Modeling configuration dynamics of harvested forest landscapes in the Canadian boreal plains

Habitat configuration has important implications for the persistence of faunal and floral populations at a variety of spatial scales. Forest harvesting alters habitat configurations. However, measuring and predicting such alterations remains challenging, in part because previously developed metrics of habitat configuration are often not statistically independent of habitat amount. Thus, their ability to measure independent effects of habitat configurations and habitat amount on ecosystem components such as wildlife populations has been limited. Here, we evaluate habitat configuration based on newly developed metrics that are independent of habitat amount but do not depend on regression residuals of abundance and configuration relationships on any population of landscapes. We use these new metrics to measure and predict changes in habitat configuration following forest harvesting in the boreal forest of Alberta, Canada. Our findings clearly demonstrate changes in habitat configuration resulting from forest harvesting can be predicted precisely with information about initial habitat patch structure and harvesting patterns. Because forest harvesting has significant implications for habitat configuration, accurately predicting these changes is critical for determining if forest harvesting strategies are sustainable for ecosystem components and processes. This study provides a set of novel, robust metrics for tracking landscape-scale changes in habitat configuration in harvested boreal forests.     

Are hedgerows effective corridors between fragments of woodland habitat? An evidence-based approach

Anthropogenic modification of the countryside has resulted in much of the landscape consisting of fragments of once continuous habitat. Increasing habitat connectivity at the landscape-scale has a vital role to play in the conservation of species restricted to such remnant patches, especially as species may attempt to track zones of habitat that satisfy their niche requirements as the climate changes. Conservation policies and management strategies frequently advocate corridor creation as one approach to restore connectivity and to facilitate species movements through the landscape. Here we examine the utility of hedgerows as corridors between woodland habitat patches using rigorous systematic review methodology. Systematic searching yielded 26 studies which satisfied the review inclusion criteria. The empirical evidence currently available is insufficient to evaluate the effectiveness of hedgerow corridors as a conservation tool to promote the population viability of woodland fauna. However, the studies did provide anecdotal evidence of positive local population effects and indicated that some species use hedgerows as movement conduits. More replicated and controlled field investigations or long-term monitoring are required in order to allow practitioners and policy makers to make better informed decisions about hedgerow corridor creation and preservation. The benefits of such corridors in regard to increasing habitat connectivity remain equivocal, and the role of corridors in mitigating the effects of climate change at the landscape-scale is even less well understood.     

Comparison and development of new graph-based landscape connectivity indices: towards the priorization of habitat patches and corridors for conservation

The loss of connectivity of natural areas is a major threat for wildlife dispersal and survival and for the conservation of biodiversity in general. Thus, there is an increasing interest in considering connectivity in landscape planning and habitat conservation. In this context, graph structures have been shown to be a powerful and effective way of both representing the landscape pattern as a network and performing complex analysis regarding landscape connectivity. Many indices have been used for connectivity analyses so far but comparatively very little efforts have been made to understand their behaviour and sensitivity to spatial changes, which seriously undermines their adequate interpretation and usefulness. We systematically compare a set of ten graph-based connectivity indices, evaluating their reaction to different types of change that can occur in the landscape (habitat patches loss, corridors loss, etc.) and their effectiveness for identifying which landscape elements are more critical for habitat conservation. Many of the available indices were found to present serious limitations that make them inadequate as a basis for conservation planning. We present a new index (IIC) that achieves all the properties of an ideal index according to our analysis. We suggest that the connectivity problem should be considered within the wider concept of habitat availability, which considers a habitat patch itself as a space where connectivity exists, integrating habitat amount and connectivity between habitat patches in a single measure.     

Effects of landscape structure and forest reserve location on old-growth forest bird species in Northern Finland

Old-growth forest birds in Fennoscandia have sharply declined in numbers during the last decades apparently due to commercial forest harvesting and fragmentation of old-growth forests. Conservation measures have led to the establishment of a forest reserve network to assure the persistence of forest birds at a regional scale. However, little is known about the effects of landscape structure within and around the reserves on the distribution of old-growth forest birds. We used a hierarchical approach to address the questions of how landscape structure and composition within forest reserves, landscape composition of surrounding areas and reserve location affect the abundance of resident, old-growth forest birds in the Northern Finnish forest reserve network. The positive role of particular landscape features on bird distribution indicates that both the proportion of old-growth forests and the structure of boreal landscape mosaic has an important role in determining the distribution of these birds. The landscape composition surrounding the reserves proved to be only a weak predictor in species distribution models, which argues against the primary role of the surrounding matrix in determining species distribution within forest reserves. Reserves located near the Russian border showed a higher abundance of old-growth birds than more western ones. Once east-west gradients in overall landscape composition had been accounted for, however, reserves did not differ significantly in the number of species present. These results suggest that landscape gradients, rather than ecological processes such as the presence of source areas located along the border with Russia, are the main determinant of the distribution of old-growth forest birds in the Finnish reserve network. We propose that to enhance regional persistence of old-growth forest birds, conservation efforts should be primarily directed towards the protection and enhancement of forest habitat quality and natural heterogeneity of landscapes within targeted areas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of patch isolation metrics in mosaic landscapes for specialist vs. generalist dispersers

We examined the effects of matrix structure and movement responses of organisms on the relationships between 7 patch isolation metrics and patch immigration. Our analysis was based on simulating movement behaviour of two generic disperser types (specialist and generalist) across mosaic landscapes containing three landcover types: habitat, hospitable matrix and inhospitable matrix. Movement, mortality and boundary crossing probabilities of simulated individuals were linked to the landcover and boundary types in the landscapes. The results indicated that area-based isolation metrics generally predict patch immigration more reliably than distance-based isolation metrics. Relationships between patch isolation metrics and patch immigration varied between the two generic disperser types and were affected by matrix composition or matrix fragmentation. Patch immigration was always affected by matrix composition but not by matrix fragmentation. Our results do not encourage the generic use of patch isolation metrics as a substitute for patch immigration, in particular in metapopulation models where generic use may result in wrong projections of the survival probability of metapopulations. However, our examination of the factors affecting the predictive potential of patch isolation metrics should facilitate interpretation and comparison of existing patch isolation studies. Future patch isolation studies should include information about landscape structure and the dispersal distance and dispersal behaviour of the organism of interest.This revised version was published online in May 2005 with corrections to the Cover Date.     

Residuals cannot distinguish between ecological effects of habitat amount and fragmentation: implications for the debate

Habitat amount and fragmentation usually covary in natural and simulated landscapes. A common way of distinguishing between their effects is to take the residuals of the fragmentation index or indices regressed on habitat amount, as the index of habitat fragmentation. We used data on prairie songbird relative abundances from southern Alberta, Canada to compare this approach with the reverse: taking the residuals of habitat amount regressed on habitat fragmentation as the index of habitat amount. We used generalized additive models (GAMs) to derive residuals, and modeled relative abundances using linear mixed-effects models. The modeling approach used strongly influenced the statistical results. Using residuals as an index of fragmentation resulted in an apparently stronger effect of habitat amount relative to habitat fragmentation. In contrast, habitat fragmentation appeared more influential than habitat amount when residuals were used as an index of habitat amount. Regression of residuals may eliminate statistical collinearity, but cannot distinguish between the ecological effects of habitat amount and fragmentation. Habitat fragmentation may therefore have a larger effect on species than previously studies have shown, but experimental manipulations of underlying mechanisms are ultimately required to address this debate.     

Accessible habitat: an improved measure of the effects of habitat loss and roads on wildlife populations

Habitat loss is known to be the main cause of the current global decline in biodiversity, and roads are thought to affect the persistence of many species by restricting movement between habitat patches. However, measuring the effects of roads and habitat loss separately means that the configuration of habitat relative to roads is not considered. We present a new measure of the combined effects of roads and habitat amount: accessible habitat. We define accessible habitat as the amount of habitat that can be reached from a focal habitat patch without crossing a road, and make available a GIS tool to calculate accessible habitat. We hypothesize that accessible habitat will be the best predictor of the effects of habitat loss and roads for any species for which roads are a major barrier to movement. We conducted a case study of the utility of the accessible habitat concept using a data set of anuran species richness from 27 ponds near a motorway. We defined habitat as forest in this example. We found that accessible habitat was not only a better predictor of species richness than total habitat in the landscape or distance to the motorway, but also that by failing to consider accessible habitat we would have incorrectly concluded that there was no effect of habitat amount on species richness.     

Population Dynamics of Songbirds in the Boreal Mixedwood Forests of Alberta,Canada: Estimating Minimum and Maximum Extents of Spatial Population Synchrony

Ecological phenomena vary over space and time and interpretation of these processes also varies depending on the measurement scale. As the spatial scale of observation increases and decreases, changes in population abundance will likely exhibit alternating patterns of asynchrony and synchrony. While the study of how and why population dynamics change with spatial scale of measurement is intrinsically interesting, most population ecologists seek to study mechanisms of population change on a discrete study area. Our study develops methods that population ecologists can use to determine spatially appropriate sampling designs, and demonstrates how such spatial scales can be determined for 25 species of songbirds using long-term data from the boreal mixedwood forest of Alberta, Canada. To determine minimum scales of synchrony in population dynamics, we calculated the average correlation of changes in population abundance over time across different numbers of fixed-radius point-count samples. We then used a randomization test to remove the effect of number of replicates from the determination of appropriate spatial scale. The maximum extent of synchrony was estimated as the distance where population dynamics were no longer correlated. Estimates of the minimum scale of synchrony differed between species, ranging from 3.1 to 18.6 ha. The maximum scale of synchrony was estimated to be greater than or equal to 8 km for 14 of the 25 species examined, and to be greater than or equal to 70 km for Tennessee Warbler (Vermivora peregrina). Maximum spatial extents were significantly correlated with body mass and territory size.     

Landscape cohesion: an index for the conservation potential of landscapes for biodiversity

In urbanising landscapes, planning for sustainable biodiversity occurs in a context of multifunctional land use. Important conditions for species persistence are habitat quality, the amount and configuration of habitat and the permeability of the landscape matrix. For planning purposes, these determinants should be integrated into simple indicators for spatial conditions of persistence probability. We propose a framework of three related indices. The cohesion index is based on the ecology of metapopulations in a habitat network. We discuss how an indicator for species persistence in such a network could be developed. To translate this network index into an area index, we propose the concept of spatial cohesion. Habitat cohesion and spatial cohesion are defined and measured for single species or, at best, for species profiles. Since species differ in their perception of the same landscape, different species will rate different values of these indices for the same landscape. Because landscapes are rarely planned for single species, we further propose the index of landscape cohesion, which integrates the spatial cohesion indices of different species. Indices based on these concepts can be built into GIS tools for landscape assessment. We illustrate different applications of these indices, and emphasise the distinction between ecological and political decisions in developing and applying such tools. This revised version was published online in August 2006 with corrections to the Cover Date.     

Separating the effects of habitat area,fragmentation and matrix resistance on genetic differentiation in complex landscapes

Little is known about how variation in landscape mosaics affects genetic differentiation. The goal of this paper is to quantify the relative importance of habitat area and configuration, as well as the contrast in resistance between habitat and non-habitat, on genetic differentiation. We hypothesized that habitat configuration would be more influential than habitat area in influencing genetic differentiation. Population size is positively related to habitat area, and therefore habitat area should affect genetic drift, but not gene flow. In contrast, differential rates and patterns of gene flow across a landscape should be related to habitat configuration. Using spatially explicit, individual-based simulation modeling, we found that habitat configuration had stronger relationships with genetic differentiation than did habitat area, but there was a high degree of confounding between the effects of habitat area and configuration. We evaluated the predictive ability of six widely used landscape metrics and found that patch cohesion and correlation length of habitat are among the strongest individual predictors of genetic differentiation. Correlation length, patch density and clumpy are the most parsimonious set of variables to predict the magnitude of genetic differentiation in complex landscapes.     

Estimating primary productivity of forested wetland communities in different hydrologic landscapes

Five forested wetland sites in western Kentucky with hydrologic regimes varying from seasonally to continuously flooded were investigated for net above-ground biomass productivity (litterfall plus biomass growth) and for possible indicators of that productivity, including abiotic (flooding frequency and depth, phosphorus concentrations in water and sediments) and biotic (biomass, tree density, basal area, structural complexity, and mean height) indices. Net biomass productivity ranged from 205 g m^-2y^-1 for a stagnant semipermanently flooded Taxodium swamp to 1,334 g m^-2y^-1 in a bottomland forest along the Ohio River. Productivity was highest in wetlands with pulsing hydroperiods, intermediate with slowly flowing systems, and lowest with stagnant conditions. Surface water flooding of the wetlands during the growing season ranged from 17 to 100 percent of the year and did not predict productivity. Phosphorus concentrations in water and in sediments were not correlated to one another and did not, by themselves, predict productivity. No single abiotic variable predicted the exact ranking of productivity of the sites. Of the biotic variables, average tree diameter was inversely related to productivity.     

Using an individual-based model to examine the roles of habitat fragmentation and behavior on predator–prey relationships in seagrass landscapes

Seagrasses, which form critical subtidal habitats for marine organisms worldwide, are fragmented via natural processes but are increasingly being fragmented and degraded by boating, fishing, and coastal development. We constructed an individual-based model to test how habitat fragmentation and loss influenced predator–prey interactions and cohort size for a group of settling juvenile blue crabs (Callinectes sapidus Rathbun) in seagrass landscapes. Using results from field studies suggesting that strong top-down processes influence the relationship between cannibalistic blue crab populations and seagrass landscape structure, we constructed a model in which prey (juvenile blue crabs) are eaten by mesopredators (larger blue crabs) which in turn are eaten by top-level predators (e.g., large fishes). In our model, we varied the following parameters within four increasingly fragmented seagrass landscapes to test for their relative effects on cohort size: juvenile blue crab (prey) predator avoidance response, hunting ability of mesopredators and predators, the presence of a top-level predator, and prey settlement routines. Generally, prey cohort size was maximized in the presence of top-level predators and when mesopredators and predators exhibited random searching behavior vs. directed hunting. Cohort size for stationary (tethered) prey was maximized in fragmented landscapes, which corresponds to results from field experiments, whereas mobile prey able to detect and avoid predators had higher survival in continuous landscapes. Prey settlement patterns had relatively small influences on cohort size. We conclude that the effects of seagrass fragmentation and loss on organisms such as blue crabs will depend heavily on behaviors of prey and predatory organisms and how these behaviors change with landscape structure.

     

Relative importance of habitat area and isolation for bird occurrence patterns in a naturally patchy landscape

There is debate among ecologists about whether total habitat area or patch arrangement contributes most to population and/or community responses to fragmented or patchy landscapes. We tested the relative effects of patch area and isolation for predicting bird occurrence in a naturally patchy landscape in the Bear River Mountains of Northern Utah, USA. We selected focal patches (mountain meadows) ranging in elevation from 1,920 to 2,860 m and in size from 0.6 to 182 ha. Breeding birds were sampled in each focal meadow during the summers of 2003 and 2004 using variable-distance point transects. Logistic regression and likelihood-based model selection were used to determine the relationship between likelihood of occurrence of three bird species (Brewer’s sparrow, vesper sparrow, and white-crowned sparrow) and area, isolation, and proximity metrics. We used model weights and model-averaged confidence intervals to assess the importance of each predictor variable. Plots of area versus isolation were used to evaluate complex relationships between the variables. We found that meadow area was the most important variable for explaining occurrence for two species, and that isolation was the most important for the other. We also found that the absolute distance was more appropriate for evaluating isolation responses than was the species-specific proximity metric. Our findings add clarity to the debate between ecologists regarding the relative importance of area and isolation in species responses to patchy landscapes.     

Role of habitat and landscape in structuring small mammal assemblages in hedgerow networks of contrasted farming landscapes in Brittany,France

In this study, we investigated the environmental factors driving small mammal (rodents and shrews) assemblages in permanent habitat patches in response to a gradient of agricultural intensification. Small mammals were sampled using a trapping standard method in the hedgerow networks of three contrasted landscapes differing by their level of land-use intensity and hedgerow network density (BOC1: slightly intensified; BOC2: moderately intensified and POL: highly intensified). We hypothesized that habitat and landscape characteristics have to be considered to understand the structure of local community. In that way, we carried out a multi-scale study using environmental variables ranging from local habitat (structure and composition of the hedgerows) to hedgerows neighbourhoods in a radius of 300 m (land cover and connectivity around hedges) and to landscape units (three sites). During 1 year, 24 hedgerows were sampled seven times, representing a total of 1,379 captures (86% of rodents and 14% of shrews) and eight species, dominated by the wood mouse (Apodemus sylvaticus) and the bank vole (Clethrionomys glareolus). Inter-site variability was significant and accounted for 18% of total variation in small mammal species abundances. But intra-site variability was also highlighted: species abundance profiles may differ greatly among hedgerows within a site. The more explanatory variables were identified at the different scales of the study: the landscape unit POL was shown to be an important factor in structuring the community, but the predominant factors explaining differences of abundances among hedgerows were about local habitat. In fact, the width of hedges and the tree species richness appeared to be significant and explaining the greatest part of the total variation of the small mammal community composition.     

Interaction of food resources and landscape structure in determining the probability of patch use by carnivores in fragmented landscapes

Studies on the distribution of mammalian carnivores in fragmented landscapes have focused mainly on structural aspects such as patch and landscape features; similarly, habitat connectivity is usually associated with landscape structure. The influence of food resources on carnivore patch use and the important effect on habitat connectivity have been overlooked. The aim of this study is to evaluate the relative importance of food resources on patch use patterns and to test if food availability can overcome structural constraints on patch use. We carried out a patch-use survey of two carnivores: the beech marten (Martes foina) and the badger (Meles meles) in a sample of 39 woodland patches in a fragmented landscape in central Italy. We used the logistic model to investigate the relative effects on carnivore distribution of patch, patch neighbourhood and landscape scale variables as well as the relative abundance of food resources. Our results show how carnivore movements in fragmented landscapes are determined not only by patch/landscape structure but also by the relative abundance of food resources. The important take-home message of our research is that, within certain structural limits (e.g. within certain limits of patch isolation), by modifying the relative amount of resources and their distribution, it is possible to increase suitability in smaller/relatively isolated patches. Conversely, however, there are certain thresholds above which an increase in resources will not achieve high probability of presence. Our findings have important and generalizable consequences for highly fragmented landscapes in areas where it may not be possible to increase patch sizes and/or reduce isolation so, for instance, forest regimes that will increase resource availability could be implemented. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The risk of ignoring fear: underestimating the effects of habitat loss and fragmentation on biodiversity

Landscape Ecology - Habitat loss and fragmentation threaten species not only through structural landscape changes and resource reduction, but also through modifications to species’...     

Modelling the Effects of Dispersal and Landscape Configuration on Population Distribution and Viability in Fragmented Habitat

Landscape configuration and dispersal characteristics are major determinants of population distribution and persistence in fragmented habitat. An individual-based spatially explicit population model was developed to investigate these factors using the distribution of nuthatches in an area of eastern England as an example. The effects of immigration and increasing the area of breeding quality habitat were explored. Predictions were compared with observed population sizes in the study area. Our model combined a nuthatch population simulator based on individual behaviour with a grid-based representation of the landscape; nuthatch life cycle and immigration parameters were user selectable. A novel aspect of the model is user-selection of habitat perceptual range. Using a realistic set of parameters, the number of breeding pairs predicted by the model matched observed numbers. According to model simulations, the main cause of nuthatch scarcity in the study area was the inability of patches to support viable populations without immigration from elsewhere. Modelled habitat management, which increased breeding quality habitat in existing woods, lowered the threshold above which the study area population became self-sustaining. The existence of a large core habitat area was critical in producing a self-sustaining population in this landscape, the same area in dispersed small woods failed to sustain populations.     

Genetic isolation by distance and landscape connectivity in the American marten (Martes americana)

Empirical studies of landscape connectivity are limited by the difficulty of directly measuring animal movement. ‘Indirect’ approaches involving genetic analyses provide a complementary tool to ‘direct’ methods such as capture–recapture or radio-tracking. Here the effect of landscape on dispersal was investigated in a forest-dwelling species, the American marten (Martes americana) using the genetic model of isolation by distance (IBD). This model assumes isotropic dispersal in a homogeneous environment and is characterized by increasing genetic differentiation among individuals separated by increasing geographic distances. The effect of landscape features on this genetic pattern was used to test for a departure from spatially homogeneous dispersal. This study was conducted on two populations in homogeneous vs. heterogeneous habitat in a harvested boreal forest in Ontario (Canada). A pattern of IBD was evidenced in the homogeneous landscape whereas no such pattern was found in the near-by harvested forest. To test whether landscape structure may be accountable for this difference, we used effective distances that take into account the effect of landscape features on marten movement instead of Euclidean distances in the model of isolation by distance. Effective distances computed using least-cost modeling were better correlated to genetic distances in both landscapes, thereby showing that the interaction between landscape features and dispersal in Martes americana may be detected through individual-based analyses of spatial genetic structure. However, the simplifying assumptions of genetic models and the low proportions in genetic differentiation explained by these models may limit their utility in quantifying the effect of landscape structure.     

Effects of habitat fragmentation on Eurasian red squirrel (Sciurus vulgaris) in a forest landscape

We studied the effects of habitat fragmentation, measured as forest stand size and isolation, on the distribution of Eurasian red squirrels (Sciurus vulgaris). Squirrel density was surveyed during four years in 46 forest stands (0.1–500 ha) in a forest landscape in south-central Sweden. The only factor that significantly influenced a density index was the proportion of spruce within a habitat fragment. Neither fragment size nor degree of isolation were significant. Furthermore, none of the interactions with year were significant, suggesting the same pattern in all four years. Thus, the effect of habitat fragmentation in this study seems to be only pure habitat loss, i.e. halving the proportion of preferred habitat in the landscape should result in a halving of the red squirrel population. Therefore, the landscape can be viewed as functionally continuous for the squirrels, although the preferred habitat was divided into fragments. The most likely explanation for the difference between this study and other studies on squirrels that found effects due to habitat fragmentation is a combination of shorter distances and less hostile surroundings in our study area. To identify landscape effects requires multiple studies because single studies usually consider only one landscape.     

Fine-scale characterization of bird habitat using airborne LiDAR in an urban park in Japan

Birds are ecosystem service providers and excellent urban ecosystem indicators because they are sensitive to habitat structure. Light detection and ranging (LiDAR) technology is a promising tool in bird habitat characterization because it can directly acquire fine-scale 3-D information over large areas; however, most of past avian ecological studies using LiDAR were conducted in North America and Europe, and there have been no studies in Asia. The robustness of LiDAR data across different habitat types remain problematic. In this study, we set 13 plots having different canopy area percentages in a large-scale urban park in Japan, and examined the usefulness of airborne LiDAR data in modeling richness and diversity of forest bird species and the abundance of Paridae species that play an important role in the urban food web. Bird surveys were conducted eight times at each plot during the birds’ breeding season, and the results were estimated using generalized linear models. In consequence, all of the response variables were explained by one or a few LiDAR variables, and the 1 × 1 × 1-m voxel-based variables were especially robust estimators. When targeting only densely-forested plots having more than 60% canopy area, the LiDAR data efficiency declined in estimation of the richness and diversity of whole forest bird species, whereas a laser penetration rate was efficient for estimating the Paridae species abundance. These results implied that the LiDAR data are useful in habitat characterization of forest birds, and even when targeting only dense forests, some LiDAR variables are effective for habitat estimation of birds preferring specific forest structures. In the future, application of LiDAR across a variety of ecosystems will greatly serve to develop adaptive conservation and management planning for urban forests.