Forest ecosystems in the United States (US) are facing major challenges such as climate change, exotic invasion, and fragmentation. It is widely believed that forest composition in the eastern US are transitioning from shade-intolerant, fire-tolerant species to shade-tolerant, fire-intolerant species, but most evidence is anecdotal or localized. No comprehensive studies exist to quantify the shifts in forest composition at a regional scale with broader taxonomic group. Here, we examine the genus-level compositional changes in eastern US forests to: (1) quantify the extent and magnitude of this transition, and (2) assess the influence of fire and shade tolerance on abundance change.
Eastern United States
We compiled genus-level data from the Forest Inventory and Analysis (FIA) database at two time periods in 37 states across the Eastern US. We analyzed changes in abundance with three metrics, stem density, basal area, and importance value, for ten most abundant genera (Acer, Betula, Carya, Fraxinus, Nyssa, Pinus, Populus, Prunus, Quercus and Ulmus). Genus-level fire and shade tolerance traits were estimated based on species-level published data, and these traits were used as predictors of abundance change in linear mixed effects models.
We found that Acer, Fraxinus, Pinus, Populus, and Prunus, in general, increased their abundance during the study period. Acer experienced the largest amount of increases among these five genera across the study area. In contrast, Carya, Nyssa and Quercus decreased their abundance in the majority of the study region, with Quercus having the largest and most extensive decline. Betula and Ulmus had relatively small overall changes.
We found that there has been a general trend of the increase in fire-intolerant, shade-tolerant species, and the decrease in fire-tolerant, shade-intolerant species across the eastern US. Moreover, traits of fire and shade tolerance are not always interchangeable when used to predict the dynamics of a genus or species.
Cite this work
Researchers should cite this work as follows:
- Fei, S., Knott, J. A. (2018). Shifts in forest composition in the eastern United States. Purdue University Research Repository. doi:10.4231/R7C827JN