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Bird Communities in Silvicultural Fragments of Holly Springs National Forest, Mississippi
Steven M. Aquilani

Southeastern Naturalist, Volume 5, Number 1 (2006): 135–148

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2006 SOUTHEASTERN NATURALIST 5(1):135–148 Bird Communities in Silvicultural Fragments of Holly Springs National Forest, Mississippi STEVEN M. AQUILANI* Abstract - I surveyed bird communities during the 1999 and 2000 breeding seasons in oak-pine sawtimber (ST) stands, pine poletimber (PT) stands, high-density pine seedling (SS) stands, and recently clearcut areas throughout Holly Springs National Forest (HSNF), in north-central Mississippi. Species richness was 25% greater in forested stands compared to clearcut areas, yet total bird density was 50% greater in clearcut areas. Bird communities ranged from open-habitat assemblages in clearcut areas to forest-obligate assemblages in ST stands. Little overlap of avian community composition was observed between ST stands and clearcut areas. PT and SS stands supported avian communities where most species were observed at intermediate abundance values compared to ST or clearcut areas. Highly fragmented, closed-canopy stands embedded within the silvicultural landscape of HSNF do not support large populations of species traditionally associated with detrimental edge effects on forest-obligate songbirds. Intensively managed PT and SS stands appear to provide suboptimal habitat for forest and grassland species. Land managers in HSNF could maximize regional avian diversity by maintaining a mosaic of large closed-canopy, oak-pine stands, and firemaintained open areas embedded among other silvicultural stand types. Introduction Maintaining biodiversity in the forest-dominated landscape of Mississippi requires that land managers understand the impacts of silvicultural habitat heterogeneity and fragmentation on songbird abundance. The area of Mississippi’s forestlands has steadily increased over the last 30 years from 6.83 million ha in 1969 to 7.49 million ha (62% of land cover) in the state today (Donner and Mines 1987, Hartsell and London 1995, Hedlund and Earles 1969, Murphy 1978). These values are in contrast to patterns in many Midwestern states, where agriculture and pastureland comprise 50 to > 75% of land cover and overall amount of forestland has decreased over the last 50 years (Summary Report, 1997 [revised 2000] USDA National Resources Inventory). Agricultural fields typically border forest fragments in Midwestern landscapes or pastureland that support high densities of corvid and mammalian nest predators (Gates and Gysel 1978, Robbins 1979, Whitcomb et al. 1981, Yahner and Scott 1988) and brood parasitic Brown-headed Cowbirds (scientific names of bird species given in Table 1; Brittingham and Temple 1983, Hoover and Brittingham 1993). Conversely, management practices in heavily forested regions may create mosaics of different stand types at different seral stages, with a high degree of edge between adjacent stands. In *Department of Biology, University of Mississippi, University, MS 38677; Current address - Department of Biology, Delaware County Community College, Media, PA 19063; saquilan@dccc.edu. 136 Southeastern Naturalist Vol. 5, No. 1 heavily forested landscapes, non-agricultural edge habitat around closedcanopy forests may not support populations of edge species associated with detrimental effects on forest-obligates (Andren 1992). Thus, foresters may be able to manage upland portions of Holly Springs National Forest (HSNF) for songbird species of concern in addition to maintaining silvicultural habitat heterogeneity. I examined avian community composition in different silvicultural stand types found at upland sites within HSNF, including closed canopy oak-pine sawtimber, open-canopy pine poletimber, high-density pine seedling, and recently clearcut stands. My study provides a novel, multivariate approach to elucidate the sorting and overlap of assemblages of bird species in and among various silvicultural stand types of HSNF. I also use Dufrene and Legendre’s (1997) indicator-species-analysis method to detect and describe the value of different species for indicating environmental conditions. I hope the results from my research provide an important first step in determining how silivicultural habitat heterogeneity influences avian biodiversity in the region and that the results of my study will provide foresters and land managers with specific information on the effects of forest management and silviculture on the abundance of individual species of birds, assemblages of birds, and entire avian communities. Field Site Description I conducted this study within HSNF in eastern Lafayette County, MS. HSNF occupies approximately 62,835 ha of Forest Service land intermingled with private lands on rolling hills between Oxford and Holly Springs, MS. Prior to Forest Service acquisition in the 1930s, most of present HSNF was non-forested agricultural land highly susceptible to erosion. Much of this land was planted with pine species (mostly Pinus taeda L. [loblolly], and P. echinata Mill. [shortleaf]) to halt soil erosion and provide a commercial timber base. HSNF is comprised of pine (61%), hardwood (29%), hardwoodpine (5%), and pine-hardwood (5%) stand types, as defined by US Forest Service classification according to the dominant and co-dominant tree species. The forest stands in HSNF are highly fragmented, averaging 24.8 ha (s.d. = 18.9 ha). Stands range from 2.4 ha to 111.0 ha and are typically bordered by stands of different type and size class. I measured bird relative abundance at points within silvicultural fragments throughout the Holly Springs and Tombigbee (Yalobusha unit only) Ranger Districts of HSNF. The US Forest Service systematically selected these points to provide a sampling of the various stand types that occur throughout the US Geological Survey compartments (including numbers 29, 30, 32, 35, 37–39, 41, 48–53, 55, 58, 59, 61, 96, 98, 102, 104–115, and 118) that contain portions of Holly Springs National Forest. The silvicultural stand types sampled included: closed-canopy, oak-pine sawtimber (ST) stands, poletimber (PT) stands, and sapling-seedling (SS) stands. ST stands are characterized as being > 10% stocked with live trees, with half or more of this stocking in sawtimber 2006 S.M. Aquilani 137 (softwood trees > 22.9 cm diameter at breast height [dbh], or hardwood trees > 27.9 cm dbh). All ST points I surveyed were located in upland, closed-canopy forests which contained mixed second-growth stands of shortleaf and loblolly pine and oaks (mostly Quercus alba L. [white], and Q. stellata Wang.[post]) that had grown back after logging early in the 20th century. Other common trees in the mature oak-pine stands were Carya spp. (hickory), Liquidambar styraciflua L. (sweetgum), and Cornus florida L. ( flowering dogwood). Less common were Q. velutina Lam. (black oak), Nyssa sylvatica Marsh. (black gum), Q. falcata Michx. (southern red oak), Q. coccinea Muenchh. (scarlet oak), and Q. marilandica Muenchh. (blackjack oak). Flowering dogwood, oak, and black gum trees dominated the forest understory of ST stands. Common saplings included sweetgum, white and post oak, blackgum, and Acer rubrum L. (red maple). PT stands are >10% stocked with live trees, with half or more of this stocking in poletimber (softwoods 12.7–22.6 cm dbh). The PT areas sampled were upland, open-canopy pine stands, dominated by loblolly pine (and to a lesser extent, shortleaf pine) in the canopy, with pine and hardwood saplings (mostly Quercus spp, sweetgum, and red maple) in the understory. SS stands are > 10% stocked with live trees, with more than half of this stocking in saplings (trees 2.5–12.4 cm dbh) and seedlings (trees < 2.5 cm dbh and > 30.5 cm tall for hardwoods and > 15.2 cm tall for softwoods). The SS sites were upland, high-density plantations dominated by pines. Methods Bird censuses I conducted breeding bird surveys using fixed-radius (50-m) point counts (Hamel et al. 1996, Ralph et al. 1993) within different silvicultural stand types and recently clearcut, early successional areas in HSNF. Points were placed within each stand so that the entire 50 m of the point was located within the stand boundary. Only one point was placed within each individual stand boundary and no points were placed within 250 m of another point in an adjacent stand. Thus, the distance between adjacent points was beyond the detectability of most Neotropical migrant bird species (Wolf et al. 1995) to ensure independence among samples. I visited each point once during the 1999 and 2000 breeding seasons (15 May to 15 June). In 1999, I surveyed 65, 22, and 36 points within ST, PT, and SS stands, respectively. In 2000, I surveyed 56, 29, 26, and 20 points within ST, PT, SS, and clearcut areas, respectively. At each point, I recorded all birds seen or heard within a 50-m radius from the plot center during a 10-minute observation period. Fly-overs were recorded, but not included in the data analysis. I conducted all surveys between 05:45 and 09:30 on calm (wind speed < 20 km/h) mornings without precipitation (Robbins 1981). Data analysis I calculated bird species abundance (mean number of individuals detected per point count) for each species for each of the stand types. Due to 138 Southeastern Naturalist Vol. 5, No. 1 the non-normal distribution of my point-count data, I used Mann-Whitney tests to test for differences in total density of birds (all species combined) between sites (Hutto et al. 1986). I examined the relationship between avian community composition and stand type using an ordination technique, detrended correspondence analysis (DCA; Hill and Gauch 1980; PC-ORD for WINDOWS 97). This analysis sorts samples and points graphically with respect to species composition. Ordinations of samples of birds were based on untransformed census counts. Rare bird species were downweighted. The results of DCA were summarized graphically by plotting samples and species. I tested site (stand-type) differences in bird species community composition by using Multi-Response Permutation Procedures (MRPP; Biondini et al. 1988, Mielke et al. 1976). MRPP is a non-parametric, multivariate procedure for exploring differences among groups of observations. To detect and describe relationships of bird abundance among the different stand types, I used indicator species analysis (using the Indicator Value [INDVAL] method, as described by Dufrene and Legendre 1997). Indicator species are defined as the most characteristic species of a specific group, being found mostly within that group and present in the majority of sites belonging to that group. INDVAL assigns indicator values for each species based on the degree to which they discriminate among groups (stand types). INDVAL analysis differs from Two-way Indicator Species Analysis (TWINSPAN) in that the indicator value generated in the former analysis is independent of the other species’ relative abundances (Dufrene and Legendre 1997). INDVAL values for each species are calculated using relative abundance (average abundance of a given species in a given group over the average abundance of that species in all plots) and relative frequency (% of plots in a given group where the given species is present) values. Indicator values range from zero (no indication) to 100 (perfect indication of a species corresponding to a study site). I used Monte Carlo tests (with 1000 permutations) to evaluate the statistical significance of maximum indicator value recorded for a given species (null hypothesis is that the maximum indicator value is no larger than would be expected by chance). Results Avian community composition within HSNF During the 1999 breeding season, 42, 34, and 38 species were observed within the ST, PT, and SS sites, respectively (Table 1). During the 2000 breeding season, 42, 38, 39, and 29 species were observed within the ST, PT, SS, and clearcut sites, respectively (Table 1). Total bird abundance did not differ among the ST, PT, and SS sites in 1999 (Kruskal-Wallis statistic = 4.686, P = 0.096; Table 1). In 2000, total bird abundance was > 50% higher in clearcut areas compared to the ST, PT, and SS stands (Kruskal-Wallis statistic = 25.271, P < 0.01; Table 1). An ordination (axis 1 and 2) of the 1999 data sorted point-count samples according to the abundance of bird species and stand types (Fig. 1). Samples 2006 S.M. Aquilani 139 sorted along axis 1 with respect to the abundance of closed-canopy, forestinterior species (including Worm-eating Warbler, Ovenbird, Hooded Warbler, Scarlet Tanager, Black-and-white Warbler, Wood Thrush, Yellowbilled Cuckoo, Red-eyed Vireo, Acadian Flycatcher, and Pileated Woodpecker) at low axis-1 scores vs. open-habitat species (Field Sparrow, Prairie Warbler, Yellow-breasted Chat, and Eastern Towhee) at high axis 1 scores (Fig. 1). Low axis-1 scores were associated primarily with mature oak-pine ST samples, whereas high axis-1 scores were associated with SS samples. PT samples were associated with intermediate axis-1 scores, with some overlap of ST and SS samples. Pine Warbler, Carolina Wren, Carolina Chickadee, Summer Tanager, Northern Cardinal, and Brown-headed Cowbird were common species associated with intermediate axis-1 sample scores. The eigenvalue for DCA axis 1 was 0.44 (47.8% of the sum of eigenvalues for axes 1 to 3). ST samples sorted along axis 2 primarily with respect to relative abundance of Ruby-throated Hummingbird, Downy Woodpecker, Scarlet Tanager, Yellow-billed Cuckoo, and Kentucky Warbler vs. Pileated Woodpecker, Wood Thrush, Ovenbird, and Black-and-white Warbler. Conversely, PS and SS samples did not illustrate strong sorting along the second axis. The eigenvalue for axis 2 was 0.26 (28.1%). Figure 1. Detrended correspondence analysis showing the sorting of bird species (represented by dots and 4-letter species code, see table 1 for species names) and sampling points (represented by symbols) within different stand types in Holly Springs National Forest, MS, from 1999 breeding season data. Sampling points were located within high-density pine seedling stands (Seedling), pine poletimber (poletimber), and mature, closed canopy oak-pine (Sawtimber) fragments. 140 Southeastern Naturalist Vol. 5, No. 1 Table 1. Relative abundance (individuals per point count) of bird species during the 1999 and 2000 breeding seasons in different silvicultural stand types within Holly Springs National Forest, MS. Stand type 1999 2000 1999 2000 1999 2000 2000 Seedling Seedling Pole Pole Timber Timber Clearcut Common name Scientific name Abbrev. (n = 36) (n = 26) (n = 22) (n = 29) (n = 65) (n = 56) (n = 20) Acadian Flycatcher Empidonax virescens Vieillot 1818 ACFL 0.08 0.08 0.18 0.03 0.29 0.08 0.00 American Crow Corvus brachyrhynchos Brehm , CL 1822 AMCR 0.08 0.04 0.05 0.00 0.14 0.03 0.85 American Goldfinch Carduelis tristis Linnaeus 1758 AMGO 0.00 0.00 0.00 0.00 0.00 0.02 0.00 American Redstart Setophaga ruticilla Linnaeus 1758 AMRE 0.03 0.00 0.00 0.00 0.00 0.00 0.00 American Robin Turdus migratorius Linnaeus 1758 AMRO 0.19 0.00 0.00 0.00 0.00 0.00 0.05 Black-and-white Warbler Mniotilta varia Linnaeus 1758 BWWA 0.17 0.38 0.09 0.24 0.15 0.39 0.25 Blue-gray Gnatcatcher Polioptila caerulea Linnaeus 1758 BGGN 0.03 0.12 0.00 0.00 0.05 0.00 0.10 Blue Jay Cyanocitta cristata Linnaeus 1758 BLJA 0.61 0.12 0.27 0.10 0.38 0.25 0.65 Brown Thrasher Toxostoma rufum Linnaeus 1758 BRTH 0.11 0.00 0.05 0.00 0.00 0.00 0.00 Broad-winged Hawk Buteo platypterus Vieillot 1823 BWHA 0.00 0.00 0.00 0.00 0.00 0.02 0.00 Brown-headed Cowbird Molothrus ater Boddaert 1783 BHCO 0.17 0.15 0.18 0.10 0.05 0.07 0.30 Carolina Chickadee Poecile carolinensis Linnaeus 1766 CACH 0.17 0.15 0.23 0.21 0.23 0.10 0.05 Carolina Wren Thryothorus ludovicianus Latham 1790 CAWR 0.25 0.04 0.09 0.14 0.20 0.14 0.00 Chimney Swift Chaetura pelagica Linnaeus 1758 CHSW 0.00 0.00 0.00 0.00 0.02 0.02 0.00 Chipping Sparrow Spizella passerina Bechstein 1798 CHSP 0.00 0.08 0.00 0.10 0.02 0.03 0.00 Northern Flicker Colaptes auratus Linnaeus 1758 COFL 0.06 0.04 0.00 0.00 0.00 0.00 0.15 Common Grackle Quiscalus quiscula Linnaeus 1758 COGR 0.00 0.04 0.00 0.03 0.00 0.00 0.00 Common Yellowthroat Geothlypis trichas Linnaeus 1766 COYE 0.17 0.19 0.18 0.14 0.02 0.12 0.25 Cooper’s Hawk Accipiter cooperii Bonaparte 1828 COHA 0.00 0.00 0.00 0.00 0.03 0.00 0.00 Downy Woodpecker Picoides pubescens Linnaeus 1766 DOWO 0.08 0.00 0.09 0.10 0.17 0.02 0.00 Eastern Bluebird Sialia sialis Linnaeus 1758 EABL 0.03 0.00 0.00 0.03 0.00 0.00 0.00 Eastern Towhee Pipilo erythrophthalmus Linnaeus 1758 RSTO 0.50 0.19 0.18 0.10 0.05 0.00 0.45 Eastern Tufted Titmouse Baeolophus bicolor Linnaeus 1766 ETTI 0.42 0.15 0.09 0.17 0.43 0.51 0.20 Eastern Wood-Pewee Contopus virens Linnaeus 1766 EAWP 0.08 0.12 0.18 0.14 0.23 0.20 0.15 Field Sparrow Spizella pusilla Wilson, A 1810 FISP 0.08 0.12 0.14 0.10 0.00 0.02 0.45 Gray Catbird Dumetella carolinensis Linnaeus 1766 GRCA 0.00 0.04 0.00 0.00 0.00 0.00 0.00 Great Crested Flycatcher Myiarchus crinitus Linnaeus 1766 GCFL 0.11 0.04 0.00 0.00 0.14 0.02 0.05 Hairy Woodpecker Picoides villosus Linnaeus 1766 HAWO 0.19 0.00 0.09 0.00 0.05 0.00 0.00 2006 S.M. Aquilani 141 Table 1, continued. Stand type 1999 2000 1999 2000 1999 2000 2000 Seedling Seedling Pole Pole Timber Timber Clearcut Common name Scientific name Abbrev. (n = 36) (n = 26) (n = 22) (n = 29) (n = 65) (n = 56) (n = 20) Hooded Warbler Wilsonia citrina Boddaert 1783 HOWA 0.03 0.08 0.18 0.21 0.22 0.31 0.00 Indigo Bunting Passerina cyanea Linnaeus 1766 INBU 1.06 0.77 0.77 0.59 0.20 0.32 1.55 Kentucky Warbler Oporornis formosus Wilson A 1810 KEWA 0.06 0.04 0.09 0.00 0.17 0.03 0.00 Louisiana Waterthrush Seiurus motacilla Vieillot 1809 LOWA 0.00 0.00 0.00 0.00 0.02 0.00 0.00 Mourning Dove Zenaida macroura Hartlaub & Finsch 1870 MODO 0.19 0.00 0.00 0.00 0.09 0.02 0.30 Northern Parula Parula americana Linnaeus 1758 NOPA 0.00 0.04 0.14 0.07 0.03 0.03 0.00 Northern Bobwhite Colinus virginianus Linnaeus 1758 NOBO 0.19 0.04 0.00 0.03 0.00 0.05 0.15 Northern Cardinal Cardinalis cardinalis Linnaeus 1758 NOCA 0.69 0.54 0.68 0.14 0.40 0.20 0.80 Ovenbird Seiurus aurocapillus Linnaeus 1766 OVEN 0.00 0.00 0.00 0.03 0.06 0.08 0.00 Pileated Woodpecker Dryocopus pileatus Linnaeus 1758 PIWO 0.03 0.04 0.00 0.03 0.20 0.14 0.30 Pine Warbler Dendroica pinus Wilson A 1811 PIWA 0.75 0.31 0.77 0.41 0.29 0.41 0.45 Prairie Warbler Dendroica discolor Vieillot 1809 PRWA 0.19 0.15 0.23 0.03 0.02 0.03 0.95 Red-bellied Woodpecker Melanerpes carolinus Linnaeus 1758 RBWO 0.17 0.15 0.09 0.17 0.35 0.34 0.80 Red-eyed Vireo Vireo olivaceus Linnaeus 1766 REVI 0.19 0.31 0.32 0.34 0.63 0.29 0.00 Red-headed Woodpecker Melanerpes erythrocephalus Linnaeus 1758 RHWO 0.06 0.12 0.18 0.31 0.00 0.07 0.90 Ruby-throated Hummingbird Archilochus colubris Linnaeus 1758 RTHU 0.00 0.00 0.00 0.00 0.05 0.02 0.00 Scarlet Tanager Piranga olivacea Gmelin 1789 SCTA 0.00 0.15 0.05 0.07 0.15 0.14 0.00 Summer Tanager Piranga rubra Linnaeus 1758 SUTA 0.33 0.27 0.32 0.48 0.31 0.27 0.65 Swainson’s Warbler Limnothlypis swainsonii Audubon 1834 SWWA 0.00 0.00 0.00 0.07 0.00 0.00 0.00 White-breasted Nuthatch Sitta carolinensis Latham 1790 WBNU 0.00 0.00 0.09 0.03 0.11 0.00 0.25 White-eyed Vireo Vireo griseus Boddaert 1783 WEVI 0.31 0.27 0.14 0.17 0.03 0.08 0.65 Wild Turkey Meleagris gallopavo Linnaeus 1758 WITU 0.00 0.00 0.00 0.00 0.02 0.10 0.00 Wood Thrush Hylocichla mustelina Gmelin 1789 WOTH 0.06 0.08 0.09 0.14 0.37 0.36 0.00 Worm-eating Warbler Helmitheros vermivorus Gmelin 1789 WEWA 0.00 0.08 0.05 0.14 0.05 0.34 0.00 Yellow-billed Cuckoo Coccyzus americanus Linnaeus 1758 YBCU 0.06 0.04 0.05 0.07 0.45 0.05 0.10 Yellow-breasted Chat Icteria virens Linnaeus 1758 YBCH 0.94 0.38 0.68 0.14 0.02 0.14 0.65 Yellow-throated Vireo Vireo flavifrons Vieillot 1808 YTVI 0.00 0.12 0.09 0.14 0.03 0.27 0.20 Yellow-throated Warbler Dendroica dominica Linnaeus 1766 YTWA 0.00 0.04 0.00 0.03 0.00 0.02 0.00 Number of species 38 39 34 38 42 42 29 Total (all species) 8.92 6.08 7.09 5.62 6.88 6.14 12.65 142 Southeastern Naturalist Vol. 5, No. 1 An ordination (axis 1 and 2) of the 2000 data also sorted sampling points according to the abundance of bird species and stand types (Fig. 2). The 2000 breeding season samples sorted along axis 1 with respect to the abundance of open-habitat species (Field Sparrow, Prairie Warbler, Yellow-breasted Chat, and Eastern Towhee) at low axis 1 scores vs. closed-canopy, forest interior species (primarily, Red-eyed Vireo, Acadian Flycatcher, Worm-eating Warbler, Ovenbird, Hooded Warbler, Scarlet Tanager, and Wood Thrush) at high axis-1 scores (Fig. 2). Low axis-1 scores were associated primarily with clearcut and SS samples, with clearcut samples associated exclusively with low axis-1 scores. Alternately, high axis-1 scores were associated with ST samples. PT samples were associated with intermediate axis-1 scores, with some overlap of ST and SS samples. Pine Warbler, Red-bellied Woodpecker, Summer Tanager, Yellow-throated Vireo, Eastern Wood-pewee, Northern Cardinal, and Brown-headed Cowbird were common species associated with intermediate axis-1 sample scores. The eigenvalue for DCA axis 1 was 0.51 (46.4% of the sum of eigenvalues for axes 1 to 3). ST samples sorted along axis 2, as was observed in 1999. ST samples sorted with respect to relative abundance of Downy Woodpecker, Scarlet Tanager, and Ovenbird vs. Pileated Woodpecker, Wood Thrush, Carolina Chickadee, and Eastern Tufted Figure 2. Detrended correspondence analysis showing the sorting of bird species (represented by dots and 4-letter species code, see table 1 for species names) and sampling points (represented by symbols) within different stand types in Holly Springs National Forest, MS, from 2000 breeding season data. Sampling points were located within clearcut areas, high-density pine seedling stands (Seedling), pine poletimber (poletimber), and mature, closed canopy oak-pine (Sawtimber) fragments. 2006 S.M. Aquilani 143 Titmouse. PT, SS, and clearcut, samples did not sort along the second axis. The eigenvalue for axis 2 was 0.32 (29.3%). Avian community composition differed among stand types in 1999 (MRPP Test statistic = -18.428; P < 0.01) and 2000 (MRPP Test statistic = -18.070; P < 0.01). Results from DCA in both years reveal that the differences can be attributed to greater abundance of open-habitat species in pine seedling and clearcut areas, and closed-canopy, forest-obligates in mature, oak-pine sawtimber stands. Sawtimber stands The INDVAL species assemblage characterizing ST areas includes Eastern Tufted Titimouse, Pileated Woodpecker, Red-eyed Vireo, Scarlet Tanager, Yellow-billed Cuckoo, Wood Thrush, and Worm-eating Warbler (Table 2). Brown-headed Cowbirds, which were not identified as indicator species for ST stands by INDVAL, had the lowest abundance value within ST areas (0.05 and 0.07 individuals per count in 1999 and 2000, respectively; Table 1) compared to the other stand types surveyed in HSNF. Poletimber stands Northern Parula, Pine Warbler, Red-headed Woodpecker, and Yellowbreasted Chat were identified as indicator species associated with PT stands (Table 2). Pine Warblers, which were common (> 0.29 individuals per point) in all stand types, had their greatest abundance within PT stands (0.77 in 1999). Brown-headed Cowbirds were less abundant within PT stands in 1999 (0.18 individuals per count) and 2000 (0.10) compared to clearcut areas. Seedling/sapling stands The species assemblage characterizing SS stands was a subset of the assemblage associated with clearcut areas (Table 2), including American Robin, Indigo Bunting, Northern Cardinal, Eastern Towhee, White-eyed Vireo, and Yellow-breasted Chat (Table 2). However, none of the species associated with SS stands was as abundant within SS stands as it was in clearcut areas (Table 1). Brown-headed Cowbirds were approximately half as common within SS stands in 1999 (0.17 individuals per count) and 2000 (0.15) compared to clearcuts. Clearcut/early successional areas Among the groups of samples analyzed using INDVAL, clearcut areas had the largest number of species composing an assemblage characteristic of a stand type in HSNF (Table 2). The species assemblage characterizing clearcut areas includes American Crow, Blue Jay, Common Flicker, Field Sparrow, Indigo Bunting, Mourning Dove, Northern Cardinal, Prairie Warbler, Red-headed Woodpecker, Eastern Towhee, White-eyed Vireo, and Yellow-breasted Chat (Table 2). This assemblage includes the 5 species with the greatest relative abundance values observed in any stand type surveyed in HSNF during 1999 and 2000 (Table 1): Indigo Buntings (1.55 individuals 144 Southeastern Naturalist Vol. 5, No. 1 per point), Prairie Warblers (0.95), Red-headed Woodpeckers (0.90), American Crow (0.85), and Northern Cardinal (0.80). These five species accounted for 40% of all birds observed in clearcut areas. Brown-headed Cowbirds had their greatest abundance within clearcut areas (0.30 individuals per point; Table 1) compared to the other stand types surveyed in HSNF. Discussion Avian community composition at upland sites within HSNF was determined by silvicultural stand type. Bird communities ranged from forestobligate assemblages in mature, closed-canopy ST stands to open-habitat assemblages in early successional areas. Relatively little overlap of avian community composition was observed between ST stands and clearcut areas. Closed-canopy species of concern in Mississippi common in ST stands, such as Hooded Warbler, Pileated Woodpecker, Wood Thrush, and Worm-eating Warbler, were rare or absent within clearcut areas. Conversely, open-habitat species of concern that were common in clearcuts, such as Eastern Towhee, Field Sparrow, Prairie Warbler, and Red-headed Woodpecker, were rare or absent within mature ST stands. Mature, closed-canopy ST and open, early successional stands each supported a separate and distinct avifauna in upland sites of HSNF. PT and SS stands support avian communities that are mixtures of closedcanopy and early-successional assemblages. Most bird species in HSNF, including all of the aforementioned species of concern that were abundant in ST or clearcut sites, had intermediate abundance values within PT or SS stands compared to other stand types. Pine Warblers were the only avian species observed in HSNF that had a greater abundance within PT and SS stands compared to ST and clearcut stands. Many of the ground- and shrubnesting, forest-obligate species common within mature oak-pine ST sites (e.g., Hooded Warbler, Kentucky Warbler, and Worm-eating Warbler) prefer sites within forest interiors with high understory cover to conceal nest sites (Ehrlich et al. 1988, Hamel 1992, Martin 1993). Therefore, it is possible that some patches within PT and SS stands also meet the needs for ground- and shrub-nesting forest songbirds. Conversely, the open-habitat species of concern common in clearcuts in HSNF require old fields, brush, deciduous forest edge, or recent clearings for nest sites (Ehrlich et al. 1988, Hamel 1992). Thus, patches within PT and SS stands with a relatively open canopy and a grassy or brushy understory may provide suitable nest-sites for open-habitat species. Thompson et al. (1992) document similar trends in the abundance of bird species in clearcut, sapling, poletimber and mature hardwood stands in the Missouri Ozarks. Future research is necessary to investigate the extent to which PT and SS stands of HSNF and other regions provide suitable microhabitat for forest-interior and open-habitat species. Total breeding bird abundance was twice as great within upland clearcut areas compared to forested tracts, yet forested areas supported approximately 2006 S.M. Aquilani 145 25% greater species richness within HSNF compared to open, early successional areas. However, total bird abundance and richness did not differ among ST, PT, or SS forest types in HSNF. Prior studies have documented increases Table 2. Indicator values1 (INDVAL) for avian species associated with different stand types and Monte Carlo test (1000 permutations) of significance values in Holly Springs National Forest, MS. Stand type SS PT ST Monte Carlo test Clearcut stand stand stand Mean s.d. P Clearcut 2000 American Crow 28 (92/30) 0 (4/4) 0 (0/0) 0 (4/3) 5.6 2.61 0.000 Blue Jay 17 (58/30) 1 (10/8) 1 (9/10) 4 (23/16) 8.4 2.95 0.016 Common Flicker 12 (80/15) 1 (20/4) 0 (0/0) 0 (0/0) 3.9 2.31 0.011 Field Sparrow 26 (66/40) 1 (17/8) 2 (15/10) 0 (3/2) 7.0 2.87 0.001 Indigo Bunting 38 (48/80) 13 (24/54) 9 (18/52) 2 (10/24) 16.8 3.24 0.000 Mourning Dove 19 (95/20) 0 (0/0) 0 (0/0) 0 (5/2) 4.1 2.29 0.001 Northern Cardinal 21 (48/45) 15 (32/46) 1 (8/14) 2 (12/14) 11.5 3.38 0.013 Prairie Warbler 49 (81/60) 2 (13/15) 0 (3/3) 0 (3/3) 8.3 3.14 0.000 Red-headed 35 (65/55) 1 (8/8) 6 (22/28) 0 (5/7) 9.8 3.15 0.000 Woodpecker Eastern Towhee 21 (60/35) 5 (26/19) 1 (14/10) 0 (0/0) 7.1 2.74 0.000 White-eyed Vireo 28 (55/50) 5 (23/23) 3 (15/17) 1 (7/7) 9.4 2.97 0.001 Yellow-breasted Chat 20 (50/40) 7 (29/23) 1 (11/10) 1 (11/12) 9.4 3.00 0.009 Seedling-sapling stand 1999 American Robin - 19 (100/19) 0 (0/0) 0 (0/0) 5.4 2.61 0.002 Eastern Towhee - 26 (68/39) 4 (26/14) 0 (6/5) 10.1 3.17 0.003 Indigo Bunting - 40 (51/78) 26 (39/67) 2 (10/21) 20.8 3.63 0.000 Northern Bobwhite - 14 (100/14) 0 (0/0) 0 (0/0) 4.5 2.40 0.002 White-eyed Vireo - 18 (64/28) 4 (30/14) 0 (7/3) 8.4 3.16 0.019 Yellow-breasted Chat - 36 (56/64) 24 (43/57) 0 (1/2) 15.5 3.62 0.000 Poletimber stand 1999 Northern Parula - 0 (0/0) 12 (82/14) 1 (18/3) 4.2 2.29 0.011 Pine Warbler - 19 (40/47) 29 (43/67) 4 (16/27) 19.1 4.18 0.028 Red-headed Woodpecker - 1 (23/6) 11 (77/14) 0 (0/0) 4.4 2.34 0.023 Yellow-breasted Chat - 36 (56/64) 24 (43/57) 0 (1/2) 15.5 3.62 0.000 Sawtimber stand 1999 Pileated Woodpecker - 0 (12/3) 0 (0/0) 17 (88/19) 7.8 3.13 0.024 Red-eyed Vireo - 3 (16/19) 7 (28/24) 31 (55/56) 18.5 3.63 0.009 Scarlet Tanager - 0 (0/0) 1 (23/5) 12 (77/16) 6.9 2.89 0.044 Wood Thrush - 1 (10/6) 2 (18/10) 22 (72/30) 11.1 3.26 0.010 Yellow-billed Cuckoo - 1 (10/6) 0 (8/5) 34 (82/41) 13.2 3.65 0.000 2000 Eastern Tufted 3 (19/15) 2 (15/12) 3 (17/17) 21 (50/41) 12.0 3.12 0.013 Titmouse Wood Thrush 0 (0/0) 1 (13/4) 3 (24/14) 18 (63/29) 9.0 2.95 0.009 Worm-eating Warbler 0 (0/0) 1 (14/8) 3 (25/14) 18 (62/29) 9.3 3.14 0.016 1INDVAL calculated by dividing the proportional abundance of a particular species in a particular group by the abundance of that species in all groups (values shown in parentheses, Dufrene and Legendre 1997) 146 Southeastern Naturalist Vol. 5, No. 1 in total bird abundance following clearcuts of forested areas in various regions (Conner and Adkisson 1975, Derleth et al. 1989, Horn 1984, Thompson et al. 1992, Yahner 1986), yet all of these studies also documented increases in species richness as well. Although clearcut areas may provide suitable habitat for many open-habitat species of concern, forest tracts of similar size in HSNF support greater species richness. Odum (1969) predicted that habitat generalists will be more common during early succession, whereas habitat specialists become more common during late succession. Thus, the greater avian species richness I observed in forested areas may be accounted for by an increased diversity of foraging (e.g., upper canopy insectivores such as Acadian Flycatchers and bark gleaners such as Downy Woodpeckers) and nesting specialists (e.g., cavity nesters such as Carolina Wrens and upper canopy nesters such as Red-eyed Vireos) in these stands. Avian nest predators (American Crow) and brood parasites (Brown-headed Cowbird) that were abundant in open habitats were less common and rare, respectively, within mature oak-pine ST stands. Although nest parasitism rates were not documented in this study, my results are consistent with previous research documenting low (< 1%) cowbird abundance and parasitism rates in nearby (but non-overlapping) mature, closed-canopy pine-oak stands of HSNF (Aquilani and Brewer 2004). These findings support the hypothesis that closed-canopy tracts embedded within a non-agricultural landscape may not support large populations of species traditionally associated with detrimental edge effects on forest-obligates. However, clearcut areas within heavily forested landscapes may provide a source population of nest predators and brood parasites that could invade forest tracts (Flaspohler et al. 2001). Land managers interested in managing for nongame avian diversity in the Southeast may be able to use the results of this study to protect local and regional diversity. Mature, closed-canopy oak-pine forest tracts appear best suited to maximize populations of forest-obligate species of concern in addition to minimizing populations of avian nest predators and brood parasites. Mature forest areas are needed to support species such as Red-eyed Vireo, Wood Thrush, and Scarlet Tanager, which were only found in late-successional forest habitats in the sites we sampled. Minimum area requirements for forest-obligates may be smaller in this region than in agricultural landscapes of the Midwest because traditional avian edge species (nest predators and brood parasites) are uncommon within mature oak-pine forests of HSNF (Aquilani and Brewer 2004). However, land managers must investigate the local and habitat factors that may be precluding edge species from mature oak-pine forest fragments. Perhaps the functional size of oak-pine stands in HSNF for forest-obligates was increased because they were surrounded by seedling and poletimber stands as opposed to open fields (Aquilani and Brewer 2004, Kilgo et al. 1997, Sargent et al. 1998). Nevertheless, my results suggest that managed areas such as highdensity seedling stands and poletimber stands are less favorable than mature closed-canopy forests stands for nesting forest songbirds and less suitable 2006 S.M. Aquilani 147 for grassland species than clearcuts. Future research is needed to investigate the nesting success and productivity of various birds in these forest types to determine source-sink dynamics for species in each stand type. Acknowledgments I thank Steve Brewer, Joel Okula, and two anonymous reviewers for comments and Carl Kilcrease for providing geographic stand data for HSNF. Chris Simmons assisted in bird surveys. This research was supported by the US Forest Service, Southern Research Station, Oxford, MS. 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