Edge influence on herbaceous plant species, diversity and soil properties in sparse oak forest fragments in Iran

Aims Forest edges have been well studied in temperate and tropical forests, but less so in open canopy forests. We investigated edge influence on plant species diversity and soil properties in sparse oak forest fragments. Methods Data were collected along three transects from the edge to the interior of three small (under 10 ha) and three large (over 10 ha) oak forest fragments in Kermanshah province, Iran. We measured herbaceous plants (< 0.5 m in height) and soil attributes at 0 (forest edge), 25, 50, 100 and 150 m. We quantified species diversity using the Shannon index, used rarefaction to compare species richness between two different sizes of fragments and applied non-metric multidimensional scaling ordination to investigate the variation in species composition. We estimated the distance of edge influence using randomization tests. Generalized linear mixed models with post-hoc Tukey's HSD tests were used to assess the effects of distance from edge and fragment size on diversity and soil properties. Important findings We found greater species richness, diversity and evenness at the edge of both small and large fragments, and lower nitrogen and organic carbon at the edge compared to the interior of large fragments, with most changes within 50 m of the edge. Species composition, organic carbon and total nitrogen were significantly different between small and large fragments. Our findings of significant edge influence on herbaceous plants and soil properties in these sparse forests provide a significant contribution to the literature on edges, especially in relation to herbaceous plants.

Trends in studies of edge influence on vegetation at human-created and natural forest edges across time and space

Forest edges, or boundaries between adjacent ecosystems, play important ecological roles. Both anthropogenic and natural forest edges affect vegetation while contributing to landscape heterogeneity. The recent proliferation of studies on vegetation at edges suggests that a comprehensive review of global edge studies is timely. We reviewed the literature on forest edges to identify trends in edge studies over time, to determine types and localities of studied edges, and to compare findings on edge influence. We found 446 studies conducted in 55 different countries that considered edge influence on vegetation structure and/or composition. Research on vegetation at anthropogenic edges has increased and expanded geographically, but studies are still scarce in some areas and at natural forest edges. Forest edges were generally characterized by greater species diversity and non-native species abundance than interior forest. Distance of edge influence on vegetation extended furthest at tropical anthropogenic forest edges compared to other edge types and locations. Edge influence on responses caused by indirect effects of edges generally extended further into the forest than on responses related to forest structure. Our findings indicate that vegetation characteristics differ between edge and forest types and should be considered in the sustainable management of heterogeneous forested landscapes.

The Persisting Influence of Edge on Vegetation in Hemiboreal Alnus Glutinosa (L.) Gaertn. Swamp Forest Set-Asides Adjacent to Recently Disturbed Stands

To increase set-aside areas and protect biodiversity values in managed hemiboreal forest landscapes, small forest parcels called Woodland Key Habitats have been designated in Baltic and Nordic countries. The aim of this study was to investigate the persisting influence of the edge on vegetation dynamics for young, medium-old and old edges in Alnus glutinosa (L.) Gaertn. Woodland Key Habitats. All of these edges are adjacent to recently disturbed (clear-cut) stands. We surveyed edge influence on vegetation in bryophyte, herbaceous, shrub and tree layers in 90 plots in 30 set-aside forest stands in Southern Latvia. We tested the differences in the number of species and projective coverage in all vegetation layers, but plant functional types were examined—separately in the herbaceous layer. We found that edge influence in protected forest stands of A. glutinosa swamp forests reflects strong changes in vegetation and plant functional types in the herbaceous layer mostly up to 20 years after clear-cut disturbance in adjacent stands. The greatest differences were between young edges (≤20 years) and old edges (≥41 years), but there were very few significant differences between medium-old (21–40 years) and old edges which signifies more rapid changes in the early stages of edge influence and gradual stabilization of vegetation later on. We found that in edges adjacent to recently disturbed stands (up to 20 years), significantly less rare and indicator epiphytic lichen species occur, but this occurrence increases over time and edge influence is no longer present beyond 20 years after disturbance. Changes in vegetation and species occurrence found in our study indicated the need to plan the allocation of set-aside patches in production forest landscapes to ensure connectivity over longer period of time. Careful planning of clear-cuts in neighboring areas over time can significantly reduce the impact of edge effect on these set-asides.