Dance with the Abundant: How Do Rare Tree Species Persist and Contribute to Forest Biodiversity?

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With few exceptions, the majority of species in nature are rare. How rare species survive competition with the abundant and the rapid changes in climate and land-use has been a major challenging question to science. Given that many species populations are declining in size due to human activities, understanding the maintenance of rare species is urgently needed. However, the causes of species rarity, particularly for long-lived tree species, are poorly known. This study takes innovative approaches to study species rarity from the perspective of community ecology. Built on a well-designed global network of stem-mapped forest plots, this study will investigate the pattern of species rarity and their maintenance mechanisms across latitudinal gradients from tropical, subtropical to temperate forests. Field observation, manipulative experimentation and modeling approaches will be taken to study the patterns and causes of rarity of tree species across spatial scales and phylogenetic hierarchies. This study has four primary research components. (1) Model geographical distribution of rare species for the purpose of predicting global rarity of species from local occurrence data. (2) Investigate the variation in seed production and seedling establishment of rare trees to test the rare species advantage hypothesis for species coexistence. (3) Model the distribution of taxon size (e.g., the size of a genus or the size of a family) to test the hypothesis whether rare species occur randomly across phylogenetic trees. (4) Develop methods for quantifying extinction risk of rare species by establishing relationships between distribution and extinction risk. This study is significant in both theory and application. The concepts, models and methods developed from this study will greatly enhance our ability to understand the contribution of rare species to biodiversity, to predict the impact of climate and land-use change on loss of biodiversity, and to better conserve and manage biodiversity in the world as well as in Canada.