Trophic level and edge history modulate the depth of edge influence

Habitat edges are increasingly important worldwide because of forest fragmentation and the loss of natural habitats. Reduction in habitat area, increased isolation of fragments are considered to be the primary cause of species decline and extinction in fragmented landscapes. Edge effect is a key determinant, since most effects of fragmentation attributed to patch area may be scaled-up edge effect. Moreover, the isolation of patches is basically determined by the filter function (permeability) of edges. The distance that edge effects extend into the adjacent core (interior) habitat (the depth of edge influence, DEI) is a central issue in edge studies, as it fundamentally influences environmental properties, composition and structure of core habitats, all which significantly control species occurrences. Most previous studies on DEI neglected the impact of origin and the processes maintaining edges, although the structural and functional properties of edges determined by their history may modulate the permeability of edges, and consequently DEI. Evaluating available information on ground beetles (Coleoptera: Carabidae) in forest edges, we show that both species traits and edge history affect DEI on ground beetles. We found that DEI on abundance of herbivore, omnivore and predator ground beetle species is similar in natural edges, and edges maintained by agriculture, while it is generally penetrated over greater distances into the forests across edges repeatedly disturbed by forestry or other anthropogenic interventions than across edges maintained by natural processes. We found extreme edge effect across edges under forestry activities, as DEI on abundance of predator species is penetrated into the forest interiors up to ≤ 300 m. According to our findings DEI is more pronounced for predators and across edges created and maintained by forestry operations, suggesting outstanding sensitivity of higher trophic level organisms to fragmentation caused by forestry activities. Our result suggests that in planning the optimal size and shape of fragments for ecosystem-based forest management, to provide a core zone, a minimum area of 50 ha of circular forest fragments is required for maintaining an intact ground beetle assemblage.

The depth of edge influence among insectivorous bats at forest–field interfaces

Species-specific variations in wing morphology and echolocation call characteristics often define which of three structural habitat types (open, cluttered, and edge) different bat species most frequently and efficiently use for foraging. Although edges are recognized as important habitats for commuting and foraging bats, no study to date has examined the depth of edge influence (DEI), the extent of quantitative changes in activity with distance from an edge, for any bat species. We focused our study on five species: northern long-eared bat, Myotis septentrionalis (Trouessart, 1897); hoary bat, Lasiurus cinereus (Beauvois, 1796); little brown bat, Myotis lucifugus (LeConte, 1831); silver-haired bat, Lasionycteris noctivagans (LeConte, 1831); big brown bat, Eptesicus fuscus (Beauvois, 1796). We predicted DEI would vary with species-specific differences in wing morphology and echolocation call characteristics. From June to August in 2010 and 2011, we passively recorded echolocation calls three to four times per month at eight sites in eastern Ontario, Canada. We found that species’ activity was highest at the edge, regardless of wing morphology and echolocation call characteristics. The DEI for all species was approximately 40 m into both forests and fields. Understanding the effects of DEI on bats will enable more effective acoustic monitoring in future studies and may provide crucial information for management decisions.

Analytical methods for defining stand–clearcut edge effects demonstrated for N mineralization

Edge effects are becoming an important forest management consideration, but information regarding the influence of edges on N cycling variables has not been well documented. In addition, the quantification of edge effects can benefit from the application of complementary spatial analysis methods. Forest floor N mineralization and environmental variables were intensively measured 5 years after harvest along transects crossing the north and south edges of a 1-ha clearcut, in a high-elevation Engelmann spruce – subalpine fir forest. Wavelet analysis and depth-of-edge influence (DEI) methods were used to locate and measure the spatial extent of edge effects on N mineralization. Then variance partitioning (partial redundancy analysis) was used to examine the influence of edges on N mineralization relative to the influence of other environmental factors. Initial NO3-N content and net nitrification markedly increased in the opening within 2–6 m of each edge. Net ammonification did not exhibit obvious edge-related spatial patterns. Spatial patterns of nitrification appeared to be more closely related to spatial changes in substrate quality than to soil temperature and moisture. Results of the wavelet and DEI analyses provided quantification of locations and functional extents of edge effects.