International audienceThis paper addresses the relationship between anthropogenic forest habitat fragmentation and the form of urban patterns. Using a two-step methodology we first generate 40 theoretical residential development scenarios following a repeatable procedure; the simulated urban forms are either moderately compact or fractal. Then, we compare the scenarios according to the functional connectivity of the remaining forest habitat using a graph-based approach. The methodology is applied to the urban region of Besançon (France), where forest surfaces are considered as a generic habitat for several animal species. Results obtained show that fractal scenarios of residential development are almost equivalent to moderately compact scenarios regarding the connectivity of forest habitat when the residential development is weak. In the case of a more intense residential development, fractal scenarios are superior to nonfractal scenarios when low dispersal distances of animals are concerned
The aim of the present work is to assess the potential long-distance effect of a high-speed railway line on the distribution of the European tree frog (Hyla arborea) in eastern France by combining graph-based analysis and species distribution models. This combination is a way to integrate patch-level connectivity metrics on different scales into a predictive model. The approach used is put in place before the construction of the infrastructure and allows areas potentially affected by isolation to be mapped. Through a diachronic analysis, comparing species distribution before and after the construction of the infrastructure, we identify changes in the probability of species presence and we determine the maximum distance of impact. The results show that the potential impact decreases with distance from the high-speed railway line and the largest disturbances occur within the first 500 m. Between 500 m and 3500 m, the infrastructure generates a moderate decrease in the probability of presence with maximum values close to -40%. Beyond 3500 m the average disturbance is less than -10%. The spatial extent of the impact is greater than the dispersal distance of the tree frog, confirming the assumption of the long-distance effect of the infrastructure. This predictive modelling approach appears to be a useful tool for environmental impact assessment and strategic environmental assessment. The results of the species distribution assessment may provide guidance for field surveys and support for conservation decisions by identifying the areas most affected.
ContextLandscape graphs are widely used to model networks of habitat patches. As they require little input data, they are particularly suitable for supporting conservation decisions (and decisions about other issues as e.g. disease spread) taken by land planners. However, it may be problematic to use these methods in operational contexts without validating them with empirical data on species or communities.
ObjectivesSince little is known about methodological alternatives for coupling landscape graphs with biological data, we have made an exhaustive review of these methods to analyze links between the main purposes of the studies, the way landscape graphs are constructed and used, the type of field data, and the way these data are integrated into the analysis.
MethodsWe systematically describe a corpus of 71 scientific papers dealing with terrestrial species, with particular emphasis on methodological choices and contexts of the studies.
ResultsDespite a great variability of types of biological data and coupling strategies, our analyses reveal a dichotomy according to the objective of the studies, between (i) approaches aimed at improving ecological knowledge, mainly based on land-cover maps and using biological data to test the influence of landscape connectivity on biological responses, and (ii) approaches with an operational aim, in which biological data are directly integrated into the graph construction and assuming a positive effect of connectivity.
ConclusionsBeyond these main contrasts, the review shows that landscape graphs can benefit from field data of different types at varying scales. The great variability of approaches adopted reveals the flexible nature of these tools.
Landscape graphs are increasingly used in ecology, conservation, and landscape planning for modeling habitat connectivity of wildlife species. We present here the follow-up of Graphab, a software application for modeling habitat networks. This application has been recently enhanced by advanced functions of spatial analysis, command-line facilities, and connections with other software applications. It has been used in many studies, first in ecological studies for analyzing the role of landscape connectivity on biological responses measured in the field, second for supporting decisions concerning biodiversity preservation. Future improvements could be made to make the links more realistic with respect to ecological processes.
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