EVALUATING SHORT-AND LONG-TERM EFFECTS OF HERBICIDES ONNON-TARGET FOREST AND RANGE BIOTA

Michael Newton and Logan A. Norris 1/

Herbicides are one of the most ecologi-cally powerful, environmentally gentle toolsavailable to the manager of forests and range-lands in the United States. These chemicaltools are used to accomplish a wide varietyof management objectives through alterationof density and composition of vegetativecommunities. Their power suggests that theycan be used as substitutes for more destructivepractices. This same power, however, dictatesthe need for thoroughness in the search forharmful effects, both through research andobservation of practice.

An adequate biological evaluation of theenvironmental impact of herbicides in forestsand rangelands requires consideration of bothshort-and long-term effects which are mediated,either directly through toxic impact or in-directly through microsite or habitat modifi-cation. The environmental statements requiredby NEPA are the vehicle with which suchevaluations are made on federally managedproperties. Environmental statements forvegetation management programs using chemicalshave markedly improved as professionals havegained experience with the environmentalstatement process. However, we find over-whelming attention has been given to consider-ation of direct toxic impact on non-targetanimals with little evaluation of the onlyprofound ecological impact of herbicide use:i.e., the alteration of the composition,density, and developmental trajectory of thevegetation. It is apparent that primary pro-ducers, and the modification thereof, have adetermining role in the lines of all otherbiota. This paper presents an approach basedon that principle for use in the preparationof environmental statements and managementplans.

1/ Professor of Forest Ecology, Oregon StateUniversity, Corvallis and SupervisoryResearch Chemist, USDA Forest Service,Pacific Northwest Forest and RangeExperiment Station, Corvallis, Oregon.

LAND MANAGEMENT SYSTEMS AND THEROLE OF HERBICIDES

Forest and rangeland management objec-tives nearly always revolve around vegetation.

Management of vegetation is basic to timberor grass production and wildlife, recreation,or water considerations. Each growing sitehas some potential for the production ofvegetation biomass. Modern land managementobjectives frequently involve capturing (orrecapturing) as much of the site potential aspossible in a desirable form of vegetation.The knowledge that ecosystems will respond incertain ways to treatment is basic to the useof these tools to effect certain changes.The ecological basis for vegetation managementcan be examined by considering the relativebiomass trajectories for four major types ofvegetation on the grassland ranges and foresttree communities in the United States duringthe last several hundred years (Figure 1).

Many ranges now dominated by shrubs werelargely occupied by grass at the time ofEuropean man's entry on the landscape. Thetree, shrub, and forb components of the com-munities were present but less prominent.Ancient man undoubtedly influenced the biomassdistribution among these four components tosome degree, but his activities were neitherintensive nor extensive. Modern man, on theother hand, has gone through a period ofresource exploitation in which selectiveforaging has resulted in a strong shift awayfrom grass and forbs towards unpalatable treesand shrubs.

The recent application of managementtechniques using selective herbicides hascaused a marked shift in allocation of siteresources back to grass. Herbicide-sensitivetrees and shrubs (the dominant parts of thetarget systems) are substantially reduced inbiomass and the resulting void is soon filledby seeded grasses and forbs and later bynative grasses or species adapted to thegrazing regime. This practice is almost areverse of the grazing effect. In the faceselective removal pressure, the resistantspecies, whether removed by herbicides oranimals, become more abundant. Because oftheir inferior competitive position, underpressure, the sensitive species subsequentlyhave difficulty returning to sites occupied

133

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by resistant species without additionaldisturbance. Therefore, chronic harvestingpressure must be complemented by a weedingprogram of comparable intensity for mainten-ance of the harvested species.

Range managers use both weeding andcontrol of harvesting (i.e., vegetation manage-ment) to stabilize primary production in pre-ferred species. Such a procedure influences

and trees to favor forbs and grasses. Thismay be type conversion where forbs and grassesare essentially no longer a major part of thepresent community. In this case seeding orplanting operations are also conducted toprovide growing stock of desirable species tooccupy the site vacated by trees and shrubs."Release" treatments are used when grassesand forbs are part of the stand but theirgrowth is restricted by deficiencies of

Figure 1. Generalized biomass trajectories forstate of periodic disturbance (fire)

the carrying capacity of the ecosystem fornon-target species and cattle. The sameset of principles appears to hold in forestsas well as rangelands.

MANAGEMENT TECHNIQUES INVOLVINGHERBICIDES

Herbicides are used for a variety ofspecified purposes in both forest and rangemanagement. Range applications nearly alwaysinvolve reduction in the density of shrubs

two major types of vegetation in their naturaland under moderate intensity management.

light, water, nutrients, and growing spacecaused by tree and shrub species. In thiscase, the application of selective chemicalsmay be augmented by seeding or some othercultural practice to ensure occupation ofvoids by desirable species.

Type conversion and grass release areby far the most extensive patterns of rangeherbicide use. Contiguous rangeland appli-cations may vary in size from only a fewhectares to several square kilometers.

134

Applications may be made by ground equipmentbut more frequently by fixed wing aircraftor helicopters. The size of the sprayed unitis important to non-target biota, and thedegree of importance is related to speciesmobility.

Herbicides are used in forestr y forpurposes which are analogous to those inrange management. Reforestation or typeconversion, for example, involves a reductionin shrub, grass, or weed tree biomass topermit establishment of desired forest treespecies. Fire frequently is used as anadjunct tool. Seeding or planting insuresoccupation of the site by desirable species."Release" spraying is used when various weeds(trees, shrubs, forbs, or grasses) preventestablished desirable tree species fromachieving site dominance because of excessivecompetition for site resources. In this kindof application, selective herbicide action(achieved through the use of a particularchemical, rate, or season of application) isused to depress the competitors and acceleratethe growth of a desirable species.

Reforestation, type conversion, andrelease treatments account for the vastmajority of herbicide applications in forestry.However, the thinning of overstocked standsand cull tree removal with chemicals areincreasing in importance as the intensity offorest management increases.

Herbicide application for type conversion,reforestation, and tree release are mostfrequently accomplished with aircraft, althoughground application equipment is used in somelocations when vegetation and terrain permit.Contiguous treatment areas are on the averagesmaller than in rangelands, but there may be alarge number of the treated units varying insize from 1 to more than 100 hectares. Largerblocks of land are seldom treated; and themosaic of treated and untreated sites offersconsiderable diversity and escape opportunityfor wildlife, including species of limitedmobility.

Herbicides are used on forest and range-lands for several purposes unrelated to specificland management objectives. These include thecontrol of vegetation on powerline, railroad,and other rights-of-way and phreatophytecontrol in riparian zones. These areintensive applications but are more limitedin scope.

The use of herbicides for modificationof wildlife habitat is also a viable manage-ment technique for both habitat improvementand for control of damage to forest

regeneration. Herbicides are not widely usedfor these specific purposes at present, butthese uses are likely to increase. A greatdeal of big game habitat improvement resultsas an incidental benefit from other vegetationmanagement practices involving herbicides.

RELATIONSHIP BETWEEN CHEMICALBEHAVIOR AND DIRECT EFFECTS ON

NON-TARGET SPECIES

Short-and long-term effects of chemicalsare dependent on exposure of organisms to abiologically significant dose of herbicide.The initial distribution, movement, per-sistence, and fate of a herbicide in aparticular environment are of paramountimportance in determining the probability oforganism exposure. Chemical behavior is theresult of an interaction between the propertiesof the chemical and the properties of theenvironment. This interaction is guided byphysical laws to produce the particularpattern of herbicide behavior observed innature (Figure 2).

Figure 2. Chemical behavior in the environ-ment determines organism exposure.

Herbicides are, for the most part, short-lived in the environment. Therefore, theirdirect toxic impacts are largely restricted tothe occurrence of an acute lethal dose. Theirindirect effects, however, can be long-lastingbecause they can alter short-term compositionand long-term trajectory of the succession ofthe plant community. Chemical behavior in theenvironment, while clearly important in deter-mining direct toxic impacts, should also beinterpreted in terms of its specificity forcertain plants when we analyze effects onvegetation and associated animal communitystructure.

135

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ANALYSIS OF SHORT-TERM CHEMICALEFFECTS - DIRECT TOXICITY

The time span in our definition of "short-term" is arbitrary. We have selected the yearof application or the duration of biologi-cally significant herbicide residues, which-ever is longer. With the possible exceptionof picloram, short-term effects will berestricted to the year of application; mostwill be a matter of days or weeks. None ofthe herbicides used in rangelands or forestshave been shown to accumulate substantiallyin animal tissues. The short-term ofpersistence eliminates chronic intoxicationas a possible effect.

A direct toxic effect of an herbiciderequires organism exposure to a significantdose. Toxicity to a given organism is aninherent chemical property. Organismresponse to exposure is produced by a com-bination of magnitude and duration ofexposure with absolute toxicity.

The nature of the dose-response relation-ship varies with both the chemical and theorganism. The pattern of dosage and potentialresponses of forest pesticides has beensummarized by Newton and Norgren (1977).Variation within species (Figure 3) isindicative of the range of dosages producing

some effect on a species. Exposure has noeffect on the population up to a thresholdlevel, then effects become progressivelygreater until nearly all organisms haveresponded. The data for acute toxicity usuallyshows a deviation from the normal distribution.There is typically a "no-effect" level anda "100-percent" response level (these extremeswould be absent if the effects followedthe normal distribution). It is only between these extremes that a herbicide hasan effect on a given population. Whencomparing among populations, however, anarray of population effects may be used toexamine the differences in sensitivityamong different classes of organisms.

The dose-response relationships for aherbicide to several organism groups, arecompared in field and laboratory exposuresin Figure 4. These examples show that broad-leaf higher plants are consistently the mostsensitive organisms to the herbicide 2,4-D,and that low sensitivity and low exposure bothcontribute to the safety of animals. This isthe basis for its use for selective controlof vegetation, and is the basis for using waterquality criteria for protection of aquaticorganisms. Most pesticides are registeredfor use to control only the organisms whichare highly sensitive. Thus, a selectivechemical effect is achieved through the

0.1 10 1,000 100,000ABSORBED DOSAGE,

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Figure 3. Typical dosage - response curve for an animal population fed a toxic substance. Notethat dosage is based on units of toxicant per unit of body weight. Threshold (noeffect level) is the dosage below which organisms detoxify chemical as fast as it isabsorbed. These curves are transformed normal distributions. In laboratory tests,slopes of curves vary among species (Muirhead-Thomson 1971).

136

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economic as well as biological screeningprocess.

The probability for toxic impacts onnon-target organisms is significant wheredose-response curves for target and non-targetorganisms overlap to a significant degree.The herbicides used in forest and rangemanagement are not known to produce directacute or chronic effects on organisms otherthan higher plants when used at registeredrates of application.

EFFECTS OF HERBICIDES ON ANIMALS

Figure 4 illustrates a large marginbetween the dosage of herbicide required formaximum effect on higher plants and the levelrequired for threshold response in animalsof all kinds. Norris (1971) and House et al.(1967) have summarized a substantial amount ofdata on herbicide residues and persistence invegetation, soil, and water, and (Newton andNorgren 1977) have summarized the impacts ofsuch residues on a variety of species in theforestry context. In general these authorsindicate that for a 2-kg/ha application,initial herbicide residue levels would (1)generally be less than 100 ppm in vegetation,(2) be less than 3 ppm in the surface 2.5 cmof soil and (3) be less than 0.05 ppm instreams, unless extensive direct applicationis made to surface water. These initialresidue levels will vary somewhat with con-ditions of application and vegetation com-position and density. Their quantities produceeffects on sensitive plant species but notanimals exposed to the same applications.

Animal exposure occurs dermally duringand immediately after application. Dermaltoxicity of herbicides is typically lowenough to be of academic importance, asattested by research data and years ofactuarial data for spraymen daily exposed tothe concentrates. Oral ingestion, however,may be significant. Given the maximum levelof 100 ppm of herbicide in treated herbage,in 1 day, an animal consuming 5 percent ofits weight per day ingests a maximum of5 mg/kg/day for each kg/ha applied,assuming all of its feed has a maximum con-centration of herbicide. Animals appear totake in less than the maximum, however.Newton and Norris (1968) reported intake ofatrazine 2/ and 2,4,5-T by deer amounting toabout 1 percent of the theoretical maximum,or less. Furthermore, deterioration of boththe herbicide and the treated vegetationlimits exposure to a relatively short period,and herbicides usually pass through thedigestive system with little or no retention

Figure 4. Typical dosage-response spectra foran insecticide and a herbicidefor five classes of organisms.Mid-points for each group areestimates; those affected only inthe range of 500 mg/kg or greaterare not as precisely defined asthose in the more sensitive groups.

or accumulation. More recently, Newton andSnyder (1978) have produced detailed evidenceof negligible residues of the TCDD con-taminant of 2,4,5-T in forest wildlife.

Herbicide movement and persistence aredifficult to generalize in reference to pre-cise levels of exposure to consumer and aquaticorganisms. Norris (1971) and House et al.(1967) again offer reasonable summaries forpersistence characteristics in vegetation andwater. In vegetation, herbicide half-livesvary from 1 to 30 days. The half-life instream water varies from less than 0.5 to 24hours, when herbicide input is restricted tothe time of application. Rapid herbicide

?./This publication reports research involvingpesticides. It does not contain recommenda-tions for their use nor does it imply that theuses discussed here have been registered.All uses of pesticides must be registered byappropriate state and/or federal agenciesbefore they can be recommended.

137

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dilution with downstream movement tends toprotect aquatic organisms, and the recurrenceof contamination by movement of soil wateris unlikely (Norris and Moore 1971 ). Kearneyet al. (1969) and Harris (1968) report indetail on the mobility and persistence ofherbicides in soil, Figure 5.

The data on residue and persistence

characteristics of a herbicide in a specificenvironment can be used to determine both themagnitude and duration of non-target organismexposure. Exposure data can then be evaluatedin terms of established dose-response relationships for the chemical and the specificorganism or a closely related species forwhich test data are available. If themagnitude and duration of exposure are lessthan the threshold response level, directtoxic effects are precluded. This kind of ananalysis consistently shows that thoseherbicides and patterns of use registered by

138

- ' -

the Environmental Protection Agency for use onforest and rangelands will not normally resultin direct toxic effects on non-target animals.Strong evidence indicates that there is a largemargin of safety in this regard even in theevent of accident or other mishap.

EFFECTS OF HERBICIDES ON PLANTS

Herbicides are the pesticides to whichplants are most sensitive. It is the intentof forest weed control to initiate a changeof vegetation type, and the herbicidepractices in use today are generally veryeffective.

For practical purposes, the herbicides inuse in forest management may be groupedaccording to the spectrum of species theycontrol. Table 1 lists the herbicidespresently registered for forestry use andgives the principal group of plants affected,the important resistant species (commercialand non-commercial), and the persistence ofbiologically active residues in the forestenvironment.

The array of effects of herbicides listedin Table 1 suggests that most forest sitescarry considerable vegetation that willsurvive virtually any herbicide applied atregistered rates, even though plants are"sensitive." The target species are usuallynot killed completely by such applications,but are injured so as to decrease theircompetitive ability. The principal immediateeffect of applying a herbicide may be expressedin terms of the model illustrated in Figure 6,which diagrams a forest ecosystem in terms ofits principal structural components.Referring back to Table 1, it is possible tovisualize at what point a forest ecosystemis affected directly by the herbicide and forhow long the direct effect influences eco-system function.

There are specific effects worthy ofmention within each part of an ecosystem.These differ with the specific nature of theherbicide, the problem for which it is used,and the distribution of the herbicide in theforest. Triazines, glyphosate, dalapon, andoccasionally pronamide or amitrole are usedfor herb control in reforestation areas wheremoisture is limiting to survival of conifers.The rates of use generally preclude thesurvival of large amounts of grass. Theseherbicides are broadcast in ecosystems inwhich seedling trees are to be planted.During a brief interval following application,there is a substantial reduction in primaryproduction, a decrease in demand on water andnutrients, and a considerable decrease in

Months ofActivity inPlants

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Table 1. Herbicides Registered for Use in Forest Management, Durationof Direct Effect, Sensitive Groups of Species and ResistantGroups of Species.

Amitrole 1/2 - 6 1/2 - 1 Shrubs, herbs Coastal conifer Hardwoods, shrubsAsulam 12 1/2 - 1 Bracken only All conifers, hardwoods All woodyAtrazine 3 1 - 4 Annuals, Deciduous Most woody Woody, fernsAmmonium ethyl 24 <1 Shrubs, hardwoods Conifers Herbs, evergreen

carbamoyl woodyphosphonate

Arsenicls,1/ 3 1 - 6 Conifers, Few Few woody, manyorganic — hardwoods herbs

Dalapon 1 1/4 - 1 Grasses Trees Trees, shrubs,forbs

Dicamba 3 - 12 2 - 12 Shrubs, hardwoods Few Some shrubs, fernsDinoseb 1/4 <1/2 All green vegetation None NoneGlyphosate 24 <1/2 Most herbs, deciduous Conifers Evergreen woody,

woody plants dormant herbs—c.J Picloram 3 - 24 2 - 12 Trees, shrubs None Few woody ever-0 green shrubs,

grasses, fernsPronamide 2 - 4 3 - 6 Grasses All woody All woody, forbsSilvex ?../ 3 - 6 1 - 2 Shrubs, trees Conifers Some trees, shrubs,

grasses, fernsSimazine 3 - 6 4 - 8 Grasses, forbs Trees Trees shrubs, ferns

some herbs2,4-D 1/2 - 1 1/4 - 1/2 Some shrubs, forbs Conifers Hardwoods, shrubs

grasses, ferns2,4,5-T 2 / 3 - 6 3/4 - 1 1/2 Shrubs, hardwoods Conifers Some hardwoods,

ferns, grass

1/Applied by injection only; effect limited to treated stem.

2/Registered uses of Silvex and 2,4,5-T on forest land were suspended by EPA on March 1, 1979.

. UTILIZATION

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Figure 6. Simplified forest ecosystem modelillustrating the allocation ofsite resources to variousvegetation groups, and thence tovarious consumers. Rectangularsymbols represent organisms capableof storing carbon; pentagonalsymbols are site factors, orresources; "bowties" are internalcontrols; dashed lines are feed-back. DR, dominance ratio; DPdominance potential; H, habitat; Rresources (from Newton, 1973b).

carrying capacity for herbivores totallydependent on grasses, especially those oflimited geographic feeding range. Warmsummer rains can move nutrients toward aleaching sink if devegetation is continuedyear after year, but areas with dry summersand those with the usual incomplete vegetationcontrol do not sustain measurable losses(Miller 1974). These treatments are usuallyapplied no more than once or twice at thetime of reforestation, and their impacts are

b r ie f , leading to establishment of a forestcover.

The brushkillers (i.e., the phenoxys,picloram, amitrole, dicamba, glyphosate andammonium ethyl carbamoyl phosphonate), areusually used either in forest site preparationor in range or forest release operations in-volving application of broadcast sprays tocomplex mixed seral communities. These spraysdamage target woody vegetation considerablybut generally leave most of the herbs and someresistant trees and shrubs. While theherbicide is still active in sensitive woodycover, primary production decreases brieflyand herbaceous cover increases rapidly.Growth of resistant woody and herbaceousvegetation increases shortly after application.Structure of the treated ecosystem changes

substantially in terms of the dominance ratioof component species (Newton 1973a). Increasedgrowth of herbs and sprouts often increasescarrying capacity for herbivores. Resistanttrees and shrubs increase in dominance,eventually resuppressing the ground cover.

Herbicides are used in comoination withfire to an increasing degree. They permitcontrolled burning when surrounding areas areunlikely to be flammable. In this procedure,the herbicides may be used for sprout control,fuel desiccation, or both. The herbicides havea substantial effect on vegetation, but theresulting fire has an overriding effect onevery species present. The immediate effectof the fire is to empty every "box" in theforest ecosystem. The interval before "green-up" has been described as very brief (Roberts1975), but the total temporary effect onecosystem composition and structure is verygreat. It is worth pointing out that thistreatment is usually very costly and isreserved for forest rehabilitation operationson very productive land supporting highlystable subclimax communities from which pastmanagement has excluded conifers. In suchcircumstances, the practice totally removesthe woody component from dominance, followedwithin weeks by development of a dense herbcover in which sprouts begin to develop.This change is not a consequence of toxicaction but of the physical evert of fire.

INTERACTION BETWEEN PLANTS AND ANIMALS

We have thus far considered the directaction of herbicides on animals and plantsand have found herbicides to be directlyeffective largely on plants. Figure 6illustrates, however, that herbivores aredirectly dependent on the plant community forfood and cover and the other animals aredependent on herbivores and cover.

Changes in primary producers clearlyhave a major influence on the animal community,independent of the direct effects of theherbicide. Numerous effects have beendocumented. Phenoxy herbicides were studiedtwo decades ago for their potential use inimproving big game habitat. The action of theherbicides in reducing the level of dominantcanopy, and also of stimulating sprouting, wasbeneficial for the winter range condition ofdeer (Krefting et al. 1960; Mueggler 1966).Keith et al. (1959T—observed that the com-position of the herb community in a part of theRockies had an important effect on the popu-lations dynamics of the pocket gopher. Morerecently Borrecco (1973) and Borrecco et al.(1972) demonstrated that several species oflarge and small mammals were responsive to

140

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management of herbaceous cover with herbicides.Their findings support the generalizationthat herbicides do not have an immediateeffect on animals, but as vegetationresponds, the animal community appears tofollow a successional pattern in accord withthe changes in habitat (Newton 1973a).Vegetation management is now regarded as apotential tool for regulating animal damageto forest plantations in the Pacific North-west.

•

ANALYSIS OF LONG-TERM EFFECTS

There are clear patterns of short-termeffects of herbicides on forest and rangecommunities. In rangelands, the usualpattern after treatment is an increase inherb cover. In forest lands with substantialshrub and crop-tree component there is anincrease in herbs after brush control and anincrease in woody cover after herb control.These short-term effects are the initialphases in long-term pathway of ecosystemdevelopment. This may be termedsuccession in the classical sense,

except that the initial inhabitants arethere by design. Furthermore, the dominanceratio (Newton 1973b) is managed by repeatapplications if the plant communities showsigns of wavering off a planned path.

Ecosystem development under forestmanagement can be very similar to naturalforest succession. It is very different fromsuccession in forests from which the dominanthigh-valued species are chronically subjectedto utilization pressure. Figure 6 indicatesthat the removal of any component of a forestecosystem will merely focus productivityamong the remaining vegetation. Plants ortrees in a dominant position after someharvesting tend to remain dominant. Thecause-effect patterns is precisely the samewhen comparing the effects of removing high-quality timber by harvest or by suppressingthe low-quality material with herbicides andthe development of undamaged parts of the system is accelerated. This is one of thefundamental silvicultural or agronomic con-cepts, and is the basis for all weeding.

The course of forest ecosystem develop-ment after application of the herbicide iscontrolled by three principal factors otherthan soil and climate. The first, and mostimportant factor, is the population ofrapidly growing tree species after herbicideresidues become inactive. Trees with highdominance potential will dominate the sitecontinuously if they are present anddominate immediately after treatment(Newton 1973b). If no such species are

present, the introduction of trees by plantinghas a major influence on the long-termdirection of ecosystem development afterherbicide application Figure 7. Because theusual purpose of treatment is to promote the

Figure 7. Development of plant groups aftera disturbance to a forest.Components are analogous tocompartments in Figure 6. Notethat when conifers of highdominance potential are planted,as in A, succession is dominatedby conifers and ground vegetationbecomes sparse. In B, however,the diagram reflects low coniferstocking or vigor, and the low-stature woody vegetation remainsdominant for much longer. Theconifers are causal, but non-targetspecies will be affected.

growth of trees, the shift to tree dominanceis the most common long-term effect ofherbicide use on the general structure offorest ecosystems. Development of thedominant tree layer has a very great impacton all non-target biota, because if affects

141

Table 2. Comparative Magnitude and Duration of Environmental Impactsof Forest Practicesl/

Timber Water Water Big SmallPractice Values Quality Yield Game Mammals

Tree planting?! Great(+) Small(+) Small(-) Great(-) Variable(if successful) Long Long Long LongLong

Vegetation Control:Chemical: 3/ Great(+) Small(-) Small(+) Moderate Moderate(-)

Herbs Long Short Short Short(-) Short andLong(+) Long

Brush Great(+) Small(-) Moderate(+) Moderate VariableLong Short Short to great(+) Long

Short

Weed trees Great(+) Small(-) Moderate(+) Moderate to Small(+)Long Short Short great(+) Short

-_,

A Short-longr\D

Mechanical:Herbs Moderate(+) Moderate Moderate(+) Great(+) Variable to

Long to great(-) Short Short great(-)Short Short

Brush Great(+) Moderate Moderate(+) Variable Creat(+-)Long to great(-) Short (+ and -) Short

Short Short

Weed trees Great(+) Great(-) Small Moderate(+) Small(+ and -)Long Short Short Short Short

1/ Plus or minus relates to a presumed value change relating to a specific resource.2/

Impact of planting depends on success, which in turn may be determined by the effectiveness of cultural measures.

--g./ Selectivity range of the particular herbicide will determine whether residual vegetation is more or less favorable habitat.

all subordinate vegetation. When thedominant tree species are natives, this effectapproaches the natural balance of some sortof subclimax vegetation. In rangelands, thepromotion of herb cover at the expense oftrees is likely to result in the slow re-invasion of trees because of their higherdominance potential. Pressure from livestockon the grass will accelerate the upswing inwoody vegetation in the absence of fire. In allsituations, the long-term impact of the manage-ment practice is largely determined by thesubsequent character of the new woody plant

dominants in the community.

Most forests are managed in a mosaic ofsmall management units. Herbicides used inan even-age management system are usedinfrequently, and in a pattern of adjacentvegetation that offers diversity and escapeopportunity for wildlife subjected totemporary shortages of cover or forage.These patterns have been described as favor-able for many species of wildlife, even withmore frequent applications than those usedin forestry (Bramble and Byrnes 1972). Thescale of range treatments reduces escapeopportunity under some circumstances, andlocal changes in plant community structurecan have effects on herbivores whose preferredforage has been removed.

Any evaluation of the effects ofherbicides on non-target species and non-timber values must take into account thecomparative effects of alternative practicesfor achieving the same goals. Table 2 listsan array of relative impacts of herbicidesand bulldozers on various non-target species,including aquatic species and their habitats.Fire is intermediate in effects on mostgroups between chemical and mechanicalmethods. Insufficient data has been recordedfor manual methods to evaluate theirsilvicultural or range benefits or impacts.

CONCLUSIONS

We have outlined our interpretations ofeffects of several kinds of disturbances inthe management of range and forest lands.Herbicides constitute one special type ofdisturbance, unique in substituting certainbiochemical properties for physical impact.In an evaluation of their effects on non-targetforest and range biota, the following con-clusions are germane to impact analysis inEnvironmental Statements:

1. Environment impact of herbicides onforests and ranges must be evaluatedin the framework of managementsystems that have already had an

effect, and whose effects will becomemore severe with no maintenance, tothe detriment of major renewableresources.

The non-target species in ecosystemspreviously disturbed by managementare already off natural baselines,including pcpulations that are aboveand below natural levels.

Direct toxic hazards of herbicideson non-target species are a matterof public concern. They thereforeneed to be mentioned. However,the likelihood of direct effect ofherbicides is low and such effectsneed to be examined in terms ofthe consequences and hazard of usingalternative methods, including non-treatment, to achieve the same re-source management goal. The infre-quent use of herbicides and theirshort lives and non-cumulative effectare documented; they reducethe risk of surprise adverseeffects.

Short-term effects of vegetationmanagement are determined byphysical impact amid ecosystemresiliency. In decreasing order,the environmental impacts ofalternative practices are:mechanical scarification, burning,and herbicides. On the basis oflimited evidence and adaptation tothe criteria by which other methodsare judged, hand clearing probablyfalls between burning and chemicalmethods. Projected development ofsurviving plant species groups areuseful for comparing and evaluatinghabitat change, reaardless of method.Impacts on animals can be expressedin terms of habitat suitability andstability.

Long-term effects of herbicides aretotally confounded by the manage-ment system in which they are used.In general, the goal of such manage-ment is maintenance in perpetuityof forest or range communities ina condition where non-target rangeand forest species have goodopportunity to thrive, regardlessof tools used.

6. Herbicides are unique in being ableto reverse past management impacts

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without causing physical impact onsoils and watersheds, or loss ofecosystem productivity.

REFERENCES

Borrecco, J.E. 1973. The Response of Animalsto Herbicide-Induced Changes. M.S.Thesis. Oregon State University,Corvallis. 92 pp.

, H. C. Black, and E.F. Hooven. 1972.Response of Blacktail Deer to Herbicide-Induced Habitat Changes. In: Proc. West.Ass'n. State Game and Fish Comm.Portland. pp. 437-451.

Bramble, W.,and W.R. Byrnes. 1972. A Long-term Ecological Study of Game Food andCover on a Sprayed Utility Right-of-Way.Purdue University Ag. Exp. Ste. Res.Bull. 885.

Harris, C.I. 1968. Movement of Pesticides inSoil. J. Agric. Food Chem. 17:80-82.

House, W.B., L.K. Goodson, H.M. Gadberry4 andK.W. Dockter. 1967. Assessment ofEcological Effects of Extensive orRepeated Use of Herbicides. U.S. Dept.of Defense. Advanced Research ProjectsAgency Order Number 1086. 369 pp.

Kearney, P.C., E.A. Woolson, J.R. Plimmer,andA.R. Isensee. 1969. Decontamination ofPesticides in Soil. Residue Reviews29:137-149

Keith, J.0., R. M. Hansen, and A.L. Ward. 1959.Effect of 2,4-D on Abundance and Foodsof Pocket Gophers. J. Wildlife Mgmt.23:137-145.

Krefting, H.L. Hansen, and R.W. Hunt.1960. Improving the Browse Supply forDeer with Aerial Applications of 2,4-D.Minn. Forestry Note #95. University ofMinnesota, St. Paul.

Miller, J. H. 1974. Nutrient Losses andNitrogen Mineralization on ForestedWatersheds in Oregon's Coast Range.Ph.D. Thesis. Oregon State University,Corvallis. 84 pp.

Mueggler, W. F. 1966. Herbicide Treatmentof Browse on a Big-Game Winter Range inNorthern Idaho. J. Wildlife Mgmt.20:141-151.

Muirhead-Thomson, R.C. 1971. Pesticides andFreshwater Fauna. Academic Press.London.

Newton, M. 1973a. Environmental Managementfor Seedling Establishment. OregonState University Forest ResearchLaboratory Res. Paper 16.

1973b. Forest Rehabilitation in NorthAmerica: Some Simplifications. Jour.Forestry 71:159-162.

and J. A.Norgren. 1977. Silviculturalchemicals and Protection of WaterQuality. U.S. Environmental ProtectionAgency. Rept. EPA 910/9-77-036. 224 pp.

,and L. A. Norris. 1968. HerbicideResidues in Blacktail Deer from ForestsTreated with 2,4,5-T and Atrazine. Proc.Western Weed Control Conference. Boise.pp. 32-34

,and Stanley P. Snyder. 1978. Exposureof Forest Herbicide to 2,3,7,8 tetrachlorodiben 30-p-diocin (TCDD) in areassprayed with 2,4,5-T. Bulletin ofEnvironmental Contamination and ToxicologyMay 1978.

Norris, Logan A. 1971. Chemical brush control:Assessing the hazard. Jour. Forestry.69: 715-720.

,and D. G. Moore. 1971. The Entry andFate of Forest Chemicals in Streams.In: Proceedings of a Symposium ForestLand Uses and Stream Environment,October 19-21, 1970. Oregon StateUniversity, Corvallis. pp 138-158

Roberts, C. A. 1975. Initial PlantSuccession After Brown and Burn Sitepreparation on an Alder-DominatedBrushfield in the Oregon Coast Range.M.S. Thesis. Oregon State UniversityCorvallis. 90 pp.

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