Large-scale responses to climate change in forests
One of the goals of global change research is to anticipate whether or not species can keep pace with the changing climate in their geographic distributions. In this project, we study eastern US forests biogeography using the USDA Forest Service’s Forest Inventory and Analysis (FIA) data set, with over 40,000 plots, 1,000,000 trees, and 1,700 variables. By comparing tree size distributions in geographic space, we found that there is not yet evidence that eastern US forests are shifting their geographic ranges to higher latitude in response to warming temperatures (Zhu et al. 2012).
This research opens up a migration paradox, where most theoretical models support rapid tree migration, but empirical data do not. To resolve this paradox, we conducted a further continental-scale analysis to compare abundance patterns of tree size distributions in climate space. We found that the majority of species are having faster population turnover as dynamics accelerate with longer growing seasons and higher temperatures, rather than poleward migration at biogeographic scales (Zhu et al. 2014). We also found that tree recruitment experiences stronger density dependence for common than rare species (Zhu et al. 2015). Taken together, we offered a new perspective on tree populations responding to climate change: they are not migrating at biogeographic scales, but are having faster turnover rates, which could have profound influences on global carbon cycles.