Recent studies have shown that frequency of occurrence among stands, rather than relative abundance when present, varies consistently along climate gradients for tree species of eastern North America. These results suggest that recruitment processes play a much more important role in abundance of tree species along climate gradients than do rates of adult growth and survival. I have tested this hypothesis using an analysis of rates of seedling recruitment, and growth and survival of seedlings, saplings and adult trees, for the 50 most common tree species in the eastern U.S. as a function of climate, using Forest Inventory and Analysis (FIA) data.
Results/Conclusions
Growth and survival of juveniles and adults vary systematically as a function of both mean annual temperature and average annual precipitation in virtually all 50 species. In most cases, the species did not reach their greatest abundance (frequency) in climates where they show the highest potential growth rates (after correcting for competition). Juveniles tended to have either similar or broader niche breadths (as defined by growth or survival) than adults along the two climate gradients. For both juveniles and adults, declines in growth and survival tended to be pronounced only near range limits. In contrast, there was striking variation in estimated per capita seedling recruitment as a function of mean annual temperature, and the patterns tended to match patterns of frequency of adults along that gradient. These results support the hypothesis that seedling recruitment plays a central role in the current distribution and abundance of tree species along climate gradients, and suggests a similarly critical role in responses of temperate forests to climate change.