The effects of forest edges on arboreal vegetation have been studied extensively in a variety of ecosystems. Most studies examine edges with sharp contrasts, such as between a mature forest and a clearcut or between a forest and a field. However, there has been much less work examining the effect of gradual, also referred to as soft or feathered edges. The influence of the edge direction has not received much attention either. We used 2 x 10 m plots along thirteen 70 m long transects to determine the species composition and percent cover of the ground layer vegetation on either side of forest edges. The transects were either at the north-eastern or the southwestern edge of the harvested areas. There were residual trees throughout, which made the edge transition more gradual. The studied forests were mixed pine-hardwood ecosystems that had experienced partial harvest in the recent past and were located on sub-xeric sites in north Alabama.
Results/Conclusions
We identified 127 species of vascular plants. The harvested area near the more mesic south-western edges had greater (at α = 0.05) mean species richness (4 to 7 species) than the area near the drier north-eastern edges (3 to 4 species). There was a gradual decrease in species richness with the increase in distance from the south-western forest edges towards the center of the harvested areas, but an increase in richness from the north eastern edges. Species richness from the edge towards the forest was also greater at the more mesic south-western edge. There was no pronounced edge effect on species richness and Shannon’s diversity index between the intact forest and the partially harvested area. Edge orientation was associated with some differences in community composition. The orientation of the forest edge should be taken into account when considering the appropriate silvicultural treatments for regeneration of desired tree species and achieving greater levels of understory diversity. Moderating the edge environment by leaving residual trees in the harvested area seems to be associated with smaller differences in richness and cover between the forest and the opening compared to those differences reported by studies that examine hard edges.