Potential Dominant Plant Functional Type and Terrestrial Carbon Redistribution in Northern North America from Future Climate Change

Abstract:

The dominant plant functional type (PFT) of an ecosystem is influenced by local climate. Climate is changing at its greatest historical rate from anthropogenic forcing, which leads to ecosystem redistribution. Climate-ecosystem empirical relationships or biogeography models are used to spatially map current ecosystem distribution and to predict redistribution from climate change. Though climate-ecosystem metrics produce maps that predict the final reorganization of species from climate change they do not generally account for time delay in establishment created by species competition, withdrawal, and invasion. Transition zones between ecosystem types, such as tundra-taiga and evergreen-deciduous, will experience a time delay to establishment from the withdrawal and invasion of species that affect the carbon balance. Dynamic global vegetation models can be used predict the future PFT distribution under different climate change, but to date have not taken a robust approach to the competition between species invasion and withdrawal that creates a delay to final ecosystem redistribution. Therefore, we validate the dominant PFT distribution under current climate conditions of an advanced ecosystem model that has competition and migration processes, against remote sensing data of PFT type across northern North America. The climate-ecosystem relationships in the model match remote sensing data of dominant PFT from current climate 76% of the time for the ~3000 half degree sites in the domain. A climate change scenario was then run and our results showed that ~50% of the domain will change dominant PFT by 2070, highlighting that species competition and invasion influences on carbon balance from climate change is important in predicting future carbon balance. A model experimental design was then run with varying migration rates, species composition and distribution, and disturbance patterns to obtain a range of potential future terrestrial carbon stock from climate change that incorporates the time delay to establishment. Our research highlights the importance of accounting for plant migration in predicting future carbon balance of terrestrial ecosystems.