PARENT SESSION
Organized Oral Session 1: Functional Ecology and the Assembly of Plant Communities
Organized by: D Ackerly and S Diaz
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 204.

Environmental change, climate variability, and biotic interactions in the assembly of late Quaternary plant communities.

Jackson, Stephen^*,1, ¹ University of Wyoming, Laramie, WY

ABSTRACT- Paleoecological studies of the late Quaternary reveal continual forcing of vegetational changes by climatic change. Plant species have invaded new landscapes and abandoned others, populations have expanded and contracted, and species associations have come and gone. All of these phenomena are predictable from the temporal plasticity of multivariate environmental space and the differing niche structures of species in environmental space. The role of biotic interactions in these dynamics is often overlooked or downplayed by paleoecologists, at least in part because consequences of biotic processes are hard to discern in the fossil record. However, the paleoecological record includes a number of natural experiments that can unmask biotic influences. A classic example is the species removal experiment comprising the catastrophic mid- Holocene hemlock decline in eastern North America, which was followed by density compensation and habitat expansion in several tree species. A new set of experiments is emerging from studies that link independent records of climate variability and vegetational history. Recent studies from both eastern and western North America indicate that late Holocene species range extensions and population expansions often followed abrupt transitions between dry and wet climate extremes. These patterns probably represent drought-related mortality of incumbent species, creating opportunities for invasion and expansion of other species during subsequent wet extremes. Community composition, while ultimately governed or constrained by the prevailing combination of environmental variables, may be contingent on the recent and not-so-recent history of climate variability and disturbance in the context of the available species pool.

Key words: paleoecology, community, niche, climate