Differential Tree Colonization of Old Fields in a Temperate Rain Forest

Abstract

Abstract Most old fields in the Queets Valley of Olympic National Park, USA, remain dominated by exotic herbs 60 y after abandonment although the fields are surrounded by temperate rain forest. However, areas of some fields have been invaded by Picea sitchensis, one of three dominant forest species (with Alnus rubra and Tsuga heterophylla). This provided an opportunity to examine local variation of factors (competition, facilitation, cervid herbivory, soils) that influence tree colonization within a set of old fields, an approach rare in previous studies. Picea sapling invasion of field edges was negatively correlated with percent cover of Agrostis gigantea and positively correlated with Anthoxanthum odoratum. Potential indicators of competition (sod thickness, thatch thickness, percent ground cover) were correlated with Agrostis cover. Picea edge invasion was also correlated with soil organic matter. In experiments, seedlings of Picea and Tsuga emerged as readily in Agrostis as in Anthoxanthum or Pteridi...