The effects of deer herbivory and forest type on tree recruitment vary with plant growth stage

Abstract

Understanding the combined effects of land-use changes and expanding generalist herbivores on the recruitment of tree species is critical to predict forest community dynamics and for fulfilling conservation purposes. We assessed how deer herbivory and forest-type affected the diversity of seedlings and saplings of dominant tree species in a temperate forest of Eastern USA, during four consecutive years. Fenced and unfenced plots were established in hardwood and pine forests and tree seedlings and saplings identified and monitored annually. Tree recruitment patterns varied widely from year to year, particularly for seedlings. Sapling communities were richer in species, more diverse and with lower indexes of dominance than seedling communities. The diversity of seedlings and saplings was significantly affected by inter-annual variation of tree recruitment but not by deer herbivory or forest type. Herb cover was reduced for more than fourfold in unfenced hardwood plots. Results show that inter-annual variation of recruitment, herbivory and forest type can combine to shape the composition of tree seedlings and saplings. When assessing effects of deer on tree recruitment interactions between biotic (e.g. herbivory) and abiotic (e.g. forest type) factors need to be considered. The outcome of such interactions depends on seedling or sapling life stage.