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1.
Prospects for biodiversity conservation in the Atlantic Forest: Lessons from aging human-modified landscapes 总被引：1，自引：0，他引：1
Marcelo Tabarelli Antonio Venceslau Aguiar Jean Paul Metzger 《Biological conservation》2010,143(10):2328-2340
Recent global assessments have shown the limited coverage of protected areas across tropical biotas, fuelling a growing interest in the potential conservation services provided by anthropogenic landscapes. Here we examine the geographic distribution of biological diversity in the Atlantic Forest of South America, synthesize the most conspicuous forest biodiversity responses to human disturbances, propose further conservation initiatives for this biota, and offer a range of general insights into the prospects of forest species persistence in human-modified tropical forest landscapes worldwide. At the biome scale, the most extensive pre-Columbian habitats across the Atlantic Forest ranged across elevations below 800 masl, which still concentrate most areas within the major centers of species endemism. Unfortunately, up to 88% of the original forest habitat has been lost, mainly across these low to intermediate elevations, whereas protected areas are clearly skewed towards high elevations above 1200 masl. At the landscape scale, most remaining Atlantic Forest cover is embedded within dynamic agro-mosaics including elements such as small forest fragments, early-to-late secondary forest patches and exotic tree monocultures. In this sort of aging or long-term modified landscapes, habitat fragmentation appears to effectively drive edge-dominated portions of forest fragments towards an early-successional system, greatly limiting the long-term persistence of forest-obligate and forest-dependent species. However, the extent to which forest habitats approach early-successional systems, thereby threatening the bulk of the Atlantic Forest biodiversity, depends on both past and present landscape configuration. Many elements of human-modified landscapes (e.g. patches of early-secondary forests and tree monocultures) may offer excellent conservation opportunities, but they cannot replace the conservation value of protected areas and hitherto unprotected large patches of old-growth forests. Finally, the biodiversity conservation services provided by anthropogenic landscapes across Atlantic Forest and other tropical forest regions can be significantly augmented by coupling biodiversity corridor initiatives with biota-scale attempts to plug existing gaps in the representativeness of protected areas. 相似文献
2.
Investigations to determine stable or source-sink animal population dynamics are challenging and often infeasible for most species due to the time and expense of mark-recapture studies and the challenge of life histories attributes that result in low detectability and low recapture probabilities. Often, managers rely solely on occupancy or relative abundance patterns to assess a species’ sensitivity to environmental changes. Greater insight into population-level responses to environmental change can be gained by consideration of a combination of readily obtainable metrics, including occupancy, relative abundance, demographic structure and body condition. We examined how these metrics can improve our understanding of population-level responses to forest disturbance, using datasets for two exemplar species of terrestrial salamanders resident to the Pacific Northwestern USA. We compared population metrics for the Del Norte salamander (Plethodon elongatus) and the Siskiyou Mountains salamander (Plethodon stormi) across the seral continuum represented by four forest age classes: pre-canopy, young, mature, and old-growth. We compared these data with those collected from reference stands in mature (P. stormi) or old-growth (P. elongatus) forest containing robust populations. P. elongatus was twice as common as P. stormi. Both occupancy and salamander counts were lowest at pre-canopy sites for both species. Although there were numerous P. elongatus detections in young forests, higher proportions of these individuals were juveniles and sub-adults when compared to populations in late-seral forests. We found a negative relationship between the proportion of immature animals and total counts at a site, indicating that the high proportion of young animals in young forest stands is likely due to dispersal of young salamanders from nearby source populations and/or low survival of adult animals in young forests. We also found reduced body condition of P. stormi populations in young forests. Our results suggest that there are costs to populations occupying early seral forests, such as skewed age class structure and reduced body condition that are indicative of sink populations. Consideration of population-level metrics beyond occupancy and relative abundance can provide important insights when assessing a species’ sustainability in managed forest landscapes. 相似文献
3.
Habitat colonization and abandonment affects the distribution of a species in space and time, ultimately influencing the duration of time habitat is used and the total area of habitat occupied in any given year. Both aspects have important implications to long-term conservation planning. The importance of patch isolation and area to colonization-extinction events is well studied, but little information exists on how changing regional landscape structure and population dynamics influences the variability in the timing of patch colonization and abandonment events. We used 26 years of Kirtland’s Warbler (Dendroica kirtlandii) population data taken during a habitat restoration program (1979-2004) across its historical breeding range to examine the influence of patch attributes and temporal large-scale processes, specifically the rate of habitat turnover and fraction of occupied patches, on the year-to-year timing of patch colonization and abandonment since patch origin. We found the timing of patch colonization and abandonment was influenced by patch and large-scale regional factors. In this system, larger patches were typically colonized earlier (i.e., at a younger age) and abandoned later than smaller patches. Isolated patches (i.e., patches farther from another occupied patch) were generally colonized later and abandoned earlier. Patch habitat type affected colonization and abandonment; colonization occurred at similar patch ages between plantation and wildfire areas (9 and 8.5 years, respectively), but plantations were abandoned at earlier ages (13.9 years) than wildfire areas (16.4 years) resulting in shorter use. As the fraction of occupied patches increased, patches were colonized and abandoned at earlier ages. Patches were abandoned at older ages when the influx of new habitat patches was at low and high rates. Our results provide empirical support for the temporal influence of patch dynamics (i.e., patch destruction, creation, and succession) on local colonization and extinction processes that help explain large-scale patterns of habitat occupancy. Results highlight the need for practitioners to consider the timing of habitat restoration as well as total amount and spatial arrangement of habitat to sustain populations. 相似文献
4.
The prevalence of secondary forests is increasing across tropical landscapes, but the effects of these environments on the population dynamics of understory species and on their capacity to regenerate after harvest remains poorly documented. We compare the population dynamics of the understory bromeliad, Aechmea magdalenae, between old-growth and secondary rainforests in Southeast Mexico. A. magdalenae is a non-timber forest product (NTFP), the ramets of which are harvested from wild populations to make forest plantations. The fates of 600 rosettes in the two forest types were monitored over 3 years to build annual transition matrices. Population projections using the matrices show that secondary forest populations have finite rates of growth significantly higher than those of old-growth populations under both ramet-harvest and no-harvest conditions. Life table response experiments indicate that differences in the capacity for re-growth after harvest was due to greater vegetative reproduction of the largest secondary forest rosettes and faster growth of their ramets. For understory NTFP such as A. magdalenae, secondary forests may offer more economic incentive and greater potential for forest conservation than old-growth forests. 相似文献
5.
Functional connectivity is a measure of the interaction of landscape structure and a species’ dispersal ability to determine the degree to which a landscape facilitates movement among patches. Dispersal through an inhospitable matrix requires that a species is willing to enter the matrix and can successfully colonize another habitat patch. Many connectivity indices have been developed which incorporate various attributes of the landscape, but little empirical evidence of the accuracy of these indices is available. We studied the ability of white-footed mice (Peromyscus leucopus), eastern chipmunks (Tamias striatus), and southern flying squirrels (Glaucomys volans) to move through agricultural fields in west-central Indiana. Radio-collared animals were translocated into corridors that either were connected to or unconnected from an associated forest patch to determine their willingness to enter the matrix. Animals also were translocated into fields to determine how motivation to find resources influences movement through the matrix. All species demonstrated a strong motivation to find the forest. Animals were capable of moving through the matrix successfully, however, we were unable to determine whether they would do so willingly. Initial bearing was an important predictor for successfully reaching a forest patch, which has implications for modeling dispersal. Additionally, abiotic variables, such as temperature and precipitation, had a strong effect on latency to move from the release site. Although weather often correlates with seasonal migration, our study emphasizes the importance of weather in influencing short-term decisions on timing of movement. 相似文献
6.
A principal challenge of species conservation is to identify the specific habitats that are essential for long-term persistence or recovery of imperiled species. However, many commonly used approaches to identify important habitats do not provide direct insight into the contribution of those habitats to population persistence. To assess how habitats contribute to overall population viability and characterize their relative importance, a spatially-explicit population viability model was used to integrate a species occurrence model with habitat quality and demographic information to simulate the population dynamics of the Ord’s kangaroo rat (Dipodomys ordii) in Alberta, Canada. Long-term productivity (births-deaths) in each patch was simulated and iterative patch removal experiments were conducted to generate estimates of the relative contribution of habitat types to overall population viability. Our results indicated that natural dune habitats are crucial for population viability, while disturbed/human-created habitats make a minor contribution to population persistence. The results also suggest that the habitats currently available to Ord’s kangaroo rats in Alberta are unlikely to support long-term persistence. Our approach was useful for identifying habitats that did not contribute to population viability. A large proportion of habitat (39%) represented sinks and their removal increased estimated population viability. The integration of population dynamics with habitat quality and occurrence data can be invaluable when assessing critical habitat, particularly in regions with variable habitat quality. Approaches that do not incorporate population dynamics may undermine conservation efforts by under- or over-estimating the value of habitats, erroneously protecting sink habitats, or failing to prioritize key source habitats. 相似文献
7.
The Lower Keys marsh rabbit (LKMR, Sylvilagus palustris hefneri), a marsh rabbit subspecies endemic to the Lower Keys, Florida was protected in 1990, however, populations continue to decline despite recovery efforts. We hypothesized on-going habitat loss and fragmentation due to succession and hardwood encroachment has lead to increased edge, reduced habitat quality, and increased activity by native raccoons (Procyon lotor). These factors reduce the suitability of patches in a later successional state, thus threatening LKMR recovery and metapopulation persistence. We surveyed 150 LKMR patches in 2008, tallying adult and juvenile rabbit pellets, estimating measures of habitat succession and quality (woody and herbaceous ground cover, distribution of herbaceous species) and recording raccoon activity (number of raccoon signs). We calculated patch edge (patch shape index) using ArcGIS. We evaluated the relationship between patch and habitat attributes and LKMR using regression analysis and model selection. We found both adult and juvenile LKMR pellet counts were lower in patches with higher shape indices and higher in patches with greater occurrence of bunchgrasses and forbs. We also found adult LKMR pellet counts were lower in patches with higher raccoon activity. Our results suggest patch edge, habitat succession and quality, and raccoons pose a threat to the persistence and recovery of LKMR populations. Recovery efforts should focus on reducing these trends through habitat management and raccoon removal implemented in carefully controlled experiments with proper monitoring. Measures of patch and habitat attributes important to LKMR should be incorporated into long-term metapopulation monitoring and used to evaluate recovery actions. 相似文献
8.
Drastic erosion in functional attributes of tree assemblages in Atlantic forest fragments of northeastern Brazil 总被引：1，自引：0，他引：1
Bráulio A. Santos Marcondes A. Oliveira Cecília P. Alves-Costa 《Biological conservation》2008,141(1):249-260
The long-term dynamics of plant communities remain poorly understood in isolated tropical forest fragments. Here we test the hypothesis that tropical tree assemblages in both small forest fragments and along forest edges of very large fragments are functionally much more similar to stands of secondary growth (5-65-yr old) than to core primary forest patches. The study was carried out in a severely fragmented landscape of the Brazilian Atlantic forest. Nine functional attributes of tree assemblages were quantified by sampling all trees (DBH ? 10 cm) within 75 plots of 0.1 ha distributed in four forest habitats: small forest fragments (3.4-79.6 ha), forest edges, second-growth patches, and primary forest interior areas within a large forest fragment (3500 ha). These habitats were markedly different in terms of tree species richness, and in the proportion of pioneer, large-seeded, and emergent species. Age of second-growth stands explained between 31.4% and 88.2% of the variation in the functional attributes of tree assemblages in this habitat. As expected, most traits associated with forest edges and small forest fragments fell within the range shown by early (<25-yr old) and intermediate-aged secondary forest stands (25-45-yr old). In contrast to habitat type, tree assemblage attributes were not affected by vegetation type, soil type and the spatial location of plots. An ordination analysis documented a striking floristic drift in edge-affected habitats. Our results suggest that conservation policy guidelines will fail to protect aging, hyper-fragmented landscapes from drastic impoverishment if the remaining forest patches are heavily dominated by edge habitat. 相似文献
9.
This study investigates the dynamics and viability of a marsh fritillary butterfly Euphydryas aurinia metapopulation in a Belgian successional landscape. Based on capture-mark-recapture and winter nest census data, we first estimated demography (survival and recruitment rates, population size, density dependence) and dispersal parameters (emigration rate, effect of patch connectivity on dispersal, mortality during dispersal). Then using RAMAS/GIS platform, we parameterised a population viability analysis (PVA) model with these parameters to simulate the future of this metapopulation under different scenarios.The metapopulation does not seem viable even if natural reforestation is controlled by adequate management. In its present state, the patch system is not able to sustain enough individuals: due to the large temporal fluctuations in demographic parameters, a carrying capacity far higher than currently would be necessary to limit extinction risk to 1%, suggesting the existence of an extinction debt for the species in Belgium. The situation of E. aurinia appears much worse compared to two other fritillary species threatened in Belgium, for which similar PVA are available. It is therefore urgent to increase the carrying capacity of the patch system. How and where it is achieved are of secondary importance for the gain in viability: improvement of habitat quality through restoration, or increase of habitat quantity via enlargement of existing patches and/or creation of new habitat in the matrix. A regime of management based on regular re-opening and maintenance of habitat patches may be the only guarantee of long-term persistence for this critically endangered species in Belgium. 相似文献
10.
Long-term effects of fragmentation and fragment properties on bird species richness in Hawaiian forests 总被引：1，自引：0，他引：1
David J. Flaspohler Christian P. Giardina Patrick Hart Cassie Ka’apu Lyons 《Biological conservation》2010,143(2):280-288
Forest fragmentation is a common disturbance affecting biological diversity, yet the impacts of fragmentation on many forest processes remain poorly understood. Forest restoration is likely to be more successful when it proceeds with an understanding of how native and exotic vertebrates utilize forest patches of different size. We used a system of forest fragments isolated by volcanic activity 153 years ago in Hawaii to examine how long-term fragmentation, as well as fragment size and structural features affect the richness of native and exotic bird species. The total number of bird species increased rapidly with forest fragment size, with most of the native species pool found in patches <3 ha. Smaller fragments were dominated by native bird species with several exotic bird species found only in the largest fragments, suggesting that exotic bird species in this landscape show greater area-sensitivity than native species. We used airborne scanning light detection and ranging (LiDAR) to assess whether fragment area was correlated with estimates of fragment vegetation volume as well as measures of tree height. Fragment area was highly correlated with vegetation volume, maximum tree height, and canopy height heterogeneity, and these variables were strong predictors of bird richness, demonstrating that remote sensing can provide key insights into the relationship between fragment structural attributes and biodiversity indicators. Overall, this work demonstrates the value of conserving small remnant mid-elevation forest patches for native birds in Hawaii. This work also provides insight into how newly created forest patches might be used by native and exotic bird species in Hawaii. 相似文献
11.
Charlotte L. Roy Nielsen Sarah M. Wakamiya Clayton K. Nielsen 《Biological conservation》2008,141(4):1043-1054
Swamp rabbits (Sylvilagus aquaticus) are state-endangered in Indiana, USA, and population decline has been attributed to habitat loss. We conducted pellet surveys as part of a long-term survey effort that has been conducted at approximate 10-year intervals over the last 40 years. We modeled patch occupancy and conducted a spatially-explicit population viability analysis (PVA). Although occupancy of individual patches varied over time, occupancy rate has been constant for the last 30 years, and Indiana swamp rabbits exist as a metapopulation that appears to be stable. Metapopulation dynamics were best characterized as being stationary, but area was an important factor in extinction rates; occupied patches (142 ± 37 ha) were significantly larger (P = 0.01) than unoccupied patches (79 ± 20 ha). We did not find strong support for models with colonization rates as a function of distance to neighboring patches, nor was distance to contiguous patches of habitat significantly different (P = 0.12) for occupied and unoccupied sites. Population viability analysis corroborated our findings based on occupancy modeling, and evaluation of the PVA model using occupancy data for the period 1985–2006 resulted in predictions that nearly matched our field observations (33% observed patch occupancy vs. 25% predicted patch occupancy). Population viability was most sensitive to reductions in survival and fecundity rates, but was otherwise robust to changes in parameters such as initial abundance and carrying capacity. Our findings provide novel insights into a poorly studied member of Sylvilagus and into species metapopulation dynamics at the edge of the range. 相似文献
12.
Population viability analyses (PVA) are frequently employed to develop recovery plans and inform management of endangered species. Translating results from PVA into meaningful management recommendations often depends on an understanding of how population parameters change with environmental conditions as well as population density. The decline of mountain caribou (Rangifer tarandus caribou) in British Columbia, Canada, is believed to be caused by apparent competition with alternative prey species following changes to the forest age structure from timber harvest and wildfire. In addition, populations have been shown to decline at faster rates at low population density. To evaluate the potential effects of habitat change and population density on population persistence, we used stochastic projection models for 10 distinct populations varying in initial size from <10 to approximately 150 females. In an initial model, we used estimates of vital rates based on information sampled from >350 radiocollared caribou between 1984 and 2004. We then compared the results of the initial model to a set of models that evaluated the effects of habitat conditions and population density via their expected relationships to female adult survival. Assuming that vital rates remain constant over a 200-year time frame, only three populations have high probabilities (>0.95) of extinction. When models incorporate the declines in adult female survival know to occur with increasing proportions of young forest and declining population densities, all 10 populations are predicted to decline to extinction within <200 years. Based on our results, we suggest that PVA models that fail to incorporate the effects of changes in vital rates with habitat and population density may lead to overly optimistic assessments of the probability of population persistence in endangered species. 相似文献
13.
14.
To evaluate the sufficiency of US federal critical habitat designations and a proposed conservation plan in promoting the long-term persistence of the endangered plant Astragalus albens, patterns of genetic diversity and landscape connectivity were examined. A. albens harbors substantial genetic variation and shows no evidence of historic bottlenecks, suggesting little risk of extinction due to genetic homogeneity (A = 2.40; P = 0.50) or inbreeding (f = −0.08) within occurrences. Low genetic differentiation among occurrences (θp = 0.01) indicates relatively high gene flow or little genetic drift. The 91 patches of A. albens were connected into a single network at a distance of 2100 m; 94% of patches were <1000 m from at least one other patch. Managing ecological conditions that maintain large population sizes and connectivity among populations throughout the species’ ecological and geographic ranges will most likely conserve existing diversity. Both reserve networks partially accomplish these goals by including most extant occurrences and >89% of the aerial extent of the species, including the largest populations, and capturing all detected alleles. However, both conservation networks fail to conserve occurrences from one portion of the species’ range, possibly speeding loss of unique local adaptations. In addition, connectivity of the whole network is reduced with the 65 patches designated as critical habitat being connected at a distance of 6200 m and the proposed reserve sites being connected at a distance of 9500 m. Although total network connectivity would be reduced, connectivity at scales most relevant to gene flow (e.g., <1000 m) remains sufficiently in tact to provide a relatively promising outlook for species persistence. 相似文献
15.
Plantation clearcuts represent an important habitat for many open-area wildlife species – including conservation-concern species – in landscapes dominated by industrial forests. However, due to the ephemeral nature of clearcuts, species using this type of environment face a “shifting mosaic” in which their ability to successfully relocate to another habitat patch may play a crucial role in the species’ persistence in the landscape. Although several studies have shown a positive effect of patch size on the persistence of open-habitat species, forest clearcutting represents a special case in which, on average, larger patches also tend to be more isolated from each other, likely creating a trade-off between area and isolation effects. We developed an individual-based spatially-explicit model to test the effect of clearcut size (a critical management variable in plantation forestry) on the persistence of generic early-successional wildlife species in a landscape dominated by forest plantations. We simulated a landscape covered with a plantation harvested regularly over a 25-year rotation and different versions of a wildlife population whose habitat was constituted only by 1–4 year-old patches. We observed that when the species could perceive the attributes of the neighboring pixels persistence time was higher at intermediate clearcut sizes agreeing with our prediction. Also, species with a high dispersal capacity were less limited by connectivity and reached their maximum persistence at higher clearcut sizes. Results also showed a positive effect of habitat lifetime on persistence. Our results suggest large clearcuts may be incompatible with the conservation of many early-successional vertebrates that have limited dispersal capacity, unless additional conservation measures, such as the use of corridors or special spatial arrangement of clearcuts, are taken to overcome the lack of connectivity. 相似文献
16.
Thresholds in the long-term responses of breeding birds to forest cover and fragmentation 总被引：1，自引：0，他引：1
Mitigating the effects of habitat loss requires estimating the minimum amount of habitat necessary for the persistence of wildlife populations in a changing landscape. Assessing minimum habitat amounts, however, relies on identifying ecological thresholds in species’ responses to landscape change. Using two repeated state-wide atlases, our objective was to investigate the responses of 25 forest birds to a range of forest cover and fragmentation. Repeat atlases allow for the analysis of four population dynamics including: (1) colonization, (2) persistence, (3) extinction, and (4) absence. Our objective was to test the hypothesis that forest birds demonstrated thresholds in these four basic dynamics to varying amounts of forest cover and fragmentation.We found thresholds to be a common, though not pervasive, characteristic of how forest birds respond to forest cover and pattern. We found that the probability of persistence was positively correlated with forest cover and 22 species demonstrated threshold responses. In addition, 15 of 25 birds demonstrated discrete thresholds in extinction dynamics. The existence of a colonization threshold has received significantly less attention in ecology. We also found that 17 out of 25 species demonstrated thresholds in their colonization response to a greater amount of forest cover. The effects of forest fragmentation, independent of forest amount, were less clear. We found support for incorporating the effects of fragmentation, but this fragmentation effect was found both below and above threshold points. We conclude that incorporating ecological thresholds in environmental planning should be species-specific and focus on populations on the verge of rapid ecological change. 相似文献
17.
Recent studies in population dynamics suggest that landscape processes and habitat quality act at different scales on population abundances, but very few have modelled their simultaneous effects. However, at a time of large declines in natural populations, it is essential to understand such multivariate components. We tested the hypothesis that natural populations of palmate newts (Triturus helveticus) are affected on three scales: breeding patch (pond), habitat complementation (terrestrial cover), and metapopulation structure (density of ponds, surrounding populations). We conducted our survey in 130 ponds from southern France (Larzac) and analysed data with generalized additive models (GAM). Two main novel results emerge from these models: (1) the three landscape scales have significant effects on newt abundance, with more newts in deep, vegetated ponds, devoid of fish and surrounded by wooded areas and inhabited ponds; (2) the quality of the surrounding breeding patches is of primary importance in determining the abundance at core sites in a complex way: high abundances are associated positively with high densities of inhabited ponds, but negatively with the number of surrounding ponds. Deforestation, invasive species and abandonment of ponds all have negative impacts on the persistence of palmate newt populations. Future studies should encompass landscapes at different scales and incorporate the habitat quality in surrounding sites to better understand population dynamics and provide adequate conservation measures. 相似文献
18.
Forest managers require an understanding of how vertebrate species respond and persist within the dynamics of changing forest environments so that management strategies can retain and recruit structural aspects necessary for the persistence of populations. Species-habitat models are often used to understand these relationships and are subsequently used to manage landscapes. We tested several species-habitat models to predict the presence or absence of a range of vertebrate species (n = 55) and to determine the potential of using vertical and horizontal measures of forest structure as a surrogate of species occurrence. We validated models with temporally and spatially independent data. Some of the models had good predictive accuracy that was retained when validated and thus have application in terms of implementation as management tools. Modelling success varied, however, depending on whether plot or stand data were used. Many models included variables related to spatial relationships of structures. Few models were reliable when applied to independent data; therefore, our results indicate that models cannot be assumed to be applicable in different years or applied outside the area where the model was developed, even with similar spatial and temporal contexts. Overall, we did not find robust relationships necessary to guide management targets for retention and recruitment of specific forest structures. Therefore, using these habitat models as surrogates for monitoring species occurrence is limited. Monitoring aspects of habitat should still be included as part of biodiversity monitoring programs because preservation of structures known to be negatively affected by harvesting (e.g., dead wood, large trees, closed canopies, continuous forests) contributes to local and landscape heterogeneity and has been shown to affect species presence in this study and others. 相似文献
19.
Saproxylic Coleoptera are diverse insects that depend on dead wood in some or all of their life stages. In even-aged boreal forest management, remnant habitats left as strips and patches contain most of the dead wood available in managed landscapes and are expected to act as refuges for mature forest species during the regeneration phase. However, use of remnant habitats by the saproxylic fauna has rarely been investigated. Our objective was to characterize the saproxylic beetle assemblages using clearcuts and forest remnants in western Québec, Canada, and to explore the effects of forest remnant stand characteristics on saproxylic beetle assemblages. We sampled both beetle adults and larvae, using Lindgren funnels and snag dissection, in five habitat locations (clearcuts, forest interiors of large patches, edges of large patches, small patches and cut-block separators) from three distinct landscapes. Adult saproxylic beetles (all feeding guilds combined) had significantly higher species richness and catch rates in small patches compared to forest interiors of large patches; the phloeophagous/xylophagous group had significantly higher species richness only. Small patches, cut-block separators and edges of large patches also had the highest snag density and basal area, increasing habitat for many saproxylic beetles. No significant differences in density of saproxylic larvae were found between habitat patches, but snag dissection nevertheless suggests that snags in forest remnants are used by comparable densities of insects. Saproxylic beetles appear to readily use habitat remnants in even-aged managed landscapes suggesting that forest remnants can insure the local persistence of these species, at least in the timeframe investigated in our study. 相似文献
20.
Fragmentation of old-growth forests and greatly reduced amounts of coarse dead wood in managed forests threat the persistence of many saproxylic species in boreal Fennoscandia. Individual old-growth forest remnants may lose species over time as they pay off their extinction debt. We tested this by comparing the observed site occupancy of individual wood-inhabiting fungal species in isolated old-growth stands (i.e. woodland key habitats; WKHs) with statistical predictions of their occupancy assuming potential extinction debt had already been paid off. The occupancy of species was analysed in two sets of WKHs differing in time since isolation (i.e. recent and old isolates).Few species occurred more frequently than expected in WKHs. However, patterns across species and across all WKHs masked important differences among species in their risk of facing future extinction. The site occupancy decreased significantly between recent and old isolates for a group of annual, red-listed specialist fungal species, suggesting that an extinction debt in WKHs may exist among specific species confined to coarse dead wood and old-growth forest habitat. Generalist species that also occur in the surrounding matrix showed no negative trends, or actually increased in site occupancy, making future extinctions less likely. Thus, continuing loss of threatened species are likely if not preservation of WKHs are combined with other conservation efforts in managed forest landscapes. Natural forest landscapes may serve as important references when aiming to identify species in risk of future extinction but more detailed knowledge about the biology of the most vulnerable species is also required. 相似文献