ROLE OF FOREST FUELS IN THE BIOLOGY AND MANAGEMENT OF SOIL

A. E. HARVEY, M. F. JURGENSEN, AND M. J. LARSEN

USDA Forest Service G e n e r a l T e c h n i c a l R e p o r t I N T - 6 5

S e p t e m b e r 1979

ROLE OF FOREST FUELS IN THE BIOLOGY AND MANAGEMENT OF SOIL

A. E. Harvey, M. F. Jurgensen, and M. J. Larsen

INTERMOUNTAIN FOREST AND RANGE EXPERIMENT STATION Forest Service

U.S. D e p a r t m e n t of A g r i c u l t u r e O g d e n , U t a h 8 4 4 0 1

THE AUTHORS

A. E. HARVEY, P l an t Pa tho log i s t , is respons ib le f o r research i n t o mic rob io l i~g ica l impacts of i n t ens ive f i b e r u t i l i z a t i o n and p r e s c r L h 4 f i r e . He is s t a t i oned a t t h e Fo re s t ry Sciences Labor&-ory, P l~s sou la , Montana. D r . Harvey received t h e B.S. d e g r ~ t An Biology (1960), t h e M.S. degree i n P l a n t Pathology ( I%)? ) , t he Ph.D. degree i n P l a n t Pathology (1968) , and an acacismlc year of postgraduate work i n P l a n t Pathology (1972) He ~ ~ ~ i n e d t h e Intermountain S t a t i o n i n 1965.

M. F. JURGENSEN, Associate Professor of Fo re s t S o i l s teaches and conducts r e sea rch i n Fores t So i l s -So i l s Microbiology. D r . Jurgensen rece ived t h e B.S. degree i n Fo re s t ry (1961), t h e M.S. degree i n S i l v i c u l t u r e (19651, and t h e Ph.D. degree i n S o i l Science (1967). He has he ld t h e p o s i t i o n s of Research Associate (1966-1967) and Ass i s t an t Professor (1966) a t North Carol ina S t a t e Universi ty. H i s p r e sen t p o s i t i o n i s wi th t h e Department o f Fo re s t ry , Michigan Technological Univers i ty , Houghton, Michigan.

M. J. LARSEN, Mycologist, i s p r e s e n t l y i nves t iga t ing t h e taxonomy and ecology of f o r e s t fungi a t t h e Center f o r Fores t Mycology Research, Fo re s t Products Laboratory, Madison, Wisconsin. D r . Larsen received t h e B.S. degree i n Botany (1960), t h e M.S. degree i n P l a n t Products Pathology (1963), and t h e Ph.D. degree i n Fo re s t Mycology (1967). He he ld a p o s i t i o n wi th t h e Canadian Fo res t ry Serv ice (1966-1970) and joined t h e Center f o r Fores t Mycology Research i n 1971.

RESEARCH SUMMARY

Microbial activities are the principal biological determinants of forest site quality. The energy source or substrate for most microbes is derived from soil organic matter (fuels). Microbial activities most critical to site quality are.nitrification, dinitro- gen fixation, decay, ectomycorrhizal symbiosis, and pathogensis. Research on these subjects supports the following conclusions.

The end product of nitrification, nitrate, is subject to leach- ing loss. Nitrification is increased by forest disturbances, partic ularly clearcutting and burning. In most cases, losses of nitrogen are small and short lived.

The quantities of nitrogen fixed in forest soil by symbiotic associations are dependent on the presence of host plants. Such hosts are sometimes scarce. Nonsymbiotic nitrogen fixers depend only on organic matter. Soil humus, decaying and decayed wood, are important sites for nonsymbiotic nitrogen fixation, particularly during dry periods or on dry sites.

Soil humus and decayed wood are also the principal substrates for ectomycorrhizal symbionts during dry seasons and on dry sites.

Decay of wood and other organic material contributes to soil development by cycling carbon and minerals. Products of decay pro- vide sites for nitrogen fixation and ectomycorrhizal activity. Decay of newly formed residues, to a point where they function in these capacities, is a long-term process.

Removing or burning forest fuels can lead to increased feeder root disease. It can also create wound entry sites for decay in living trees. In some instances this provides active centers of nitrogen fixation. Infected wood in root disease centers is a po- tential source for inoculation and further spread of the diseases.

Adequate quantities of woody residue, and other soil organic matter sources, are critical to optimal forest growth. Except where wood constitutes potential for disease or intense wildfire or where it is replaced in relatively short time spans (warm, moist sites) it should be conserved. This is particularly true of marginal (dry or cold) sites. Excess accumulation or inadequate supplies of wood provides an opportunity for site protection and enhancement through fuel management.

CONTENTS

Page

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 1

EFFECTS OF FUEL DISTURBANCE ON SOIL BIOLOGICAL ACTIVITIES . . . 1

Nitrification . . . . . . . . . . . . . . . . . . . . . . 1 Nitrogen Fixation . . . . . . . . . . . . . . . . . . . . 2 Decay . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Ectomycorrhizal Activity . . . . . . . . . . . . . . . . . 4

. . . . . . . . . . . . . . . . . . . . . Disease Activity 5

. . . . . . . . . . MANAGEMENT IMPLICATIONS AND RECOMMENDATIONS 6

Forest Fuels.. An Asset . . . . . . . . . . . . . . . . . . 6 Forest Fuels.. A Liability . . . . . . . . . . . . . . . . 6 Forest Fuels.. An Opportunity . . . . . . . . . . . . . . . 6

PUBLICATIONS CITED . . . . . . . . . . . . . . . . . . . . . . 7

INTRODUCTION

The q u a l i t y of a f o r e s t s i t e i s governed by i t s phys ica l condi t ions (temperature, moisture, s o i l parent ma te r i a l s ) a s they a f f e c t p l a n t and s o i l . Microbes g r e a t l y a f f e c t s o i l development. Thei r a c t i v i t i e s mediate n u t r i e n t s t a t u s through r e l e a s e , acqu i s i t i on , r e t e n t i o n , and recyc l ing . Microbes, i n p a r t , a r e respons ib le f o r s o i l phys ica l s t a t e , t i l t h , and water r e t e n t i o n , by c o n t r o l l i n g type and quan t i t y of organic ma te r i a l s . These f a c t o r s , i n t u r n , a f f e c t microbial p l a n t symbionts and pathogens. Thus, microbial a c t i o n i n many types of organic f u e l s is a major b i o l o g i c a l determinant of s i t e q u a l i t y .

I n t e r a c t i o n s between f o r e s t uses and t h e i r r e s idues ( fue l s ) o r lack of them b r ing about changes i n both populat ion s i z e and types of s o i l microorganisms (Bell 1974). Most microbes a r e dependent on organic ma te r i a l s (p l an t bodies) e i t h e r f o r t h e i r energy source o r a s a growing medium ( s u b s t r a t e ) . Therefore, d i s rup t ion of t h e quan t i t y , type, and d i s t r i b u t i o n of humus, l i t t e r , and wood imposes con t ro l s on t h e i r populat ions. The chemical-physical na tu re of organic mat te r a l s o a f f e c t s microbes. Water content , temperature, and r e a c t i o n (pH) a r e a l l inf luenced by f o r e s t use , e s p e c i a l l y harves t ing and burning (DeByle 1976; Bollen 1974).

EFFECTS OF FUEL DISTURBANCE ON SOIL BIOLOGICAL ACTIVITIES

S i l v i c u l t u r a l a c t i v i t i e s and o t h e r f o r e s t r y p r a c t i c e s can inf luence type and quan t i t y o f f o r e s t f u e l s and hence have numerous e f f e c t s on s o i l biology. Five b io log ica l e f f e c t s a r e p a r t i c u l a r l y s i g n i f i c a n t :

(1) The conversion of o t h e r forms of n i t rogen i n t o n i t r a t e ( n i t r i f i c a t i o n ) and i t s p o t e n t i a l l o s s by leaching.

( 2 ) F ixa t ion of atmospheric n i t rogen .

(3) Decay of organic ma t t e r , with i t s e f f e c t s on f u e l reduct ion , mineral cyc l ing , n i t rogen acqu i s t i on , and organic s t r u c t u r i n g of t h e s o i l .

(4) A c t i v i t i e s of mycorrhizal symbionts.

(5) Development of and damage caused by c e r t a i n p l a n t d i s ease fungi (Harvey and o t h e r s 1976a).

Knowledge accumulated on these sub jec t s and r e s u l t s of cu r r en t research i n t h e nor thern Rocky Mountains suggests t h e following conclusions.

Nitrification

Nitrogen i s u sua l ly t h e most l im i t i ng n u t r i e n t i n f o r e s t ecosystems. I t s q u a l i t y and form i n t h e s o i l i s almost t o t a l l y dependent on microbial ac t i on (Stone 1973). Consequently much i n t e r e s t i s now developing with regard t o t h e inf luence of f o r e s t uses on t h e ecology of t h e mocroorganisms t h a t func t ion i n t h e cyc l ing of n i t rogen .

Decay o r f i r e r e l e a s e s n i t rogen from organic ma te r i a l i n t h e form of ammonia. A s e l e c t group of au to t roph ic s o i l b a c t e r i a , p a r t i c u l a r l y Nitrosomonas and Nitrobacter, obta in t h e i r energy from a range of n i t rogen compounds, e s p e c i a l l y ammonia. As a r e s u l t o f ox ida t ion by these organisms, ammonia is converted t o n i t r a t e . N i t r a t e i s not bound t o s o i l exchange s i t e s and c r e a t e s a p o t e n t i a l f o r leaching l o s s .

C lea rcu t t i ng can dramat ica l ly i nc rease t h i s n i t r i f i c a t i o n process (Rice and Pan- choly 1972; Likens and o t h e r s 1970). I-lowever, l o s se s a r e u sua l ly small and sho r t l i ved (Reinhart 1973).

Nitrogen Fixation

Another c l a s s of mircoorganisms of importance t o t h e cyc l ing of n i t rogen a r e those t h a t e x t r a c t n i t rogen from t h e atmosphere and convert it i n t o forms use fu l t o p l a n t s . There a r e two c l a s s e s of n i t rogen f i x e r s :

(1) The symbiotic forms assoc ia ted with p l a n t nodules, u sua l ly t h e genus Rhizobiwn.

(2) A v a r i e t y o f nonsymbiotic n i t rogen f i x e r s t h a t de r ive t h e i r energy from t h e breakdown of s o i l o rganic mat te r o r from sun l igh t .

The r e l a t i v e con t r ibu t ions of symbiotic and nonsymbiotic forms t o t h e n i t rogen economy of f o r e s t s is not well understood (Borman and o the r s 1977; Wollum and Davey 1975; Jurgensen 1973; Jurgensen and Davey 1970). However, i n many f o r e s t ecosystems, nodu- l a t e d p l a n t s a r e inf requent . In c o n t r a s t , nonsymbiotic n i t rogen f i x e r s a r e widely d i s t r i b u t e d , being found i n nea r ly a l l f o r e s t s o i l s .

The e f f e c t s o f f u e l d i s turbance on symbiotic n i t rogen f i x e r s depends on t h e impact on d i s t r i b u t i o n of t h e nodulated p l a n t s on which symbionts depend. Legumes and a l d e r a r e examples of p l a n t s i n t h e western United S t a t e s t h a t a r e favored by c l e a r c u t t i n g (Youngberg and Wollum 1970). Opening f o r e s t s tands a l s o i nc rease leguminous p l a n t s i n t h e southeas te rn United S t a t e s (Schultz 1976).

Nonsymbiotic n i t rogen f i x e r s a r e dependent on s o i l o rganic mat te r . Our da t a from western Montana show t h a t humus and decayed wood a r e t h e p r i n c i p a l s i t e s f o r nonsymbio- t i c n i t rogen - f ix ing a c t i v i t i e s . Smaller amounts a r e cont r ibu ted by mineral s o i l and l i t t e r . Decaying woody ma te r i a l s , no t y e t incorporated i n t o t h e s o i l , provide t h e highest-per-uni t-weight n i t rogen-f ix ing capac i ty of any ma te r i a l widely a v a i l a b l e on t h e f o r e s t f l o o r ( t a b l e 1) .

Table 1.--Mean da i l y nitrogen fixation rates f m a D o u g Z a s - f i r / k ~ h stand (ABLA/CLUN)' i n western Montana (June 24, 19761 based on five sampZes per stratum.

Soil strata Grams N,/gram of dry substrate

Mineral soil

Humus (02)

Decayed wood in soil (o3l3

Decaying log

' ~ b i e s Zasiocarpa/CZintonia m i f l o r a is a habitat type designation in western Montana (Pfister and others 1977).

2 ~ 1 1 fixations rates reported herin were determined by acetylene reduction (Hardy and others 1968) .

3The 0 horizon designation is used here to depict localized concentrations of 3

brown cubicle decayed wood with mineral soil horizons that are clearly distinguishable from the litter layer (01 horizon) and humus layer (02 horizon).

The processes and organisms involved i n decay o f organic ma t t e r a r e e s s e n t i a l t o s o i l development through carbon and mineral cyc l ing .

Pas t research has shown increased l i t t e r decomposition accompanies t imber harves t - ing with a t t endan t n u t r i e n t r e l e a s e and leaching from t h e s o i l (Packer and Williams 1976; Hart and DeByle 1975; Piene 1974; Cole and Gessel 1965). For most s i t e s such l o s s e s a r e smal l . Th i s was t h e r e s u l t a t our experimental s i t e i n western Montana.

The e f f e c t o f ha rves t i ng on t h e decay o f l a r g e f u e l s ( logs) i s p r e s e n t l y uncer ta in ; however, t h e end r e s u l t o f t h i s process is known. Decaying logs a r e a s i g n i f i c a n t s i t e f o r n i t r ogen - f i x ing a c t i v i t y (Larsen and o t h e r s 1978; Borman and o t h e r s 1977; Cornaby and Waid 1973). The decayed r e s idue , i n t h e form of brown, crumbly wood on o r i n t h e s o i l provides a s i t e f o r continued n i t rogen f i x a t i o n ( t a b l e 1 ) . Decayed wood becomes

Y t h e primary s i t e f o r t h i s a c t i v i t y dur ing d ry per iods o r on d ry s i t e s ( t a b l e 2 ) . This i s probably due t o a unique a b i l i t y of decayed wood t o r e t a i n l a r g e q u a n t i t i e s o f

1 moisture ( t a b l e 3 ) . I t a l s o has a much h ighe r c a t i o n exchange capac i t y than o t h e r s o i l components, t hus i nc r ea s ing s o i l c a t i on exchange capac i t y . Decayed wood has been repor ted t o make up 15-30 percent o f t h e t o p 12-15 inches of var ious f o r e s t s o i l s (Harvey and o t h e r s 1976b; McFee and Stone 1966).

Table 2.--Mean daily nitrogen fixation rates from various forest s i t e s on July 24, 1976, (beginning of the sununer dry period) based on three samples per stratum

Soil Strata

Site

Grams N3/gram of dry substrate -

1 (PSME/PHMA) warm-dry 5.9

2 (ABLA/CLUN) cool-moist 15.8

3 (TSHE/CLUN) warm-moist 39.5

'soil strata are: 02, humus; 03, decayed wood in soil; MI, first 5 cm mineral soil.

Table 3.--Mean moisture content of so i l s trata from various forest s i t e s , based on 150 random samples per s i t e , June throl~gh September, 1976

Site Soil Strata Moisture content (Pct. dry wt.)

1 (PSMEJPHMA) Litter (01)

warm-dry Humus ( 02 )

Decayed wood in soil (03)

Mineral (MI)

2 (ABLA/CLUN) cool-moist

3 (TSHE/CLUN) warm-moist

Our preliminary estimates indicate that the input of functional decayed woody material into summer dry, winter cold forest soils characteristic of the northern Rocky Mountains may require hundreds of years.

Ectomycorrhizal Activity

The failure of afforestation efforts in areas lacking ectomycorrhizal associates for conifers attests to the obligate nature of the association between tree roots and fungi (Mikola 1973). Presence of the ectomycorrhizal association is particularly im- portant to the ability to extract water, nitrogen, and phosphate from infertile soils (Bowen 1973; Melvin and Nilsson 1952).

Intense post-harvest burning is known to reduce mycorrhizal activity in subsequent regeneration (Wright and Tarrant 1958). This is probably a result of an alkaline shift in soil reaction, a high nutrient flux, and a reduction in soil organic matter. All these are detrimental to mycorrhizal development if they are extreme. The first two effects are transitory, the latter (decayed wood, etc.) is not.

In a mature ecosystem, upwards of 90 percent of the mycorrhizal activity in a stand is supported by organic matter (Harvey and others 1976b). During dry periods (Harvey and others 1978) or on dry sites most ectomycorrhizal activity is directly supported in decayed wood (table 4 and 5).

Table 4.--?lean numbers o f ac t ive mycorrhizaZ root t i p s per Ziter and moisture content of soiZ from a Douglas-fir larch (ABLA/CLUNlsite i n westel-z L'ontana, by EO- day periods during the 1975 g~%u?:ng season

Sampling period Soil strata Active tips/liter Pct. H20

May-June

July-August

September-October

Litter (01) 5.9 Humus (02) 369.0 Decayed wood in soil (02) 75.4 Mineral (MI) 13.5

Table 5.--Mean numbers o f active mycorrhiza2 root t i p s per Ziter of soiZ from various forest s i t e s , based on I S 0 random samples per s i t e , June through October 1976

Site Soil strata Active tips/liter

1 (PSME/PHMA) warm-dry

2 (ABLA/CLUN) cool-moist

3 (TSHE/CLUN) warm-moist

Litter (01) llumus (02) Decayed Wood (0 ) Mineral (M )

1

Thus, excess ive r e s idue removal could adverse ly impact some s i t e s throughout one o r more r o t a t i o n s , depending on t h e t o t a l amounts of woody ma te r i a l added t o t h a t s i t e and t o i t s r a t e o f decay and incorpora t ion i n t o t h e s o i l .

Disease Activity

Harvest ing and burning can provide a major source of i n f e c t i o n f o r many r o o t and stem pathogens p r imar i l y due t o wound damage i n r e s i d u a l t r e e s o r changes i n s o i l chemistry (Harvey and o t h e r s 1976a).

Burning may inc rea se t h e a c t i v i t i e s o f t h e p o t e n t i a l l y damaging Rhizina r o o t r o t (I\lorgan and Driver 1972) o r o t h e r f eede r r o o t d i s ea se s of young con i f e r s (Wright and Bollen 1961). Thus f a r , i n our l i g h t l y burned experimental p l o t s , d i s e a s e has made only minor con t r i bu t i ons t o regenera t ion m o r t a l i t y .

I n a c t i v e r o o t d i s ea se c e n t e r s l a r g e , bur ied r e s idues , stumps, and r o o t s i n f ec t ed o r sub j ec t t o i n f e c t i o n a r e known t o pe rpe tua t e d i s ea se s (Nelson and Harvey 1974; Kaarik and Renner fe l t 1957; G i l l and Andrews 1956).

The presence of r o o t and stem d i s e a s e should n o t , i n a l l c a se s , be considered bad. We have discovered a t l e a s t some types of pa thologica l decay, a s with r e s idue (sapro- phyt ic ) decay, p rovide a s i t e f o r n i t r ogen f i x a t i o n ( t a b l e 6 ) .

In overmature s t ands pa tho log i ca l decay con t r i bu t e s t o p r epa ra t i on of t h e s i t e f o r f u tu r e s t ands . This f i b e r l o s s can, t h e r e f o r e , be an energy investment i n , a s wel l a s a t h r e a t t o f u t u r e s i t e p roduc t iv i t y .

Table 6.--Daily nitrogen f ixat ion rates from wood i n l i v e , standing western Hemlock and down, dead Douglas-fir. Decayed by Echinodontium t inc tor ium ( E l l . & Ev. ) and Fomitopsis p i n i c o l a (Swortz ex F t . ) Korst., respect ively , based on 5 samples per decay type

E. t i n e t o r i m F. pinicola

Decay s t a g e Grams N2/gram of s u b s t r a t e (lo-")

Undecayed (no v i s u a l d i s co lo ra t i on ) 20.7 17.1

Inc ip i en t decay ( l i g h t d i co lo ra - t i o n , wood f i rm)

Advanced decay (h ighly d i s co lo red , wood s o f t )

MANAGEMENT IMPLICATIONS AND RECOMMENDATIONS

Forest Fuels - An Asset

Forest managers and forest users should recognize the benefits, equivalent to long- term fertilization and moisture conservation, of retaining wood and other organic materials in forest ecosystems. Three separate lines of evidence (nitrogen fixation, decay rate, ectomycorrhizal activity) indicate these materials should be considered an important, functional part of forest soils, particularly on droughty sites.

Extreme scarification, intensive pile and burn, or hot wildfire that drastically reduces organic matter are potentially dangerous to dry sites. Such treatments may provide good early regeneration but poor ultimate survival and slow growth. This is primarily because both nitrogen and moisture reserves are lost from the root zone.

In extreme cases, because of slow decay rates on dry or cold sites, one or more rotations may be required to rebuild soil too low in organic matter to support the growth potential of that site.

Forest Fuels - A Liability

In specific areas, for example where fuel loading represents potential for highly destructive wildfire, or where woody residues are sources of pathogens from destructive disease centers, the benefits of removal will likely exceed those of preservation. Similarly, accumulations of organic matter in excess of site requirements may be un- desirable. The potential for such circumstances is highest on cool, moist sites. This aspect of forest soil ecology is not, as yet, well documented.

High productivity and rapid decay render warm, moist forests less sensitive to long-term damage by depletion of soil organic matter either by fire or by other of man's activities.

Forest Fuels - An Opportunity

The vital role of wood in the functions of forest soil biology provides an oppor- tunity for control of the soil system through harvest management. Where soils are low in organic matter, wood can be left on the site. Here it will gradually decay to pro- vide nitrogen and moist microsites for ectomcorrhizal activity. Conversely, where wood has accumulated in quantity it can be removed and utilized or burned in place. Where the soil system is adequately supplied with organic matter it can be maintained in that condition. Thus, knowledgeable fuels management can improve, at least protect, any forest site where comtemplated use has the potential to disturb the distribution, quantity, or type of organic matter on that site.

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ecology of f o r e s t s . USDA For. Serv. Gen. Tech. Rep. INT-28, 46 p. In te rmt . For. and Range Exp. S t n . , Ogden, Utah.

Harvey, A . E . , M . J . Larsen, and M . F. Jurgensen. 197613. D i s t r i b u t i o n o f ectomycorrhizal i n a mature Douglas - f i r / l a rch f o r e s t s o i l i n

western Montana. For. S c i . 22:393-398. Jurgensen, M . F.

1973. Rela t ionsh ip between nonsymbiotic n i t r ogen f i x a t i o n and s o i l n u t r i e n t s t a t u s - - a review. J . S o i l S c i . 24:512-522.

Jurgensen, M . F. , and C . 8. Davey. 1970. Nonsymbiotic n i t r ogen f i x i n g micro-organisms i n ac id s o i l s and t h e rh izosphere .

S o i l s F e r t . 33:435-446. Kaarik, A . , and E . Renner fe l t .

1957. I n v e s t i g a t i o n on t h e fungal f l o r a of spruce and p ine stumps. S t a t u s Skogsfor- skn ings in s t . (Sweden), lifedd. 47: 1-88.

Larsen, M . J . , M . F . Jurgensen, and A. E . Harvey. 1978. Nitrogen f i x a t i o n a s soc i a t ed wi th wood and wood decay fungi i n western Montana.

Can., J . For. Res. ( I n p r e s s ) .

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Harvey, A. E., M. F. Jurgensen, and M. J. Larsen 1979. Role of Forest Fuels in the Biology and Managbnt of soil. USDA For. Serv. Gen. Tech. Rep. INT-65, 8 p. Intermountain Forest and Range Experiment Station, Ogden, Utah 84401.

Reviews current understanding of and provides research data on the relationship between forest fuels.(organic matter accu- mulations) and forest soil productivity. Concludes that soil organic matter and woody residues are important to ectomycor- rhizal and nitrogen-fixing activities. Protecting site qual- ity will likely become an important factor in residue manage-

KEYWORDS: prescribed fire, wildfire, residues-fuel management, soil organic reserves, nitrogen fixation, ectomycorrhizal,

Harvey, A. E., M. F. Jurgensen, and M. J. Lazsen 1979. Role of Forest Fuels in the Biology and Managenrent of soil. USDA For. Serv. Gen. Tech. Rep. INT-65, 8 p. Intermountain Forest and Range Experiment Statfont Ogden, Utah 84401.

Reviews current understanding of and provides research data on the relationship between forest fuels (organic matter accu- mulations) and forest soil productivity. Concludes that soil organic matter and woody residues are important to ectalycor- rhizal and nitrogen-fixing activities. Protecting site qual- ity will likely become an hportant factor in residue uianage-

KEYWORDS: prescribed fire, wildfire, residues-fuel management, soil organic reserves, nitrogen fixation, ectomycorrhizal,

nitrificetio

Headquarters for the Intermountain Forest and Range Experiment Station a r e in Ogden, Utah. Field programs and research work units a r e maintained in: e

Billings, Montana Boise, Idaho Bozeman, Montana (in cooperation with - Montana State University) w a n , Utah (in cooperation with Utah State

University) Miss,oula, Montana (in cooperation with

University of Montana) Moscow, Idaho (in cooperation with the

University of Idaho) Provo, Utah (in coqperation with Brigham

Young University) Reno, Nevada (in -cooperation with the

University of Nevada)