environmental effects of harvesting forests for energy

Forest Ecology and Management, 4 (1982) 79--94 79 Elsevier Scientific Publishing Company, Amsterdam - -Pr in ted in The Netherlands

ENVIRONMENTAL EFFECTS OF HARVESTING FORESTS FOR ENERGY*

R.I. VAN HOOK, D.W. JOHNSON, D.C. WEST and L.K. MANN

Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 (U.S.A.)

(Accepted 22 June 1981)

ABSTRACT

Van Hook, R.I., Johnson, D.W., West, D.C. and Mann, L.K., 1982. Environmental effects of harvesting forests for energy. Forest Ecol. Manage., 4: 79--94.

Present interest in decreasing U.S. dependence on foreign oil by increasing the use of wood for energy may bring about a change in our forest uti l ization policies. In the past , forests have been removed in areas believed to be suited for agriculture, or sawtimber and pulp have been the only woody material removed in any quant i ty from land not generally considered tillable. The new demands on wood for energy are effecting a trend toward (1) removing all woody biomass from harvested areas, (2) increasing the frequency of harvesting second growth forests, and (3) increasing product ion with biomass plantations. Considering the marginal quali ty of much of the remaining forested land, the impacts of these modes of product ion could be significant. For example, it is anti- cipated that increased losses of nutrients and carbon will occur by direct forest removal and through erosion losses accelerated by forest clearing. There are, however, control measures that can be util ized in minimizing both direct and indirect effects of forest harvesting while maximizing woody biomass production.

INTRODUCTION

Utilization of woody biomass for energy is not without attendant environmental effects. These potential effects are associated with the entire wood fuel cycle: site preparation--planting--management(including fertilization and pesticide use)--harvest--conversion--waste disposal. This paper is concern- ed with the potential effects associated with harvesting wood; both conventional harvest and more recent complete aboveground biomass removal (whole-tree harvest), and harvesting intensive silvicultural systems. Typical impacts associated with these various forms of tree harvest are illustrated in

*Research supported by the Biomass Energy Systems Division of DOE under contract W-7405-eng-26 with Union Carbide Corporation. Publication No. 1849 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830.

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i REMOVAL OF 1 ~ Ip DECOMPO~IT)ON

elOMASS

. . . . . . . . . MORE EXTREME INCREASED REMOVAL OF SOIL RATE OF

~NCREAEEO QUANTITY AND tNTENSITY

OF PRECIPITATION REACHtNG FOREST FLOOR

INFILTRATION OF EROSION PRECIPITATION;

INCREASED RUNOFF

iMMEDIATE LOSE

LOU OF ORGANIC MATTER

AND NUTR fENTE

CONTINUING LOSS

ORNL-DWG 79.16E6g

IMPACTSTO SITE: CHANOESIN

PRODUCTIVITY, COMMUNITYETRUCTURE

IMPACTETO DOWNSTREAM ENVIRONMENTS-

SEOIMENTATION, EUTROPHICATION

Fig.1. Potential environmental effects of forest biomass harvesting. (Source: Environmental Assessment, Biomass Energy Systems Program, April 1980, Oak Ridge National Laboratory.)

TABLE I

Effects of increased woody biomass removal

Direct effects: Nutrient loss in wood removal Soil disturbance and compaction Regeneration of new stands Exposures of soil and litter Fire hazard-Air pollution

Indirect effects: Erosion Leaching } altered nutrient cycles

Wildlife habitat changes

Fig.1 and range from immediate on-site effect to subsequent changes in off-site streams and rivers receiving increased sediment and nutrient inputs.

The effects of harvesting wood may becategorized as direct and indirect (Table I), with indirect effects generally being the more significant. In the following paragraphs, we consider forest harvesting impacts in terms of direct and indirect effects and discuss mitigative techniques that may serve to minimize the impact while maximizing wood availability.

DIRECT EFFECTS

Nutrient removal

There are several ways in which the effects of increased biomass removal upon site nutrient balance can be calculated, none of which are adequate

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to realistically predict the impacts upon site fertility and the productivity of subsequent rotations. It is relatively simple to demonstrate and very well known that the nutrient costs per unit biomass are many-fold greater for intensive harvesting than for current practices involving stem removal only (Boyle et al., 1973; Kimmins, 1977). This is due to the fact that nutrients are most concentrated in those plant tissues not currently harvested. Cur- rently, a static approach is employed to determine the magnitude of nutrient drain associated with intensive harvesting. This approach involves estima- tion of the nutrient content of all biomass components, the soil (to a prescrib. ed depth), and natural residues (litter) removed from the site. Calculated in this way, the effects of intensive harvesting on site nutrient status are highly species and soil type dependent.

Marion (1979) surveyed much of the literature on stand nutrient content and found that the ratio of biomass to nutrient content, defined as nutrient efficiency, is of the order temperate coniferous > temperate broadleaf > boreal > tropical. On this basis, he suggests that temperate coniferous forest species are the least damaging in terms of site nutrient drain.

Most calculations indicate that while intensive harvesting will increase nutrient removal many-fold relative to conventional harvesting, the percent of total site nutrient capital removed in either case is relatively modest (e.g., < 10%; Wells and Jorgensen, 1979). Important exceptions do occur, such as P in the southern coastal plain, which may become potential problems with intensive harvesting systems (Humphreys and Pritchett, 1971; as cited by Wells and Jorgensen, 1979). Calculations of nutrient removal in conventional harvesting and whole-tree harvesting for several U.S. forests are illustrated in Table II. In each case, whole-tree harvesting approximately doubles or triples the nutrient drain in biomass removal, although the ac- tual amounts vary with species and stand age. Among the four sites compar- ed in Table II, by far the greatest N and P drains would occur at the H.J. An- drews site OR presumably because of its much greater age and biomass. With K and Ca, however, drains in the deciduous forest ecosystems at Walker Branch (TN) and Hubbard Brook (NH) approach or exceed those at the Andrews site, because of greater concentrations of these nutrients in deciduous species (Cole and Rapp, 1980).

The next level of complexity in nutrient effects calculations involves a more dynamic approach in which nutrient drains by biomass harvest are balanced against atmospheric inputs over the rotation period. While there are several important considerations still lacking in this approach, it provides considerably more insight into potential nutritional problems than the static approach does (Cole, 1978; Wells and Jorgensen, 1979). Nutrient drain by this calculation is highly dependent upon the length of rotation employed and the amount of atmospheric nutrient input in addition to species and soil content. For short-rotation intensive silvicultural systems, there appears to be little doubt that nutrient drains will exceed inputs (except for N in the case of N-fixing species) and fertilization will be required to maintain site

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TABLE II

Nutrients in biomass harvesting (kg/ha) in four representative U.S. forested watersheds (from Cole and Rapp, 1980)

N P K Ca

Walker Branch (Harris, Henderson) Mixed deciduous (60 years) Conventional 135 8 90 307

harvest Whole-tree 267 21 172 537

harvest

Input 8.7 0.54 3.2 14.4

H.J. Andrews (Grief) Douglas-fir (450 years) Conventional 349 36 48 401

harvest Whole-tree 566 86 189 687

harvest

Input 2 0.3 1.2 3.1

Hubbard Brook (Whittaker and Likens) Northern Hardwood (60 years) Conventional 134.6 11 70.8 193.2

harvest Whole-tree 367.2 32.7 153.7 402.0

harvest

Input 6.5 0.04 0.9 2.2

North Carolina-Duke Forest (Wells) Loblolly pine (16 years) Conventional 79 10.7 65 74

harvest Whole-tree 257 30.9 165 187

harvest

Input 9.6 0.5 12.3 6

ferti l i ty (Hansen and Baker, 1979). With regard to whole-tree harvest or residue removal, the net nut r ient removal is no t as severe but may nevertheless result in long-term declines in site nu t r ien t content .

Net nutr ient removals calculated in this way for the four U.S. forested watersheds illustrated in Table II change the complexion o f harvesting effects assessment somewhat. The situation with respect to N is similar to the static approach, with the Andrews site having the greatest drain, but Hubbard Brook has the greatest potent ia l ne t P drain because of the low P inputs (Tables II and III). Walker Branch Watershed and Duke Forest (NC) have the lowest potential ne t nut r ient drains in general due to the relatively high atmospheric inputs at these part icular sites. Hubbard Brook and H.J. Andrews

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TABLE III

Number of years of annual precipitation input required to equal nutrient drain by conventional and whole-tree harvesting

N P K Ca

Walker Branch Conventional 15.5 a 14.8 28.1 21.3 WTH 30.7 38.9 53.8 37.3

H.J. Andrews Conventional 174.5 120.0 40.0 129.4 WTH 283.0 286.7 157.5 221.6

Hubbard Brook Conventional 20.7 275.0 78.7 87.7 WTH 56.5 817.5 170.8 182.7

Duke Forest Conventional 8.2 21.4 5.3 12.3 WTH 26.8 61.8 13.4 31.2

ayears.

sites have greater potential nutrient drains due to lower atmospheric input and, in the case of the Andrews site, greater direct nutr ient removal through harvesting. Assessment of potential whole-tree harvest effects in this manner, i.e., comparing removal with atmospheric inputs, indicates a higher potential for long-term depletion of P, K, and Ca than for N at all sites but the Douglas- fir forest in the Pacific Northwest (H.J. Andrews site). Wells and Jorgensen (1979) noted that whole-tree harvest generally results in a net annual nutrient decline calculated in this way, whereas bole-only harvesting usually does no t (except in the case of phosphorus). In the cases of N and S, the accelerated atmospheric inputs due to air pollution may be beneficial in terms of offsetting the nutrient drains by intensive harvesting. The situation for P, the nutr ient commonly limiting in the southern coastal plain, is less encouraging since atmospheric inputs are frequently less than removal in biomass (calculated on an annual basis; Wells and Jorgensen, 1979). Similar- ly, Boyle et al. (1973) predicted that Ca reserves will be depleted and productivity will decline after several rotations in an aspen-mixed-hardwood stand in Wisconsin.

While this method of calculating nutrient drain is useful in identifying potential problems, it has several shortcomings. The most serious problem is that it does not account for the potential effects of intensive harvesting upon nutrient availability. Normally only a small port ion of the total soil pool of a given nutr ient is available to plants and therefore calculations utilizing total nutr ient content may well predict erroneously small impacts of intensive harvesting on site fertility. There are several methods of oh-

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taining nutrient availability indices (the most widely accepted of which is exchangeable cation extraction), but these indices provide only relative values, not quantitative estimates of available soil nutrient content. Furthermore, nutrient availability in soils is affected by a number of dynamic processes such as rock weathering (Clayton, 1979), immobilization and mineralization by microorganisms (Alexander, 1963) and frequently by plant roots themselves. For example, Fisher and Stone (1969) found evidence that conifers increased the availability of N and P within their rooting zones. Similarly, Boyle and Voigt (1973) found that organic acids exuded by pine roots and associated fungi weathered primary silicate minerals and released potassium into available forms. Clearly, nutrient availability is a dynamic attribute of site fertility which is difficult to define and even more difficult to predict. Some reasonable qualitative predictions will be made in a subsequent section concerning intensive harvesting effects on nutrient availability (especially for N), however.

Other shortcomings of the total nutrient budget approach are that nutrient losses via erosion, leaching, and in the case of N, denitrification are not accounted for, predictions of atmospheric inputs over long rotations are usually based upon only a few years' data, and, in the case of N, estimates of fixation rates over long rotations are very uncertain. Factors affecting some of these important processes are considered in greater detail in the section on "indirect effects".

Soil disturbance and compaction

An obvious added impact of more intensive harvesting would be additional soil compaction in areas where overland vehicles are used during biomass removal. The degree of soil compaction depends on many factors such as time of year of harvesting, soil type, climate, and type of vehicle used (Moehring and Rawls, 1970). Compaction of the soil and the associated litter disturbance contribute to increased runoff and erosion (DiNovo et al., 1978). The primary effects are compaction and puddling of soil, reducing porosity and thus moisture storage capacity and infiltration rates of the soil. Campbell et al. (1973) found that logging by wheel skidders disturbed 23% of the site and that 5 to 10% of the area had changes in soil conditions that could restrict tree growth. He found that these changes persist for many years; as much as 18 years may pass before the upper 5 cm of soil in logging roads returns to precut texture conditions. At greater depths, much longer periods were required to regain pre~ut characteristics. Increased traffic from more intensive harvesting can be expected to cause additional soil compaction; however, because of the accumulation of overland water flow in compacted roadways, this increase may result in a greater-than-linear increase in negative impact.

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Regeneration of new stands

The effects of forest residues on the regeneration of new stands has been of particular concern to foresters in the Pacific Northwest. Excessive amounts of residue left on-site after typical harvests of old-growth timber can inhibit natural regeneration by providing a barrier to mineral soil (a requirement for seed germination in Douglas-fir) and interfere with both mechanical and manual replanting (Miller et al., 1974; Edgren and Stein, 1974). Severe drying and high temperatures of slash can also adversely affect seedling survival (Ruth, 1974). On the other hand, residues can enhance microclimatic conditions for seed germination and survival by providing shade and prevent- ing excessive moisture loss in dry summer months and reducing freezing and frost heave in winter (Miller et al., 1974). Malkonen (1979) pointed out that decomposing slash ,provides much of the nutrient requirements of regenerat- ing stands in cold-region forests as well. Seidel (1974) concluded that a moderate amount of slash cover is desirable from the perspective of forest regeneration, but the optimal point between the positive and negative impacts may be difficult to discern and undoubtedly varies from one region and forest type to another.

Exposure of soil and litter

Voigt (1979) expressed concern that removal of forest residues removes one layer of buffering capacity against acid rain. The long-term effects of intensive harvesting upon surface soil organic matter content may be even more serious in this regard, since sources of humus, high in cation exchange capacity, will probably be reduced by such practices. The results obtained by McCoU (1978) following clearcutting in a Eucalyptus stand are especially interesting from the perspective of both carbonic acid leaching and interactions with acid rainfall. He found lower concentrations of nitrate, bicarbonate, total anions and total cations in soil solutions from a clearcut site where residues were removed than in an adjacent Eucalyptus forest. He attributed the reduction in bicarbonate concentration to a combination of lowered pH (from 7.0 to 6.2) presumed to be brought about by direct inputs of acid ~ain to the soil, and to a reduction in CO2 evolution brought about by residue removal. While these speculations are not entirely verifiable f rom the data presented, this study points out some of the interesting complexi- ties and interactions that can come into play as a result of intensive forest harvesting.

Fire hazard-air pollution

The fire hazards associated with leaving residues on-site have been a primary concern of.foresters in the Pacific Northwest. To cope with this problem and to improve seedbed conditions, several residue treatment pro-

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gramS have been employed, including controlled broadcast burning, piling and burning, and yarding unutilized material without burning. The latter generally involves the greatest expense and still involves some fire hazard, so burning has usually been employed. With the advent of the Clean Air Act in 1970, burning as a means of residue treatment came under close scrutiny and some criticism (Cramer, 1974). Residue removal or whole-tree harvest obviously alleviates both the problems of fire hazard and air pollution by controlled burning.

INDIRECT EFFECTS

E r o s i o n

One of the more important indirect effects of intensive harvesting may well be from soil erosion. This holds because soil erosion means increased stream sediment loading and, soil loss which could be serious enough to effect subsequent plant establishment, growth, and ultimate site productivity because of alterations in major nutrient cycles associated with nutrient loss.

Results of studies in Oregon and Washington showed that 15% of logged areas suffered deep soil disturbance as a result of tractor logging; cable logging produced the same degree of disturbance on only 1.9% of the area. Distur- bance on slopes greater than 40% grade was 2.8 times greater than on less steep slopes (Copeland, 1963). A comparison of clear versus selective cutting in Arkansas showed 3.6 tons of topsoil loss in clearcutting with 1.3 tons lost in selective cuts. Assuming all conditions equal, a more intensive harvest (i.e., removal of slash and cull from the site) might be expected to result in even more erosion than from clearcutting (Lull and Reinhart, 1972).

Erosion after soil disturbance accelerates nutrient loss in solution and in organic and mineral forms. Pritchett and Wells (1978) stated that because erosion first transports organic matter particles which are followed by the organic-matter mineral-soil complex, nutrient loss is greater by a factor of two or more than expected from soil analysis and sediment loading alone because these analyses do not include the organic fraction. Since, especially in southern soils, most of the N reserve and much of the P is contained in the organic fraction of the soil, loss of this component could play a significant role in the depletion of site nutrient requirements.

L e a c h i n g . . . .

The experimental deforestation and herbicide treatment at Hubbard Brook, NH, caused a flurry of controversy over the effects of forest harvesting upon nutrient leaching (primarily nitrate and associated cations) and the consequences thereof on water quality (Likens et al., 1969). Previous studies by Cole and Gessel (1965) and subsequent studies on commercial clearcuts throughout the country (including others at Hubbard Brook) produced less

87

severe nitrate and cation leaching losses (Likens et al., 1978; McCoU and Grigal, 1979) but there is continuing interest in the factors affecting nitrification and nitrate leaching in disturbed ecosystems (Vitousek et al., 1979; Vitousek and Melillo, 1979). No comprehensive answers to the question of what regulates nitrate leaching axe yet available, but some reasonable speculations can be made as to the potential effects of intensive harvesting vs commercial harvesting on nitrate leaching. Removal of woody residues, which have low C/N ratios, may result in greater net ammoniilm mineralization (due to less N immobilization in decomposing wood). If ammonium mineralization exceeds plant uptake and no nitrification inhibitors axe present, the resultant increases in ammonium availability may stimulate greater rates of nitrification than in commercial harvesting. Nitrate produced in excess of that taken up by regrowing vegetation will, in the presence of adequate water input, be leached from the soil along with an equivalent amount of cations to maintain electrochemical neutrality in solution.

On the other hand, removal of N-rich residues such as foliage may well result in lower rates of N mineralization and nitrification than where such residues are left in place. The C/N ratios of decomposable residues can play an important role in determining the net effects of harvesting or other dis- turbances upon nitrogen availability and nitrate leaching. In a mixed deciduous forest in eastern Tennessee, Johnson and Edwards (1980) were able to manipulate N mineralization and nitrification rates by selective additions of ammonium and carbon (sucrose) substrates to the forest floor. In cases where harvesting increases net N mineralization, both the timing and rates of mineralization, nitrification, and plant uptake will determine the net outcome in terms of nitrate leaching. In some cases, such as at the subalpine Findley Lake site in Washington state, net NH~ mineralization following disturbance is substantial but delays in the commencement of nitrification are quite long; in some cases, up to 2 years (Vitousek et al., 1979; P.M. Vitousek, personal communication, 1979). At Hubbard Brook, nitrification apparently increases quite rapidly following disturbance but vegetative re- growth (mainly pin cherry) and uptake are very rapid also, thus offsetting much of the potential nutrient loss (Marks, 1974).

Wildlife habitat

Few if any definitive studies have been done regarding the potential effects (Fig.2) of intensive forest harvesting on wildlife and plant populations. However, many studies exist which describe mammalian response to clearcutting, although some questions arise as to the similarity of habitat remaining following a clearcut versus all residue removed. With clearcutting, both an increase in density and abundance was seen for small mammals in deciduous and coniferous forest in the northern Appalachians (Kirkland, 1977). This increase diminished until a pre-cut level of population density was reached at about 15 years of cutting.

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ORN L-OWG 79-15870

MANAGEMENT HABITAT CHANGES IMPACT ON WILOLtFE

J I I REDUCED NUMBERS OF CAVITY

NESTING SPECIES. WOODPECKERS. ETC.

= LESS FOOD AVAILABLE FROM DEAD TREES. ROTTING LOGS

/ ' /j / FAVORABLE EFFECTS ON BRUSH- / DWELLING SPECIES

CREATION OF EARLY-GROWTH HARVEST OF HABITAT UNDERUTILIZED - - - - . . . . . . . . . . . . . . . . . . MODERATE REDUCTION IN FOREST \ / - I E . . . . . . S . . . . . . . . . EN-AGE I I W,LOL,FE . . . . . S,TY

N , S T A N D S . . . . . . . . . . . . . . . . . . x ~ ~ . . . . . TIONS D . . . . . . . . . . . . ERSITY

WITH STAND DEVELOPMENT

/ \×" ~

7 ) H REPLACEMENT OF INDIGENOUS CHANGES IN TYPES OF WILDLIFE VBGETATION

SILVICULTURE I P ENERGY FARM8 WITH DEB RED TRBE S E C l E S . . . . . . . . . . . . . . . . . .

I . . . . . . . . . . . . . . . . . r - - t - ° . . . . . . . . . . . . ..... MONOCULTURE STANDS IN WILDLIFE DIVERSITY

Fig.2. Potential impacts to wildlife of increased forest biomass harvesting. (Source: Environ- mental Assessment, B i o m ~ Energy Systems Program, April 1980, Oak Ridge National Laboratory.)

Although a similar increase in species density and abundance occurs in herbaceous and shrubby plant components of wildlife habitat following clearcutting, species composit ion changes rapidly. Thirty percent of the original species in a clearcut Douglas Fir stand in the Cascade Mountains of Oregon were eliminated within 6 years of cutt ing and 50% were drastically reduced in abundance (Dyrness, 1973). It is not known what time interval is required for re-establishment of species or what additional effects residue removal will have on species persistence.

Despite changes in plant species composit ion, the ultimate effects of intensive harvesting, on both mammalian and avian species, will probably be related to spatial consideration of forest removal. Based on related studies (Lay, 1938; Kirkland, 1977; Anderson et al., 1979), an increase in diversity of vegetative cover results in an increase in diversity of small mammals and birds. One can reasonably infer from these studies that intensively harvesting (viz. clearcutting) in patches within a homogeneously forested landscape would probably increase diversity and abundance. For intensively harvested areas in which seed germination, sprouting, and seedling growth occurs rapidly, the effects of woody biomass removal can probably be expected to be similar to that caused by clearcutting. However, as with clearcutting, two unanswered questions remain regarding intensive harvesting: (1) What is the optimal

spatial arrangement of harvested patches? ; and (2) What time frame of re- peated harvesting can be performed without resulting in adverse and long- term effects on plant and animal populations?

MITIGATION TECHNIQUES

There are a number of environmental control measures which can be and are being used to minimize both direct and indirect effects of intensive wood removal (Table IV). These techniques range from application of fertilizer to promote yields on marginal sites to utilization of regional scale planning for intensive harvesting programs.

TABLE IV

Mitigative techniques for intensive harvesting

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Fertflization Strip cutting Dorman season harvesting Cable logging Harvesting on frozen ground or snow pack Good road construction Buffering stream channels Lengthened rotat ion on poorer sites Regional scale planning

Ballard (1979) and Wells and Jorgensen (1979) caution that it cannot be assumed that fertilization will easily cure problems of nutrient depletion by intensive harvesting. Usually less than 50% of applied fertilizer is utilized by trees, the remainder being lost by vohtilization, leaching, and immobilization in the soil (Wells and Jorgensen, 1979). Furthermore, fertilizer prescrip- tion technology is not yet sufficient to predict with assurance that fertilized stands will respond (Ballard, 1979). Total soil reserves far exceed tree nutritional needs even in deficient stands, and responses to fertilization are due to additions to the available nutrient poolb not to total nutrient pool. Fertilizer N is very rapidly immobilized in the soil in undisturbed stands (i.e., within 4--6 months; Johnson, 1979; Johnson et al., 1980), but it is difficult to predict the reactions of fertilizer in disturbed soils from which N-immobilizing woody residues have beenremoved. It is quite possible that fertilizer N additions to such soils-will further stimulate already active nitrifier populations, causing unacceptable rates of nitrate leaching. Fertilizer treatments will have to be carefully controlled in both timing and amount in order to effectively off set nutrient drains and avoid additional nutrient leaching losses and water contamination.

The potential environmental effects of forest fertilization are too numerous to discuss in detail here. Suffice it to say that there areseveral potentially

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positive impacts (decreased susceptibility to insect, disease, and air pollution damage as well as increased tree growth) as well as potentially negative impacts (increased susceptibility to insect and disease damage if fertilization creates nutr ient imbalances) aside from those discussed here (Weetman and Hill, 1973; Johnson, 1980). The net overall effect of fertilization on the health of the target organisms {trees) as well as the surrounding environment will vary according to site and conditions at the t ime of application (including the presence or absence of residues). With the limited information now at hand, many of these potential effects remain a matter of conjecture.

There are a variety of options in harvesting techniques and strategies that may prevent undesirable effects of intensive harvesting. One very promising technique for minimizing nutrient losses on a watershed level is strip cutting (Hornbeck et al., 1975). In this method alternate strips are cut over a 3-year (or more) period, thus providing a shelterwood effect for regeneration and allowing adjacent vegetated strips {occupied by either uncut or regrowing vegetation) to absorb nutrients leached from harvested strips. This would also provide refugia for plant and wildlife species unable to persits in clearcut a r e a s .

Whole-tree harvesting of deciduous species in the dormant season reduces the nutr ient drain by that amount returned to the forest floor in litteffall and crownwash during the growing season. This practice also provides a reserve of readily-mobilized nutrients (low C/N ratio leaf litter) for regenerat- ing vegetation.

Harvesting practices that minimize road construction and vehicular traffic (i.e., skyline logging; whole-tree harvest involving only one pass over the landscape as opposed to residue removal requiring two passes) are likely to minimize erosional losses.

Experiences with second rotation productivity declines in Radiata pine plantations in Australia (Keeves, 1966; Boardman et al., 1979) and New Zealand (Will and Ballard, 1966; Whyte, 1972) may be of great utility in predicting the impacts of intensive harvesting upon continued site productivity and the measures that may be required to maintain productivity. This decline has been attributed to a number of factors including nutrient depletion, soil physical and microbiological conditions (Keeves, 1966), and non- soil-related factors such as weed control and overstocking (Whyte, 1972; Boardman et al., 1979). The most promising approach being taken to rec- tify the second rotation decline involves a combination of treatments including fertilization, utilizing seedling stock of improved genetic potential, weed control in early stages of regeneration, and cultivation (Boardman et al., 1979).

C O N C L U S I O N S

Utilization of woody biomass for fuel and chemical feedstocks in addition to its current uses for lumber and paper will definitely result in increased

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demands which will be met through increased harvesting of existing forests and through intensive silvicultural systems. Both of these approaches are accompanied by potential adverse environmental effects above and beyond those effects associated with conventional forest harvesting.

Immediate direct effects of wood harvest include nutrient removal, soil and litter disturbance, and production of fire hazards and are generally less severe than indirect effects. Nutrient removal in wood harvest is generally minimal, even with whole-tree harvest, and fire hazards along with associated air pollution is becoming less of a problem because of residue removal programs coming into use. Soil and litter disturbance, on the other hand, are of more concern because of the potential long-term productivity de- creases that may occur as a result of alteration in nutrient cycles.

Indirect effects of woody biomass removal including erosion, leaching, and wildlife habitat changes are more subtle than direct effects and can be far-reaching. Again the major concern is one of long-term productivity de- creases associated with nutrient cycle modifications and nutrient loss. Loss of well-developed soil containing available nutrient concentrations can re- quire several thousands of years for replacement through soil development. Less desirable species may also result on these poor sites during soil development and stand re-establishment. Wildlife habitat impacts are usually associated with changes in species composition from forest ypes to more open area types during early stages of stand regeneration. More severe are those impacts on endangered species where habitats are eliminated and species cannot return.

Most potential environmental effects associated with conventional harvest, residue removal, whole-tree harvest, and intensive silvicultural systems can be minimized if appropriate, intelligent, environmental control measures are utilized. Impacts associated with nutrient losses leading to decreased productivity can be minimized through an integrated use of good road construction, logging techniques that cause little disturbance to the forest floor, fertilization, and proper selection of harvest season. Attention should be given to fertilizer loss during application, lengthening harvest cycles on marginal sites, judicious selection of replacement species and stand re-establishment, and use of buffer areas both between harvest sites and along stream channels. On a regional scale, woody biomass harvesting can be planned to optimize the amount of biomass removed against the potential environmental effects. Using this level of planning, harvesting forests in a major drainage basin can be planned such that certain stands are clearcut, others strip cut, and still others have'only sawtimber removed to minimize sediment loading, provide wildlife and plant species refugia, and allow for varying intensity of harvest as a function of site quality in a given region.

REFERENCES

Alexander, M., 1963. Introduction to Soil Microbiology. John Wiley and Sons, New York, 472 pp.

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Anderson, S.H., Shugart, H.H. and Smith, T.M., 1979. Vertical and temporal habitat utilization within a breeding bird community. In: J.G. Dickson, R.N. Connor, R.R. Fleet, J.A. Jackson and J.C. Kroll (Editors), The Role of Insectivorous Birds in Forest Ecosystems. Academic Press, New York, pp. 203--216.

Ballard, R., 1979. Use of fertilizers to maintain productivity of intensively managed forest plantations. In: A.L. Leaf (Editor), Effects of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, pp. 321--342.

Boardman, R., Boomsma, D.B., Zed, P.G. and Cellier, K.M., 1979. Maintaining plantation productivity with Radiata pine in south Australia. In: A.L. Leaf (Editor), Effects of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, p. 391.

Boyle, J.R. and Voigt, G.K., 1973. Biological~weathering of silicate minerals. Implications for tree nutrition and soil genesis. Plant Soil, 38: 191--201.

Boyle, J.R., Phillips, J.J. and Ek, A.R., 1973. "Whole tree" harvesting: Nutrient budget evaluation. J. For., 71 : 760---762.

Campbell, R.G., 1973. The impact of timber harvesting and site preparation on selected soil conditions and plant growth. Ph.D. Dissertation, Univ. of Georgia, 65 pp., mimeo- graphed.

Clayton, J.L., 1979. Nutrient supply by rock weathering. In: A.L. Leaf (Editor), Effects of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, pp. 75--96.

Cole, D.W., 1978. Ecosystem research in the natural managed forest with regard to new problems in tneding. Proc. IUFRO Division I Meeting, Ossiach, Austria, pp. 75--91.

Cole, D.W. and Gessel, S.P., 1965. Movement of elements through forest soil as influenced by tree removal and fertilizer additions. In: C.T. Youngberg (Editor), Forest Soil Re- lationships in North America. Oregon State University Press, Corvallis, OR, pp. 95-- 104.

Cole, D.W. and Rapp, M., 1980. Elemental cycling. In: D.E. Reichle, (Editor), Dynamic Properties of Forest Ecosystems. Cambridge University Press, London, pp. 341--409.

Cole, D.W., Crane, W.J.B. and Grier, C.C., 1975. The effect of forest management practices on water chemistry in a second-growth Douglas-fir ecosystem. In: B. Bernier and C.H. Winger (Editors), Forest Soils and Land Management. Proceeding~ of the Fourth North American Forest Soils Conference. Les Presses de L'Universite Laval, Laval, Que., pp. 195--208.

Copeland, O.L., 1963. Land use and ecological factors in relation to sediment yields. Fed. Interagency Sediment Conf. Proc. USDA, Misc. Publ. 970, 238 pp.

Cramer, O.P., 1974. Air quality influences. In: Environmental Effects of Forest Residues Management in the Pacific Northwest, A State-of-Knowledge Compendium. USDA For. Serv. Gen. Tech. Rep. PNW-24, Pac. Northwest For. Range Exp. Sta., Portland, OR, pp. F-I--F-46.

DiNovo, S.T., Ballantyne, W.E., Curran, L.M., Baytus, W.C., Duke, K.M., Cornaby, B.W., Matthews, M.C., Weing, R.W. and Vigon, B.W., 1978. Preliminary environment assessment of biomass conversion to synthetic fuels. EPA-600/7-78-204, Industrial Environ- mental Research Laboratory, Cincinnati, OH.

Dyrness, C.T., 1973. Early stages of plant succession following logging and burning in the western Cascades of Oregon. Ecology, 54(1): 57--69.

Edgren, J.W. and Stein, W.I., 1974. Artificial regeneration. In: Environmental Effects of Forest Residues Management in the Pacific Northwest, A Stata-of-Knowledge Compendium. USDA For. Serv. Gen. Tech. Rep. PNW-24. Pac. Northwest For. Range Exp. Sta., Portland, OR, 352 pp.

Fisher, R.F. and Stone, E.L., 1969. Increased availability of nitrogen and phosphorus in the root zone of conifers. Soil Sci. Soc. Am. Proc., 33: 955--961.

93

Hansen, E.A. and Baker, J.B., 1979. Biomass and nutrient removal in short rotation intensively cultured plantations. In: A.L. Leaf (Editor), Effects of Intensive Harvest- ing on Forest Nutrient Cycling. State University of New York, Syracuse, NY, pp. 130--151.

Hornbeck, J.M., Likens, G.E., Pierce, R.S. and Bormann, F.H., 1975. Strip cutting as a means of protecting site and streamwater quality when clear-cutting northern hard- woods. In: B. Bernier and C.H. Winget (Editors), Forest Soils and Land Management, Proceedings of the Fourth North American Forest Soils Conference. Les Presses de L'Univeraite Laval, Laval, Que., pp. 209-225.

Humphreys, F.R. and Pritchett, W.L., 1971. Phosphorus adsorption and movement in some sandy forest soils. Soil Sci. Soc. Am. Proc., 35: 395--500.

Johnson, D.W., 1979. Some nitrogen fractions in two forest soils and their changes in response to urea fertilization. Northwest Sci., 53: 22--32.

Johnson, D.W., 1981. Environmental impacts of forest fertilization on terrestrial ecosystems. In: S.P. Bessel, R.M. Kenady and W.A. Atkinson (Editors), Forest Fertiliza- tion Conference, Contrib. No. 40. Institute of Forest Products, University of Washington, Seattle, WA.

Johnson, D.W. and Edwards, N.T., 1980. The effects of stem girdling on biogeochemical cycles within a mixed deciduous forest in eastern Tennessee. II. Soil nitrogen mineraliza- ti~on and nitrification rates. Oecologia, 40: 259--271.

Johnson, D.W., Edwards, N.T. and Todd, D.E., 1980. Nitrogen mineralization, immobilization and nitrification following urea fertilization of a forest soil under field and laboratory conditions. Soil Sci. Soc. Am. J., in press.

Keeves, A., 1966. Some evidence of loss of productivity with successive relations of Pinus radiata in the southeast of south Australia. Aust. For., 30: 51--63.

Kimmins, J.P., 1977. Evaluation of the consequences for future tree productivity of loss of nutrients in whole tree harvesting. Forest Ecol. Manage., 1 : 169--183.

Kirkland, G.L., 1977. Responses of small mammals to the clearcutting of northern Appalachian forests. J. Mammal., 57: 600--609.

Lay, D.W., 1938. How valuable are woodland clearings to bird life? Wilson Bull., 50: 254--256.

Likens, G.E., Bormann, F.H. and Johnson, N.M., 1969. Nitrification: Importance to nutrient losses from a cutover forest ecosystem. Science, 163: 1205--1206.

Likens, G.E., Bormann, F.H., Johnson, N.M. and Pierce, R.S., 1978. Recovery of a deforested ecosystem. Science, 199: 492--496.

Lull, H.W. and Reinhart, K.G., 1972. Forests and floods in the eastern United States. U.S.D.A. For. Serv., Res. Pap. NE-226, Northeast For. Exp. Sta., Upper Darby, PA, 94 pp.

Malkonen, E., 1979. Biomass and nutrient removal in whole tree harvesting in some coniferous stands thinned for the first time. In: A.L. Leaf (Editor), Effects of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, p. 405.

Marion, G.K., 1979. Biomass and nutrient removal in long-rotation stands. In: A.L. Leaf (Editor), Impact of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, pp. 98--110.

Marks, P.L., 1974. The.role of pin cherry (Prunus pensylvaniea L.) in the maintenance of stability in northei~ hardwood ecosystems. Ecol. Monogr., 44:73--88.

McColi, J.G., 1978. Ionic composition of forest soil solutions and effects of clearcutting. Soil Sci. Soc. Am. J., 42: 358--363.

McColl, J.G. and Grigal, D.F., 1979. Nutrient losses in leaching and erosion by intensive forest harvesting. In: A.L. Leaf (Editor), Effects of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, pp. 231--248.

9 4

Miller, R.E., WiUiamson, R.L. and Silen, R.R., 1974. Regeneration and growth of coastal douglas-fir. In: Environmental Effects of Forest Residues Management in the Pacific Northwest, A State-of-Knowledge Compendium. USDA For. Serv. Gen. Tech. Rep. PNW-24, Pac. Northwest For. Range Exp. Sta., Portland, OR, pp. J-I--J-34.

Moehring, O.M. and Rawls, I.W., 1972. Detrimental effects of wet weather logging. J. For., 68: 166--167.

Pritchett, W.L. and Wells, C.G., 1978. Harvesting and site preparation increase nutrient mobilization. In: A Symposium on Principles of Maintaining Productivity on Prepared Sites. Miss. State Univ., Starkville, MS, pp. 98--110.

Ruth, R.H., 1974. Regeneration and growth of west-side mixed conifers. In: Environ- mental Effects of Forest Residues Management in the Pacific Northwest, a State~)f- Knowledge Compendium. USDA For. Serv. Gen. Tech. Rep. PNW-24, Pac. Northwest For. Range Exp. Sta., Portland, OR, pp. K-I--K-18.

Seidel, K.W., 1974. Natural regeneration of east-side conifer forests. In: Environmental Effects of Forest Residues Management in the Pacific Northwest, a State-of-Knowledge Compendium. USDA For. Serv. Gen. Tech. Rep. PNW-24, Pac. Northwest For. Range Exp. Sta., Portland, OR, pp. L-I--L-21.

Vitousek, P.M. and Melillo, J.M., 1979. Nitrate losses from disturbed forests: Patterns and mechanisms. For. Sci., 25: 605--619.

Vitousek, P.M., Gosz, J.R., Grier, C.C., Melillo, J.M., Reiners, W.A. and Todd, R.L., 1979. Nitrate losses from disturbed ecosystems. Science, 204: 469--474.

Voigt, G.K., 1979. Acid precipitation, forest ecosystems, and intensive harvesting. In: A.L. Leaf (Editor), Effects of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, pp. 33--48.

Weetman, G.F. and Hill, S.B., 1973. General environmental and biological concerns in relation to forest fertilization. In: A.L. Leaf and R.E. Leonard (Editors), Forest Fer- tilization. USDA Forest Service Tech. Rep. NE-3, Upper Darby, PA, pp. 242--246.

Wells, C.G. and Jorgensen, J.R., 1979. Effects of intensive harvesting on nutrient supply and sustained productivity. In: A.L. Leaf (Editor), Impact of Intensive Harvesting on Forest Nutrient Cycling. State University of New York, Syracuse, NY, pp. 212--230.

Whyte, A.G.D., 1972. Productivity of first and second crops ofPinus radiata on the mon- tere gravel soils of Nelson. N.Z.J. For., 18: 87--103.

Will, G.M. and Ballard, R., 1966. Radiata pine --soil degrader or improver N.Z.J. For., 21 : 2 4 8 - - 2 5 2 .

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