Challenges and implications of global modeling approaches that are alternatives to using constant plant functional types

Abstract:

In recent years a number of approaches have been developed to provide alternatives to the use of plant functional types (PFTs) with constant vegetation characteristics for simulating vegetation responses to climate changes. In this presentation, an overview of those approaches and their challenges is given. Some new approaches aim at removing PFTs altogether by determining the combination of vegetation characteristics that would fit local conditions best. Others describe the variation in traits within PFTs as a function of environmental drivers, based on community assembly principles. In the first approach, after an equilibrium has been established, vegetation composition and its functional attributes can change by allowing the emergence of a new type that is more fit. In the latter case, changes in vegetation attributes in space and time as assumed to be the result intraspecific variation, genetic adaptation and species turnover, without quantifying their respective importance. Hence, it is assumed that -by whatever mechanism- the community as a whole responds without major time lags to changes in environmental drivers. Recently, we showed that intraspecific variation is highly species- and trait-specific and that none of the current hypotheses on drivers of this variation seems to hold. Also genetic adaptation varies considerably among species and it is uncertain whether it will be fast enough to cope with climate change. Species turnover within a community is especially fast in herbaceous communities, but much slower in forest communities. Hence, it seems that assumptions made may not hold for forested ecosystems, but solutions to deal with this do not yet exist. Even despite the fact that responsiveness of vegetation to environmental change may be overestimated, we showed that -upon implementation of trait-environment relationships- major changes in global vegetation distribution are projected, to similar extents as to those without such responsiveness.