

would be managed under ecological forestry principles, and others would be operated

as plantation systems for highly efficient output of timber. “One could, in theory, set

aside 3-5 hectares of ecological reserve for every hectare shifted into production

forestry, with no net loss in overall timber production,” (Seymour and Hunter 1999).

Perhaps this system could be successful in perpetuating both successful Douglas-fir

plantations and priceless old-growth Douglas-fir forests. It seems that, with so many

new tools for change, the goal of forest managers and landowners as a community

must now be to undergo a reorganization of priorities to address the growing need to

respect the ecological needs of forests in balance with the practical economic

necessities of the modern economy.

Figure 1: Range of Douglas Fir (nps.gov)

Figure 2: Single Cohort Establishment of Douglas Fir in Commercial, Natural Conceptual Model, and Unmanaged Stands (Freund et al 2014)

Figure 3: Development of Douglas-Fir Stands (Kuiper 1988)

Figure 4: Example of Eco-Units in a PNW Conifer Forest (Kuiper 1988)

Works Cited

Burns, R. M., and Honkala, B.H. 1990. Silvics of North America. Vol. 1. Washington: U.S. Dept. of Agriculture, Forest Service.

Curtis, R. O., DeBell, D.S., Miller, R.E., Newton, M., St. Clair, J.B., and Stein, W.I. 2007. Sivicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region. Rep. no. PNW-GTR-696. Forest Service Pacific Northwest Research Station.

Franklin, J.F., Mitchell, R.J., and Palik, B.J. 2007. Natural disturbance and stand development principles for ecological forestry. Gen. Tech. Rep. NRS-19.Newtown Square, PA:-U.S. Department of Agriculture, Forest Service, Northern Research Station. 44 p.

Freund, J.A., Franklin, J.F., Larson, A.J., and Lutz, J.A. 2014. "Multi-decadal Establishment for Single-cohort Douglas-fir Forests."Canadian Journal of Forest Research 44.

Hermann, R.K., and Lavender, D.P. 1990. "Pseudotsuga Menziesii."Silvics of North America. Vol. 1. N.p.: U.S. Dept. of Agriculture, Forest Service. 527-540. Print.

Kohm, K.A., and Franklin, J.F. 1997. Creating a Forestry for the 21st Century: The Science of Ecosystem Management. Washington, D.C.: Island Press.

Kuiper, L. C 1998. "The Structure of Natural Douglas-fir Forests in Western Washington and Western Oregon." Agricultural University Waginengen Papers 88.5.

North, M.P., and Keeton, W.S. 2008. Emulating natural disturbance regimes: an emerging approach for sustainable forest management. In: Lafortezza, R. Chen, J.,Sanesi, G., and Crow, T.R (eds) “Patterns and Processes in Forest Landscapes – Multiple Use and Sustainable Management. Springer Science. Pp. 341-372.

Orians, G.H., and Schoen, J.W. 2013. Natural Disturbance Patterns in the Temperate Rainforests of Southeast Alaska and Adjacent British Columbia. North Pacific Temperate Rainforests: Ecology & Conservation. N.p.: U of Washington. 73-88. Print.

Prudham, W.S. 2005. Knock on Wood: Nature as Commodity in Douglas Fir Country. New York: Routledge. Print.

Seidl, R., Rammer, W., and Spies, T.A. 2013. Disturbance Legacies Increase the Resilience of Forest Ecosystem Structure, Composition, and Functioning. Ecological Applications: 2063-2077.

Seymour, R.S., and Hunter, M.L. Jr. 1999. Principles of ecological forestry. In: Hunter, M.L. Jr (ed) Maintaining Biodiversity in Forest Ecosystems. Cambridge University Press. Cambridge, MA, pp. 22-61.

Seymour, R.S., White, A.S., and deMaynadier, P.G. 2002. Natural disturbance regimes in northeastern North America-evaluating silvicultural systems using natural scales and frequencies. For. Ecol Manage. 155: 357-367.