The development of forests on abandoned agricultural lands provides an ideal context to examine the relative roles of disturbance history and environmental conditions in shaping plant communities. Herbaceous plants typical of uncleared forests may remain absent from forests regrowing after agriculture, either because dispersal limits their distributions, or because lasting environmental changes limit their ability to establish and persist. Here I investigate how these processes affect plant distributions across the post-agricultural landscape of central New York, focusing on three fern species.

First I review relevant literature on the recolonization of post-agricultural forests by herbaceous plants. Next, in 20 adjacent pairs of forests that were never cleared for agriculture and forests that established 85-100 years ago on plowed fields, I assess the influence of past agriculture on present environmental conditions, including tree community structure and composition, soil physical and chemical properties and light availability. Compared to soils of adjacent uncleared stands, post-agricultural forest soils were similar in physical properties and chemical properties associated with pH, but had less organic matter, carbon and phosphorus, and reduced spatial heterogeneity in pH and water content. I examine how individual species interact with post-agricultural habitats by comparing the demography of three fern species with contrasting distributions across forests of different history, Dryopteris carthusiana, Dryopteris intermedia, and Polystichum acrostichoides, using descriptive and experimental approaches to specify which life history stages limit colonization, and which traits explain the species? distributions. Among the three species and between forests types, I compare the size and fecundity of adult plants; the deposition and storage of spores; the reproductive success and selfing ability of gametophytes; rates of germination and establishment in various microsites; and the distribution of juvenile plants across these microsites. As adult plants of all three species had similar or greater performance in post-agricultural forests, and spore availability far exceeded recruitment rates, the availability of suitable sites for establishment appeared to limit population growth and spread. In both field and laboratory experiments, the species? reproductive success and selfing ability matched their distributions, suggesting that selfing may facilitate colonization in these species, and their reproductive biology may determine their distributions.