Abstract: Forests are dynamic in both structure and species composition, and these dynamics are strongly influenced by climate. Models have been created to predict shifts in tree species ranges with scenarios of future climate change. Among those, the DISTRIB model is one of the few species-specific vegetation models, and provides the most extensive coverage of species (80 tree species) and area (east of the 100th meridian in the U.S.) in North America. The overarching objective of this work was to model community-level predictions of potential species range shifts and create predictions of the sign and magnitude of the impacts on NPP that will be associated with alterations in species composition. These model outputs were combined with a physiologically based, generalized forest carbon balance model (PnET-II) to estimate the net primary production (NPP) contributed by the respective tree species. We selected four 200 x 200 km areas in Wisconsin, Maine, Arkansas, and the Ohio-West Virginia area, representing focal areas of potential species range shifts. We archived an extensive documentation of leaf traits (leaf nitrogen content, specific leaf weight, and longevity) of mature trees in North America from the published literature. Based on the leaf trait database, we determined the central tendency of leaf traits and species-specific parameterization of the PnET-II model was made possible. PnET-II model simulations were performed assuming that all forests achieved steady state, of which the species compositions were predicted by DISTRIB model with no migration limitation. The potential effects of CO2 fertilization were not reflected in this model due to the uncertainty of its long-term effects. The total NPP under the current climate ranged from 552 to 908 g C m-2 y-1. The effects of potential species redistributions on NPP were moderate (-12% to +8%) compared to the influence of future climatic changes (-60% to +25%). We expect more negative effect of species redistribution on NPP if species migration in the future were obstructed by landscape fragmentation. The direction and magnitude of climate change effects on NPP were largely dependent on the degree of warming and water balance. Thus, the magnitude of future climate change can affect the feedback system between the atmosphere and biosphere.

Key words: carbon sequestration, climate change, leaf traits, net primary production, tree species range shifts.