Abstract
Biological edge effects are often assessed in high quality focal habitats that are negatively influenced by human-modified low quality matrix habitats. A deeper understanding of the possibilities for positive edge effects in matrix habitats bordering focal habitats (e.g. spillover effects) is, however, essential for enhancing landscape-level resilience to human alterations. We surveyed epixylic (dead wood inhabiting) forest-interior cryptogams (lichens, bryophytes, and fungi) associated with mature old-growth forests in 30 young managed Swedish boreal forest stands bordering a mature forest of high conservation value. In each young stand we registered species occurrences on coarse dead wood in transects 0–50 m from the border between stand types. We quantified the effect of distance from the mature forest on the occurrence of forest-interior species in the young stands, while accounting for local environment and propagule sources. For comparison we also surveyed epixylic open-habitat (associated with open forests) and generalist cryptogams. Species composition of epixylic cryptogams in young stands differed with distance from the mature forest: the frequency of occurrence of forest-interior species decreased with increasing distance whereas it increased for open-habitat species. Generalists were unaffected by distance. Epixylic, boreal forest-interior cryptogams do occur in matrix habitats such as clear-cuts. In addition, they are associated with the matrix edge because of a favourable microclimate closer to the mature forest on southern matrix edges. Retention and creation of dead wood in clear-cuts along the edges to focal habitats is a feasible way to enhance the long-term persistence of epixylic habitat specialists in fragmented landscapes. The proposed management measures should be performed in the whole stand as it matures, since microclimatic edge effects diminish as the matrix habitat matures. We argue that management that aims to increase habitat quality in matrix habitats bordering focal habitats should increase the probability of long-term persistence of habitat specialists.
Highlights
Habitat destruction and fragmentation are considered major threats to biodiversity [1]
Species composition The species composition of epixylic cryptogams in the young stands was affected by distance from the mature forest: transect one differed from all other transects except number eight, and transect two differed from transect four and six (Table 1)
The non-metric multidimensional scaling (NMS)-ordination revealed that edge distance (r = 0.67) and the occupancy of one open-habitat species (C. botrytes, r = 0.49) were positively correlated with NMS-axis two, whereas the occupancies of two forest-interior (A. hellerianum, r = 20.74; A. serialis, r = 20.73) species were negatively correlated with axis two (Fig. 2)
Summary
Habitat destruction and fragmentation are considered major threats to biodiversity [1]. Edges between ‘focal’ (high quality) and ‘matrix’ (low quality, often human-modified) habitats dominate many landscapes shaped by human land use, and abiotic and biological changes in and near edges (edge effects) are major causes for the impact of fragmentation on the distribution of species [2]. The strength of biological edge effects, and the distance at which they occur are influenced by microclimatic gradients, propagule flow, species interactions, and resource quality and availability across edges [2,3,4,5]. Since the 1990s, the majority of studies investigating edge effects have concentrated on focal habitats that are negatively influenced by bordering matrix habitats [6]. The possibilities for positive edge effects in matrix habitats bordering focal habitats (e.g. spillover effects) have, received little attention
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