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1.
Species distributions are determined by complex interplays between multi-scale factors. Conservation management, however, often occurs at a single scale of the site level. This is true for bird communities of restored savannas and mixed woodlands in the central U.S. In this region, many historic open-canopy oak savanna habitats have become closed canopy mixed woodlands due to loss of landscape-scale disturbance from fire and grazing. Site-level management efforts return some mixed woodland habitats back to savanna through fire and mechanical thinning. Savanna and woodland historically formed complex mosaic landscapes at the ecotone between prairies and Eastern deciduous forests and now exist within landscapes that vary in amount of open (e.g., perennial grassland and row crop agriculture) and woodland habitat. To understand the interplay between site and landscape level factors in savanna restoration, we sampled the breeding bird community in four combinations of site and landscape: restored savanna in open landscapes, restored savanna in woodland landscapes, and closed canopy woodland in both landscapes. We found that the outcome of site-level savanna restoration depended on the surrounding landscape. Compared to other treatment types, restored savannas in open landscapes supported a distinctive bird community characterized by high species richness, bird abundance, and percent of ground feeders, shrub nesters, and edge species. Both savanna and woodland sites in the open landscape had a higher percent of species of conservation concern, while at both site and landscape levels, woodland was associated with a higher percent of area sensitive species and habitat specialists. Our results suggest savanna restoration efforts should focus on sites that exist either in open country or on edges where closed canopy forest meets open country. This strategy would combine site and landscape level benefits of savanna restoration for avian diversity, while also preserving the conservation benefits of large tracts of intact forest.  相似文献   

2.
Tropical conservation and research focus primarily on protected areas and often ignore conservation values of surrounding agricultural lands. Understanding how species utilize agricultural land will maximize conservation efforts. We compared bird community composition in four habitats in northeastern Costa Rica: shade-grown cacao, live fences, riparian forest buffers, and preserved late-successional rainforest. Point counts over 2 months found 167 species from 36 families. Rainforest contained the most species unique to a habitat although richness per point was lower than in agricultural habitats. Half, 31, of the rainforest species did not occur in other habitats, while 106 species, mostly those preferring open areas, occurred in agroforest habitats but not rainforest. While agricultural habitats had fairly similar species composition to each other as determined by distance in an ordination, each also contained significant numbers, 9–30, of unique species. While intact rainforest remains central to conservation of tropical birds, agricultural lands with substantial trees, e.g., live fences, riparian buffers, and plantations with shade trees, can support a high richness of birds. These avian communities are not simply subsets of the rainforest species but include substantial numbers of unique species. Conservation contributions of these lands to species richness and complexity should be considered in conservation, and trees in these habitats preserved.  相似文献   

3.

Context

The remaining riparian stretches are often the unique suitable habitats for forest breeding birds in Mediterranean landscapes undergoing long-term changes. Understanding the interactions between riparian zones and their surroundings is critical to establish successful management actions.

Aims

We assessed the influence of surrounding matrix on riparian bird communities and the use of riparian galleries as surrogate habitats for the forest passerine communities of southwestern Iberia.

Methods

We used point counts in three simultaneous sampling stations, one in the riparian gallery and two in the adjacent matrix. Three matrix types were selected with a decreasing tree density gradient: dense montado, sparse montado, and open agricultural areas. Data were analysed with redundancy analysis and differences in species’ occurrences were tested with one-way ANOVA.

Results

In riparian galleries, we found bird species belong to three ecological guilds: riparian, woodland, and edge guilds. The richness of bird guilds and the occurrence of some species depended on the surrounding matrix type. Riparian bird richness was constant in all surrounding matrices, woodland bird guild was richer in galleries embedded in dense montados, and edge guild in riparian galleries surrounded by sparse montados. Five among 19 assessed species were influenced by matrix type, within particular a few strictly riparian species. Species richness increased close to riparian galleries, due to the increase in habitat heterogeneity and resource availability for birds in densely vegetated riversides. However, the occurrence of some bird species differed according to the type of surrounding matrix.

Conclusion

The matrix type explained most of the variance in riparian bird assemblages. Some woodland birds have used riparian galleries as surrogate habitat. Our study suggests that land use in the surrounding matrices must be taking into account for the management and rehabilitation of watercourses and bird conservation actions.  相似文献   

4.
We investigated patterns of moth occurrence among habitats in two different landscapes surrounding roosts of the endangered Ozark big-eared bat (Corynorhinus townsendii ingens) from May to August 2005, and compared these data with published results on the diet of this subspecies. Landscapes were situated in the Ozark Mountains, USA, and consisted of a fragmented, agricultural landscape and a contiguous national forest. We captured 8720 moths constituting ≥314 species and 22 families. Pastures demonstrated a lower abundance and richness of moths than other habitats in the fragmented landscape (p < 0.05). Neither abundance nor richness of moths varied by habitat in the forested landscape, but we did observe variation among roost locations (p < 0.05). Abundant families of moths (n ≥ 100 specimens captured) did vary in abundance among habitats in both landscapes (p < 0.05), with poletimber stands, riparian forest and upland forest selected, and pasture, forest edge, sawtimber and sapling stands avoided by at least one family of moths. Density and richness of woody plant species were correlated with the occurrence of moths at sampling sites. We recommend maintaining habitat heterogeneity around roosts of the Ozark big-eared bat to encourage an abundance and richness of moth prey, and suggest that forested riparian corridors are important habitat elements for Ozark big-eared bats foraging in fragmented landscapes.  相似文献   

5.
The role of land uses outside protected areas in conserving tropical biodiversity remains poorly understood and contested. This paper summarizes the results of plant and bird surveys conducted in three rural landscapes in the East Usambara Mountains of Tanzania, covering a gradient from Village forest reserves to tree-based and other agricultural land uses. The species richness and occurrence of conservationally important species across the land uses were analyzed. Twelve plots of 0.2 ha, stratified among land use types, were established to survey the large trees, with sub-plots of 1 × 40 m for tree saplings, shrubs and non-woody plants, and 5 × 40 m plots for small trees. Avian richness was measured in the same sites as the plants through mist netting and timed species counts. The village forests had higher plant species richness and more conservationally important plant species compared to other land uses. Agroforest and fallows supported a relatively high number of plant species, but the species composition was largely different to the adjacent village forests. Bird species of conservation importance were recorded across all land uses. Village forest reserves and some of the tree-based agricultural land uses were found to contribute to biodiversity conservation goals in tropical landscape mosaics. There is a need to better integrate them, and address their multiple functions, in village land-use planning and conservation efforts at the landscape level.  相似文献   

6.
Agroforestry practices, such as Shaded Coffee and Homegardens, may provide habitat for forest butterflies and contribute to their conservation in fragmented agricultural landscapes. To determine the influence of agroforestry practices in an agricultural mosaic, the distribution of fruit-feeding butterflies was studied using a systematic approach that compared butterfly species richness in six land-use practices (Eucalyptus [Eucalyptus spp.], Shaded Coffee, Homegardens, Secondary Growth, Pastures, and monocultures of Cassava [Manihot esculenta] and Sugarcane [Saccharum officinarum]), and in natural habitat (secondary Forest Edge and Interior) in two study areas (agricultural landscapes). In each study area, Van Someren-Rydon butterfly traps were placed as a grid every 150 m, creating quadrants of 2.2 and 2.4 km2 that encompassed the different land-use practices. Land-use, plot area, number of traps and distance to the forest were set as covariates to compare species richness values. Butterfly species composition was compared using linear discriminant analysis (LDA). With the exception of Pastures, Cassava and Sugarcane, significant differences were not identified between the rest of the agricultural land-use practices and the forest habitats (edge and interior). The species composition in the agricultural practices was however, different to that found in forest habitats. Overall, Shaded Coffee practices that represent long-term mixed tree and crop stands have a better potential of conserving forest butterfly species compared to monoculture practices.  相似文献   

7.
Afforestation of agricultural land is increasingly used to deliver environmental benefits, but their effects on biodiversity remain poorly understood. This paper tests the hypothesis that afforestation changes predation processes in surrounding farmland, examining how the characteristics and landscape context of forest plantations affect predator (birds and mammalian carnivores) and key prey (rabbits and hares) abundances, and bird nest predation rates in Iberian cereal-steppes. Lagomorphs and predators were surveyed in fallow fields around 50 forest plantations, where predation rates were estimated using artificial nests set at 0, 100, 200 and 300 m from the forest edge. Recent plantations structurally similar to sparse (oak) or dense (pine) shrublands were associated with the highest hare and rabbit abundances, respectively, whereas both species avoided landscapes with high eucalyptus cover. In contrast, mature eucalyptus plantations showed strong positive effects on typical nest predators such as corvids and carnivores. Open farmland fragmentation favoured the abundance of lagomorphs and carnivores. Despite these effects and the high predation rate on artificial nests (49%), there was neither evidence for increased predation near plantation edges nor higher predation in fields with more lagomorphs and predators. However, predation tended to increase with cover by young oak plantations and overall forest plantation cover, to decrease with eucalyptus cover at both the local and landscape scales, and to peak in landscapes with intermediate edge densities. These results suggest that afforestation may have strong effects on bird nest predation rates by changing landscape composition and configuration, rather than by inducing local increases in predator and prey populations. Nevertheless, increased abundances of generalist predators associated with forest plantations may still be considered of conservation concern, thus supporting the recommendation for strongly restricting afforestation in areas important for open grassland birds. Where this is unavoidable, monitoring should be undertaken to provide early signals for bird population declines associated with predator increases, eventually triggering conservation action such as predator exclusion or removal.  相似文献   

8.
To halt biodiversity loss in the humid tropics of developing countries, it is crucial to understand the roles and effects of human-modified landscapes with fragmented forest remnants in maintaining biodiversity while fulfilling the demands of local communities and reducing poverty. To implement appropriate landscape planning for conserving biodiversity and ecosystem functioning, appropriate information is required about parameters of habitat suitability among various anthropogenic habitats with a range of distances to forests and vegetation characteristics, but such information is limited. We examined differences in avian communities between a remnant forest and four types of man-made forest (two mature plantations and two agroforests) in a forest–agricultural landscape of West Java, and we analyzed the effects of both local and landscape factors on various types of species richness in this landscape. The results from non-metric multidimensional scaling revealed avifauna in the two types of agroforest was clustered separately from that in the remnant forest, mainly because drastic declines in the abundance of forest specialists (including IUCN red-listed species) and their replacement with open-habitat generalists. The mixed-tree agroforests were colonized by 30 % of forest specialists and forest-edge species found in the remnant forest, and maintained the highest richness of species endemic to Indonesia among man-made forests, implying that some forest specialists and endemics might have adapted to ancient landscape heterogeneity. High proportion of insectivorous birds was found in the remnant forest (more than 50 %) and drastically decline in man-made forests, although the species richness of insectivores did not decline significantly in broad-leaved plantations. We concluded that protection of remnant forests should be prioritized to conserve forest bird diversity. However, as different environmental factors affected the richness values of different ecological groups, appropriate landscape design and habitat management could improve functional diversity in forest–agricultural landscapes in the tropics.  相似文献   

9.
Field margin vegetation is among the last vestiges of semi-natural habitat for birds in many agricultural landscapes of tropical regions. However, field margins differ in size, structure, and flora, and their value to birds depends on all these factors and on species-specific habitat preferences. Therefore, we analyzed data on resident and neotropical migratory birds found in 40 field margins of the agricultural landscape of El Bajío, Guanajuato, Mexico. The structural and botanical characteristics of the field margin, and those of the adjacent landscape, were related to bird species richness and abundance. We recorded 61 species of birds of which 36 were migratory. Locally, the size of the field margin (width, height, volume), its vegetative vertical complexity, and the abundance of trees and tree species had a positive effect on bird species richness and abundance. Native trees, especially mesquites, were especially important for many birds observed foraging, nesting, and perching. The most important landscape-scale variables were the density of hedgerows around field margins and the distance to natural vegetation remnants (scrub forest). Bird species richness and abundance were positively affected by the length of the hedgerows within 100 and 200-m-radius circles centered on each field margin. Field margins closer to natural vegetation also had more bird species and individuals. On the basis of our results, we suggest some general management recommendations for improving the habitat for birds in tropical agricultural landscapes.  相似文献   

10.
Despite concern over a putative “global pollination crisis”, we still have an incomplete understanding of how bee communities respond to land-use change. I studied the responses of social stingless (or “meliponine”) bees (Hymenoptera: Apidae: Meliponini) to surrounding forest cover and floral resources in 35 sites in a largely deforested landscape in Costa Rica over three years, sampling bees with a standardized netting protocol. I recorded a diverse fauna of meliponines, comprised of 20 species and nine genera. I found that meliponine species richness and abundance are strongly related to forest cover, but not floral resource variables (blooming plant species richness and abundance). The effect of forest on meliponine abundance, but not diversity, disappeared when the most common meliponine species, Trigona fulviventris (which comprised ∼45% of sampled individuals), was excluded from analyses. Meliponine community composition, by contrast, was related most strongly to plant species richness, only weakly to forest cover, and not related to blooming plant abundance. This work differs from past work in the same landscape, which did not find evidence of changes in species richness or abundance of meliponines and forest-related variables (distance to forest or forest fragment size), but did find shifts toward meliponine-dominated communities near forests, especially larger ones. The larger true sample size (i.e. number of sample sites) of the present work likely improved the statistical power to detect these relationships. While meliponines are forest dependent, I recorded some species in the smallest forest fragments in the landscape, and as a group they respond strongly to overall forest cover in the landscape (i.e. including both small and large patches of forest). Both of these observations support arguments for preserving even small fragments of forest in agricultural landscapes. Given the ecological and economic importance of meliponine bees, it is imperative that we better understand their long-term conservation needs in the changing tropical landscapes of the world.  相似文献   

11.
Most studies of the effects of fragmentation and landscape patterns on plant communities focus on particular patches and on local species richness (α-diversity), while few studies examine different patch-types at the whole landscape level and address effects on abundance and composition of species or functional groups. The present study aims to identify and characterize relationships between patch-type metrics and species density and abundance of trees using four tropical subdeciduous forest landscapes in the Yucatan Peninsula considering the entire landscape as the unit of study. Species density and abundance of different groups of tree species resulting from hierarchical clustering were related to landscape patterns of patch-types (area, edge, shape, similarity and contrast) using regression analysis and Akaike Information Criterion (AIC). The abundance of tree species in the oldest stages of succession was associated with percentage of land of a patch-type. Total area may favor the establishment of shade-tolerant tree species in the study area because as the area of forest patches increases, the area of forest interior conditions also increases. Conversely, the abundance of species at early and intermediate stages was related to total edge contrast and edge density, respectively. Fragmentation increases the proportion of edge zones of a patch-type, creating contrasting microclimate conditions that could promote the establishment of pioneer and light-demanding species. Thus, the combined effect of total area and edge length of a patch-type may enhance total tree species richness in the study area by favoring species with different life-history strategies. The appearance of area, shape, edge and contrast in most of the regression models suggests that some generalization can be made about the effects of spatial geometry of patch-types on species composition and abundance of tropical trees. Understanding associations between landscape metrics and species density and abundance of objectively derived groups or guilds of species can provide important insights on the effects of fragmentation and landscape pattern on these guilds and on overall α-diversity, as well as guidelines for their conservation and management.  相似文献   

12.
Conservation value of dispersed tree cover threatened by pasture management   总被引：1，自引：0，他引：1  
Trees dispersed in pastures are a prominent feature of many Central American landscapes, particularly in cattle producing regions where farmers retain trees to serve as shade, fodder, timber and firewood. The presence of dispersed trees in pastures is often considered as important for the conservation of biodiversity by providing habitat and enhancing landscape connectivity. However, despite their critical productive and environmental roles, little is known about tree distribution within pastures or how farmers’ management decisions influence the trees themselves and their impact on farm productivity and biodiversity conservation. Here, we present a synthesis of (a) the abundance, composition, and size of dispersed trees in four important cattle producing regions of Costa Rica (Caňas and Río Frío) and Nicaragua (Rivas and Matiguás), based on inventory of 18,669 trees on 1492 ha of pasture, (b) the local knowledge, management and use of trees by cattle farmers, and (c) opportunities for ensuring sustainable management of dispersed trees in pasture-dominated landscapes. Dispersed trees were common in all four landscapes, with mean frequency ranging from 8.0 trees ha−1 in Caňas to 33.4 trees ha−1 in Matiguás. A total of 255 tree species were found in pastures across the four landscapes. The total number of tree species per landscape varied from 72 in Rivas to 101 in Caňas and Rio Frio, with mean species richness per farm ranging from 22.9 in Rio Frio to 45.9 in Matiguás. In all four landscapes, a handful of tree species dominated the pastures, with the ten most abundant species in each landscape accounting for >70% of all trees recorded. Most of these common tree species provide fruits or foliage eaten by cattle, or are important timber or firewood species, and are deliberately retained by farmers for these uses. In all four landscapes, farmers had a detailed knowledge of tree attributes affecting pasture and animal productivity, and influenced tree cover through pasture management activities and occasional tree cutting. Current farm management practices are gradually decreasing the diversity of trees in pastures, and in some cases also tree density, reducing their contribution to farm productivity and biodiversity conservation. To reverse this trend, incentives are required to encourage cattle farmers to retain and enhance tree cover in pastures, through the adoption of pasture management practices that favor the regeneration and persistence of a diverse range of tree species.  相似文献   

13.
A relatively common observation in forest environments has been that gullies support higher species richness and individual abundance than elsewhere in the landscape. We completed a detailed case study of birds to contrast species richness and assemblage composition between gullies and other parts of the topography of landscapes in three closely related and spatially adjacent wet ash forest types – those dominated by Mountain Ash (Eucalyptus regnans), Alpine Ash (E. delegatensis) or Shining Gum (E. nitens) – in the Central Highlands of Victoria, south-eastern Australia. We also quantified the influence of a wide range of other measures of stand structure and plant species composition on the bird assemblage and on individual bird species.  相似文献   

14.
Numerous studies have explored the influence of forest management on avian communities empirically, but uncertainty about causal relationships between landscape patterns and temporal dynamics of bird communities calls into question how observed historical patterns can be projected into the future, particularly to assess consequences of differing management alternatives. We used the Habplan harvest scheduler to project forest conditions under several management scenarios mapped at 5-year time steps over a 40-year time span. We used empirical models of overall avian richness, richness of selected guilds, and probability of presence for selected species to predict avian community characteristics for each of the mapped landscapes generated for each 5-year time step for each management scenario. We then used time series analyses to quantify relationships between changes in avian community characteristics and management-induced changes to forest landscapes over time. Our models of avian community and species characteristics indicated habitat associations at multiple spatial scales, although landscape-level measures of habitat were generally more important than stand-level measures. Our projections showed overall avian richness, richness of Neotropical migrants, and the presence of Blue-gray Gnatcatchers and Eastern Wood-pewees varied little among management scenarios, corresponding closely to broad, overall landscape changes over time. By contrast, richness of canopy nesters, richness of cavity nesters, richness of scrub-successional associates, and the presence of Common Yellowthroats showed high temporal variability among management scenarios, likely corresponding to short-term, fine-scale changes in the landscape. Predicted temporal variability of both interior-forest and early successional birds was low in the unharvested landscape relative to that in the harvested landscape. Our results also suggested that early successional species can be sensitive to both availability and connectivity of habitat on the landscape. To increase or maintain the avian diversity, our projections indicate that forest managers need to consider landscape-scale configuration of stands, maintaining a spatially heterogeneous distribution of age classes. Our findings suggest which measures of richness or species presence may be appropriate indicators for monitoring effects of forest management on avian communities, depending on management objectives.  相似文献   

15.
We hypothesized that edge density more strongly influences species abundances in more productive environments. To test this hypothesis we collected songbird point count data across broad biophysical gradients and gradients in forest patch edge density in the west and east slopes of the Cascade Mountains of Oregon and Washington, U.S.A., which differ in ecological productivity. We then analyzed bird response (75 species) at both the species and community level to gradients in edge density (m/ha) of open and closed-canopy forest within 1-km radius landscapes. We found that (1) differences in vegetation and structural conditions between open and closed-canopy stands were significantly greater at a highly productive landscape than a landscape with intermediate levels of productivity; (2) more bird species responded to changes in edge density in more productive west-slope Cascade forests than less productive east-side Cascade forests; (3) pooled abundance data from both sites showed that 25 of the 60 most abundant bird species responded significantly to the interaction between forest productivity and changes in landscape-level edge density; and, (4) at the community level, ordinations showed that bird community similarity in the productive west-slope Cascade forests differed across low and high levels of edge density whereas no such differentiation occurred in harsh, east-side Cascade forests. These results provide some of the first evidence supporting the hypothesis that edge effects are more pronounced in productive west-side forests where higher levels of edge density benefit generalist and open-canopy species while negatively influencing closed-canopy species. Consequently, forest management aimed at supporting species diversity will be most effective if tailored to ecosystem productivity.  相似文献   

16.
In some urban parks in Tokyo,semi-natural habitat patches are maintained as nature reserves for birds,called bird sanctuaries.Bird censuses and vegetation surveys were conducted in eight urban parks in Tokyo from December 2015 to July 2016 to determine the effectiveness of bird sanctuaries on avian species composition.The relationship between avian species composition and environmental conditions was analyzed by partial redundancy analysis(partial RDA) using vegetation variables,number of visitors,presence or absence of reserves within the same park,area of wooded parts,and normalized difference vegetation index(NDVI)in the surrounding area.The results of the partial RDA are as follows:(1) Area,lower vegetation cover,higher vegetation cover,tree species composition obtained from detrended correspondence analysis(DCA) on vegetation survey data,and NDVI in the surrounding area were considered as covariates and explained 17.4-33.6% of the total variation in bird species composition,(2) The presence or absence of sanctuary significantly explained bird species compositional variation regardless of season,indicating that the sanctuaries were beneficial for urban avoider species not only in the sanctuaries but also in the surrounding wooded area,and(3)Tree coverage within a 100 m range and leaf litter coverage also influenced avian species composition.We concluded that bird sanctuaries and other nature reserves can be beneficial to bird conservation,even within Tokyo.The positive effect of sanctuaries could be due to the limited influence of human presence and the developed vegetation within them.These reserves may play the role of core habitats within the studied urban parks.  相似文献   

17.
Live fences are common elements in neotropical agricultural landscapes and could play important roles in the conservation of biodiversity by enhancing landscape connectivity, however, little is known about their abundance and spatial arrangement. The objectives of this study were to characterize the abundance and spatial patterns of live fences in a fragmented landscape dominated by pastures in Río Frío, Costa Rica, to determine their contribution to landscape structure and connectivity and to examine their role as tools for landscape conservation planning. Live fences accounted for 45.4% of all fences in the landscape and occurred with a mean density of 50.5 linear meters per hectare. Although live fences covered only a small total area of the landscape (<2%), they had an important effect on landscape structure and connectivity, increasing total tree cover, dividing pastures into smaller areas, creating rectilinear networks that cross the landscape and providing direct physical connections to forest patches. Simulations showed that the conversion of all existing wooden fences to live fences would greatly enhance landscape connectivity by more than doubling the area, density and number of direct connections to forest habitats, and reducing the average distance between tree canopies. Our study demonstrates that live fences play key roles in defining the structure and composition of neotropical agricultural landscapes and merit consideration in both conservation efforts and agricultural policies designed to enhance landscape connectivity and promote biodiversity conservation.  相似文献   

18.
蒋静慧 《广东园林》2020,42(3):15-21
筏子溪位于我国台湾地区台中市区城市与乡镇结合的位置,有大面积的农田,常年多风害,农业生产环境不稳定。通过对农田林网的研究梳理及案例研究,归纳出林网的布局、林带的构成、树种的选择和作物的种植方式4个构建农田林网的要素。对筏子溪流域的农地从树种选择、林网构建、时序设计3个方面进行设计实践,完善农田林网景观的设计体系。最后,讨论了农田林网的生态效应、经济效益、文化服务3种景观服务功能。农田林网景观设计是农业生产应对全球气候变化和可持续发展的有效途径。  相似文献   

19.
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.  相似文献   

20.
Traditional harvesting practices frequently result in simplification of the structure and composition within managed forest stands in comparison to their natural counterparts. In particular, loss of heterogeneity within stands may pose a problem for maintaining biodiversity in perpetuity. In this study, we survey breeding bird diversity and abundance in response to different spatial harvesting patterns in mature red pine forests located on the Chippewa National Forest of northern Minnesota, USA. Treatments are designed to increase structural complexity over time and include three overstory manipulations (dispersed retention, aggregate retention with small gaps, and aggregate retention with large gaps), one understory manipulation (brush removal), and controls (no harvesting, and/or no brush removal). In 2003, the first breeding season following the harvest, we found little difference in bird community composition between control and treatment stands. In 2005, the third breeding season following harvest, avian abundance, richness, and diversity were all greater within treatments. Species associated with edge, shrub, and early successional habitats generally show positive response to treatments (e.g. Chestnut-sided Warbler [Dendroica pensylvanica], Mourning Warbler [Oporornis philadelphia], Chipping Sparrow [Spizella passerine]), as do some species associated with mature forest (e.g., Pine Warbler [Dendroica pinus], Rose-breasted Grosbeak [Pheucticus ludovicianus]). Ovenbirds (Seiurus aurocapilla) and Black-throated Green Warblers (Dendroica virens) were more abundant in control stands. There are, as of yet, no discernable differences in avian community composition among the three overstory treatments or between the single understory treatment and the understory control, but differences are expected as the treatments diversify due to understory development. While overstory retention harvests provide habitat for a diverse and abundant bird community, the temporal divergence in avian community composition that we observed between treatment and control stands reveals the importance of uncut, mature red pine forest as a component of a biodiverse landscape.  相似文献   

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