Plant biogeography: Missing links in physiology, genetics, ecology, and extreme events

Background/Question/Methods Global change, including greenhouse gas accumulations and linked climate change, is driving changes in vegetation.  The changes are anticipated to be dramatic for vegetation itself and consequently for all other biota and for climate itself via feedbacks in biogeochemical cycles.  Vegetation changes are being mediated by changes in the abiotic environment per se (temperature, precipitation, and CO₂ itself) and in the biotic environment (disease prevalence, species loss, invasive species).  Many efforts to predict the outcome over various time spans are in progress, but there are a number of daunting challenges.  Both experiments and theory, on scales necessarily limited to date, imply great diversity among species or even ecotypes in their responses, as well as a high dimensionality to species interactions.

Results/Conclusions

I present a short review of: 1) species-specific differences in physiological responses, particularly to CO₂ directly; 2) the hidden but likely changing role of extreme events, which have unique attributes; 3) phenomena beyond autecological climatic responses (pollinators, diseases, etc.); 4) genetic responses, including rate limitations, population-genetic constraints, and an expected lack of adaptive genetic variation for responding to elevated CO₂ and associated phenomena that are setting in rapidly on ecological and evolutionary time scales; and 5) limitations in characterizations of driving factors, extending beyond uncertainties in scenarios (CO₂ emissions, land-use change, etc.) and climate model physics, to include fundamental changes in the spectra of extreme events.  I also review some recent progress, such as the JEDI model of stable trait combinations in plant functional types.  I conclude that we need much more species-specific data, improved climate models, new orders of statistics, and an effort to bridge the gap between biogeographic models (emphasizing the abiotic) and theory (emphasizing the biotic).  Nonetheless, we should expect that for several decades, at a minimum, we will be unable to predict major patterns and will have to use post hoc analyses very efficiently.