Ant-dispersed herb colonization lags behind forest re-establishment1

摘要

Dispersal ability is as integral to plant conservation as habitat integrity. If plants fail to disperse into disjunct habitats, those habitats remain unoccupied no matter how suitable. A decrease in herbaceous species richness from primary to secondary forests in the eastern United States may reflect the poor dispersal ability of ant-dispersed species previously extirpated by forest clearing, so much so the presence of ant-dispersed herbs may act as a proxy for ecosystem integrity. We examined the correspondence between forest stand age and the abundances of an ant-dispersed herb, Hexastylis arifolia, and a wind-dispersed herb, Goodyera pubescens. Vegetation was sampled in various-age forest stands in the Bent Creek Experimental Forest in the southern Appalachian Mountains, USA, and variance in H. arifolia and G. pubescens presence and abundance was assessed as a function of tree age and density. Both plants were absent from plots where trees were < 20 years, and H. arifolia did not occur in stands < 34 years. Hexastylis arifolia abundance increased significantly with proximate tree age whereas G. pubescens abundance did not. These results suggest G. pubescens propagules colonize re-established understory habitat relatively quickly whereas H. arifolia propagules may fail to access habitat in secondary forests decades after it becomes suitable. This exemplifies the difficulty ant-dispersed plants exhibit in tracking suitable habitat and suggests that deforestation and fragmentation limit their function in understory herbaceous communities. [PUBLICATION ABSTRACT]