Stand structure and plant species occurrence in forest edge habitat along different aged roads on Okinawa Island, southwestern Japan

Abstract

We compared stand structure and plant species occurrence on the shoulders of 3-, 10- and 20-year-old roads in a subtropical evergreen broad-leaved forest to document temporal changes in edge effects of forest roads. We recorded 154 vascular species in the study plots, including 3 non-native species. We used generalized linear mixed models to analyze changes in forest structure and plant species composition in relationship to the distance from forest roads. The spatial patterns in stand structure at different distances from roads differed with road age. The large canopy openness on the edge of 3-year-old roads decreased with time after the construction. A progressive decrease in tree height on roadsides was observed after the road construction, suggesting tall trees could not withstand the dry and windy roadside environment. The edge effect on the canopy tended to be larger at higher elevation sites. The spatio-temporal pattern of species occurrence based on distance from roads differed by species. Typical pioneer species such as Schima wallichii and Eurya japonica increased along the edge, while less aggressive pioneer species and understory species decreased. As time passed after the road construction, some climax and understory species decreased at the forest edge, while other climax and understory species increased. The modeling methods proposed in this study could be applied to different roadside and edge study sites.

Keywords:

• Edge effect
• Okinawa Island
• Road age
• Spatio-temporal change
• Subtropical forest

Acknowledgments

We thank the members of the Yona Field and Laboratory of Entomology, Faculty of Agriculture, University of the Ryukyus for their help with field surveys. We also thank Y. Kubota for critically reading and for providing valuable comments on an early version of the manuscript. This research was financially supported by the project of Science and Technology Promotion Division of Okinawa Prefecture and by Grant-in-Aid for Scientific Research (B) 21310025.