D forestcanopy [..] soil- floor

key:270

210a)aU

150 —a)Eco6 90—

A12 24 36

time after spraying, months

Fig. 1. Graph showing DDTR (DDT residues) disappear-ance from forest ecosystem.

30

Water level control. Forest drainage, or more„.,•,selv, regulation of the soil water regime, has,.,, practiced with varying success in several

„ninnies. In the southeastern United States aAmber of pulp and paper Companies regulate,ter levels to increase tree growth on coastal

. 1 , wetlands, including organic and high-water-!.thlt• mineral soils. A few companies in the north-,,, Lake States are also interested in controllingAter levels for both pulpwood production andmistma s tree crops. However, control of water,cis to increase timber growth has received the

,J eatest emphasis in northern Europe, where,..entries such as Sweden, Finland, Poland, and

l • Soviet Union have large areas of peatland for-producing needed supplies of wood.

'Ile N inrush program of water level control in-. a■ies topographic surveys, detailed examinationt the organic soil, and careful design of ditches.

%lain ditches and secondary contour ditches aretag by plows and ditching machines. Contouritches, designed to lead water to the main outlet.iit■ h, are usually 90-170 ft apart and 15-20 in.deep. Other cultural activities such as tree plant-

thinning of dense stands, and application of:•itilizers are often practiced on ditched areas tornhance the forest resource.

Not all attempts at water level control on peat-!Aids are successful. Effectiveness varies with the:% t ie of peat material and its physical properties in,ddition to the basic design of the drain system. In

1 .4 . atlands with undecomposed sphagnum mosst eats, water tables can be lowered effectively withwidely spaced ditches, as much as 175 ft apart.llowever, with decomposed peats, very close spac-.ng of ditches (as near as 12 ft apart) may be neces-- try to properly control soil water because of the,env slow water movement. This would be uneco-,,mical in most forest situations.For background information see FOREST ECOLO-

.•): P EAT in the McGraw-lull Encyclopedia of Sci-, Hue and Technology. [ROGER R. BAY]

Bibliography: R. R. Bay, J. Hydrol., 9:90-102,''t o9: D. If. Boelter, Proceedings of the 3d Interna-

• •,nal Peat Congress, Quebec, pp. 150-154, 1970;D. II. Docker, J. Hydrol., 15:329-340, 1972; Fin-

Peatland Society, Finnish Peatlands andTheir Utilization, 1972.

Pesticidei ' ,. sticides are important tools for food and fiberp r oduction and for the protection of public health,ut their improper use can adversely affect desir-

-, l1e organisms. Recent studies of DDT behavior in'Le forest indicate that this insecticide does not',1., ve deep into the soil profile and has a half-life of

Years in the forest floor. The mechanisms ofloss from the forest have not been clearly

t ablislied. Concern about long-term, far-reach-ecological impacts remains. Herbicides, which

! t • also important tools in forestry, are fairly rapid-' degraded by microorganisms in the forest floor,

except for brief periods during application,:;17.itt'insis. little opportunity for them to enter

The burgeoning human population requires an"' leasing flow of food and filter from the land to..t ititait t a hiat standard of living. The agricultur-

alist and the forester are trying to meet the de-mands for increased food and fiber from a land-production base which is constantly diminishingbecause of urban sprawl, freeway construction,and the assignment of large areas to recreationalpurposes. Intensive management and the applica-tion of advanced technology are necessary to coun-terbalance this continuing reduction in the land-production base. The use of chemical pesticides,including insecticides, herbicides, fungicides, androdentieides, is an integral part of intensive agri-culture, forestry, and public health protection. Theuse of these materials, however, must not diminishthe quality of the environment shared by all.

Determining the probable effects from the use ofa particular pesticide on desirable organisms livingin or near treatment areas requires considerationof two factors: the toxicity of the chemical, and theprobability or likelihood that the organism will beexposed to a biologically significant amount ofchemical. The toxicity characteristics of most pes-ticides have been widely studied. Much less atten-tion has been given to the size of the dose and theduration of exposure that organisms in the fieldwill receive after a specific pesticide has been ap-plied. Pesticide movement, persistence, and meta-bolic fate are the principal factors which deter-mine the degree and duration of exposure. Thesefactors have received some study in the agricultur-al environment but little in the forest.

Use of DDT. The insecticide DDT remains apoint of controversy as strong pressure developedto use the chemical during the early summer of1973 to control a 400,000-acre (1 acre= 4047 in2)infestation of Douglas fir tussock moth in Oregonand Washington forests. Federal regulatory agen-cies.denied permission for the use of DDT becauseof concern about its possible effects on desirableorganisms and because a natural virus was expect-ed to destroy the tussock moth infestation by theend of the summer. Some other short-lived insecti-cides were scheduled for use on a small part of theinfested area to minimize defoliation. Intensivesalvage operations were planned to make full useof insect-killed timber.

Earlier studies implied that (1) significant quan-

atlands t„ Pratt,,ripe and to afor fo -stryydrologic charact,soils is not unifot

retention, or stunt-.A water rover:,rough peatlands

properties of lirga•. Y.

I pore space and /”.,.ling to how the p..tition. Undecomp,—,yd at the surface: by volume at saint.:large pores that p,

id water move/mi.the peat may heabout 50-80% of ttimage. However, a.!.• often found loweres which retain wahtter movement. 'Hueir water to draina;,,)e less than tow-tent!

ge space available I.water to streamswater available

teat type. These att.:success of draina..,

unoff from peatland•tits, surrounding g•.:of the organic soil-

tin and snow provide •r to most peatland•ceive water from

These are eallt•more nutrients at,

inflow, a greater van:his type of peatlan•

regulating effectis during dry slum, r

ype of peatland.Ind separate from ti,

and their primat,ntation, which is rci.,

growth is general,dwater bogs. Most •-•his type of bog occw •water tables are hity through the pot,-••

dry periods, eS,11-•r water tables, andire decomposed si•-ating in perched •ins of these two h.t.

them peatlandsIt the year. Also, cdinns may be dela■■is related to tie • t!-,ity in the peat al.•.type of peat throit-

1160

1973. P. 329-330 in Daniel N. Lapedcs,ed. Yearbook of Science and Technology.McGraw—Hill, NY. 465 p.,

120

100

90

80

70

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40

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20

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Gainerttons

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330 PESTICIDE

0 20 40 60 80 100time, days

titles of DDT were washed from the forest canopyto the forest floor for several years after applica-tion, (2) the chemical was leached by rainwaterdeep into the soil profile, and (3) it persisted forvery long periods of time in the forest floor (in thelayer of newly fallen and decomposing leaves). Themost recent studies indicate otherwise.

R. F. Tarrant and associates made an intensivestudy of the entry. movement, and persistence ofDDT in the forest floor and soil after a 0.75 lb/acre(1 lb = 0.45 kg) application in a forest in easternOregon in 1965. This study established severalimportant concepts about DDT behavior in theforest (Fig. 1). (1) DDT is largely confined to theforest floor, and relatively little . moves into theupper 3 in. (1 in.= 2.54 cm) of mineral soil. Be-cause of this kind of behavior. DDT is not likely toleach through the soil profile and contaminategroundwater. (2) The total amount of DDT (andmetabolites) in the forest floor and soil declineswith time. In this instance, only half of the DDTthat was present 1 month after spraying remained3 years later. (3) Relatively little DDT is in rain thatfalls through the forest canopy. This is not surpris-ing, because DDT is not very water soluble (aboutI part DDT will dissolve in 1,000,000,000 parts ofwater). (4) When the needles Or leaves fall from asprayed tree, some DDT will be added to the forestfloor. About 6% of the DDT applied to the foliagereached the forest floor in the form of falling leavesor needles, according to the Oregon study. Most ofthe emit ribution from this source occurred duringthe first 18 months after application.

R. N. Yule measured DDT residues in the forestfloor and soil under a central New Brunswick for-est that had received 4.4 lb/acre of DDT in variousapplications between 1956 and 1067 to control thespruce budworm. This investigation also revealedthat DDT residues were confined to the uppermostlayers of forest floor and soil, where DDT had ahalf-life of 3-5 years.

Thu Sc studies indicate that DDT is not a perma-

nent part of the forest after spraying, but it;,.mechanisms of loss from the immediate vicium,have not been identified with certainty. A cond,,nation of chemical. physical, photochemical,biological degradation processes and volatilitatim,are probably the most important. DegradationDDT may lead to formation of DDE, which is in,,r;volatile than DDT and therefore more likek b,leave treated areas and enter global transpor t 'v.terns. Scientists do not agree on the importance o:the global distribution of DDT and DDE, in relatioi,to their impact on various organisms, but all a11-1,

that the potential for such long-term, far-reachim:impacts must be considered when spray project.are proposed.

Herbicides. Herbicides are equally as impitrt amas insecticides are in forestry, but their use ha.generated much less public concern. Herbicide.are used to kill or inhibit the growth of bru.h%plants which compete with more desirable tree.for light, water, nutrients, and growing space. Tiltphenoxy herbicides (2.4-D and 2,4,5-T), aminotriazole (amitrole), and picloram are frequenthused in forestry. As a group, they are relati‘cklow in toxicity to fish and wildlife and do Inapersist for long periods in the environment.studies with forest floor material these herbicide.were all degraded but at different rates (Fig. 2t. Inthe forest environment 2,4-D and amitrole are notlikely to persist for more than a few month.:2,4,5-T may he present for 1 year; and piclorammay last for one or more growing seasons.

Biological degradation rate. Degradation ofpesticides in the forest is important because itthe only means by which the total environmentalload of these materials can be reduced. Biologicaldegradation is the principal means of loss of man■pesticides in the forest' floor and soil, althoughstrictly chemical degradation processes arc inipor•tam for some compounds. The rate of biological de-gradation of a particular pesticide will vary ae•lird-ing to the density of the microbial population .111.1

according to environmental factors like soil temperature, moisture, oxygen, and nutrient level-.which influence the rate of microbial metabolism.

Protection of the aquatic environment is impor-tant in forestry because streams are the habikoof numerous biological communities, and high-quality water is critical to downstream users.Large quantities of pesticide seldom occur inforest streams. Relatively rapid degradation inforest floor and soil and limited movement over theforest floor or through the soil profilelung-term pesticide entry to streams. Pesticid e -can enter streams for brief periods, however, dur-ing application, when spray materials fall directi%on surface waters. Proper spray equipment andchemical formulations and careful locationspray unit boundaries to avoid streams are mean.that responsible forest managers use to miliinuiethe entry of spray materials to forest streams.

[LOGAN A. NO1■10%1Bibliopraphy: L. A. Norris, J. Forest., 69:71-,.

1071; IL F. Tarrant et al., Pestir. Monit.1972; C. T. Youngberg and C. R. Davey (eds.), /telGrowth and Forest Soils, 1070; W. N. Yule, Bull.Enriron. Contam.Taxicol., 9:57, 1973.

120 . 140

160 180

Fig. 2. Graph showing degradation of four herbicides in forest floor material duringa period of 120 days after application. The chemical was applied directly to thematerial.