comparison of soil microfungal populations in disturbed and undisturbed forests in northern...

Comparison of soil microfungal populations in disturbed and undisturbed forests in northern Wisconsin

DONALD T. WICKLOW' A N D W. F. WHITTINGHAM Deprirttrlent r?f'Botrrny, Utii~v~..sity of Wiscot~sitl, Mrrrli.sot7, WI, U.S.A. 53706

Received August 7, 1975

WICKLOW, D. T., ilnd W. F. WHITTINCHAM. 1978. Comparison of soil microfungal populations in disturbed and undisturbed forests in northern Wisconsin. Can. J . Bot. 56: 1702-1709.

Soil dilution plates were used to isolate populations of microfungi associated with the different soil horizons of five secondary successional forests, which arose after fire or clear-cutting, and three virginal (reference) stands. Ordinations of the populations within each horizon, based on similarities in the species composition of the microfi~ngal communities, revealed the disturbed stands differed from their respective reference stands, although there was no consistent dis- placement of the stands in the ordinations. Most of the differences entailed alterations in frequency and (or)density, although a few species were predominant in one forest type but not in itscounterpart. The most recently disturbed areasexhibited thegreatest displacementsfrom their reference stands. The ordinations suggested there is a sequential recovery of the mycoflora in the disturbed stands on loamy sand soils which would eventually result in a population similar to that in the reference stand.

Introduction It is widely accepted that each type of vegeta-

tional community harbors a characteristic soil mycofloral population, particularly the assemblage of the more predominant species. However, there is no evidence that the microfungi form discrete communities; rather they constitute a continuum, the species composition gradually changing with differences in the vegetational cover and soil characteristics. For example, several studies have shown that there is a shift in the species composi- tion of the soil mycoflora which parallels pioneer vegetational succession (Brown 1958; Cooke and Lawrence 1959; Pugh 1962, 1963; Wohlrab et al. 1963). A number of surveys of the microfungi in- habiting the A, soil horizon of a wide variety of undisturbed plant communities in Wisconsin have demonstrated a similar correlation between the composition of the fungal community and the vege- tational cover (see bibliography in Christensen 1969). Whereas most of the microfungi exhibited broad amplitudes of tolerance in the prairie con- tinuum (Orpurt and Curtis 1957), Christensen (1969) found an abundance of narrow-amplitude species in the soils of northern conifer-hardwood forests. She concluded that there were "...deter- minable distribution patterns within a multidimen- sional environmental complex." However, there has been little definitive work in identifying the factors which influence the character of the mycofloral population. A number have been pro- posed, including the composition of the cover vege-

'Present address: Northern Regional Research Center, Sci- ence and Education Administration, United States Department ofAgricuiture, Peoria, IL, U.S.A. 61604.

tation, the structural and chemical characteristics of the litter and (or) mineralized soil, root exudates, and mycorrhizae (Orpurt and Curtis 1957; Cooke and Lawrence 1959; Kendrick and Burges 1962; Christensen 1969; Wicklow 1973).

This investigation was conducted to characterize the microfungal populations associated with selected secondary successional forests that arose as a result of fire or clear-cutting. These popula- tions are compared with those isolated from virgi- nal stands having edaphic features similar to those of the secondary forests and believed to be similar in composition to the original vegetation of the disturbed sites. This could provide a means of evaluating the persistence of, and changes in, com- ponents of the mycoflora with an abrupt change in the vegetative covers and litter input.

Study Areas and Methods The forests, located in Menominee County, Wisconsin, were

selected from the 50 whose vegetation and soils had been thoroughly documented by Goff (1967) and Baxter (1967). They are part of the conifer-hardwood complex that covered much of nol-the~n Wisconsin prior to settlement. Today, the forested regions in this area form a mosaic of virgin areas interspersed among forests in various stages of secondary succession which arose as a result of disastrous fires or l o ~ i n g . A brief summary of the main features of the forests included in this study appears in Table 1. Additional floristic and edaphic data were reported by Wicklow and Whittingham (1974), Goff (1967). and Baxter (1967). There was no evidence that the three virginal stands had experienced a major disturbance within the past two or three centuries. These served as reference ('control') stands with which vegetation of the latter stands was deduced by Goff (1967), using evidence from tree stumps and cradle knolls, the species composition of adjacent forests, and soil characteristics of the site. Although replication would have been desirable, it would be virtually impossible to locate stands having identical edaphic and climatic features, histories, and vegetational com-

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WICKLOW A N D WHITTINGHAM

TABLE I . Sunlnlary of the vegetational and edaphic features of the forest comn~unities included in this study (reference stands in capital letters)

Stand Stand designation Vegetation History Soil no. -

HEMLOCK Mixed conifer-hardwoods : Virginal Loamy sand 4 white pine and hemlock (undisturbed) dominant; sugar maple, beech, hemlock, and basswood in understory

Pine Second-growth white pine Fire in 1890 Loamy sand dominant; mixed hard- woods in understory

Aspen Second-growth quaking Fire in 1930 Loamy sand aspen dominant; black cherry and white pine in understory

Birch Second-growth yellow Clear-cut in Loamy sand birch dominant; mixed 1900-1910 hardwoods in understory

BEECH Mixed conifer-hardwoods: Virginal Sandy loam hemlock, beech, and (undisturbed) sugar maple dominant and in understory

Oak Second-growth red oak Fire in 1900- Sandy loam dominant; mixed hard- 1910 woods and quaking aspen in understory

BASSWOOD Mixed conifer-hardwoods : Virginal Silt loan1 hemlock, basswood, (undisturbed) yellow birch, and sugar maple dominant and in understory

Second-growth hardwoods : Fire in 1925 sugar maple, basswood, and American elm dominant; mixed hard- woods in understory

Silt loam

position. Therefore, we recognize the results are not conclusive but can serve as a comparative reference for additional studies of this type.

The isolation procedures were identical with those reported by Wicklow and Whittingham (1974). Briefly, each forest was sampled at five randomly selected sites. Samples of the Iitter(L), fermentation (F), humus and A,(HIA,). and each of the recog- nizable mineral horizons were placed in separate, sterile, plastic bags and transported in an ice chest to the laboratory where they were stored at either 4°C (L and F samples) or 10°C (remaining samples). Inocula were prepared by homogenizing a 4-g sub- sample in 1961111 of 0.2% water agar, and additional dilutions prepared so there would be 30-40 colonies on each isolation plate when i t was inoculated with 1.0ml of the suspension. The sample populations were randomly isolated from a modified nutrient medium (DPYA) recommended by Papavizas and Davey (1959) after a 6-day incubation at room temperature (22-25°C). A 200-membered population was isolated from each stand horizon, 40 isolates from each site sample. After7-12 days of incubation, the tube cultures were segregated into groups of presumptive species and one isolate maintained for identifica- tion. The number of sites of occurrence (frequency) and the total number of isolates (density) were recorded for each presumptive taxon.

The species used to compare populations with one another had an importance index ( I n of 6 or greater, where I I = number of stands of occurrence x number of sites of occurrence. Esti- mates of similarity among the populations were calculated using the ~ ) v / ( N + b) coefficient developed by Bray and Curtis (1957) and later modified by Beals (1960, 1965).

Results Comparison of tlze Three Reference Stands

When this investigation was initiated, we had hoped the three reference stands could serve as replicates, although there were differences in community composition and soil texture. From previous work using the same techniques employed in this study, similarity coefficients (SC) of 80% or higher were obtained for replicate populations iso- lated from the same forest (Novak and Whitting- ham 1968; Christensen 1969), indicating the methods permitted a reasonable degree of repeat- ability. This level was not attained for any of the horizon populations of the reference stands (Table

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1704 CAN. J. BOT. VOL. 56, 1978

TABLE 2. Similarity coefficients among stand populations isolated from specific soil horizons (reference stands in capital letters)

Horizon Pine Aspen Birch BEECH Oak BASSWOOD Elm

Litter HEMLOCK Pine Aspen Birch BEECH Oak BASSWOOD

Fermentation HEMLOCK Pine Aspen Birch BEECH Oak BASSWOOD

Humus/A, HEMLOCK Pine Aspen Birch BEECH Oak BASSWOOD

HEMLOCK Pine Aspen Birch BEECH Oak BASSWOOD

Bhir and B2 HEMLOCK Pine Aspen Birch BEECH Oak BASSWOOD

The similarity coefficients of the mineralized horizons exhibited the greatest range (37-70), the lowest coefficients being associated with 'HEM- LOCK,' a stand that has a highly developed podzolic profile and a soil texture that is coarser than the other two reference stands. Table 3 in- cludes the species exhibiting major differences in the sample populations. Although the coefficients for the mineralized horizons in 'HEMLOCK' and 'BASSWOOD' were low, those for the organic layers were considerably higher, suggesting that the organic substrata do not serve as primary inocu- la for the mineralized horizons. Similar observa- tions have been made by others (Soderstrom 1975 and literature cited therein).

Since there were conspicuous differences among the populations in the three reference stands, they did not offer an opportunity to assess sampling error. However, from the work cited earlier, we

2). The populations isolated from the H/A, layer were most similar to one another (SC 61-69) with the L populations exhibiting an overlapping range (SC 53-64). The two low coefficients for the F layers (SC 37 and 43) appear to be associated with 'BEECH,' and this is the only stand that had an abundance of earthworms (recognized after the study was well underway). Their selective feeding on specific types of litter (Lofty 1974 and literature cited therein) and changes in the substrate (e.g., aeration, mixing action) arisingfrom their tunneling may account for these discrepancies. The major differences in the mycoflora of the organic layers can be attributed to the high frequencies and den- sities of Mortierella alpina and Triclzoderma spp. in 'HEMLOCK' and 'BASSWOOD' while FLIS- arium tricinctum, Paecilomyces farinosus, and Mycelia sterilia (5141) were relatively predominant in 'BEECH' (Table 3).

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WICKLOW AND b

can expect a reproducibility of at least 80% and are reasonably confident that any differences men- tioned are real rather than inherent sampling errors. Hereon, comparisons will be made among the forests that occur on the same soil type.

Silt Loam Soils The area occupied by the 'elm' stand experi-

enced a disastrous fire about 1925. If our supposi- tion is correct that the area previously had sup- posted a community similar to 'BASSWOOD,' there has been a detectable alteration in the mycofloral communities in all horizons. The simi- larity coefficients ranged from 46 to 54 (Table 2), a level considerably lower than expected for repli- cate samples. Both quantitative and qualitative dif- ferences are apparent, which could be anticipated in the organic layers because of the differences in litter input. Alternaria alterrzata, Penicil- lirrnz lntzosllrn, and Thysanoplzorn penicilloides accounted for 20% of the isolates in the 'BASS- WOOD' litter but only 1% of the population in 'elm,' while Vollrtella sp. was predominant in the latter. Species of Trichoderma attained relatively high densities in the 'BASSWOOD' F and H/A,. The populations in the mineralized horizons of 'BASSWOOD' can be distinguished from those of 'elm' by the greater densities of Mortierella Izrlmilis, M . vitzacea 11, and Verticillirlm sp. in the A? horizon and Bearlvar.ia bassiatla in the underly- ing horizon.

Sandy Loarn Soils The temporal successional status of the 'oak'

forest is similar to that of 'elm,' but the canopy dominants and understory are distinctly different (Table I). However, the similarity coefficients for- the various horizons of the disturbed stands with their respective reference stands were similar to one another, those of 'BEECH'-'oak' generally being slightly higher. Examination of the similarity coefficients between the two disturbed stands re- veals that their mycofloral populations differed considerably from one another.

The major differences in species composition be- tween 'BEECH' and 'oak' are included in Table 3. About equal numbers of species had higher fre- quencies and densities in the 'BEECH' L , F, and B horizons as those having lower values, when com- pared with the 'oak' populations. However, the 'oak' H and A, populations harbored two to five times as many species having lower frequencies and densities than found in 'BEECH.'

Loamy Sand Soils The three disturbed stands that occurred on

loamy sand soils are believed to have sustained, prior to disturbance, a forest similar in composition to 'HEMLOCK' (Goff 1967). Two of the catas- trophes occurred within 10-20 years of one another, which afforded an opportunity to surmise the difference between fire and clear-cutting on the fungal populations. The 'pine' stand is believed to represent a secondary successional community be- tween 'HEMLOCK' and 'aspen.'

The similarity coefficients for the various hol-i- zons in 'HEMLOCK' and 'aspen' ranged from 43 to 54, the absolute values being close to those calcu- lated for 'BASSWOOD' and 'elm,' the latter being burned over 5 years befose 'aspen.' Interestingly, the frequency of Volrltella sp. was higher in the litter of both of the disturbed stands, although its density in 'aspen' was considerably lower than in 'elm.' Also, the incidence of Trichoderma was con- sistently lower in the organic layers of the two disturbed stands. The data in Table 3 illustrate other major differences in the population composi- tion of specific horizons in 'HEMLOCK' and 'as- pen.' Notable among them were Cylirzdrocarpotz didyrnum and Phoma sp. (5177) in the litter, Ac- remonium sp., Mortierella nlpina, Mycelia sterilici (5141), and species of Trichodermcr in the F layers, and Cylindrocarpon didymlrm, Gyrnnonsctls reesii, Mortierella parvispora, Paecilomyces carrzeus , and Penicillitrm nigricans in the H/A,. The major differences in the population composition of the mineralized horizons of 'HEMLOCK' and 'aspen' are primarily quantitative.

The 'pine' stand, which was burned about 1890, is now dominated by white pines 60-65 years old. The phanerogamic community comprising the un- derstory suggests that eventually the area would become a forest similar to 'HEMLOCK.' With the exception of the litter layer, the microfungal popu- lations in the various soil horizons exhibit higher similarity coefficients (63 or greater) with the virgi- nal reference stand than any of the stand pairs discussed above. It would appear that within 80 years after a terminal (climax) forest on loamy sand soil has been destroyed by fire, conditions in the soil profile have recovered to a point which permits colonization by a mycoflora similar to that occur- ring in a stand that has not been disturbed for 370 years. Brown (1958) has reported a similar situation in coastal dune soils where, within 20 years, a "semifixed dune grass" mycoflora was replaced by one typical of a heath community. Less radical changes occurred during the next 100 years while a "southern heath" community developed.

The area now occupied by the 'birch' stand was clear-cut in the early 1900's (10-20 years after fire

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TABLE 3. A selected list of species exhibiting differences in frequency (number of sites of occurrence) and (or) density (number of isolates in parentheses) in disturbed forests and undisturbed reference stands (in capital letters)

Soil type and stand

Loamy sand Sandy loam Silt loam Soi I horizon and --

. . . . . . . fungal isolate HEMLOCK Birch Pine Aspen BEECH Oak BASSWOOD Elm . . . . . . . .~ . Litter layer

Acretnot~irrtn sp. (5209) 1(1) 1 0 ) 3(4) 1(2) Altertrnria altertrato 2 0 ) 4(6) 3 6 ) 2(2) 2(4) 4( 10) I@) Clndospo~ilrttr clndosl~orioides 5(15) 5(25) 2(5) 5(32) 4(9) 3(10) Cotriothyrirrttr sp. (5 1 13) 2(3) 1(1) 5(35) 2(3) 3(4) 4(13) Cotriothyrirrttr sp. (5934) 4(38) 4(15) 4 0 1) 2(5) 2 0 ) 3(9) l(2) Cylit~drocarpotz rliryttlirtt~ 3(1O) l(1) 1(1) Hynlohtldrotz sp. (51 17) 1(1) 4(14) 1(1) 4(12) 3(14) 2(2) Mortierello paruisporn 1(1) 4(10) 2 0 ) 2(2) Penicillirrttr godleir~skii l(5) 2(9) 3(7) 1 0 ) Petricillirrttl Introsrrttr 3(7) 1(1) 1(1) 2(10) 3(20) 3(19) Pet~icil l i~~tt~ t~1111ticoIor 3(3) Photna sp. (5105) 3(4) 2(4) 3(1O) 4(28) Pllottra sp. (5 177) 3(15) 1(1) Tlrysmzoplrorn petricillioides 2(8) 1(1) 1(1) 1(1) % l a Triclloden~~n sp. 5(32) 3(3) 3(7) 1(1) 2(4) Trichodennn polysporrrt~r 2(19) 4(8) 5(35) 3(6) 1(4) 3(3) VerticiIIirrtn sp. (5443) 3(6) Volrrtelln sp. (5206) l(1) 4(8) I(]) 2(8) 5(42) Mycelin sterilia (5 176) ] ( I ) l(1) 3(6) 5(10) 3(6) Mycelin stnilin (5201) 1(1) ] ( I ) 3(6) Mycelia stnilin (5247) l(3) 3(4) 2(8) 1(1)

Fermentation layer Acretlrotrirrtn sp. (5590) 4(15) 1(1) Cotriotl~yrir~ttr sp. (5934) 3(7) Cylitldrocnrpotr didyttrrrttr 4(27) 4(10) 4(18) 2(3) 5(61) 2(6) 2(3) Frrsnrirrrn tricitrctrrttl 1 0 ) 5(10) 1(3) Mortierelln alpitm 405) 4(37) 5(37) 2(5) 3(52) 5(80) 5(95) Mortierello jenkitri 3(3) 1(2) Myrotlrecirrttr uerrrrcnrin 1(1) 2(13) 3(4) Pnecilottryces cnrtrerrs 11 3(7) 4(19) 2(2) l(1) 2(4) 2(2) PoeciIotnyces faritzosrrs l(2) 4(13) ((3) Pnecilott~yces j4auescet1s l(2) 3(3) Penicillirrtt~ ttrrrlticolor 3(3) 2(20) Pet~icilli~rr~~ tlrottrii 4(4) 3(5) 2(2) Plrottta sp. (5758) 2(2) 4(4) 1(1) Pl~ott~a sp. (5180) 1(3) 4(7) Triclloderttla sp. 5(53) 4(21) 5(30) 4(15) 2 0 ) 4(6) 5(36) 3(4) Triclroderttm polysporrrrtr 5(14) 3(14) 4(26) 2(5) 1(1) 4(7) 3(4) Verticillirrrtr sp. (5443) 4(5) 1(2) 3(7) 2(2) 3(3) 3(4) 1(1) Mycelin sterilin (5141) 2(4) 2(2) 4(39) 4(25) 1(4) 1(1) Mycelia sterilia (520 1 ) 1(1) 1(3) 3(13)

Humus/A, layer C/~rysosporirrttr pn~rt~orrrttr 4(8) l(3) l(3) 5(9) 5(37) 2(5) 5(12) 3(7) Cotriotliyrirrtt~ sp. (5934) 2(2) 5(5) 1 0 ) l(2) Cylindrocarpon didytt~rrt~r 409) 1(1) 2(2) 3(5) 2(3)

,. . . . Gyttrt~oascrrs reesii l(1) 4(24) 4(11) 2 0 ) l(1) . . . .. - . . . . . . . . . . . Mortierelln elotlgnta

. . . , . . . . . _ . . . . . , 4(6) 4(6) 5(15) 2(5) 4(7) 2(2)

Mortierella l~rrtt~ilis 1 0 ) 3(9) 1(4) 4(7) Mortierella poruisporn 2(3) 507) 1(1) Pnecilornyces cartlerrs 5(28) 5(35) 5(62) l(14) 4(31) 5(39) 5(70) Pnecilotnyces tlrarqrratrdii 3 (5) Petricillirrttr oclrro-clrlororr l(2) 3(8) 3(3) I@) 3(9) Penicillirrttz nigvicans 1(1) 2(8) 1 0 ) 3(19) l(1) 4(16) Penicillirrtlr sp. (5462) 2 0 ) 2 0 ) 3(7) Pe~ricillirrtt~ sp. (6009) 3 (4) 1(1) Triclzoderrtm polysporrrtt~ 3(7) 2(3) 3(7) 1(1) 4(17) 1(2) 5(32) 2(2) VerticiIIirrttl sp. (5443) 3(8) 3(4) 3(3) 3(11) 1 0 ) 4(6)

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TABLE 3 (Co~~cllrded)

Soil type and stand

Loamy sand Sandy loam Silt loam Soil horizon and

fungal isolate HEMLOCK Birch Pine Aspen BEECH Oak BASSWOOD Elm .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~ . . . . . . . . . . . . . . . . AZ horizon . . . . . . . . . . . . . . . . . . . . . . . . . C~~lin~irocarpotl didyttlutt1 3(4)

Gyttlr~oosclrs reesii 5(61) 5(82) 3(26) 1(22) 4(13) l(2) 1(3) Mortierello hrntlilis 5(11) 3(17) 1 0 ) Morfierella isobellitla 1(3) 2 1 1) 2(7) 2(5) 3(4) 1(1) Morfierella paroispora l(14) 5(85) 1(2) Morfierello vitracco I1 2(3) 4(21) 3(22) 5(19) 5(25) 4(27) 3(15) Oidiodet~drorl flovrrttl 1(6) 1(4) 3(5) 5(34) 3(13) 5(25) 3(12) ~etliciIli~trtz tligricatls l(1) 1(2) 3(8) 2 3 )

. ) Rhit~oclodiella sp. 3(8) TricRocladirrttt opacrrtn 3(5) 3(10) Trichodertl~a spp. 2(3) 2(4) l(11) 2(5) 5(15) 4(11) 5(41) 2(54)

. . . . Trichorlernta polysporro?~ 1(2) 2(9) 3(7) 3(7) 4(24) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Verticilli~rtll sp. (5443) 3(14) 3(20)

Bhir and B, horizons Aspergillrrs ttrrtons 3(35) 5(88) 5(58) 3(4) 1(3) Bearrvoria bassiorlo I(]) 1(2) 2(13) 2(40) 4(22) Gyn7tlooscrrs roserrs 5(79) l(7) 5(74) 5(19) 4(7) 2(15) 3(48) 4(38) Mor fierello ttana 4(7) 4(16) 3(6) 5(46) 2 6 ) Mortierella poruispora 4(11) 4(6) 2(6) Morfierella vit~acea I1 l(7) 1(2) 3(6) 5(5) 3(6) 1(2) 3(6)

had totally destroyed the forest in the area occupied by the 'pine'stand). The similarity coefficients for the organic layers ranged from 53 to 58, which are somewhat lower for the F and HIA, layers than those for the 'HEMLOCK1-'pine' (but higher than the more recently disturbed 'aspen' stand). The lower coefficients for 'birch' may arise from the lack of coniferous litter input into the organic layers, since the coefficient for the 'pine1-'birch' litter layers is relatively low (38) while the

. . . . . . . . . . . . . .

. . coefficients for the other two organic horizons are comparable with those of 'HEMLOCK'-'birch.'

Ordination of Horizon Populations Two-dimensional ordinations of,the populations

isolated from each horizon were constructed to illustrate graphically the spatial relationships in species composition between the disturbed stands and their reference counterparts. Two examples are shown in Fig. 1. There was no consistency in the dispersion of the stands among the ordinations of the five horizons, although the reference stands were near the middle of the first axis in most hori- zons and 'birch' was in the central region in all of the ordinations. 'Elm' was always at one extreme on the first axis, to the right in the upper three horizons and to the left in the A, and B horizons, there being no obvious reason for the change in position. There was considerable variation in the location of the remaining three stands.

70 r HUMUS / A , LAYER ---

1 O a k * V h ~ ~ ; , m elm

HEMLOC;/O pine BASSWOOD

a I I

0 0 100 g 70 1 aspen*,A~ HORIZON

m elm HEMLOCK

BASSWOOD BEECH

0 100 FIRST AXIS

FIG. 1. Ordinations of the humuslA, and A, horizon rnycofloral populations. Open symbols and capitals are undis- turbed reference forests and closed symbols are disturbed stands. 0 , loamy sand soils; A , sandy loam soils; 0. silt loam soils.

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1708 CAN. J . BOT. VOL. 56. 1978

The positions of the four stands on the loamy sand soil exhibit a pattern consistent with the no- tion that they represent successional stages. 'As- pen,' the most recently disturbed stand, was further from 'HEMLOCK' than 'pine' in four of the five horizon ordinations, the litter layer being the lone exception. The latter might be expected be- cause of the large differences in the chemical con- stitution of the substrate. Furthermore, the two disturbed stands are displaced along the two axes in the same direction from the reference stand in the F, A,, and B horizons, suggesting there could be a sequential relationship in the species composition of the mycoflora among the three forests. In the H/Al layers, they are displaced in the same direc- tion along the first axis, but in opposite directions along the second axis. The 'birch' stand, clear-cut between the times when 'aspen' and 'pine' were burned, exhibits a directional displacement like that of 'aspen' in all horizons except L , but the distances from the reference stand are comparable with 'pine.'

The generally radiate dispersion of the disturbed stands, from the centrally located reference stands, in the H/A, layer corresponds with differences in their vegetational composition, an observation that has been reported by several authors (see bibliog- raphy in Christensen 1969). The more recently burned stands ('aspen' and 'elm') lie at greater dis- tances from their respective reference stands than 'oak' and 'pine,' which have had a longer time to recover. Since 'birch' was relatively close to 'HEMLOCK' in all five horizon ordinations, it might suggest that harvesting induces less distur- bance in the mycoflora than fire. We do not have any chemical data for this horizon, or the overlying organic layers, which could be plotted on the ordi- nation to detect gradients. However, there are sev- eral soil characteristics available for the A, horizon (Wicklow and Whittingham 1974). There was a general decrease in pH, K, Mg, and Ca along the first axis, although 'HEMLOCK' exhibited an ele- vated Ca content. The latter could be attributed to the large number of sugar maple and basswood saplings in the understory, the litter of both being high in calcium (Lutz and Chandler 1946). The sec- ond axis appears to separate soil textures, the coarser textures being in the upper portion of the ordination and the two finer textures in the lower portion.

Discussion In this investigation, we have attempted to assess

the impact that secondary successional forests have on the microfungal populations harbored in

the various organic and mineralized soil horizons. ?'he ordinations suggest that a major vegetational change is accompanied by a change in the mycoflora of all horizons within 50 years of the disturbance. However, the fungal populations that presumably displaced those associated with the forests prior to the disasters (as represented by the reference stands) did not follow the same succes- sional pathway, as suggested by the scattered dis- persion of the stands in the various horizon ordina- tions. This could have been expected in the highly organic layers, especially the Land F layers, where differences in the more readily available chemical constituents of the litter input could exert a selec- tive pressure for different fungal species.

The populations associated with the various horizons in the disturbed stands exhibited a number of species in common with their respective refer- ence stands and at similar densities and frequen- cies. If the area now occupied by the disturbed stand formerly supported a forest similar in compo- sition to that of the reference stand, then these data suggest that competitive ability of certain fungal soil inhabitants is not affected by a change in the vegetational cover. Some of these species were relatively common in the population whereas others exhibited low frequencies and (or) densities.

However, as the ordinations illustrate, there were differences in the population composition of the disturbed stands when compared with the ref- erence stands. Most of the differences were altera- tions in frequency and (or) density, although there were some conspicuous differences among the rela- tively few predominant members of the popula- tions. The environmental conditions in the dis- turbed forests apparently enhanced the competi- tive ability of some species, while that of other species was impeded. This would be in accord with previous investigations on the microfungi found in the Al horizon of undisturbed plant communities in Wisconsin (Tresner et al. 1954; Orpurt and Curtis 1957; Christensen and Whittingham 1965,; Christ- ensen 1969). The results suggested that within each vegetational unit (prairies, deciduous forests, con- ifer-hardwood forests), shifts in the species com- position of the higher plant populations are paral- leled by shifts in the soil mycoflora. Christensen (1969) also suggested that there is considerable en- vironmental diversity in northern Wisconsin forest soils, such as differences in physiochemical proper- ties and nature of the litter input, which may ac- count, in pal-t, for the high percentage of narrow- amplitude species along the vegetational con- tinuum. In our study, the first axis of the A, ordina- tion corresponded to gradients in pH and certain

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cations, while the second axis separated popula- tions frorn the coarser, loamy sand so~ls frorn the finer textured soils. Soil texture has been show to affect oxygen and carbon dioxide relationships as well as moisture content and nutrient availability, all of which have been proposed as influencing the microfungal community composition (Griffin 1963).

The two ordinations presented in this paper are representative of those for the other soil horizons relative to the distances between the disturbed stands and thelr reference stands. The two stands most recently burned over, 'aspen' and 'elm,' were located at greater distances from their respective reference stands than were the other three forests;

\ i.e., they exhibited the greatest population differ- ences. 'Oak' resided at intermediate distances from its reference while 'birch' and 'pine' were usually closest to their reference stand, the latter having the longest periods of recovery. Although 'birch' and 'oak' were disturbed within a decade of one another, 'birch' invariably was closer to its refer- ence stand than 'oak,' suggesting that the perturba-

I tion arising from clear-cutting is less than that

I I

caused by fire. This would be expected considering I that fire would totally destroy the organic layers

and probably the organic material in the uppermost mineralized horizon, whereas clear-cutting would not have this effect. The dispersion of the stands in the ordinations suggests that a catastrophic distur- bance does alter the soil mycoflora, probably as a result of the change in cover vegetation. However, as time passes, the populations gradually change in their species composition, becoming more like those of undisturbed forests. The four forests on loamy sand soil particularly support this conten- tion.

Acknowledgment This research was supported by National Sci-

ence Foundation grant G24235. BAXTER, F. P. 1967. Genesis of upland soils. In Soil resources

and forest ecology of Menominee County, Wisconsin. Edited by C. J . Milfred, G. W. Olson, and F. D. Hole. Bull. 85. Soil Ser. No. 60. State of Wisconsin, Madison, Wisconsin. pp. 91-101.

BEALS, E. W. 1960. Forest bird communities in the Apostle Islands of Wisconsin. Wilson Bull. 72: 156181.

1965. Species patterns in a herbarium poterietum. Veg- etatio, 13: 69-87.

BRAY, J. R., and J. T . CURTIS. 1957. An ordination of the upland forest communities of southern Wisconsin. Ecol. Monogr. 27: 325-349.

BROWN, J . C. 1958. Soil fungi of some British sand dunes in relation to soil type and succession. J. Ecol. 46: 641-664.

CHRISTENSEN, M. 1969. Soil microfungi of dry to mesic con- ifer-hardwood forests in northern Wisconsin. Ecology. 50: 9-27.

CHRISTENSEN, M., and W. F. W H I ~ I N G H A M . 1965. The soil fungi of open bogs and conifer swamps in Wisconsin. Mycologia, 57: 882-896.

COOKE, W. B.. and D. B. LAWRENCE. 1959. Soil mould fungi isolated from recently glaciated soils in southeastern Alaska. J. Ecol. 47: 529-549.

GOFF, F. G. 1967. upland vegetation. In Soil resources and forest ecology of Menominee County, Wisconsin. Edited by C. J. Milfred, G. W. Olson, and F. D. Hole. Bull. 85. Soil Ser. No. 60. State of Wisconsin, Madison, Wisconsin. pp. 60-90.

GRIFFIN, D. M. 1963. Soil moisture and the ecology of soil fungi. Biol. Rev. Cambridge Philos. Soc. 38: 141-166.

KENDRICK, W. B., and A. BURGES. 1962. Biological aspects of the decay of Pinrrs sylvestris leaf litter. Nova Hedwigia Z. Kryptogamenkd. 4: 3 13-342.

LOFTY, J . R. 1974. Oligochaetes. In Biology of plant litter de- composition. Vol. 2. Edited by C. H . Dickinson and G. J. F. Pugh. Academic Press, London and New York. pp. 467-488.

LUTZ, H. J. , and R. F. CHANDLER. 1946. Forest soils. John Wiley and Sons, New York.

NOVAK, R. 0.. and W. F. W H I ~ I N G H A M . 1968. Soil and litter microfungi of a maple-elm-ash floodplain community. Mycologia, 60: 776787.

ORPURT, P. A,, and J. T. CURTIS. 1957. Soil microfungi in relation to prairie continuum in Wisconsin. Ecology, 38: 628-637.

PAPAVIZAS, G. C., and C. B. DAVEY. 1959. Evaluation of vari- ous media and antimicrobial agents for isolation of soil fungi. Soil Sci. 88: 112- 117.

PUGH, G. J. F. 1962. Studies on fungi in coastal soils. 11. Fungal ecology in a developingsalt marsh. Trans. Br. Mycol. Soc. 45: 560-566.

1963. Ecology of fungi in developing coastal soils. In Soil organisms. Edited by J. Doeksen and J. Van Der Drift. North-Holland Publ. Co., Amsterdam. pp. 439-445.

SODERSTROM, B. E. 1975. Vertical distribution of microfungi in a spruce forest soil in the south of Sweden. Trans. Br. Mycol. SOC. 65: 419-425.

TRESNER, H. D., M. P. BACKUS, and J. T. CURTIS. 1954. Soil microfungi in relation to the hardwood forest continuum in southern Wisconsin. Mycologia, 46: 314-333.

WICKLOW, D. T. 1973. Microfungal populations in surface soils of manipulated prairie stands. Ecology, 54: 1302-1310.

WICKLOW, D. T., and W. F. W H I ~ I N G H A M . 1974. Soil micro- fungal changes among the profiles of disturbed con- ifer-hardwood forests. Ecology, 55: 3-16.

WOHLRAB, G., R. W. TUVESON, and C. E. OLMSTEAD. 1963. Fungal populations from early stages of succession in Indidna dune sand. Ecology, 44: 734-740.

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