Soil seed bank analysis of planted and naturally revegetating thermally-disturbed riparian forests

Abstract

Accelerating the reestablishment of a mature, biotic community following a disturbance is a common goal of restoration ecology. In this study, we describe the relative successional status of a recently disturbed riparian seed bank when compared with less recently disturbed and undisturbed systems, and the short-term effects of restoration on seed bank development within the recently disturbed system. The study location, the U.S. Department of Energy's Savannah River Site in South Carolina, provides a unique opportunity to investigate the development of wetland seed banks following a severe disturbance, in this case the release of elevated temperature and flow effluent from nuclear reactor operations. To assess the recovery of wetland seed banks over time, we compared seed banks of naturally recovering riparian corridor and swamp delta sites of two different ages since disturbance (nine years and 30 years) with undisturbed forested corridor and swamp sites. To assess the potential effects of restoration efforts (site preparation and planting of seedlings) on seed bank development, we compared seed banks of naturally recovering (unplanted) and planted riparian corridor and swamp delta sites in the more recently disturbed system. We expected total germinants and species richness to be highest in the recently disturbed sites and decline as wetland systems matured. Within recently disturbed sites, we expected planted sites to have higher abundance and richness than unplanted sites. We also expected a greater abundance of woody species in the undisturbed forested sites. The number of germinants differed among the sites, ranging from 748 individuals per m² in the undisturbed swamp area to 10,322 individuals per m2 in the recently disturbed planted swamp delta. When corridor and delta sites within a stream system were combined, the mean number of germinants was greater in the recently disturbed system, intermediate in the 30-year (mid-successional) system, and lowest in the undisturbed system. Seed banks from the recently disturbed and mid-successional sites were more similar in composition than they were to the undisturbed systems. Across all stream systems, riparian corridors had greater mean species richness than swamp deltas, though differences in seed bank abundances were not significant. Sedges and rushes were the predominant life forms in the recently disturbed and mid-successional sites, while undisturbed sites had a greater proportion of herbs and woody seedlings. In addition, there were more germinants from planted sites than from unplanted sites. The dominance by early successional species at recently disturbed planted sites may be an unintended consequence of site preparation treatments, and such potential effects should be recognized and weighed during the development of restoration plans.

Keywords

riparian restoration, successional gradient, thermal disturbance

Citation

Landman, George B.; Kolka, Randall K.; Sharitz, Rebecca R. 2007. Soil seed bank analysis of planted and naturally revegetating thermally-disturbed riparian forests. Wetlands, 27(2): 211-223.