THE EFFECTS OF CLEARCUT SIZE ON THE BIRD COMMUNITY IN THE SECOND COLLEGE GRANT
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THE EFFECTS OF CLEARCUT SIZE ON THE BIRD COMMUNITY IN THE SECOND COLLEGE GRANT

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Abstract. This study examines the effects of forest opening (clearcut) size on the surrounding forest-bird community with the objective of offering management suggestions for foresters who employ the ...

Abstract. This study examines the effects of forest opening (clearcut) size on the surrounding forest-bird community with the objective of offering management suggestions for foresters who employ the clearcut method. I hypothesized that large and small clearcuts would have different effects on the forest-bird assemblage associated with each. I used the point-count method to assess bird abundance in clearcuts, on the edges, and 100 m into the forest from the edges of large and small clearcuts. I found that Neotropical migrant birds and forest-interior birds were the most affected by large clearcuts showing significantly lower abundance in forest areas 100 m from large clearcut edges than in forest areas 100 m from small clearcuts. Edge-open birds were more abundant in large clearcut openings and edges than in small clearcut openings and edges. Blue jays (an avian nest predator) were more abundant on the edges of large clearcuts than on the edges of small clearcuts. A recent study found that forest-interior bird abundance levels off after 100 m distance from small (0.4 ha) forest openings. This result combined with my findings suggest that small openings in the Second College Grant represent less of a disturbance to Neotropical migrants and forest-interior birds. Additionally, given higher abundances of an avian nest predator in large clearcuts, reproductive success could be much lower in areas associated with large clearcuts. Some species such as the White-throated Sparrow (Zonotrichia albicollis), however preferred large clearcuts suggesting that there are some benefits to overall bird abundance by including large clearcuts in a managed landscape.

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    THE EFFECTS OF CLEARCUT SIZE ON THE BIRD COMMUNITY IN THE SECOND COLLEGE GRANT THE EFFECTS OF CLEARCUT SIZE ON THE BIRD COMMUNITY IN THE SECOND COLLEGE GRANT Document Transcript

    • THE EFFECTS OF CLEARCUT SIZE ON THE BIRD COMMUNITY IN THE SECOND COLLEGE GRANT JOSHUA R. MOONEY Abstract. This study examines the effects of forest opening (clearcut) size on the surrounding forest-bird community with the objective of offering management suggestions for foresters who employ the clearcut method. I hypothesized that large and small clearcuts would have different effects on the forest-bird assemblage associated with each. I used the point-count method to assess bird abundance in clearcuts, on the edges, and 100 m into the forest from the edges of large and small clearcuts. I found that Neotropical migrant birds and forest-interior birds were the most affected by large clearcuts showing significantly lower abundance in forest areas 100 m from large clearcut edges than in forest areas 100 m from small clearcuts. Edge-open birds were more abundant in large clearcut openings and edges than in small clearcut openings and edges. Blue jays (an avian nest predator) were more abundant on the edges of large clearcuts than on the edges of small clearcuts. A recent study found that forest-interior bird abundance levels off after 100 m distance from small (0.4 ha) forest openings. This result combined with my findings suggest that small openings in the Second College Grant represent less of a disturbance to Neotropical migrants and forest-interior birds. Additionally, given higher abundances of an avian nest predator in large clearcuts, reproductive success could be much lower in areas associated with large clearcuts. Some species such as the White-throated Sparrow (Zonotrichia albicollis), however preferred large clearcuts suggesting that there are some benefits to overall bird abundance by including large clearcuts in a managed landscape.INTRODUCTIONBalancing timber management with bird conservation is a difficult endeavor. However,given recent evidence of declines in many Neotropical migrant bird species (Robbins etal. 1989a, Askins et al. 1990) it has become increasingly important to manage forestedlands to maintain avifauna diversity and abundance. Threats to migratory land birds intheir North American breeding ground include habitat destruction, degradation,fragmentation, and loss of habitat diversity (Germaine et al. 1997). Forest fragmentationincreases the ratio of edge habitat to forest interior. Historically, edge habitat has beenseen as beneficial to a wide array of forest dwelling wildlife (e.g., Leopold 1933);however, edge zones may contribute to reduced populations of bird species that require
    • large areas of forest interior habitat (Gates and Gysel 1978, Ambuel and Temple 1983,Robinson 1992). It is important to study Neotropical migratory birds because these birds provide auseful model for developing general programs of land management and improvingcurrent management schemes (Martin 1995). Neotropical migratory birds are modelorganisms because: (1) they are ubiquitous; (2) they include a wide diversity ofcoexisting species with varying ecologies; (3) they are sensitive to environmentalperturbations because they are mobile, short-lived, and differ in their environmentalrequirements; and (4) their behaviors, demographic characters (fecundity, survival),physiology, species interactions, and habitat use can be readily studied for many species(Martin 1995). In addition, knowledge of their habitat requirements is critical toconserving forest land to allow for successful breeding. Given that a dominant proportion of birds that breed in the Northeast are Neotropicalmigrants (MacArthur 1959), it is possible that factors affecting survival in their winteringhabitat may be more important than events in the breeding habitat. Some research hasfound that migrants are limited chiefly by events and conditions in tropical winteringgrounds (Lack 1968, Fretwell 1972, 1986, Morse 1980b, Alerstam and Hogstedt 1982,Baillie and Peach 1992, Morton 1992, Rappole et al. 1992). On the other hand,fragmentation of forest habitats in eastern North America has been strongly implicated asone cause of reduced breeding success, and consequently lowered breeding densities ofsome songbird populations (Robbins 1979, Whitcomb et al. 1981, Ambuel and Temple1983, Wilcove and Whitcomb 1983, Lynch and Whigham 1984, Wilcove and Robinson1990). Long-distance migrants seem to be limited by both breeding and winteringhabitat; however, there is no clear study suggesting one is more important than the other.Sherry and Holmes (1995) develop the idea of summer and winter limitation for migrantbirds, stating that “migrant bird populations appear to be limited contemporaneously bytheir need for quality habitats in which to maintain high fecundity in summer and in
    • which to maintain high survival in winter.” Changes in breeding habitat are therefore atleast one of the important factors that could have profound effects on overall populationsof Neotropical migrant birds. Thus, it is important to study how forest management innortheastern North America affects bird communities. Factors associated with timber harvesting that affect bird communities can begenerally categorized in one of two ways: factors associated with increased edge resultingfrom habitat fragmentation (“edge effects”), and those associated with reduced area ofsuitable forest habitats (“area effects”) (Welsh and Healy 1993). Many studies have beenconducted in highly fragmented forests and have found that fragment area is a majorfactor in determining the number and diversity of bird species present (Blake and Karr1987, Askins et al. 1990). In addition, Donovan et al. (1995) found that small forestfragments may be sink habitats for some species of Neotropical migrants requiringimmigration from nearby source areas to maintain populations. Many areas of the Northeast include large tracts of contiguous forest. This is quitedifferent from many of the highly fragmented regions in which the aforementionedstudies were conducted. In areas of continuous forest, some studies have found increasedbird species richness and density near forest edge created by clearcuts, rivers, fields, orpower lines (McElveen 1979, Strelke and Dickson 1980, Hansson 1983, Germaine et al.1997). However, other studies have not found such relationships (Kroodsma 1982, Smalland Hunter 1989). Bird species diversity is often higher in managed forest areas (where timberharvesting occurs – clearcutting, selective harvesting...) than in reserved forest areas dueto the increase in habitat diversity (Welsh and Healy 1993). However, it is important totake this question to the next level and ask how bird species diversity (and abundance) isaffected by clearcut size in a managed area. Simply because some studies have shownthat bird species diversity is higher in areas where timber management occurs (Germaineet al. 1997), should we assume that creating forest openings will increase diversity? The
    • answer to this question will have implications for timber management in the Northeastand throughout the country. In some cases managing for diversity is not always theanswer. When a sensitive or endangered species is present, it may be more prudent toensure its survival. Clearcutting is a relatively common practice in the Second CollegeGrant and elsewhere in the Northeast. The size of clearcuts varies to a great degree.Thus, it is important to look at the effects of clearcut size on bird communities, and tocome to some conclusion as to which size affords the greatest benefits. Communication between researchers and forest managers is essential to designingappropriate wildlife management schemes. The Second College Grant, where this studywas conducted, is a perfect forum for this type of discourse. Currently, the forester isimplementing a Wildlife Project, the goal of which is to manage the Grant for wildlifewhile still harvesting timber. In order to implement a sound program the forester needsinput from researchers. This study will assist the Wildlife Project by providingsuggestions for bird management. This study reports results of point count censuses of birds conducted in the SecondCollege Grant, a 10,930 ha parcel of land in northern New Hampshire owned byDartmouth College. The objectives were: (1) to examine the differences in bird diversity,abundance, and species assemblage between large and small clearcuts, (2) to look at thesedifferences in detail by examining the effects of clearcut size on bird guilds across ahabitat gradient from inside the clearcuts to the edge to 100 m into the surrounding forest,and (3) to focus specifically on how Neotropical migratory birds were affected. I testedfor these effects by comparing species diversity, similarity of species composition, andthe abundance of birds in several guilds in large (6.0 – 7.0 ha) and small (0.3 – 1.0 ha)clearcuts. These variables were compared within the clearcuts, on the edges of theclearcuts, and 100 m into the forest from the clearcut.METHODS
    • STUDY AREASThis study was conducted from 20 June - 30 July 1997 in the Second College Grant innorthern Coos County, NH. I selected four small and four large structurally similar studysites by field reconnaissance. These sites were dominated by hardwood trees, but alsoincluded coniferous tree species. Hardwood species included sugar maple (Acersaccharum), white and yellow birch (Betula papyrifera, B. alleghaniensis), and beech(Fagus grandifolia). Coniferous species were red spruce (Picea rubens), balsam fir(Abies balsamea), and some Eastern hemlock (Tsuga canadensis). Aerial photos wereexamined to ensure that substantial areas of forest surrounded each cut. The clearcutsstudied were of similar age; all had been harvested within 5 years. Small sites ranged insize from approximately 0.3 - 1.0 ha. Large sites ranged in size from 6.0 - 7.0 ha (sizesdetermined using a Global Positioning System and Trimble’s Pfinder GIS software).VEGETATION MEASUREMENTSTo test whether my sites were structurally similar, I measured basal area of all trees largerthan 7.5 cm in an 11 m radius around my point count sites which were inside theclearcuts, on the edges of the clearcuts, and 100 m into the forest from the clearcut edges(see Figure 1). These measurements were taken in the four large sites and in the foursmall sites. One of the large sites was excluded from the study because it differedstrongly in forest composition being composed chiefly of spruce.BIRD CENSUSING
    • I recorded all birds heard or seen within a 50 m radius of my point count site during a 6minute period. Point counts were conducted between 05:00 and 08:00 from 29 Junethrough 19 July. Three census points were established at each site (Fig. 1) and marked byflagging. One point was located inside the clearcut, 100 m from the edge. The secondwas located on the edge. The third was located 100 m into the interior forest. The pointswere situated in a straight line to avoid overlap. Each census point was visited four timesthroughout the course of the study period. Figure 1. Clearcut, Edge, and Forest point count layout for a typical clearcut site in the Second College Grant, New Hampshire.BIRD GUILDS To look at finer-scale differences in how birds were affected by clearcut size, I firstcategorized the common bird species observed in the Grant on the basis of migratorygroup. There were three categories: Neotropical migrants, Nearctic migrants, andresident species. I then separated these species into groups based on habitat preference.Forest-interior birds are those species with breeding territories concentrated away fromthe forest edge. Interior-edge birds are species with territories both near the forest edge
    • and in the interior. Edge-open species are those with territories both in edge areas and inopenings (Whitcomb et al. 1981). Thirdly, I classified the species into foraging guildsbased on information in the literature (Ehrlich et al. 1988). Foliage-gleaners are thosespecies that forage insects from the leaves of trees. Ground-foragers are those speciesthat manipulate the forest floor in search of insects, and bark-probers probe into the barkof trees with their bills for insects.DATA ANALYSISBasal area, and diversity (Simpson’s Index) were analyzed with an ANOVA model thatincluded clearcut size, location (clearcut, edge, or forest), clearcut nested within clearcutsize, and clearcut size x location. Abundance within guilds (migratory group, habitatassociation, and foraging strategy) was analyzed with an ANOVA model that included allthe above terms and additionally: guild, size x guild, and location x guild. All terms weretreated as fixed effects. Similarity between large and small habitat groups was determined using the Bray-Curtis (1957) measurement of species composition and relative abundance measures ascomparison criteria (Germaine et al. 1997), where: " similarity = $ (∑ 2Wi ) % ( A + B ) × 100% # &and: Wi = lower abundance of each species i present in both plots, A = number ofindividuals present in assemblage 1 and B = number of individuals present in assemblage2.
    • RESULTSBasal area of coniferous trees was similar in large and small sites (Table 1; Fig 2). Basalarea of hardwood trees was also similar in large and small sites (Table 1; Fig 3).Table 1. Summary of mean squares and F statistics for ANOVA models run with basal area of coniferoustrees and hardwood trees, and bird diversity as variables. Basal Area (H) Basal Area (C) Bird Diversity df MS F MS F MS FSize 1 4.52 1.89 1.66 0.73 1.24 0.18Site (Site) 5 1.39 0.58 1.06 0.46 3.88 0.58Location 2 6.94 2.90 2.48 1.08 53.01 7.92**Size x Location 2 0.77 0.32 0.07 1.03 0.91 0.14Error 10 2.40 -- 2.28 -- 6.69 --P < 0.05; ** P < 0.01; *** P < 0.001(H) = Hardwood Trees; (C) = Coniferous Trees .)tseroF dna ,egdE ,tucraelC( .)tseroF dna ,egdE ,tucraelC( etis hcae ta snoitacol eerht ta nekat serusaem etis hcae ta snoitacol eerht ta nekat serusaem aera lasaB .)4=n( setis llams dna )3=n( setis egral aera lasaB .)4=n( setis llams dna )3=n( setis egral ni seert suorefinoc fo aera lasab naeM .2 erugiF ni seert doowdrah fo aera lasab naeM .3 erugiF tucraelC egdE tseroF tucraelC egdE tseroF 0 0 ).mc .qs( aera lasab naeM).mc .qs( aera lasab naeM 5.0 5.0 1 1 5.1 5.1 llamS llamS egraL egraL 2 2 I registered a total of 39 bird species (Appendix I) within 50 m of 21 point countstations. Only species for which I recorded more than five individuals throughout thedata collection period (18 species) were included in the analyses. In addition, pointcounts were inappropriate for censusing some species (Ruffed Grouse, Cedar Waxwing,
    • Chimney Swifts, hawks), consequently these birds were not included (see Appendix I forlist of all birds encountered). Bird species diversity did not differ in large and small sites in the three locations(clearcut, edge, forest) (Table 1; Fig 4). However, there was a highly significant effect oflocation when diversity values of large and small sites were pooled (Table 1; Fig 4).Diversity inside the clearcut (in both large and small sites) was significantly lower thanedge and forest values (F1,10 = 9.52, P = 0.01). There was no difference between diversityin edge and forest areas (F1,10 = 0.41, P = 0.54). tucraelC egdE tseroF .)ES ± naem( 7991 ,erihspmaH weN ,tnarG 0 egelloC dnoceS eht ni setis )4 = n( llams dna )3 = n( 1 egral rof seirogetac tatibah eerht ni )xednI ytisreviD snospmiS( seiceps drib fo ytisrevid naeM .4 erug2 iF 3 4 )xednI snospmiS( ytisreviD naeM 5 6 7 8 9 01 llamS 11 21 egraL Though diversity did not differ with clearcut size, the percent similarity between largeand small sites was low (Table 2). The differences in bird species present can be seen bylooking at the species common in each type of habitat (Table 3). Inside large and small
    • clearcuts, few of the species overlap suggesting very different bird assemblages. In edgeareas of large and small clearcuts more species overlap, and in forest areas a majority ofthe species overlap indicating the relative similarity between the assemblages.Table 2. Percent similarity within the bird community in clearcuts, edge zones, and interior forest zones oflarge and small clearcut plots, Second College Grant, New Hampshire, 1997. Small Clearcut Small Edge Small Forest Large Clearcut 0.195 -- -- Large Edge -- 0.275 -- Large Forest -- -- 0.325Table 3. Representation of where each species was relatively common (birds/site > 0.10) in the SecondCollege Grant, New Hampshire. Point counts were conducted inside clearcuts, on the edges of clearcutsand in the forest 100 m from clearcut edges. Bird species are separated by migratory group. Small site: Large Site: Small Site: Large site: Small Site: Large Site: Migrant Group/Species Clearcut Clearcut Edge Edge Forest Forest *Neotropical Migrants Blackburnian warbler X X X Black-throated blue warbler X X X X Black-throated green warbler X X X Common yellowthroat X X X Hermit thrush X X X X Magnolia warbler X X X Mourning warbler X X X Northern parula X X X X Ovenbird X X X Red-eyed vireo X X X X XNearctic Migrants White-throated sparrow X X X X Winter wren X X X X Yellow-bellied sapsucker X Yellow-rumped warbler XResidents Black-capped chickadee X Blue jay X X Dark-eyed junco X X X X X X Golden-crowned kinglet X X X X The finer details of these differences in similarity are revealed by separating thespecies observed into several groupings and analyzing the differences. The mostinteresting result from analysis of the effects of size and location on the migratorygroupings (Neotropical migrant, Nearctic migrant, or Resident) was that there were
    • significantly more Neotropical migrant birds in the interior forest surrounding smallclearcuts than in the interior forest surrounding large clearcuts (F1,40 = 10.64, P = 0.002;Figure 5). The other migratory status groups did not show any significant relationshipswith size and location. .50.0 < P * .)ES ± naem( 7991 ,erihspmaH weN ,tnarG egelloC dnoceS eht ni setis )4 = n( llams dna )3 = n( egral rof seirogetac tatibah eerht ni sdrib tnargim fo ecnadnuba naeM .5 erugiF tucraelC egdE tseroF 0 )etis/sdrib#( ecnadnuba naeM 1.0 2.0 3.0 4.0 llamS 5.0 * egraL The second grouping was based on habitat associations similar to those of Whitcombet al. (1981) and Germaine et al. (1997). There were significantly more forest-interiorbirds in the forest 100 m from small clearcuts than in the forest 100 m from largeclearcuts (F1,40 = 5.64, P = 0.02; Figure 6). In contrast, there were significantly moreedge-open birds associated with large clearcuts (F1,40 = 5.05, P = 0.03; Figure 7) andclearcut edges (F1,40 = 8.07, P = 0.007; Figure 7) than with small clearcuts and clearcutedges. Interior-edge birds showed a preference for interior and edge zones as expected,while exhibiting low abundance in clearcut areas (Appendix II). There was no effect ofclearcut size for interior-edge species (Table 4).
    • .50.0 < P * .)ES ± naem( 7991 ,erihspmaH .50.0 < P * .)ES ± naem( 7991 ,erihspmaH weN ,tnarG egelloC dnoceS eht ni setis )4 = n( weN ,tnarG egelloC dnoceS eht ni setis )4 = llams dna )3 = n( egral rof seirogetac tatibah eerht n( llams dna )3 = n( egral rof seirogetac tatibah eerht ni sdrib roiretni-tserof fo ecnadnuba naeM .6 erugiF ni sdrib nepo-egde fo ecnadnuba naeM .7 erugiF tucraelC egdE tseroF tucraelC egdE tseroF 0 0 )etis/sdrib#( ecnadnuba naeM 1.0)etis/sdrib#( ecnadnuba naeM 1.0 2.0 2.0 3.0 3.0 4.0 llamS 4.0 llamS 5.0 * egraL egraL 6.0 5.0 * *Table 4. Summary of mean squares and F statistics for ANOVA models run with migratory group, habitatassociation, and foraging strategy as variables. Migratory Group Habitat Association Foraging Strategy df MS F MS F MS FSize 1 0.89 0.16 0.48 1.20 0.89 0.14Site (Site) 5 2.17 0.40 0.43 1.08 2.17 0.34Location 2 121.52 22.34*** 10.42 26.30*** 121.52 19.27***Guild 2 234.51 43.11*** 0.57 1.44 359.85 57.07***Size x Location 2 31.20 5.73** 1.69 4.26* 31.20 4.95*Size x Guild 2 10.96 2.01 2.13 5.37** 7.35 1.16Location x Guild 4 76.62 14.08*** 4.70 11.85*** 55.57 8.81***Error 44 5.44 -- 0.40 - 6.31 -*P < 0.05; ** P < 0.01; *** P < 0.001 The third grouping was based on foraging strategies (Ehrlich et al. 1988). Theabundance of foliage-gleaning birds increased from clearcut to forest (F4,40 = 8.80 P <0.001; Figure 8). Ground-foraging birds were most abundant in clearcut areas and edgeareas of large sites and in interior areas of small sites (Figure 9). There were no Yellow-bellied Sapsuckers (the only commonly encountered bark-probing species) associatedwith large clearcuts and they were most abundant in interior areas associated with smallclearcuts (see Appendix II).
    • large clearcuts than in small sites (Figure 10). predators. They were more abundant in edge areas and interior areas associated withFinally, I looked at the abundance of blue jays, which are potentially important nest egraL 5.0 5.0 llamS * egraL * 4.0 llamS 4.0 3.0 3.0 * 2.0 2.0 1.0 1.0 )etis/sdrib#( ecnadnuba naeM )etis/sdrib#( ecnadnuba naeM 0 0 tseroF egdE tucraelC tseroF egdE tucraelCsdrib gnigarof-dnuorg fo ecnadnuba naeM .9 erugiF sdrib gninaelg-egailof fo ecnadnuba naeM .8 erugiFllams dna )3 = n( egral rof seirogetac tatibah eerht ni llams dna )3 = n( egral rof seirogetac tatibah eerht ni weN ,tnarG egelloC dnoceS eht ni setis )4 = n( weN ,tnarG egelloC dnoceS eht ni setis )4 = n( erew snaem - * .)ES ± naem( 7991 ,erihspmaH .)ES ± naem( 7991 ,erihspmaH .)50.0 < P( tnereffid yllacitsitats
    • .50.0 < P * .)ES ± naem( 7991 ,erihspmaH weN ,tnarG egelloC dnoceS eht ni setis )4 = n( llams dna )3 = n( egral rof seirogetac tatibah eerht ni )srotaderp tsen( syaj eulb fo ecnadnuba naeM .01 erugiF tucraelC egdE tseroF 0 )etis/sdrib#( ecnadnuba naeM 1.0 2.0 3.0 4.0 5.0 6.0 * llamS 7.0 egraLDISCUSSIONClearcuts of different sizes affect the forest-bird community in different ways.Neotropical migrant bird species and forest-interior species appear to be the mostsensitive bird groups to large (6.0 - 7.0 ha) clearcut disturbances in the Grant. Nearly allbird species in eastern North America that showed declining trends from the late 1940suntil the late 1980s were Neotropical migrants or forest-interior birds and interior-edgebirds (Whitcomb et al. 1981). In light of this finding and others showing declining trendsin migratory songbirds and birds associated with forest-interior (Askins et al. 1990,Robbins et al. 1989a) management strategies in the Second College Grant should reflect aconcern for these groups of birds. Forest-interior and bark-probing birds are able to maintain relatively high abundancesaround small clearcuts while they are at low abundance or are absent from areasassociated with large clearcuts. In addition, though ground-foraging birds showed highabundances in large clearcuts and edge associated with large clearcuts, they also
    • maintained high abundances in forest 100 m from small clearcuts. This suggests thatlarge open areas are not necessary for maintaining high abundances of these species. Edge-open birds did prefer large clearcuts and edge areas of large clearcuts oversmall clearcuts and edge areas. These species were also present in small clearcuts (Table3) suggesting that overall bird diversity in the Second College Grant does not benefitfrom the presence of large openings. The overall abundance of birds, however, isenhanced by the presence of large clearcut openings given that species such as the White-throated Sparrow (Zonotrichia albicollis), Red-eyed Vireo (Vireo olivaceus), and WinterWren (Troglodytes troglodytes) were much more abundant in large clearcuts than insmall clearcuts (Appendix II). Of course, just how large openings should be to support ahigher abundance of edge-open birds must be determined for the Grant. This studysuggests that 6.0 – 7.0 ha clearcuts are more beneficial to edge-open species althoughclearcuts smaller than 6.0 ha may support equally high abundances of edge-open species.This question is important given that there may be some intermediate size clearcut thatNeotropical migrants, and forest-interior birds and edge-open species can all utilize. Large clearcuts represent a major disturbance to the local landscape in which they arecarried out. Relative to small clearcuts, they destroy a larger amount of habitat for forest-interior birds. Most importantly, it appears from my data that the effects of these largedisturbances extend further into the surrounding forest than the effects of a small clearcut.Germaine et al. (1997) found that forest-interior bird abundance leveled off after 100 mdistance from small (0.4 ha) forest openings. My abundance measures 100 m from smallclearcuts in the Grant may therefore be representative of areas even further from clearcuts(interior forest). If this is so, birds must be further away from large clearcuts than fromsmall clearcuts in order to maintain high abundance. Of course, we must note thecumulative effect of many small clearcuts totaling to equal the size of one large clearcut.It could be possible that many small clearcuts disturb more habitat for Neotropicalmigrants and forest-interior birds. To assess this we must know the distance from a large
    • clearcut at which the abundance of migrants and forest-interior birds equals theabundance 100 m away from a small clearcut. This information would be very useful fordeveloping a strategy to manage for Neotropical migrants and forest-interior birds whichare showing declines recently. Blue jays, potentially important nest predators, are also more of a concern in largeclearcuts than in small clearcuts in the Grant. Their greater abundance in large sites mayexplain why forest-interior birds and Neotropical migrants were more abundant in forest100 m from small clearcuts than in forest 100 m from large clearcuts. In addition, forestassociated with large clearcuts may be more detectable or exploitable than forest adjacentto small clearcuts by nest predators such as chipmunks, squirrels and avian nest predatorsthan the more discontinuous edges of small clearcuts (Germaine et al. 1997). Anincreased presence of nest predators could have serious implications for reproductivesuccess. I did not measure nest success, but the differences I saw in abundance may beeven more pronounced in terms of reproductive success. Measuring reproductive successin and around large and small clearcuts would provide land managers with an importantinsight into the nature of the effects of clearcut size on the bird community. This study shows the importance of looking beyond diversity measures as anindication of management success. If management in the Grant based assessment ofdifferent strategies strictly on the diversity of the bird assemblage present, much wouldbe overlooked. For instance, sensitive groups such as Neotropical migrants and forest-interior species showing population declines would not show up in such an analysis. To manage for Neotropical migrant and forest-interior species in the Second CollegeGrant, managers should limit clearcut size. Additional timber could be harvested usingselective cutting although the effects of this practice should be examined in future studiesas well. Such a strategy may be prudent given the nature of surrounding timbermanagement schemes. The land immediately east of the Grant is owned by a large papermill that harvests large tracts of forest (much larger than 6.0 – 7.0 ha) using the clearcut
    • method. Thus, in terms of larger landscape dynamics, edge-open birds may have anabundance of habitat outside the Grant’s borders while Neotropical migrants and forest-interior birds are more limited. To manage for overall bird abundance within the Grant, management strategiesshould include large and small clearcuts. This would benefit the most number of speciesin terms of abundance. Again it is important to remember, however, that reproductivesuccess may be lower in forest associated with large clearcuts and one must be hesitant inadopting a strategy that includes large clearcuts if the goal is to manage for edge-openbird abundance. Of course, it is important to consider the habitat requirements of wildlife other thanbirds such as moose, bear, deer, and aquatic organisms. In addition, timber productionand the economics driving it are important factors to consider. Future studies should attempt to synthesize concerns for other organisms with myresults for forest birds to provide the forester at the Grant with the necessary informationto implement a sound and effective Wildlife Program. In addition future work couldattempt to determine whether many small clearcuts which add up to the same amount ofarea as one large clearcut would be more beneficial to the bird assemblage.LITERATURE CITEDAlerstam, T., and G. Hogstedt. 1982. Bird migration and reproduction in relation to habitats for survival and breeding. Ornis. Scand. 13:25-37.Ambuel, B., and S. A. Temple. 1983. Area-dependent changes in bird communities and vegetation of southern Wisconsin forests. Ecology 64:1057-1068.Askins, R. A., J. F. Lynch, and R. Greenberg. 1990. Population declines in migratory birds in eastern North America. Current Ornithol. 7:1-57.Baillie, S.R., and W. J. Peach. 1992. Population limitation in Palearctic-African migrant passerines. Ibis 134 (Suppl. 1): 120-132.Blake, J. G., and J. R. Karr. 1987. Breeding birds of isolated woodlots: area and habitat relationships. Ecology 68:1724-1734.Bray, J. R., and J. T. Curtis. 1957. An ordination of the upland forest communities of southern Wisconsin. Ecol. Monogr. 27:325-349.
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