PBIO Colloquium | Predicting Plant Responses to Climate Change, Dec. 8

Dr. Rebecca Snell

The Environmental & Plant Biology Colloquium Series presents Dr. Rebecca Snell on “Predicting plant responses to climate change: a process-based approach using dynamic vegetation models” on Tuesday, Dec. 8, at 9 a.m. in Porter 104.

Snell is a Postdoctoral Researcher at the Swiss Federal Institute of Technology Zurich, Forest Ecology group.

Abstract: A central issue in climate change research is to identify what species will be most affected by variations in temperature, precipitation or CO₂ and via which underlying mechanisms. Dynamic vegetation models (DVMs) are process-based models which include representations of reproduction, establishment, growth, competition and mortality. These models simulate how individual plant performance is influenced by biotic interactions and environmental conditions, which make them particularly suitable for addressing questions about historical and future climate change. In this talk, I will present two examples in which DVMs were used to increase our understanding of how vegetation may respond to climate change.

First, can trees migrate fast enough to track rapid climate change? Climate change is expected to cause major shifts in species distributions. To keep up with the projected climate change, some plant species would be required to migrate more than 1 km yr^-1. Although the pollen record indicates rapid plant migration rates following the retreat of the last glacier, modern seed dispersal measurements support much slower potential migration rates. To help explain how rapid historical migration rates were achieved, I used a physiologically based dynamic global vegetation model (LPJ-GUESS). I describe how I integrated seed dispersal limitations into the model, and used the model to simulate two proposed theories (i.e., long distance seed dispersal and northern refugia). Simulated migration rates with long distance seed dispersal alone were generally much slower than historical migration estimates. The results support the importance of northern refugia and suggest that trees may not be able to track rapid future climate change.

Second, how will climate change and management influence woody encroachment in alpine pastures? Pasture-woodlands are unique semi-natural landscapes that result from the combined influences of climate, management, and intrinsic vegetation dynamics. Highly heterogeneous landscape patterns result from fine-grained intensive management and grazing by cattle, which lead to different successional stages between grassland and forest. Pasture-woodlands are expected to change in the future due to increasing land abandonment and climate change. To improve our understanding of the processes and interactions that shape these systems, I modified a dynamic forest landscape model by including an herbaceous layer, selective grazing by livestock, and interactions between grazing pressure and tree regeneration. The simulation results show current landscape structure is in disequilibrium with current grazing pressure, indicating future encroachment is likely even without climate change. Climate change will exacerbate the rate of encroachment, but increasing grazing pressure can help. Improving the representation of processes increases confidence in model results and reduces the uncertainty regarding future impacts of climate change in terrestrial ecosystems.