A TRANSIENT, NUTRIENT-BASED MODEL OF ARCTIC PLANT COMMUNITY RESPONSE TO CLIMATIC WARMING

We developed a nutrient-based, plant community and ecosystem model (ArcVeg) designed to simulate the transient effects of increased temperatures on the biomass and community composition of a variety of arctic ecosystems. The model is currently parameterized for upland, mesic ecosystems in high Arctic, low Arctic, treeline, and boreal forest climate zones. A unique feature of ArcVeg is that it incorporates up to 18 plant functional types including a variety of forbs, graminoids, shrubs, and nonvascular plants that are distinguished by a set of five parameters. Timing and rate of growth, as well as nutrient use, are particularly important in defining competitive interactions in the model and in explaining coexistence in complex communities.

Simulations of climatic warming, which increase nitrogen mineralization and growing season length, suggest an increase in total biomass for high and low Arctic zones over 200 yr, and an increase in shrub biomass at the expense of other plant functional types. The initial community response to warming was a function of the initial dominance structure, whereas the long-term response reflected adaptations of plant functional types to the new environment. Therefore, long-term responses (decades to centuries) differed in both direction and magnitude from initial responses. In addition, warming resulted in the formation of novel, stable plant communities after 200 simulation years that were not typical of current zonal vegetation types in the Arctic of northwestern North America.