Plant Migrations Role on Future Carbon Balance from Climate Change

Current efforts to forecast the future of forested systems often oversimplify or overlook the role of plant migration in carbon balance. Research on plant migrations influence on the carbon balance from climate change has been limited from challenges that arise when the ecosystem characteristics of this fine scale process are modeled over large domains. The computational time required to simulate migration lends itself to studies with representative forests while still limiting domain size. For higher resolution runs without limiting domain size migration was introduced to the Ecosystem Demography (ED) model. ED is an individual tree based model that uses a size and age-structured approximation for the first moment of the stochastic ecosystem model. Hence it can simulate large domains at high spatial resolution with reduced computational intensity. As it is an approximation, the specific location of an individual tree within a site is unknown so binomial probability of dispersal distance with respect to patch size was added to the model to determine when migration to a new site should occur. Migration probability also depends on the number of months reproduction occurs at a given site for deciduous and evergreen plant functional types. The maximum paleoecological data migration rate of 100 km per century was used for both functional types and calibrated in ED in a test domain of the eastern United States. After validation, meteorological data from NARCCAP for current and future climate were used to simulate migration at three rates (none, instantaneous and 100 km per century) with a North America domain at quarter degree resolution. Comparison of scenarios highlights plant migrations role on the terrestrial carbon balance under climate change simulations, particularly with regard to transition zones where biomes are expected to expand and contract.