Components Of Landscape Structure Research Articles

Effects of landscape structure and land use on turtle communities across the eastern United States

Landscape context is integral to population ecology, affecting a range of life history parameters, yet very little is known about how landscape structure influences many taxa. We sampled wetlands at 531 sites across 16 states in the eastern U.S. to examine the influence of landscape heterogeneity and anthropogenic land use on the relative abundance of freshwater turtles, one of the most endangered vertebrate clades in the world. Specifically, we aimed to understand how two components of landscape structure — compositional heterogeneity (wetland diversity) and configurational heterogeneity (wetland aggregation) — influence turtles with varying life history traits. Our results suggest that wetland configuration can modulate the relationship between relative abundance and anthropogenic land use. For example, spotted turtle (Clemmys guttata) was negatively associated with hay/pasture cover when wetlands were less aggregated, but this relationship subsided as aggregation increased. Notably, the way wetland aggregation modulated land use relationships varied across species. These results suggest that some anthropogenic cover types are not strictly positive or negative for certain species, but are instead context-dependent. Relative abundance also generally increased with higher wetland diversity, indicating the potential importance of landscape supplementation for turtles. We report a range of responses to roads that did not strictly correspond with well-established predictions related to body size and terrestrial activity patterns, including positive associations for certain species. Overall, our study supports the use of context-driven approaches to land use-related conservation and management decisions rather than blanket prescriptions, and further emphasizes that effective conservation of freshwater systems requires a landscape-level perspective.

The relative effects of forest amount, forest configuration, and urban matrix quality on forest breeding birds

Urbanization modifies landscape structure in three major ways that impact avian diversity in remnant habitat: habitat amount is reduced and habitat configuration and matrix quality are altered. The relative effects of these three components of landscape structure are relatively well-studied in agricultural landscapes, but little is known about the relative effect of urban matrix quality. We addressed this gap by investigating the relative effects of forest amount, forest configuration, and matrix quality, indicated by degree of urbanization and agriculture amount, on the diversity of three guilds of forest birds using data from 13,763 point counts from Pennsylvania, USA. Forest amount had the largest independent effect on forest bird diversity, followed by matrix quality, then forest configuration. In particular, urbanization had strong negative effects on the relative abundance and species evenness of all forest birds and the relative abundance of forest generalist birds. To our knowledge, these are the first results of the effect of urban matrix quality on forest bird relative abundance and species evenness independent of forest amount and forest configuration. Our results imply that conservation practitioners in human-modified landscapes prioritize maximizing forest amount, then reducing the effects of disturbances originating in the matrix, and then preserving large, spatially-dispersed forest patches to most effectively conserve forest birds.

Landscape composition is more important than landscape configuration for phyllostomid bat assemblages in a fragmented biodiversity hotspot

Human-modified landscapes are composed of different types of land covers in differing proportions (landscape composition), and each with differing spatial physiognomy (landscape configuration). Unfortunately, the information on the relative impact of these two components of landscape structure on biological assemblages is scarce, but urgently needed to improve conservation strategies. We assessed the relative influence of the composition (landscape forest cover and matrix composition) and configuration (degree of forest fragmentation and forest edge density) of 100-ha and 500-ha landscapes on the abundance, diversity, and evenness of phyllostomid bat assemblages in the Lacandona rainforest, Mexico. We assessed the complete bat assemblage and frugivorous bats separately, and we grouped frugivores into understory foragers and canopy foragers. Landscape forest cover was the main predictor of the complete bat assemblage, positively affecting species diversity, particularly the number of rare species. Thus, community evenness decreased in landscapes with higher forest cover. Although weaker, species diversity was positively related to fragmentation and negatively associated with edge density. Landscape composition also was relatively more important than configuration for frugivores. The number of common and dominant frugivorous species and the abundance of understory frugivores increased in landscapes with lower forest cover and dominated by secondary forests in the matrix. The abundance of canopy frugivores showed the opposite response. Thus, to preserve bat assemblages and their important functional roles, conservation initiatives should prioritize a reduction in deforestation and the increase of secondary forests in the matrix. Maintaining all remaining forest patches is needed to favor landscape complementation and supplementation dynamics.

Influence of landscape structure and stand age on species density and biomass of a tropical dry forest across spatial scales

Three central related issues in ecology are to identify spatial variation of ecological processes, to understand the relative influence of environmental and spatial variables, and to investigate the response of environmental variables at different spatial scales. These issues are particularly important for tropical dry forests, which have been comparatively less studied and are more threatened than other terrestrial ecosystems. This study aims to characterize relationships between community structure and landscape configuration and habitat type (stand age) considering different spatial scales for a tropical dry forest in Yucatan. Species density and above ground biomass were calculated from 276 sampling sites, while land cover classes were obtained from multi-spectral classification of a Spot 5 satellite imagery. Species density and biomass were related to stand age, landscape metrics of patch types (area, edge, shape, similarity and contrast) and principal coordinate of neighbor matrices (PCNM) variables using regression analysis. PCNM analysis was performed to interpret results in terms of spatial scales as well as to decompose variation into spatial, stand age and landscape structure components. Stand age was the most important variable for biomass, whereas landscape structure and spatial dependence had a comparable or even stronger influence on species density than stand age. At the very broad scale (8,000–10,500 m), stand age contributed most to biomass and landscape structure to species density. At the broad scale (2,000–8,000 m), stand age was the most important variable predicting both species density and biomass. Our results shed light on which landscape configurations could enhance plant diversity and above ground biomass.

Landscape Connectivity and Population Distributions in Heterogeneous Environments

Landscape connectivity refers to the functional relationship among habitat patches, owing to the spatial contagion of habitat and the movement responses of organisms to landscape structure. Heterogeneous landscapes provide a particular challenge for modelling population-level responses to habitat fragmentation, because individuals may be utilizing multiple habitats to varying degrees across the landscape. We apply neutral landscape models to understand how species' habitat affinities interacted with landscape structure (i.e., habitat abundance, distribution, and quality as measured by carrying capacity) to affect the redistribution of individuals. Two types of neutral models are presented: random maps, in which the distribution of habitat is spatially independent, and fractal maps, in which habitat exhibits an intermediate level of spatial dependence. The neutral landscapes comprised varying proportions of three habitat types, for which species exhibited a preference gradient (high, medium, low). We performed a series of simulation experiments as a factorial design of parameter states to tease apart the underlying factors responsible for population distributional patterns (random vs clumped) in spatially complex mosaics. Landscape connectivity is a threshold phenomenon, in which even a minimal loss of habitat near the critical threshold (p c ) is likely to disconnect the landscape, and which may have consequences for population distributions. The exact value of p c depends upon the spatial arrangement of habitat; fractal landscapes exhibited connectivity across a greater range of habitat abundance (p) than random maps (fractal p c = 0.29-0.50. random p c = 0.59). Although the spatial arrangement of habitat (random vs fractal) was the most important determinant of population distributional patterns, different landscape factors were important in structuring populations in the two types of maps. The relative abundance of habitat had the greatest effect on populations in random landscapes, whereas scale-dependent patterns were evident in fractal landscapes. At fine scales, population dispersion was determined by habitat abundance in both random and fractal maps, although populations were more aggregated (as measured by Morisita's Index, l m ) at this scale in random landscapes. But at coarse scales on fractal maps, population distribution was primarily influenced by species' habitat affinities. Assessment of the independent effects of habitat affinity and habitat carrying capacity on population distributions revealed that the differential interaction of species with landscape structure (i.e., different residence probabilities in each habitat type) was the primary determinant of distributional patterns. Neutral landscape models thus provide a useful tool for determining the relative importance of various components of landscape structure that affect population distributions.

Effects of Settlement and Fire Suppression on Landscape Structure

Natural landscapes subject to disturbances have a patchy structure that is important to many species living in these landscapes. This structure may be modified when the disturbance regime is altered by either climatic change or human influences (e.g., fire suppression), yet little is known about how this structure will change. I used a GIS (geographic information system)—based spatial model and data on historical changes in fire sizes and intervals to simulate the effects of settlement and fire suppression on the structure of the landscape in the Boundary Waters Canoe Area, Minnesota. I used seven measures to assess change in landscape structure. Settlement and fire suppression altered some but not all components of landscape structure. Settlement produced an immediate significant effect on some measures (age, shape, Shannon diversity, richness, and angular second moment), but no effect on other measures (size, fractal dimension). In contrast, suppression produced an immediate response in fewer measures (shape, Shannon diversity, richness), a delay for several decades in the case of some measures (age, fractal dimension), and a delay for hundreds of years in the case of other measures (size, angular second moment). Landscapes that have been altered by settlement and fire suppression cannot be restored using traditional methods of prescribed burning, which will simply produce further alteration. Causes of landscape change cannot be separated without control landscapes that lack prescribed burning, fire suppression, or other alterations of the natural fire regime.