PLANT FUNCTIONAL TYPES AS PREDICTORS OF TRANSIENT RESPONSES OF ARCTICVEGETATION TO GLOBAL CHANGE

The plant functional types (growth forms) traditionally recognized by arctic ecologists provide a useful framework for predicting vegetation responses to, and effects on, ecosystem processes. These functional t ypes are similar to those objectively defined by cluster analysis ba,e d on traits expected to influence ecosystem processes. Principal compo nents analysis showed that two major suites of traits (related to grow th rate and woodiness) explain the grouping of species into functional types. These plant functional types are useful because they (1) influ ence many ecological processes (e.g. productivity, transpiration, and nutrient cycling) in similar ways, (2) predict both responses to and e ffects on environment, including disturbance regime, and (3) show no s trong relationship with traits determining migratory ability (so that no functional type will be eliminated by climatic change simply becaus e it cannot migrate). Circumstantial evidence for the ecological impor tance of these functional types comes from the distribution of types a long environmental gradients and the known ecological effects of trait s (e.g., effects of litter quality on decomposition and of plant heigh t on winter albedo) that characterize each functional type. The paleor ecord provides independent evidence that some of these functional type s have responded predictably to past climatic changes. Field experimen ts also show that plant functional types respond predictably to change s in soil resources (water and nutrients) but less predictably to temp erature. We suggest that evidence for the validity of arctic plant fun ctional types is strong enough to warrant their use in regional models seeking to predict the transient response of arctic ecosystems to glo bal change.