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1.
We tested the effects of increased landscape corridor width and corridor presence on the population dynamics and home range use of the meadow vole (Microtus pennsylvanicus) within a small-scale fragmented landscape. Our objective was to observe how populations behaved in patchy landscapes where the animals home range exceeded or equaled patch size. We used a small-scale replicated experiment consisting of three sets of two patches each, unconnected or interconnected by 1-m or 5-m wide-corridors, established in an old-field community (S.W. Ohio). Control (0-m) treatments supported significantly lower vole densities than either corridor treatment. Females were the dominant resident sex establishing smaller home ranges (<150m2) than males (>450m2). Significantly more male voles dispersed between patches with corridors than between patches without corridors. However, no difference was observed regarding the number of male voles dispersing between patches connected by corridors when compared to the number dispersing across treatments. Dispersal between connected patches was restricted to corridors based on tracking tube data. Corridor presence was more important than corridor width regarding the movement of male voles within their home range. 相似文献
2.
The storm that struck France on december 26th and 28th 1999 felled 140 million m3 of timber and had a high economic, social and landscape impact. This event offered the opportunity to study large-scale patterns in populations of forest insect pests that would benefit from the abundant breeding material. A large-scale survey was carried out in France in 2000 to sample the most frequently observed species developing on spruce (Ips typographus, Pityogene schalcographus) and pine (Tomicus piniperda, Ips sexdentatus) in 898 locations distributed throughout wind-damaged areas. The local abundance of each species scored on a 0 to 5 scale was analysed using geostatistical estimators to explore the extent and intensity of spatial autocorrelation, and was related to site, stand, and neighbourhood landscape metrics of the forest cover (in particular the interconnection with broadleaf forest patches) found within dispersal distance. All species but I. sexdentatus, which was much less abundant, displayed large-scale spatial dependence and regional variations in abundance. Lower infestation levels per tree (windfalls and standing trees) were observed in stands with a high proportion of wind-damaged trees, which was interpreted as the result of beetles distributing themselves among the available breeding material. More infestations were observed in wind-broken trees as compared to wind-felled trees. More importantly, populations showed significant relationships with the structure of coniferous stands (in particular with the number of coniferous patches). T. piniperda population levels were negatively correlated to the amount of coniferous edge shared with broadleaf forest patches, possibly because of the disruptive effect of non-host volatiles on host-finding processes at the landscape-scale. The differences observed between species regarding patterns and relationships to site, stand, and forest cover characteristics are discussed in relation to the ecological characteristics of each species. 相似文献
3.
To assess corridor effects on movement in Peromyscus polionotus (old-field mice), we used a set of three experimental landscapes that contained multiple patches (1.64 ha) of usable, open habitat embedded in a loblolly pine (Pinus taeda) forest matrix. Some patches were connected by corridors and others were isolated (unconnected). We introduced mice to nest boxes in experimental patches and followed them through the landscapes via trapping. We found weak evidence that the presence of corridors decreased the probability that P. polionotus (particularly females) would disperse or disappear from a patch. In the process of live trapping the patches, we also encountered `feral' P. polionotus, Sigmodon hispidus (cotton rats), and Peromyscus gossypinus (cotton mice). The average number of feral animals did not differ between isolated and connected patches. This suggests that corridors do not act as drift fences that `sieve' individuals out of the matrix and into the patches. However, more male than female P. polionotus and S. hispidus were trapped in isolated patches. This intersexual difference did not exist in connected patches. 相似文献
4.
In fragmented landscapes, plant species persistence depends on functional connectivity in terms of pollen flow to maintain
genetic diversity within populations, and seed dispersal to re-colonize habitat patches following local extinction. Connectivity
in plants is commonly modeled as a function of the physical distance between patches, without testing alternative dispersal
vectors. In addition, pre- and post-dispersal processes such as seed production and establishment are likely to affect patch
colonization rates. Here, we test alternative models of potential functional connectivity with different assumptions on source
patch effects (patch area and species occupancy) and dispersal (relating to distance among patches, matrix composition, and
sheep grazing routes) against empirical patch colonization rates at the community level (actual functional connectivity),
accounting for post-dispersal effects in terms of structural elements providing regeneration niches for establishment. Our
analyses are based on two surveys in 1989 and in 2009 of 48 habitat specialist plants in 62 previously abandoned calcareous
grassland patches in the Southern Franconian Alb in Bavaria, Germany. The best connectivity model S
i
, as identified by multi-model inference, combined distance along sheep grazing routes including consistently and intermittently
grazed patches with mean species occupancy in 1989 as a proxy for pre-dispersal effects. Community-level patch colonization
rates depended to equal degrees on connectivity and post-dispersal process. Our study highlights that actual functional connectivity
of calcareous grassland communities cannot be approximated by structural connectivity based on physical distance alone, and
modeling of functional connectivity needs to consider pre- and post-dispersal processes. 相似文献
5.
Roland F. Graf Stephanie Kramer-Schadt Néstor Fernández Volker Grimm 《Landscape Ecology》2007,22(6):853-866
Inter-patch connectivity can be strongly influenced by topography and matrix heterogeneity, particularly when dealing with
species with high cognitive abilities. To estimate dispersal in such systems, simulation models need to incorporate a behavioral
component of matrix effects to result in more realistic connectivity measures. Inter-patch dispersal is important for the
persistence of capercaillie (Tetrao urogallus) in central Europe, where this endangered grouse species lives in patchy populations embedded in a mountainous landscape.
We simulated capercaillie movements with an individual-based, spatially explicit dispersal model (IBM) and compared the resulting
connectivity measure with distance and an expert estimation. We used a landscape comprising discrete habitat patches, temporary
habitat, non-habitat forests, and non-habitat open land. First, we assumed that dispersing individuals have perfect knowledge
of habitat cells within the perceptual range (null model). Then, we included constraints to perception and accessibility,
i.e., mountain chains, open area and valleys (three sub-models). In a full model, all sub-models were included at once. Correlations
between the different connectivity measures were high (Spearman’s ρ > 0.7) and connectivity based on the full IBM was closer
to expert estimation than distance. For selected cases, simple distance differed strongly from the full IBM measure and the
expert estimation. Connectivity based on the IBM was strongly sensitive to the size of perceptual range with higher sensitivity
for the null model compared to the full model that included context dependent perceptual ranges. Our heuristic approach is
adequate for simulating movements of species with high cognitive abilities in strongly structured landscapes that influence
perception and permeability. 相似文献
6.
Walker Nathan J. Schaffer-Smith Danica Swenson Jennifer J. Urban Dean L. 《Landscape Ecology》2019,34(8):1859-1875
Context
Graph-theoretic evaluations of habitat connectivity often rely upon least-cost path analyses to evaluate connectedness of habitat patches, based on an underlying cost surface. We present two improvements upon these methods.
ObjectivesAs a case study to test these methods, we evaluated habitat connectivity for the endangered San Martin titi monkey (Plecturocebus oenanthe) in north-central Peru, to prioritize habitat patches for conservation.
MethodsFirst, rather than using a single least-cost path between habitat patches, we analyzed multigraphs made up of multiple low-cost paths. This allows us to differentiate between patches connected through a single narrow corridor, and patches connected by a wide swath of traversable land. We evaluate potential movement pathways by iteratively removing paths and recomputing connectivity metrics. Second, instead of performing a sensitivity analysis by varying costs uniformly across the landscape, we generated landscapes with spatially varying costs.
ResultsThis approach produced a more informative assessment of connectivity than standard graph analyses. Of the 4340 habitat patches considered across the landscape, we identified the most important 100, those frequently ranked highly through repeated network modifications, for multiple metrics and cost surfaces.
ConclusionsThese methods represent a novel approach for assessing connectivity, better accounting for spatial configurations of habitat patches and uncertainty in cost surfaces. The ability to identify habitat patches with more possible routes to other patches is of interest for resiliency planning and prioritization in the face of continued habitat loss and climate change. These methods should be broadly applicable to conservation planning for other wildlife species.
相似文献7.
Cultural landscapes of Germany are patch-corridor-matrix mosaics for an invasive megaforb 总被引：1，自引：0，他引：1
Predicting the vulnerability of landscapes to both the initial colonisation and the subsequent spread of invasive species
remains a major challenge. The aim of this study was to assess the relative importance of sub-patch level factors and landscape
factors for the invasion of the megaforb Heracleum mantegazzianum. In particular, we tested which factors affect the presence in suitable habitat patches and the cover-percentage within invaded
patches. For this purpose, we used standard (logistic) regression modelling techniques. The regression analyses were based
on inventories of suitable habitat patches in 20 study areas (each 1 km2) in cultural landscapes of Germany. The cover percentage in invaded patches was independent from landscape factors, except
for patch shape, and even unsatisfactorily explained by sub-patch level factors included in the analysis (R
2 = 0.19). In contrast, presence of H. mantegazzianum was affected by both local and landscape factors. Woody habitat structure decreased the occurrence probability, whereas vicinity
to transport corridors (rivers, roads), high habitat connectivity, patch size and perimeter-area ratio of habitat patches
had positive effects. The significance of corridors and habitat connectivity shows that dispersal of H. mantegazzianum through the landscape matrix is limited. We conclude that cultural landscapes of Germany function as patch-corridor-matrix
mosaics for the spread of H. mantegazzianum. Our results highlight the importance of landscape structure and habitat configuration for invasive spread. Furthermore,
this study shows that both local and landscape factors should be incorporated into spatially explicit models to predict spatiotemporal
dynamics and equilibrium stages of plant invasions. 相似文献
8.
The understanding and prediction of the responses of animal populations to habitat fragmentation is a central issue in applied
ecology. The identification of habitat variables associated to patch occupancy is particularly important when habitat quality
is affected by human activities. Here, we analyze the influence of patch and landscape characteristics on patch occupancy
by the subterranean herbivorous rodent Ctenomys porteousi. Patch occupancy was monitored in a network of 63 habitat patches identified by satellite imagery analysis which extends
along almost the whole distributional range for C. porteousi. Suitable habitat for the occurrence of C. porteousi is highly fragmented and represents <10% of the total area in its distributional range. The distribution of C. porteousi in the patch network is affected not only by characteristics of the habitat patches, but also by those of the surrounding
landscape matrix. Significant differences between occupied and empty patches were found in several environmental variables.
Overall, occupied patches were larger, less vegetated, more connected, and had larger neighbor patches than empty patches.
A stepwise procedure on a generalized linear model selected four habitat variables that explain patch occupancy in C. porteousi; it included the effects of habitat quality in the matrix surrounding the patch, average vegetation cover in the patch, minimum
vegetation cover in the matrix surrounding the patch, and the area of the nearest neighbor patch. These results indicate that
patch occupancy in C. porteousi is strongly influenced by the availability and quality of habitat both in the patch and in the surrounding landscape matrix. 相似文献
9.
Corridors are predicted to benefit populations in patchy habitats bypromoting movement, which should increase population densities, gene flow, andrecolonization of extinct patch populations. However, few investigators haveconsidered use of the total landscape, particularly the possibility ofinterpatch movement through matrix habitat, by small mammals. This studycompares home range sizes of 3 species of small mammals, the cotton mouse(Peromyscus gossypinus), old-field mouse (P.polionotus) and cotton rat (Sigmodon hispidus)between patches with and without corridors. The study site was in S. Carolina,USA. Corridor presence did not have astatistically significant influence on average home range size. Habitatspecialization and sex influenced the probability of an individual movingbetween 2 patches without corridors. The results of this study suggest thatsmall mammals may be more capable of interpatch movement without corridors thanis frequently assumed.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
10.
Identification of functional corridors with movement characteristics of brown bears on the Kenai Peninsula,Alaska 总被引：2，自引：1，他引：2
Tabitha A. Graves Sean Farley Michael I. Goldstein Christopher Servheen 《Landscape Ecology》2007,22(5):765-772
We identified primary habitat and functional corridors across a landscape using Global Positioning System (GPS) collar locations
of brown bears (Ursus arctos). After deriving density, speed, and angular deviation of movement, we classified landscape function for a group of animals
with a cluster analysis. We described areas with high amounts of sinuous movement as primary habitat patches and areas with
high amounts of very directional, fast movement as highly functional bear corridors. The time between bear locations and scale
of analysis influenced the number and size of corridors identified. Bear locations should be collected at intervals ≤6 h to
correctly identify travel corridors. Our corridor identification technique will help managers move beyond the theoretical
discussion of corridors and linkage zones to active management of landscape features that will preserve connectivity. 相似文献
11.
Eric A. Treml Patrick N. Halpin Dean L. Urban Lincoln F. Pratson 《Landscape Ecology》2008,23(1):19-36
The dispersal of individuals among marine populations is of great importance to metapopulation dynamics, population persistence, and species expansion. Understanding this connectivity between distant populations is key to their effective conservation and management. For many marine species, population connectivity is determined largely by ocean currents transporting larvae and juveniles between distant patches of suitable habitat. Recent work has focused on the biophysics of marine larval dispersal and its importance to population dynamics, although few studies have evaluated the spatial and temporal patterns of this potential dispersal. Here, we show how an Eulerian advection–diffusion approach can be used to model the dispersal of coral larvae between reefs throughout the Tropical Pacific. We illustrate how this connectivity can be analyzed using graph theory—an effective approach for exploring patterns in spatial connections, as well as for determining the importance of each site and pathway to local and regional connectivity. Results indicate that the scale (average distance) of dispersal in the Pacific is on the order of 50–150 km, consistent with recent studies in the Caribbean (Cowen, et al. 2006). Patterns in the dispersal graphs highlight pathways for larval dispersal along major ocean currents and through island chains. A series of critical island ‘stepping stones’ are discovered providing potential pathways across the equatorial currents and connecting distant island groups. Patterns in these dispersal graphs highlight possible pathways for species expansions, reveal connected upstream/downstream populations, and suggest areas that might be prioritized for marine conservation efforts. 相似文献
12.
Fine-scale landscape change can alter dispersal patterns of animals, thus influencing connectivity or gene flow within a population.
Furthermore, dispersal patterns of different species may be influenced by the landscape in varying ways. Our research first
aimed to examine whether the spatial genetic structure within populations of closely related bird species differs in response
to the same landscape. Second, we examined whether individual-level movement characteristics are a mechanistic driver of these
differences. We generated a priori predictions of how landscape features will influence dispersal (particularly the response
of individuals to habitat boundaries both natural and human-induced) based on a movement model developed by Fahrig (Funct
Ecol 21:1003–1015, 2007). This model allowed us to predict genetic relatedness patterns in populations of two passerine bird species with different
life-history traits from Queensland, Australia (yellow-throated scrubwren Sericornis citreogularis, a habitat specialist; white-browed scrubwren Sericornis frontalis, a habitat generalist). We quantified our predictions using cost-distance modelling and compared these to observed pairwise
genetic distances (a
r
) between individuals as calculated from microsatellite markers. Mantel tests showed that our a priori models correlated with
genetic distance. Euclidean distance was most closely correlated to genetic distance for the generalist species (r = 0.093, P = 0.002), and landscape models that included the avoidance of unsuitable habitat were best for the specialist species (r = 0.107, P = 0.001). Our study showed that predictable movement characteristics may be the mechanism driving differences in genetic
relatedness patterns within populations of different bird species. 相似文献
13.
Small mammals in heterogeneous environments have been found to disperse along corridors connecting habitat patches. Corridors may have different survivability values depending on their size and the degree of cover they provide. This deterministic model tests the effects of varying corridor quality on the demographics of a metapopulation of Peromyscus leucopus. Two types of corridors are defined based on the probability of survival during a dispersal event. Results indicate that mortality during movement through corridors influences metapopulation demographics. We found that:
- Any connection between two isolated patches is better than no connection at all in terms of persistence and population size at equilibrium.
- Metapopulations with exclusively high quality corridors between patches have a larger population size at equilibrium than do those with one or more low quality corridors.
- Increasing the number of high quality corridors between patches has a positive effect on the size of the metapopulation while increasing the number of low quality corridors has a negative effect.
- The addition to a metapopulation of a patch connected by low quality corridors has a negative effect on the metapopulation size. This suggest the need for caution in planning corridors in a managed landscape.
- There is no relationship between the number of corridors and the metapopulation size at equilibrium when the number of connected patches is held constant.
- Geometrically isolated patches connected by low quality corridors are most vulnerable to local extinctions.
14.
The distribution of the northern brown bandicoot (Isoodon macrourus), a medium-sized ground-dwelling marsupial, was examined in habitat fragments within the urban landscape of the city of Brisbane,
Australia. From surveys conducted in 68 fragments, bandicoots were found to be present in 33 (49%) despite widespread habitat
loss and fragmentation. Logistic regression analysis revealed that of 13 measured independent variables, functional connectivity
was the only factor that significantly predicted the presence of bandicoots within fragments, with connectivity positively
correlated with the likelihood of occupation. Functional connectivity was equated to the likelihood of bandicoot immigration
into the focal fragment from the nearest occupied fragment, based on the estimated resistance to movement offered by the intervening
matrix. Within Brisbane, riparian habitat fragments typically have a relatively high level of functional connectivity, as
thin strips of vegetation fringing waterways serve as corridors between larger riparian areas and facilitate the movement
of bandicoots between patches. Analyses based on the Akaike Information Criterion revealed that the optimal model based on
landscape context variables was convincingly better supported by the data than the optimal model produced from fragment characteristics.
However, it is important to examine both internal attributes of habitat fragments and external features of the surrounding
landscape when modelling the distribution of ground-dwelling fauna in urban environments, or other landscapes with a highly
variable matrix. As urban centres throughout the world expand, it is crucial that the ecology of local wildlife be considered
to ensure functional connection is maintained between habitat patches, especially for the conservation of species that are
highly susceptible to fragmentation. 相似文献
15.
T. Basaki M. Mardi M. Jafarkhani Kermani S.M. Pirseyedi M.R. Ghaffari A. Haghnazari P. Salehi Shanjani P. Koobaz 《Scientia Horticulturae》2009,120(4):538-543
The genetic diversity among 128 Iranian Rosa persica (R. persica) accessions in the different populations was analyzed. Amplified fragment length polymorphisms (AFLP) technique was used to produce 171 polymorphic fragments. The number of polymorphic loci ranged from 101 to 147 and the polymorphism information content (PIC) varied from 0.289 to 0.073, with an average of 0.16. This shows extreme variability and genetic diversity among the studied R. persica populations. An indirect estimate of the number of migrants per generation (Nm = 0.376) indicated that gene flow was relatively low among populations of the species. Cluster analysis using the UPGMA method grouped all accessions into six clusters. The results did not show relative agreement with the genotypes’ region of origin. Based on an analysis of molecular variance, 48% of the genetic variation of R. persica was within population and 52% was among populations. The present analysis revealed that Iranian R. persica genotypes are highly variable and genetically distinct from their origins. The apparent unique nature of the R. persica genotypes revealed by our results supports the case for the implementation of more intense characterization and conservation strategies, and provides useful information to address breeding programmes and germplasm resource management in Rosa spp. 相似文献
16.
Individual movement is a key process affecting the distribution of animals in heterogeneous landscapes. For specialist species in patchy habitat, a central issue is how dispersal distances are related to landscape structure. We compared dispersal distances for cactus bugs (Chelinidea vittiger) on two naturally fragmented landscapes (≤ 4% suitable habitat) with different matrix structures (i.e., vegetation height of nonsuitable habitat between suitable patches). Using mark-release-recapture studies, we determined that most transfers between cactus patches occurred during the mating season. Dispersal distances were reduced by > 50% on the landscape that had reduced structural connectivity due to relatively high matrix structure and low patch density. An experiment with detailed movement pathways demonstrated that greater matrix structure decreased mean step lengths, reduced directionality, and thus decreased net displacement by > 60%. However, habitat edges between two matrix elements that differed substantially in resistance to movement were completely permeable. Therefore, the difference in distributions of dispersal distances between the two landscapes mainly reflected the average resistance of matrix habitat and not the level of matrix heterogeneity per se. Our study highlights the merits of combining estimates of dispersal distances with insights on mechanisms from detailed movement pathways, and emphasizes the difficulty of treating dispersal distances of species as fixed traits independent of landscape structure. 相似文献
17.
Treml Eric A. Halpin Patrick N. Urban Dean L. Pratson Lincoln F. 《Landscape Ecology》2007,23(1):19-36
The dispersal of individuals among marine populations is of great importance to metapopulation dynamics, population persistence, and species expansion. Understanding this connectivity between distant populations is key to their effective conservation and management. For many marine species, population connectivity is determined largely by ocean currents transporting larvae and juveniles between distant patches of suitable habitat. Recent work has focused on the biophysics of marine larval dispersal and its importance to population dynamics, although few studies have evaluated the spatial and temporal patterns of this potential dispersal. Here, we show how an Eulerian advection–diffusion approach can be used to model the dispersal of coral larvae between reefs throughout the Tropical Pacific. We illustrate how this connectivity can be analyzed using graph theory—an effective approach for exploring patterns in spatial connections, as well as for determining the importance of each site and pathway to local and regional connectivity. Results indicate that the scale (average distance) of dispersal in the Pacific is on the order of 50–150 km, consistent with recent studies in the Caribbean (Cowen, et al. 2006). Patterns in the dispersal graphs highlight pathways for larval dispersal along major ocean currents and through island chains. A series of critical island ‘stepping stones’ are discovered providing potential pathways across the equatorial currents and connecting distant island groups. Patterns in these dispersal graphs highlight possible pathways for species expansions, reveal connected upstream/downstream populations, and suggest areas that might be prioritized for marine conservation efforts.
相似文献18.
Landscape connectivity can have profound consequences for distribution and persistence of populations and metapopulations.
Evaluating functional connectivity of a landscape for a species requires a measure of dispersal rates through landscape elements
at a spatial scale sufficient to encompass movement capabilities of individuals over the entire landscape. We evaluated functional
connectivity for a rock-dwelling mammal, the mountain vizcacha (Lagidium viscacia), in northern Patagonia. Because of the strict association of mountain vizcachas with rocks, we hypothesized that connectivity
for this species would be influenced by geology. We used molecular genetic estimates of gene flow to test spatially explicit
models of connectivity created with GIS cost-distance analysis of landscape resistance to movement. We analyzed the spatial
arrangement of cliffs with join counts and local k-function analyses. We did not capture and genotype individuals, but sampled
at the population level through non-invasive collection of feces of mountain vizcachas. The model of landscape connectivity
for mountain vizcachas based on geology was corroborated by the pattern of genetic structure, supporting the hypothesis that
functional connectivity for mountain vizcachas is influenced by geology, particularly by the distribution of appropriate volcanic
rocks. Analysis of spatial arrangement of cliffs indicated that occupied cliffs are clustered and confirmed that rivers act
as barriers to dispersal for mountain vizcachas. Our methods could be used, within certain constraints, to study functional
landscape connectivity in other organisms, and may be particularly useful for cryptic or endangered species, or those that
are difficult or expensive to capture. 相似文献
19.
Fine-scale effects of habitat loss and fragmentation despite large-scale gene flow for some regionally declining woodland bird species 总被引：3，自引：3，他引：0
Katherine A. Harrisson Alexandra Pavlova J. Nevil Amos Naoko Takeuchi Alan Lill James Q. Radford Paul Sunnucks 《Landscape Ecology》2012,27(6):813-827
Habitat loss and associated fragmentation effects are well-recognised threats to biodiversity. Loss of functional connectivity (mobility, gene flow and demographic continuity) could result in population decline in altered habitat, because smaller, isolated populations are more vulnerable to extinction. We tested whether substantial habitat reduction plus fragmentation is associated with reduced gene flow in three ??decliner?? woodland-dependent bird species (eastern yellow robin, weebill and spotted pardalote) identified in earlier work to have declined disproportionately in heavily fragmented landscapes in the Box-Ironbark forest region in north-central Victoria, Australia. For these three decliners, and one ??tolerant?? species (striated pardalote), we compared patterns of genetic diversity, relatedness, effective population size, sex-ratios and genic (allele frequency) differentiation among landscapes of different total tree cover, identified population subdivision at the regional scale, and explored fine-scale genotypic (individual-based genetic signature) structure. Unexpectedly high genetic connectivity across the study region was detected for ??decliner?? and ??tolerant?? species. Power analysis simulations suggest that moderate reductions in gene flow should have been detectable. However, there was evidence of local negative effects of reduced habitat extent and structural connectivity: slightly lower effective population sizes, lower genetic diversity, higher within-site relatedness and altered sex-ratios (for weebill and eastern yellow robin) in 10 × 10?km ??landscapes?? with low vegetation cover. We conclude that reduced structural connectivity in the Box-Ironbark ecosystem may still allow sufficient gene flow to avoid the harmful effects of inbreeding in our study species. Although there may still be negative consequences of fragmentation for demographic connectivity, the high genetic connectivity of mobile bird species in this system suggests that reconnecting isolated habitat patches may be less important than increasing habitat extent and/or quality if these need to be traded off. 相似文献
20.
Elk, fire and climate have influenced aspen populations in the Rocky Mountains, but mostly subjective studies have characterized
these factors. A broad-scale perspective may shed new light on the status of aspen in the region. We collected field measurements
of aspen (Populus tremuloides Michx.) patches encountered within 36 randomly located belt transects in 340 km2 of Rocky Mountain National Park, Colorado, to quantify the aspen population. Aspen covered 5.6% of the area in the transects,
much more than expected based on previously collected remotely sensed data. The distribution and structure of aspen patches
were highly heterogeneous throughout the study area. Of the 123 aspen patches encountered in the 238 ha surveyed, all but
one showed signs of elk browsing or had conifer species mixed with the aspen stems. No significant difference occurred in
aspen basal area, density, regeneration, browsing of regeneration and patch size, between areas of concentrated elk use (elk
winter range) and areas of dispersed elk use (elk summer range). Two-thirds of the aspen patches were mixed with conifer species.
We concluded that the population of aspen in our study area is highly variable in structure and that, at a landscape-scale,
evidence of elk browsing is widespread but evidence of aspen decline is not.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献