RELATIONSHIPS BETWEEN PLANT TRAITS AND CLIMATE IN WESTERN NORTH AMERICA

A better understanding of the relations between plant traits and climate is needed to improve both paleoclimatic reconstructions and model simulations of past and future vegetation change. We examined the relationships between plant traits (i.e., measurable plant characteristics that are assumed to represent environmental adaptations) and climatic (e.g., temperature and precipitation) and bioclimatic (e.g., growing degree days) variables in western North America. Plant traits for approximately 500 plant taxa in North America were assigned from field observations, field guides, and taxonomic descriptions. Our analyses focused on those plant taxa that had well-mapped geographic distributions. The geographic distributions of traits were compared with present-day climatic and bioclimatic variables calculated on a 25-km equal-area grid of North America. Several plant traits, including those related to growth form, stem, and leaf characteristics, showed strong relationships with particular climatic and bioclimatic parameters. A similar analysis was done for plant traits assigned to pollen taxa for 6000 yr B.P. from pollen sites in the western United States. The results of this research will improve trait-based definitions of plant functional types, which in turn will improve reconstructions of paleoclimates from paleovegetation data. Plant trait-climate relationships identified in this study will also be used to refine the representation of plant functional types in vegetation models to improve simulations of both past and future vegetation response to climate change.