Spatial graphs as templates for habitat networks in boreal landscapes

Network topology serves as a useful model for biological systems at various scales. Contrary to many biological systems, spatial reference is crucial for habitat networks. Boreal forest landscapes provide a wide gradient of spatial patterns and, thus, unique network structures. Assuming forest-dwelling organisms in general aim to minimize travel distances during foraging, dispersal, etc., linear links across the landscape matrix constitute expected movement routes among forested areas in boreal landscapes. We quantified the number and length of links in a set of 57 boreal forest landscapes for four hierarchically nested graphs in order to compare the incremental changes in characteristics of resulting graph measures. The forest cover graphs consisted of the same set of forest patches, and hierarchical link types extracted from real landscapes: nearest neighbour graph (NN), minimum spanning tree (MST), Gabriel graph (GG) and minimum planar graph (MPG). Most of the links in graphs were NN and GG links. Commonly links were 100–200 m in length, but link lengths particularly in the GG and MPG shorten when the proportion of forest in landscapes increased. Most nodes had 3–5 links each, but the number of links per node depended on node size and the proportion of forest cover. GG and MPG graphs retain the topology of the underlying node layout. Changes in node pattern alter the NN and MST graphs more than GG and MPG. Variation in regional network topologies is likely to affect connectivity patterns in a landscape and, thus, many ecological processes that occur at a local scale. An appropriate network analysis enables the discovery and comparison of distinctive network patterns. Understanding network topologies provide practical tools for land use planning and biodiversity management of broader areas that target functional habitat networks.