Chainsawing for conservation: Ecologically informed tree removal for habitat management

Summary In many ecosystems, increases in vegetation density and the resulting closure of forest canopies are threatening the viability of species that depend upon open, sunlight‐exposed habitats. Consequently, we need to develop management strategies that recreate open habitats while minimizing the impacts on non‐target areas. Selective logging creates canopy gaps, but may result in undesirable effects in other respects. Thus, chainsaws have not been a popular tool for conservation. We conducted a landscape‐scale experiment to test whether selective tree removal can restore patch‐level habitat quality for Australia’s most endangered snake (Hoplocephalus bungaroides) and its main prey (the lizard Oedura lesueurii). We selectively removed canopy trees surrounding 25 overgrown rock outcrops and compared the resultant habitat structure and abiotic conditions to 30 overgrown, shady outcrops and 20 open, sunny outcrops. Removing vegetation decreased canopy cover by 19% in experimental plots and increased incident radiation and thermal regimes. These changes increased the availability of suitable shelter sites for our target species by 131%. At the landscape scale, our manipulations had a trivial effect on forest habitat; by increasing the area of sun‐exposed outcrops, we decreased forest cover by <0.1%. Our results show that targeted canopy removal can increase the availability of sun‐exposed habitat patches for endangered species in biologically meaningful ways. Thus, selective tree felling may be an effective conservation tool for open‐habitat specialists threatened by vegetation overgrowth.     

Habitat management to reduce competitive interactions: case study of native and invading cottontails

Habitat management recommendations are often based on best available science determined through retroductive and inductive hypotheses. Such recommendations are not frequently tested, potentially resulting in the implementation of unreliable practices for management of imperiled species. The New England cottontail (Sylvilagus transitionalis) is an imperiled shrubland-obligate species whose recovery efforts include habitat management and restoration. Researchers suggest former best management practices for the species may result in ecological traps and new recommendations have been developed. We evaluated these newly revised best management practices designed to retain higher tree canopy closure to promote New England cottontails without encouraging eastern cottontails (Sylvilagus floridanus). We compared New England and eastern cottontail density between management plots (tree canopy thinned with all downed trees left on the ground, with or without invasive shrub treatment) and control plots (unmanaged) and examined the influence of management on resource selection and survival. Management strategies retaining higher canopy closure promoted stronger selection by New England cottontails than by eastern cottontails. Catch per unit effort of New England cottontails was greater than for eastern cottontails in management plots (P = 0.002). For both species, the proportion of the 95% home range overlapping managed areas was greater than the proportion of managed area in the habitat patch; however, for the 50% core area of the home range, this was only true for New England cottontails. When post-treatment canopy cover was >75%, New England cottontails selected canopy-thinning treatments without invasive shrub removal over unmanaged areas, but selection by eastern cottontails was unaffected by management treatment or canopy cover. Survival probability of both species was high and uncorrelated with time spent in management areas. Survival probability decreased as the average distance a rabbit moved in a 7-day period increased. Our results illustrate the need to revise management strategies that emphasize eliminating canopy cover when improving New England cottontail habitat is an objective, particularly where they are sympatric with eastern cottontails.     

Habitat selection of riparian birds at restoration sites along the Trinity River,California

Riparian habitats in the western United States are imperiled, yet they support the highest bird diversity in arid regions, making them a conservation priority. Riparian restoration efforts can be enhanced by information on species response to variation in habitat features. We examined the habitat selection of four riparian birds known as management indicators at restoration and reference sites along the Trinity River, California. We compared vegetation structure and composition at nest sites, territories, and random points to quantify used versus available habitat from 2012 to 2015. Vegetation in focal species' territories differed between site types, and from available habitat, indicating nonrandom site choice. Birds selected aspects of more structurally complex habitats, such as greater canopy cover, canopy height, and tree species richness. Yellow‐breasted Chats preferred greater shrub cover, and Yellow Warblers preferred greater cover by non‐native Himalayan blackberry. Territory preferences on restoration sites were often a subset of those on reference sites. One exception was canopy height, which was taller on restoration site territories than random points for all species, suggesting that birds preferentially used patches of remnant habitat. Few variables were significant in nest site selection. Restoration plantings along the Trinity River were only 3–10 years old during this study, and have not developed many of the characteristics of mature riparian habitat preferred by birds, but may improve in habitat value over time. Understanding habitat selection is especially important in recently human‐modified environments, where indirect cues used to assess habitat quality may become disassociated from actual habitat quality, potentially creating ecological traps.     

Intermediate habitat associations by hybrids may facilitate genetic introgression in a songbird

Hybridization or the interbreeding of genetically discrete populations or species can occur where ranges of genetically distinct units overlap. Golden‐winged warblers Vermivora chrysoptera, a species that has been in steady decline for decades, highlight the potential population‐level consequences of hybridization. A major factor implicated in their decline is hybridization with their sister species, the blue‐winged warbler Vermivora cyanoptera, which has likely been exacerbated by historic and current land‐use practices. We examined habitat associations of golden‐winged and blue‐winged warblers, phenotypic hybrids, and cryptic hybrids (i.e. mismatch between plumage phenotype and genotype as identified by mitochondrial DNA) in an area of relatively recent range overlap and hybridization in northern New York, USA. To explore the robustness of these results, we then compared the patterns from New York with habitat associations from the central Pennsylvanian Appalachian Mountains where blue‐winged warblers either do not occur or are in very low abundance, yet cryptic golden‐winged warbler hybrids are present. From 2008 to 2011, we captured 122 birds in New York and 28 in Pennsylvania and collected blood samples, which we used to determine maternal ancestry. For each bird captured, we measured territory‐level (50‐m radius circles) habitat, and later used remote‐sensing data to quantify habitat on the territories and in surrounding areas (100‐, 250‐, and 500‐m radius circles). In New York, golden‐winged warblers occupied structurally heterogeneous territories surrounded by homogeneously structured, contiguous deciduous forest, far from urban areas. Blue‐winged warblers showed opposite associations, and hybrids’ habitat associations were typically intermediate. In Pennsylvania, the habitat associations of golden‐winged warblers and their cryptic hybrids were remarkably similar to those in New York. These findings suggest that patterns of habitat occupancy by hybrids may promote contact with golden‐winged warblers and thus likely facilitate genetic introgression, even in areas where the parental species are not sympatric.     

A Molecular and Fitness Evaluation of Commercially Available versus Locally Collected Blue Lupine Lupinus perennis L. Seeds for Use in Ecosystem Restoration Efforts

Dependence on wild seed sources is often impractical for large‐scale habitat restoration programs. Reliance on commercial seed supplies of unknown provenance and fitness is thereby warranted. Little consideration has been given, however, to how the large volumes of seed required should be sourced. We evaluated commercial and locally collected seed sources for potential use in a New York State‐based, landscape‐scale program for restoring blue lupine Lupinus perennis. Through analysis of microsatellite markers we determined that “native” lupine designations by some commercial suppliers were in fact interspecific hybrids and therefore unreliable; at least two commercial sources, however, were genetically as close to native New York populations as native New York populations were to one other. Common garden experiments revealed that seed source influenced first‐year overwintering survival and subsequent height growth of surviving plants; seed sources more closely related genetically to native New York populations survived better and produced more stems per individual in the field in the area targeted for restoration. We conclude that (1) commercial suppliers often but not always offer reliably characterized seed sources of sufficient genetic similarity to native populations to warrant their use in restoration projects and (2) genetic affinity of potential seed stock to native populations is positively related to its fitness in the environment targeted for restoration.     

Response of butterflies to structural and resource boundaries

1. Two aspects of landscape composition shape the behavioural response of animals to habitat heterogeneity: physical habitat structure and abundance of key resources. In general, within-habitat movement behaviour has been investigated in relation to resources, and preference at boundaries has been quantified in response to physical structure. 2. Habitat preference studies suggest that responses to resources vs. structure should differ, e.g. between male and female animals, and effects of responses to structure and resources may also interact. However, most studies of animal movement combine various aspects of behavioural responses to 'habitat', implicitly assuming that resources and structure are broadly equivalent. 3. We conducted a large-scale experiment of the movement of Fender's blue (Icaricia icarioides fenderi), an endangered butterfly, to investigate butterfly response to physical structure of the landscape (prairie, open woods and dense woods) and to resources [presence or absence of Kincaid's lupine, Lupinus oreganus (larval hostplant patches)]. The experiment included 606 butterfly flight paths across four habitat types and nine ecotones. 4. Responses to physical structure and resource patches were not congruent. Butterflies were attracted to resource patches within both prairies and open woods and moved more slowly when in resource patches. Butterflies tended to prefer prairie at prairie-forest edges but tended to move faster in prairies than in open woods. Physical structure and resources also interacted; butterflies did not respond to physical habitat structure when resource patches spanned prairie - open woods ecotones. 5. Even dense woods were not perfect barriers, in contrast to a large body of literature that assumes insects from open habitats will not enter dense forests. 6. Movement of both males and females responded to resources and structure. However, female butterflies had stronger responses to both resources and structure in most cases. Females had strongest response to resource (hostplant) patches at patch edges, whereas the strongest preference of males was to return to prairie from open forest. 7. If other species behave like Fender's blue, then combining different definitions of 'habitat' (physical structure vs. resources), different aspects of movement (edge preference vs. within-habitat movement) and/or males and females within species could all lead to misleading conclusions. Our results highlight the importance of investigating these responses, and our study provides a framework for separating them in other systems.     

Impacts of habitat on butterfly dispersal in tropical forests,parks and grassland patches embedded in an urban landscape

Dispersal distances of 17 species of butterflies in tropical Singapore were significantly greater in forest than in urban habitat. Butterflies in urban plots frequently moved within suitable habitat (park/grassland) patches but rarely crossed non-habitat patches suggesting potential isolation and a need for urban corridors.     

A native nitrogen-fixing shrub facilitates weed invasion

Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds.     

Nest-site selection by Common Black-Hawks in southwestern New Mexico

ABSTRACT.   Despite the interest of resource managers and conservationists in the status of Common Black-Hawk ( Buteogallus anthracinus ) populations in the southwestern United States, little is known about their nesting success and habitat requirements. Because such information is essential for effective population and habitat management, I examined the nesting success and nest-site selection of Common Black-Hawks in southwestern New Mexico during 2000 and 2001. Of the 37 nesting attempts in 21 territories, ≥1 young fledged from 25 nests (68%). Comparison of nest-sites and nonused sites suggested that breeding Common Black-Hawks selected nest-sites in areas with a sparser and shorter subcanopy tree layer and in trees with a smaller trunk diameter and a greater minimum crown diameter. These differences appear to be related to variation in forest ages within territories, with nonused sites having fewer, but older, canopy trees than nest-sites. Sites with younger, smaller subcanopy trees may provide forest structure for more effective foraging, whereas the characteristics of younger nest tree canopies may reduce the risk of nest predation or offer more protection from inclement weather. Due to the limited range of this species in the southwestern United States, efforts to encourage the establishment and maturation of riparian forests in Common Black-Hawk breeding areas could be important in sustaining available nesting habitat and, in turn, maintaining or expanding current population levels.     

Competition and habitat selection in Namib desert tenebrionid beetles

Summary We tested whether intra- and interspecific competition could affect habitat selection in the two most abundant tenebrionid beetles,Physadesmia globosa andOnymacris rugatipennis, in a dry riverbed in the Namib desert. The spatial distributions of these beetles at the microhabitat scale were negatively correlated. We performed a removal experiment, progressively removing first 25% and then a further 25% of the population of the most abundant species,P. globosa, under the trees where most of the preferred food of both species is concentrated. There was no response ofO. rugatipennis to this removal in the tree habitat. In the open, barely-vegetated habitat where mostO. rugatipennis are found, the number of this species caught in pitfall traps increased following both removals and decreased followingP. globosa replacement under the trees. It appears that intraspecific competition forces someP. globosa to occupy the open habitat. Interspecific competition betweenP. globosa andO. rugatipennis in the open habitat reduces the number ofO. rugatipennis that can co-exist withP. globosa there. Removal ofP. globosa under the trees allows conspecifics in the open habitat to move under the trees, releasingO. rugatipennis in the open habitat from competition. This then results in an increase in the numbers ofO. rugatipennis in the open habitat as a result of immigration from neighbouring areas. We found that differences in foraging efficiency, measured as giving-up times in artificial food patches, create a likely mechanism of co-existence that explains the distinct preferences of these two species for tree and open habitats.     

Woody species as landscape modulators: their effect on the herbaceous plants in a Mediterranean maquis

“Landscape modulators” are ecosystem engineers that have an impact on community structure by creating patches in the landscape mosaic. Our aim was to study the effect of evergreen-trees, as landscape modulators, on herbaceous plants in a Mediterranean maquis system in northern Israel. We examined the effects of canopy removal and cattle grazing on species richness, plant functional types, and rare plant species in two patch-types: (1) woody—under tree canopy (or the location of a removed canopy); (2) herbaceous—in open areas with no tree canopy. Patch-type and tree removal affected species richness and plant functional types. The extreme negative effect of the woody patch-type on species richness disappeared soon after the removal of the landscape modulator canopy. We conclude that the dominant effect of the evergreen woody landscape modulators can be regulated by canopy removal and grazing for maintaining patch-type and landscape diversities, and consequent high species richness in Mediterranean ecosystems, which is a main goal of global nature conservation policy.     

Woodland structure,rather than tree identity,determines the breeding habitat of Willow Warblers Phylloscopus trochilus in the northwest of England

Capsule Woodland structure, rather than tree species, is the most important determinant of breeding habitat selection by Willow Warblers in North West England.

Aims To examine how habitat characteristics predict the occurrence of male Willow Warbler territories.

Methods Woodland structure (trunk density, trunk diameter, canopy cover and understory cover), tree species and food abundance were compared between woodland areas within and outside of male territories at a site in the UK.

Results Territories contained higher trunk numbers, had a narrow range of trunk diameters, and intermediate canopy cover. Food abundance did not differ with occupancy. Willow and alder were the most common trees within territories, in contrast to birch which has been found in previous studies. The habitat structure matches young woodlands, where birches often grow. However, at the study site the birches were large and mature, and therefore unsuitable. Moreover, woodland structure variables were better predictors of occupancy than any particular tree genera.

Conclusion The results indicate that vegetation structure, but not tree species or food availability, influence breeding habitat selection by Willow Warblers. The preferred structure is similar to coppice woodlands; therefore, the Willow Warbler decline may be linked to the loss of this traditional management across south England.     

Microhabitat use by larvae and females of a rare barrens butterfly,frosted elfin (<Emphasis Type="Italic">Callophrys irus</Emphasis>)

The frosted elfin (Callophrys irus) is a localized and declining butterfly found in xeric open habitats maintained by disturbance. We described the effects of woody plant canopy cover, topography and host plant size and density on the quality of microhabitat of wild indigo (Baptisia tinctoria) host plants containing late instar frosted elfin larvae at four study sites in southeastern Massachusetts, United States. We also assessed whether females preferentially depositing eggs on host plants within specific microhabitats, therefore conferring greater survivorship to the larvae through the late-instar stage. We found that moderate amounts of canopy cover and large plant size characterized larvae-occupied host plants. In the absence of tree canopy cover, late instar larvae density remained low even when host plant density was high. However, females oviposited on wild indigo plants without regard to any of the vegetative or environmental variables we measured. These results indicate that canopy cover was an important characteristic of microhabitats containing late instar larvae, and late instar larvae occupancy was determined by suitable microhabitat conditions, and not female oviposition selection. Managing for canopy cover and microhabitat heterogeneity within relatively open habitats is recommended for the maintenance of frosted elfin populations.     

An Analysis of Overstory Tree Canopy Cover in Sites Occupied by Native and Introduced Cottontails in the Northeastern United States with Recommendations for Habitat Management for New England Cottontail

The New England cottontail (Sylvilagus transitionalis) is a high conservation priority in the Northeastern United States and has been listed as a candidate species under the Endangered Species Act. Loss of early successional habitat is the most common explanation for the decline of the species, which is considered to require habitat with dense low vegetation and limited overstory tree canopy. Federal and state wildlife agencies actively encourage landowners to create this habitat type by clearcutting blocks of forest. However, there are recent indications that the species also occupies sites with moderate overstory tree canopy cover. This is important because many landowners have negative views about clearcutting and are more willing to adopt silvicultural approaches that retain some overstory trees. Furthermore, it is possible that clearcuts with no overstory canopy cover may attract the eastern cottontail (S. floridanus), an introduced species with an expanding range. The objective of our study was to provide guidance for future efforts to create habitat that would be more favorable for New England cottontail than eastern cottontail in areas where the two species are sympatric. We analyzed canopy cover at 336 cottontail locations in five states using maximum entropy modelling and other statistical methods. We found that New England cottontail occupied sites with a mean overstory tree canopy cover of 58% (SE±1.36), and was less likely than eastern cottontail to occupy sites with lower overstory canopy cover and more likely to occupy sites with higher overstory canopy cover. Our findings suggest that silvicultural approaches that retain some overstory canopy cover may be appropriate for creating habitat for New England cottontail. We believe that our results will help inform critical management decisions for the conservation of New England cottontail, and that our methodology can be applied to analyses of habitat use of other critical wildlife species.     

云南大中山黑颈长尾雉栖息地选择周年变化

采用比较利用和可利用栖息地的方法,分别对云南大中山黑颈长尾雉秋冬季、春季和夏季栖息地展开调查。检验和Bonferroni置信区间分析结果表明,黑颈长尾雉不同季节均偏向选择常绿阔叶林,偏向选择或回避选择的乔木、灌木和草本的种类不尽相同。利用和可利用样方差异性检验显示,不同季节对地形因素的选择性不明显,仅夏季距水源距离一个因子差异显著;植被因子中,春季差异显著的仅有乔木层盖度因子,夏季有乔木密度、乔木层盖度、落叶层盖度和草本层盖度等4个因子,秋冬季有乔木层盖度、草本层盖度和藤本密度等3个因子。主成分分析表明,不同季节利用样方负荷绝对值较大的因子在各主成分中的序位不尽相同,即栖息地选择的主要生态因子随季节发生变化。单因素方差分析和逐步判别分析表明,秋冬季与春季栖息地特征较接近,而与夏季差别较大。χ2     

Establishment and reproduction of Aeschynomene virginica (L.) (Fabaceae) a rare,annual, wetland species in relation to vegetation removal and water level

Aeschynomene virginica is a rare annual plant found in freshwater tidal wetlands of the eastern United States. We hypothesized that standing vegetation and water inundation were two important environmental factors in its population dynamics. To test these hypotheses, we sowed seeds into plots with undisturbed vegetation or plots with all aboveground vegetation removed in 1998 and 1999. Presence/absence of seedlings was noted and seedling survival to reproduction, final size, and seed set were measured throughout both growing seasons. Seedling establishment from germination to the first true leaf stage increased with decreasing water depth. Vegetation removal plots had greater seedling establishment, higher seedling survival, and higher seed set per plant than non-removal plots. In a greenhouse study designed to test the effects of water level on seed germination and seedling establishment, no seedlings established in submerged soils, and seed germination and seedling establishment were lower in waterlogged soil than in wet soil. Physical stress associated with deeper water likely limits the distribution of A. virginica to higher elevations, where seeds that colonize patches with low vegetative cover are more likely to produce reproductive adults that produce more seeds relative to patches with established vegetation. A. virginica appears to be a fugitive species specializing on open habitat patches in tidal wetlands. This species may be dependent on disturbances for population establishment and maintenance.     

The effects of habitat manipulation on population distribution and foraging behavior in meadow voles

Individuals, free to choose between different habitat patches, should settle among them such that fitness is equalized. Alternatives to this ideal free distribution result into fitness differences among the patches. The concordance between fitnesses and foraging costs among inhabitants of different quality patches, demonstrated in recent studies, suggests that the mode of habitat selection and the resulting fitness patterns may have important implications to the resource use of a forager and to the survival of its prey. We studied how coarse scale selection between habitat patches of different quality and quitting harvest rate in these patches are related to each other and to fine scale patch use in meadow voles (Microtus pennsylvanicus). To demonstrate these relationships, we manipulated habitat patches within large field enclosures by mowing vegetative cover and adding supplemental food according to a 2×2 factorial design. We tracked vole population densities, collected giving‐up densities (GUDs, a measure of patch quitting harvest rate), and monitored the removal of seeds from lattice grids with 1.5 m intervals (an index of fine‐scale space use) in the manipulated habitat patches. Changes in habitat quality induced changes in habitat use at different spatial scales. In preferred habitats with intact cover, voles were despotic and GUDs were low, but increased with the addition of food. In contrast, voles in less‐preferred mowed habitats settled into an ideal free distribution, GUDs were high and uninfluenced by the addition of food. Seed removal was enhanced by the presence of cover but inhibited by supplemental food. Across all treatments, vole densities and GUDs were strongly correlated making it impossible to separate their effects on seed removal rates. However, this relationship broke down in unmowed habitats, where GUDs rather than vole density primarily influenced seed removal by voles. GUDs and seed removal correlated with predation on tree seedlings formerly planted into the enclosures, demonstrating the mechanisms between coarse‐scale habitat manipulations and community level consequences on a forager's prey.     

Maintaining Critical Habitat in a Heavily Managed Landscape: Effects of Power Line Corridor Management on Karner Blue Butterfly (Lycaeides melissa samuelis) Habitat

The Karner blue butterfly (KBB) (Lycaeides melissa samuelis), a federally listed species, has historically been a component of barren and savannah ecosystems in the northeastern and midwestern United States. In New York, it now occurs primarily on managed, early‐successional sites such as power line corridors (utility rights‐of‐way) from Albany to Glens Falls. Blue lupine (Lupinus perennis), the exclusive larval food source of the KBB, has been suggested to be the most limiting factor for the butterfly within the eastern portion of its range. Power line corridor management maintains early‐successional habitats by suppressing the regrowth of woody species, creating potentially important habitat for the conservation and restoration of the KBB complex. This research compared the effects of several vegetation‐clearing methods on Blue lupine populations and associated communities of nectar species for KBB over an 8‐year period. Methods evaluated differed in intensity (annual, 4‐, or 8‐year intervals) and type (herbicide or mechanical). Blue lupine and plant community responses did not significantly differ among the treatment types applied to the power line corridors. However, Blue lupine cover, clump size, and density of stems per clump increased following the application of treatments in general. The number and cover of nectar species, total herbaceous cover, and species richness also responded positively to treatment overall. The percentage of non‐native species temporarily increased following treatment but declined to near pre‐treatment levels again as woody cover increased. Temporal changes in plant community composition were not related to management methods. The management tools assessed, mowing and herbicide application, will accomplish the goal of halting or reversing succession, maintaining critical habitat for the KBB in a landscape that provides little other suitable habitat.     

Home range size of willow tits: a response to winter habitat loss

We examined the behavioral response to habitat loss and fragmentation of willow tits (Parus montanus) in winter in a mosaic forest landscape in northern Finland. We studied habitat preference, flock size and home range size of 16 flocks, half of which had their territories in forests fragmented by forestry and half in continuous forest. We predicted that birds would respond to habitat loss by enlarging their home range and/or diminishing group size. In addition, to compensate for fragmentation effects, willow tits might be expected to include more optimal habitat into their territories. Flocks included on average 3.9 birds and occupied territories of 12.6 ha. Willow tits avoided open areas (clear cuts and young sapling stands) and preferred mature forests and older sapling stands or pine bogs equally. Birds responded to habitat loss by enlarging their home ranges but not by reducing the group size. Large territories included a smaller proportion of mature forests, but the proportion of sapling and pine bog habitat did not change. Birds on territories that included a large proportion of open habitat localized their activity on several distinct habitat patches that were distributed over a wide area. We conclude that willow tits adjust territory use to compensate for the inclusion of unsuitable habitat within home ranges, and older sapling areas and pine bogs serve as surrogates for mature forests. However, birds did not enlarge the proportion of forest habitat in their territories with increasing habitat loss. Thus, our data do not suggest a strong effect of fragmentation, but imply that forestry practices reduce suitable wintering habitat and carrying capacity in the area. Thus winter habitat loss may explain the observed population decline of willow tits in Finland during recent decades.     

Scale-specific correlations between habitat heterogeneity and soil fauna diversity along a landscape structure gradient

Habitat heterogeneity contributes to the maintenance of diversity, but the extent that landscape-scale rather than local-scale heterogeneity influences the diversity of soil invertebrates—species with small range sizes—is less clear. Using a Scottish habitat heterogeneity gradient we correlated Collembola and lumbricid worm species richness and abundance with different elements (forest cover, habitat richness and patchiness) and qualities (plant species richness, soil variables) of habitat heterogeneity, at landscape (1 km²) and local (up to 200 m²) scales. Soil fauna assemblages showed considerable turnover in species composition along this habitat heterogeneity gradient. Soil fauna species richness and turnover was greatest in landscapes that were a mosaic of habitats. Soil fauna diversity was hump-shaped along a gradient of forest cover, peaking where there was a mixture of forest and open habitats in the landscape. Landscape-scale habitat richness was positively correlated with lumbricid diversity, while Collembola and lumbricid abundances were negatively and positively related to landscape spatial patchiness. Furthermore, soil fauna diversity was positively correlated with plant diversity, which in turn peaked in the sites that were a mosaic of forest and open habitat patches. There was less evidence that local-scale habitat variables (habitat richness, tree cover, plant species richness, litter cover, soil pH, depth of organic horizon) affected soil fauna diversity: Collembola diversity was independent of all these measures, while lumbricid diversity positively and negatively correlated with vascular plant species richness and tree canopy density. Landscape-scale habitat heterogeneity affects soil diversity regardless of taxon, while the influence of habitat heterogeneity at local scales is dependent on taxon identity, and hence ecological traits, e.g. body size. Landscape-scale habitat heterogeneity by providing different niches and refuges, together with passive dispersal and population patch dynamics, positively contributes to soil faunal diversity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.