Ruffed grouse-habitat preference in the central and southern Appalachians

Ruffed grouse (Bonasa umbellus; hereafter grouse) populations in the central and southern Appalachians (CSA) are declining due to widespread maturation of forest cover. Effective management of this species requires a sex- and age-specific understanding of habitat preferences at multiple temporal and spatial scales. We used multivariate logistic regression models to compare habitat within 1440 grouse home ranges and 1400 equally sized buffered random points across 7 CSA study areas. On most sites, grouse home ranges were positively associated with roads and young forest (<20 years old). Sex and age status affected habitat preference. In general, males used younger forest than females, likely because of differences in habitat use during reproductive periods. Juveniles had fewer vegetation types preferred by adult grouse and more of the avoided vegetation types within their home ranges, indicative of competitive exclusion. Adult females had the greatest specificity and selectivity of habitat conditions within their home ranges. Habitat selection varied among seasons and years on most sites. Winter habitat use reflected behavior that maximized energy conservation, with open vegetation types avoided in the winter on the northernmost study areas, and topography important on all areas. Summer habitat selection reflected vegetation types associated with reproductive activities. Scale influenced habitat preference as well. Although roads and forest age predominantly influenced grouse home range location within the landscape, mesic forest types were most important in determining core area use within the home range. This was likely a result of increased food availability and favorable microclimate. Habitat management efforts should attempt to maintain ∼3–4% of the landscape in young forest cover (<20 years old), evenly distributed across management areas. Roads into these areas should be seeded as appropriate to enhance brood habitat and provide travel corridors connecting suitable forest stands.     

Multi-scale nest-site selection by black-backed woodpeckers in outbreaks of mountain pine beetles

Areas of mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreaks in the Black Hills can provide habitat for black-backed woodpeckers (Picoides arcticus), a U.S. Forest Service, Region 2 Sensitive Species. These outbreaks are managed through removal of trees infested with mountain pine beetles to control mountain pine beetle populations and salvage timber resources. To minimize impacts to black-backed woodpeckers while meeting management objectives, there is a need to identify characteristics of these areas that support black-backed woodpeckers. We examined the habitat associations of this species nesting in areas of beetle outbreaks in the Black Hills, South Dakota in 2004 and 2005. We used an information theoretic approach and discrete choice models to evaluate nest-site selection of 42 woodpecker nests at 3 spatial scales—territory, nest area, and nest tree. At the territory scale (250 m around nest), availability and distribution of food best explained black-backed woodpecker selection of beetle outbreaks versus the surrounding forest. Selection at the territory scale was positively associated with densities of trees currently infested by mountain pine beetles and indices of wood borer (Cerambycidae and Buprestidae) abundance, and was greatest at distances of 50–100 m from the nearest patch of infestation. At the nest-area scale (12.5 m radius around the nest), densities of snags positively influenced nest-area selection. Finally, at the nest-tree scale, aspen (Populus tremuloides) and 3–5-year-old ponderosa pine (Pinus ponderosa) snags were important resources. The association between abundant wood-boring insects and black-backed woodpeckers creates a difficult challenge for forest managers. In the absence of fire, areas of beetle outbreak might serve as the only substantial source of habitat in the Black Hills. Regulating insect populations via salvage logging will reduce key food resources to black-backed woodpeckers during nesting. Therefore, given the relatively infrequent occurrence of large-scale fire in the Black Hills, management should recognize the importance of beetle-killed forests to the long-term viability of the black-backed woodpecker population in the Black Hills.     

Habitat assessment for forest dwelling species using LiDAR remote sensing: Capercaillie in the Alps

Large-scale information on habitat suitability is indispensable for planning management actions to further endangered species with large-spatial requirements. So far, remote sensing based habitat variables mostly included environmental and land cover data derived from passive sensors, but lacked information on vegetation structure. This is a serious constraint for the management of endangered species with specific structural requirements. Light detection and ranging (LiDAR), in contrast to passive remote sensing techniques, may bridge this gap in structural information at the landscape scale. We investigated the potential of LiDAR data to quantify habitat suitability for capercaillie (Tetrao urogallus), an endangered forest grouse in Central Europe, in a forest reserve of 17.7 km². We used continuous variables of horizontal and vertical stand structure from first and last pulse LiDAR data and presence–absence information from field work to model habitat suitability with generalized linear models (GLM). The two final habitat suitability models explained the observed presence–absence pattern moderately well (AUC of 0.71 and 0.77) with horizontal structure explaining better than vertical structure. Relative tree canopy cover was the most important variable with intermediate values indicating highest habitat suitability. As such, LiDAR allowed us to translate the results from habitat modeling at the landscape scale to effective management recommendations at the local scale at a level of detail that hitherto was unavailable for large areas. LiDAR thus enabled us to integrate individual habitat preferences at the scale of entire populations and thus offers great potential for effective habitat monitoring and management of endangered species.     

Habitat selection by forest-dwelling caribou in managed boreal forest of eastern Canada: Evidence of a landscape configuration effect

Habitat alteration caused by forest harvesting seems to contribute to the decline of forest-dwelling caribou, an ecotype of woodland caribou (Rangifer tarandus caribou) inhabiting the boreal ecosystem. To serve as basework to the establishment of conservation measures for the species, we have studied the hierarchical habitat selection of forest-dwelling caribou in a boreal landscape of Québec strongly impacted by logging. Fifteen females were surveyed by GPS telemetry between April 2004 and March 2006. Home ranges showed a high proportion of 90–120 year-old forests, a low proportion of regenerating forests (20–40 years old) and a tendency to include a greater proportion of 6–20 year-old clearcuts in relation to their availability in the study area. At the home range scale, selection patterns differed between periods, possibly reflecting specific requirements linked to caribou life cycle. Caribou selected open lichen woodlands throughout the year while mature closed forests (≥50 years) were selected uniquely during summer. The 6–20 year-old clearcuts were avoided during calving, in summer and during the rutting period but were selected during spring. Our results indicate that mature forest and open lichen woodlands are highly selected forest cover types by caribou at both spatial scales. Although clearcuts were generally avoided at the home range scale, such avoidance was not observed at the larger scale, the search for 90–120 year-old forests being hampered by a uniform distribution of clearcuts. An a posteriori landscape analysis highlighted the spatial association between 6–20 year-old clearcuts and 90–120 year-old forests, an association that can be explained by the current regulations used in Québec. Our results underline the importance of pursuing research concerning the impact of such an exploitation regime on the long-term maintenance of the forest caribou in the boreal landscape.     

Male Kirtland's Warblers’ patch-level response to landscape structure during periods of varying population size and habitat amounts

Forest planners must evaluate how spatiotemporal changes in habitat amount and configuration across the landscape as a result of timber management will affect species’ persistence. However, there are few long-term programs available for evaluation. We investigated the response of male Kirtland's Warbler (Dendroica kirtlandii) to 26 years of changing patch and landscape structure during a large, 26-year forestry-habitat restoration program within the warbler's primary breeding range. We found that the average density of male Kirtland's Warblers was related to a different combination of patch and landscape attributes depending on the species’ regional population level and habitat amounts on the landscape (early succession jack pine (Pinus banksiana) forests; 15–42% habitat cover). Specifically, patch age and habitat regeneration type were important at low male population and total habitat amounts, while patch age and distance to an occupied patch were important at relatively high population and habitat amounts. Patch age and size were more important at increasing population levels and an intermediate amount of habitat. The importance of patch age to average male density during all periods reflects the temporal buildup and decline of male numbers as habitat suitability within the patch changed with succession. Habitat selection (i.e., preference for wildfire-regenerated habitat) and availability may explain the importance of habitat type and patch size during lower population and habitat levels. The relationship between male density and distance when there was the most habitat on the landscape and the male population was large and still increasing may be explained by the widening spatial dispersion of the increasing male population at the regional scale. Because creating or preserving habitat is not a random process, management efforts would benefit from more investigations of managed population responses to changes in spatial structure that occur through habitat gain rather than habitat loss to further our empirical understanding of general principles of the fragmentation process and habitat cover threshold effects within dynamic landscapes.     

Predicting breeding bird occurrence by stand- and microhabitat-scale features in even-aged stands in the Central Appalachians

Spatial scale is an important consideration when managing forest wildlife habitat, and models can be used to improve our understanding of these habitats at relevant scales. Our objectives were to determine whether stand- or microhabitat-scale variables better predicted bird metrics (diversity, species presence, and abundance) and to examine breeding bird response to clearcut size and age in a highly forested landscape. In 2004-2007, vegetation data were collected from 62 even-aged stands that were 3.6-34.6 ha in size and harvested in 1963-1990 on the Monongahela National Forest, WV, USA. In 2005-2007, we also surveyed birds at vegetation plots. We used classification and regression trees to model breeding bird habitat use with a suite of stand and microhabitat variables. Among stand variables, elevation, stand age, and stand size were most commonly retained as important variables in guild and species models. Among microhabitat variables, medium-sized tree density and tree species diversity most commonly predicted bird presence or abundance. Early successional and generalist bird presence, abundance, and diversity were better predicted by microhabitat variables than stand variables. Thus, more intensive field sampling may be required to predict habitat use for these species, and management may be needed at a finer scale. Conversely, stand-level variables had greater utility in predicting late-successional species occurrence and abundance; thus management decisions and modeling at this scale may be suitable in areas with a uniform landscape, such as our study area. Our study suggests that late-successional breeding bird diversity can be maximized long-term by including harvests >10 ha in size into our study area and by increasing tree diversity. Some harvesting will need to be incorporated regularly, because after 15 years, the study stands did not provide habitat for most early successional breeding specialists.     

Do the size and landscape context of forest openings influence the abundance and breeding success of shrubland songbirds in southern New England?

Early successional birds have declined in the northeastern United States due to the regeneration of forest on abandoned farm fields and the suppression of natural disturbances that once provided appropriate habitat. These species have become increasingly dependent on early successional habitats generated by such activities as timber harvesting. Recent approaches of timber harvesting, which range from single-tree harvesting to clearcutting, create forest openings of different sizes and configurations embedded in landscapes with different land use patterns. To assess the importance of forest openings created by timber harvesting for shrubland birds, we surveyed birds on 50 m radius plots in 34 harvest sites (0.5–21 ha). We collected data on multi-scaled habitat variables ranging from plot-level vegetation characteristics to land use patterns within 1 km of each study site. We also monitored mating and nesting success of Blue-winged Warblers (Vermivora pinus) in 10 forest openings.

The abundance of most shrubland species was influenced by plot-level habitat variables, such as tree density and vegetation height, rather than shrubland area or the composition of land uses in the surrounding landscape. Only Eastern Towhees (Pipilo erythrophthalmus) were more frequent in survey plots in larger forest openings. In contrast, neither abundance nor reproductive activity of Blue-winged Warblers was correlated with the size of the forest opening. Their abundance was negatively related to vegetation height, however. Only 54% of the territorial male Blue-winged Warblers in forest openings were mated. We documented relatively low nest success rates of 21.1% during the egg laying and incubation nest stages, but increased success rates during the later stages of nesting.

Our results indicate that even small forest openings with low vegetation provide habitat for Blue-winged Warblers and other shrubland birds. The overall reproductive rate of territorial male Blue-winged Warblers in forests openings was low during the 2 years of the study, however. Further studies are needed to assess the long-term value of this type of habitat for sustaining shrubland bird populations.     

Using multitemporal satellite imagery to characterize forest wildlife habitat: The case of ruffed grouse

Like many similar forest species, ruffed grouse (Bonasa umbellus; hereafter grouse) populations in the central and southern Appalachians (CSA) are strongly affected by forest composition at the landscape scale. Because these populations are in decline, managers require accurate forest maps to understand how stand level characteristics affect the survival and reproductive potentials of individual birds to design management strategies that improve grouse abundance. However, traditional mapping techniques are often labor-intensive and cost-prohibitive. We used a normalized difference vegetation index (NDVI) from each of 8 Landsat images and the digital elevation model (DEM)-derived variables of elevation and aspect in discriminant analyses to classify 7 study areas to 3 overstory classes (evergreen, hardwoods, and oak) and distinguish evergreen and deciduous understories in the CSA, 2000–2002. Overall accuracy was 82.08%, varying from 83.59% for oak to 79.79% for hardwoods overstories. Periods with large phenological differences among classes, particularly early and late spring, were most useful for discriminating overstory vegetation types. Alternatively, winter NDVI in combination with elevation was critical for differentiating evergreen and deciduous understories. Multitemporal image sets used in concert with DEMs provided a cost-effective alternative to hyperspectral sensors for improving wildlife habitat classification accuracy with Landsat imagery. This allowed for enhanced understanding of grouse-habitat relationships and habitat affects on grouse populations that allowed for improved management. With the incorporation of simple adjustments for local forest plant species phenology into the model, it may be used to better classify wildlife habitat of similar species in areas with comparable forest communities and topography. Multitemporal images can also be used to differentiate grassland communities, monitor wetlands, and serve as baseline data for detecting changes in land use over longer temporal scales, making their use in forest wildlife habitat studies cost-justifiable.     

Gap-, stand-, and landscape-scale factors contribute to poor sugar maple regeneration after timber harvest

Natural regeneration in canopy gaps is a key process affecting long-term dynamics of many forests, including northern hardwood forests. The density and composition of regenerating trees are often highly variable, reflecting sensitivity to a suite of driving factors operating at different scales (e.g., harvest gap to regional landscape), including production of seeds, physical characteristics of gaps and stands, competition with non-tree vegetation, and browsing by animals. Multivariate analyses over broad geographic areas provide insights into the relative effects of these factors and permit exploration of spatial patterns in regeneration. We examined the effects of gap-, stand-, and landscape-scale factors on densities of tree seedlings (<1 m tall) and saplings (1-2 m tall) in 59 selection-harvested northern hardwood stands located across a 4500 km² region of Michigan's Upper Peninsula. We used Bayesian multilevel modeling to account for the hierarchical structure of the data and assess uncertainty in parameter estimates. Sugar maple (Acer saccharum) saplings were absent from 61% of 154 m² plots centered in harvest gaps (n = 347) despite its high shade tolerance and overstory dominance, but densities were high in other gaps. Densities of sugar maple seedlings and/or saplings were negatively associated with a combination of greater stand-scale densities of white-tailed deer (Odocoileus virginianus), greater gap-scale cover of non-tree vegetation, and lower gap-scale light availability, with deer density having the greatest effect. Densities of unpalatable and commercially less valuable ironwood (Ostrya virginiana), the second most common regeneration species, were positively related to gap-scale seed-production potential but were unrelated to factors affecting sugar maple. Ironwood tended to replace sugar maple saplings in areas with high deer density. At the landscape scale, densities of sugar maple seedlings and saplings decreased with decreasing latitude and snow depth and increasing winter deer densities. These inverse spatial patterns suggest that deer herbivory can lead to landscape-scale variation in regeneration success. However, the spatial distribution of habitat types (a proxy for soil moisture and nutrient conditions) confound this observation, with higher densities of sugar maple generally located on stands with less nutrient-rich habitat types. Results demonstrate that combinations of factors operating at different scales, and with different relative magnitudes of impact, contribute to high variation in regeneration composition and density following timber harvest. Selection silvicultural practices, as currently applied, do not ensure regeneration of desirable species; practices might require modifications in general (e.g., increasing gap size) and to match them to regionally varying factors like deer density.     

A method for integrating the Breeding Bird Survey and Forest Inventory and Analysis databases to evaluate forest bird–habitat relationships at multiple spatial scales

The limited spatial scales of many bird–habitat studies restrict inference regarding large scale bird–habitat relationships. A potential solution to this challenge is integrating the USFS Forest Inventory and Analysis (FIA) and USGS Breeding Bird Survey (BBS) databases. We describe a methodology for integrating these databases into a uniform dataset for modeling bird–habitat relationships at multiple spatial scales. We accumulated route-level BBS data for four species guilds (canopy nesting, ground-shrub nesting, cavity nesting, early successional), each containing a minimum of five bird species. We developed 43 forest variables at the county level using FIA data from the 2000 inventory cycle within 5 physiographic regions in 14 states. We examined spatial relationships between the BBS and FIA data at three hierarchical scales: (1) individual BBS routes, (2) FIA units, and (3) physiographic sections. At the BBS route scale, we buffered routes at 100 m, 1 km, and 10 km radii, intersected these buffers with county boundaries, and developed weighted averages for each forest variable within each buffer width. Weights were a function of the percent of area each county had within a buffer. We calculated 29 landscape structure variables from 1992 National Land Cover Data (NLCD) imagery using Fragstats within each buffer width. At the BBS route scale, we developed models relating variations in bird occupancy and abundance to forest and landscape structure within each buffer width using classification and regression trees (CART). We aggregated the FIA variables to the FIA unit and physiographic section scales and recalculated the landscape variables within each unit and section using NCLD imagery resampled to a 400 m pixel size. We used regression trees (FIA unit scale) and general linear models (GLM, physiographic section scale) to relate variations in bird abundance to the forest and landscape variables. At the BBS route scale, 80% of the best CART models accounted for >50% of the variation in bird occupancy and abundance. Among FIA units and physiographic sections, the regression trees accounted for an average of 54.1% and the GLMs accounted for an average of 66.3% of the variability in bird abundance, respectively. This methodology shows promise for integrating independent databases for evaluating bird–habitat relationships across broad spatial extents, and the hierarchical nature of these models provides a potentially consistent means of evaluating management options at varying spatial scales.     

Avian population and community processes in forest ecosystems: Long-term research in the Hubbard Brook Experimental Forest

Long-term studies in relatively undisturbed forest ecosystems, such as occur in many of the USFS’ Experimental Forests, provide valuable insight into bird population and community processes, information pertinent to forest management and bird conservation. Major findings from 40 years of research in the Hubbard Brook Experimental Forest in north-central New Hampshire reviewed here show that the distributions and abundances of bird species are dynamic, even within well-developed and mature forests, and that species respond differently to habitat (vegetation) structure, food availability, and other features of the forest environment. At the local scale, bird population demography is most affected by factors that influence fecundity and recruitment, mainly food availability, weather, nest predators, and density dependent processes. Fecundity is strongly correlated with subsequent recruitment and is critical for maintaining breeding population size. Events in the non-breeding season, however, also influence the abundance and demography of breeding populations, indicating the need to assess factors operating throughout the species’ annual cycle. At the landscape scale, populations in temperate forests are spatially structured by each species’ response to habitat and environmental patterns, but also by social interactions such as competition and conspecific attraction. Settlement patterns and ultimately reproductive performance depend on habitat quality, based on vegetation structure, food availability and nest predator effects that vary across the landscape. Results from these long-term studies centered at Hubbard Brook provide a mechanistic understanding of avian population dynamics and community responses. The results provide a framework for predicting how future changes in habitat quality, climate, and other environmental threats may influence bird populations and communities in north-temperate forests.     

Differential effects of vegetation restoration in Mediterranean abandoned cropland by secondary succession and pine plantations on bird assemblages

Two contrasting trajectories for vegetation restoration in agricultural landscapes are secondary succession following cropland abandonment that can regenerate woodlands (passive restoration) and conversion of cropland to tree plantations (active restoration), which have mostly focused on pine species in the Mediterranean Basin. We compared the effects of these two contrasting trajectories of vegetation restoration on bird assemblages in central Spain. Vegetation structure differed in the two restoration trajectories, pine plantations attaining higher tree cover and height (31% and 4.1 m, respectively) but lower strata complexity than secondary shrubland and holm oak woodland (which attained 10% and 1.4 m of tree cover and height, respectively). Bird species richness differed in stands under active or passive restoration trajectories, the former collecting a higher total number of species (4.2 species per 0.78 ha plot) than the latter (3.5 species per plot). The number of forest species increased with vegetation maturity in both restoration trajectories, but especially in stands under active restoration. The occurrence of woodland generalist species increased and of species inhabiting open habitats decreased in actively restored stands, being some of these latter species of high conservation priority in the European context but relatively common at the regional level. Bird species inhabiting pine plantations had broader habitat breadth at the regional level than those inhabiting secondary shrublands and woodlands. Maximum regional density did not differ between both restoration trajectories, but it increased with development of the herbaceous layer only at the secondary succession trajectory. The relative importance of species of European biogeographic origin was higher in mature pine plantations (58.9% of total bird abundance) than in mature holm oak woodlands (34.4%), whereas that of Mediterranean species was considerably higher in the latter (40.1%) than in the former (20%). Bird assemblages of relatively small patches of pine plantations are unable to reflect the regional avifauna, in contrast with the relationships between local and regional assemblage characteristics that can be found in isolated natural forests. We conclude that programs of vegetation restoration should base upon a range of approaches that include passive restoration, active restoration with a variety of tree and shrub species, and mixed models to conciliate agricultural production, vegetation restoration and conservation of target species.     

Thinning and chipping small-diameter ponderosa pine changes understory plant communities on the Colorado Front Range

Novel fire mitigation treatments that chip harvested biomass on site are increasingly prescribed to reduce the density of small-diameter trees, yet the ecological effects of these treatments are unknown. Our objective was to investigate the impacts of mechanical thinning and whole tree chipping on Pinus ponderosa (ponderosa pine) regeneration and understory plant communities to guide applications of these new fuel disposal methods. We sampled in three treatments: (1) unthinned forests (control), (2) thinned forests with harvested biomass removed (thin-only), and (3) thinned forests with harvested biomass chipped and broadcast on site (thin + chip). Plots were located in a ponderosa pine forest of Colorado and vegetation was sampled three to five growing seasons following treatment. Forest litter depth, augmented with chipped biomass, had a negative relationship with cover of understory plant species. In situ chipping often produces a mosaic of chipped patches tens of meters in size, creating a range of woodchip depths including areas lacking woodchip cover within thinned and chipped forest stands. Thin-only and thin + chip treatments had similar overall abundance and species richness of understory plants at the stand scale, but at smaller spatial scales, areas within thin + chip treatments that were free of woodchip cover had an increased abundance of understory vegetation compared to all other areas sampled. Relative cover of non-native plant species was significantly higher in the thin-only treatments compared to control and thin + chip areas. Thin + chip treated forests also had a significantly different understory plant community composition compared to control or thin-only treatments, including an increased richness of rhizomatous plant species. We suggest that thinning followed by either chipping or removing the harvested biomass could alter understory plant species composition in ponderosa pine forests of Colorado. When considering post-treatment responses, managers should be particularly aware of both the depth and the distribution of chipped biomass that is left in forested landscapes.     

The impact of landscape disturbance on grizzly bear habitat use in the Foothills Model Forest,Alberta, Canada

The Rocky Mountains in Alberta, Canada are subject to a growing number of human activities that cause landscape disturbances. This region is important for large carnivore species such as grizzly bears, whose population decline is a serious management concern. Understanding the impact of landscape disturbance on grizzly bear habitat use is necessary to effectively manage this region and beyond. The goal of this research is to explore the spatial–temporal pattern of habitat use and to characterize the impact of disturbance on use through time. Research was conducted using radio-telemetry location data of female grizzly bears from 1999 to 2003. Kernel home ranges were created annually for three foraging seasons: hypophagia, early hyperphagia, and late hyperphagia. For each season, locations (30 m × 30 m grid cells) were characterized by the temporal persistence or variability in annual use by grizzly bears. Spatial–temporal trends were then compared for disturbed and undisturbed landscapes. Results indicate that in some foraging seasons, particularly hypophagia, the grizzly bear population's use of disturbed areas was proportionally higher than use in undisturbed areas. In other foraging seasons the trends are less clear, but all show instances of preferential selection of disturbed areas. Given that grizzly bear mortality tends to rise when bears use disturbed areas, this preferential selection of disturbed areas is a management concern. To enhance conservation efforts it may be beneficial to control human use in high-quality habitats. This protection may be most important for high-quality habitats used in the spring, as bears appeared to use smaller areas during this period.     

Distribution and nest site selection of red-shouldered hawks (Buteo lineatus) in forests of northeastern Wisconsin (USA)

Red-shouldered hawks (Buteo lineatus) are threatened in Wisconsin and when nest sites are found during the cruising or marking stage of timber harvesting, the harvest is altered to accommodate the hawks. If nest site locations are known before initiation of timber harvest, foresters can employ a proactive approach to manage red-shouldered hawks while maintaining timber production. We searched for red-shouldered hawks nest sites on Marinette County Forest (MCF) which encompasses 94,000 ha in northeastern Wisconsin and is the second largest county forest in the state. We used a comparative modeling approach to evaluate distribution and habitat relationships of red-shouldered hawk nest sites in relation to a suite of environmental variables in MCF. Models were used to develop forest management recommendations for red-shouldered hawks in Wisconsin. During the spring of 2006 and 2007, we broadcasted conspecific calls to survey 1121 calling stations along forest roads and trails. We located 20 and 25 active nesting territories in 2006 and 2007, respectively (11 of which were active in both years). To understand nest site selection, we measured 22 habitat variables within 0.04-ha plots at active nest sites (n = 34) and at stratified random sites (n = 61). Logistic regression with information-theoretic model selection identified a model including greater tree species richness and closeness to forested wetland as the best-approximating model. Variable selection with Discriminant Function Analysis (DFA) indicated that nest selection was best explained by greater number of tree species, closer distance to forested wetlands, greater volume of downed woody debris, fewer small sawlogs, and increased proximity to streams. Univariate comparisons identified four of the five aforementioned variables in the DFA model as significant. Red-shouldered hawks are likely more common in Wisconsin than their state status suggests. Forest management for red-shouldered hawk nest sites should focus on increasing tree species richness, increasing down woody debris volume, and protecting forested wetlands. These recommendations may assist property managers to locate and plan for continued persistence of this species on MCF.     

Successional development of silviculturally treated and untreated high-latitude Populus tremuloides clearcuts in northern Alberta,Canada

Seventy 1–28-year-old clearcuts were sampled to characterize post-harvest vegetation development and to determine the effect of mechanical site treatment and Picea glauca (Moench) Voss (white spruce) crop-seedling planting on regenerating boreal forest stands in the John D’Or—Wood Buffalo National Park area of northern Alberta in western Canada (58°35′N, 114°37′W). Natural Populus tremuloides/Rosa–Viburnum stands of wildfire origin (n = 25), widespread occurrence, and 52–91-year-old were sampled as a benchmark for comparison. Clearcut Populus-Picea and Picea stands reverted to early successional Populus tremuloides Michx. (trembling aspen)—dominated vegetation, with maximum sucker densities (mean 18 716, S.D. 13 239) within 4 years after stand initiation. Stem exclusion occurred most intensively 5–20 years after initiation, but was expected to continue until stands were >40–50-year-old. In untreated clearcuts, tree and understory shrub cover peaked near natural stand levels 18–20 years after harvesting, and graminoid cover remained constant (∼3%) but elevated compared to natural levels (<1%); whereas forb cover decreased linearly to natural stand levels by Year 28. The early composition of clearcuts was primarily composed of species that were common to the natural stands and also vegetatively reproduced. Mechanical site treatment and crop-seedling planting delayed attainment of maximum tree cover by 7 years, with total cover similar to natural stands. Site treatment reduced total shrub cover and prolonged the occurrence of elevated forb and graminoid cover values, probably in response to disruption of the pre-treatment ground vegetation. Calamagrostis canadensis L., a common crop-seedling competitor, was typically of minor importance on the sampled clearcuts compared to levels associated with more southerly boreal clearcuts. Detrended correspondence analysis ordinations based on species cover suggested untreated and treated clearcuts >13–16-year-old approximated the composition of natural stands. The data also suggested that silvicultural planting of P. glauca will accelerate stand development toward late-successional conifer-dominated vegetation relative to unplanted and natural stands.     

Effect of stand age on bird communities in late-successional Macedonian pine forests in Bulgaria

To gain insight into the question of which vegetation characteristics have the most influence on avian assemblages in late-successional forests, the habitat preferences of bird-guilds in old-growth endemic forests of Macedonian pine were studied over 3 years in the Pirin National Park, Bulgaria. Bird–habitat relationships were investigated by comparing vegetation characteristics, and bird species richness, diversity, abundance, and guild structure of birds (determined according to food type, foraging and nesting sites) between mature (60–100 years old) and over-mature (>120 years old) Macedonian pine forest stands. Studied forest age-classes differed mainly by the density, height and diameter of trees, and the amount of dead wood. The first one of these parameters decreased and the latter two parameters increased with the forest succession. The difference in the vegetation structure affected the abundance of bird-guilds and thus, the overall bird abundance and the structure of avian assemblages within Macedonian pine forests. There was no significant difference in bird diversity among studied forest age-classes, but the overall bird abundance increased with forest maturation. Analyzed by study plots, species richness was higher in over-mature forests, but at cluster level, there was no significant difference between mature and over-mature forest age-classes. Half of the studied (insectivorous, hole- and ground-nesters, bark- and canopy-foraging bird species) guilds were more abundant in over-mature forests, while there was no bird-guild exhibiting a preference for mature forest stands. The abundances of bird-guilds were correlated with tree height, diameter at breast height and the amount of dead wood between the studied forest age-classes and this might explain their preferences for over-mature pine forests. Therefore, for future sustainable management of these endemic forests and the conservation of their avifauna, efforts should focus on protecting the remaining native old-growth forest stands and the importance of the structure of Macedonian pine forests on their bird assemblages should be considered in forestry practices.     

Contemporary pollen flow and mating patterns of a subtropical canopy tree Eurycorymbus cavaleriei in a fragmented agricultural landscape

China's subtropical forests have experienced severe deforestation and most native forests have been fragmented into an archipelago-like landscape. The genetic effect of habitat fragmentation depends largely on the level of gene flow within and among population fragments. In the present study, Eurycorymbus cavaleriei, a canopy tree found throughout subtropical China, was selected as a representative insect-pollinated plant species to assess genetic consequence of forest fragmentation. Contemporary pollen dispersal and mating patterns were estimated in two physically isolated stands of E. cavaleriei within fragmented forests using six highly polymorphic microsatellite loci. We found high genetic diversity (H_E = 0.670–0.754) in both adults and offspring in the fragmented agricultural landscape, suggesting that habitat fragmentation did not necessarily erode genetic diversity of E. cavaleriei. Although substantial pollen travelled less than 100 m, paternity analysis revealed that a large amount of long-distance pollination events occurred, with the average pollen dispersal distance being 1107 m and 325 m for the two stands, respectively. Extensive pollen immigration (39.3–42.6%) indicated that there was effective genetic connectivity among E. cavaleriei stands in the fragmented forests. twogener analysis revealed that the exponential power model was the best-fitting dispersal curve with a fat-tailed (b < 1) dispersal feature. The results from a multilocus mating system analysis suggested that a small amount of biparental inbreeding and some correlated mating events occurred in the fragmented forests, which were similar to our parallel findings in the continuous forests of E. cavaleriei. Estimates of pollen pool structure (Φ_FT = 0.128–0.174) indicated large genetic differences between pollen clouds accepted by maternal trees. The number of effective pollen donors (N_ep) in E. cavaleriei, estimated using both mltr (N_ep = 4.2–5.3) and twogener (N_ep = 2.9–3.9) models, was equivalent to the number of effective pollen donors detected in continuous forests of E. cavaleriei. The pollen dispersal and mating patterns detected here indicated that habitat fragmentation did not have a negative impact on pollen movement in E. cavaleriei, possibly due to its generalist pollination system and the resilient foraging behavior of its pollinators in response to changes in landscape structure. The long distances of pollen-mediated gene flow between patches highlight the conservation value of remnant forest fragments in maintaining genetic connectivity at the landscape scale in subtropical China.