LTREB: Assessing Mechanisms of Primary Succession on Mount St. Helens

University Of Washington, Seattle WA

Investigators

Abstract

0087040 del Moral This LTREB proposal is to extent the continuous record of primary plant succession on Mount St. Helens to 25 years. It will clarify and extend the understanding of primary succession mechanisms developed in earlier studies. Public documentation includes data from permanent plots, grids, and photographs available from two web sites. It will improve our comprehension of how communities are structured and will help to develop more effective strategies to rehabilitate landscapes devastated by human impacts. Previous work has shown how distance affects community development, that microsites were crucial in early succession and that chance dominates early species assembly. By now, pioneer species have established, but initial patterns dictated by habitat stress, heterogeneity and isolation persist. There is scant evidence that initial colonists are being replaced by better-adapted ones. This study will compare development on widespread substrates and atypical, geographically isolated sites. It will investigate the development of community homogeneity and of positive associations among establishing species, assess evidence for deterministic control of community structure, evaluate the importance of habitat heterogeneity, attempt to determine rates at which species expand their distributions, and evaluate how rapidly developing habitats affect their immediate surroundings. Permanent plots and grid monitoring remain the backbone of this study. These data will be augmented by studies of species composition in relationship to environment, development of stable, repeatable assemblages, effects of trees on invasion, dispersal limits along transects, landscape effects and turnover rates in permanent plots. At the end of this study, a comprehensive discussion of how communities are initiated, developed and invaded will be possible.