Monday, March 08, 2010, 12:00PM - 1:00PM
U.S. Geological Survey
Full title: "Inherited latitudinal variation in cold hardiness of native and introduced trees: Climate change implications."
Phenological shifts such as earlier flowering time have provided some of the clearest evidence of biological effects of climate change, and models relating phenology to temperature, photoperiod, etc., can be used to predict future responses of biota to changing climate. However, in wild populations some of the variation in phenology over space and time is a consequence of genetic variation. Correctly modeling the response to climate change requires distinguishing the effects of genetic variation from those of climate. We used a common garden consisting of paired collections of native and introduced riparian trees sampled along a latitudinal gradient to explore the genetic component of latitudinal phenological variation. The garden in Fort Collins, Colorado (latitude 40.6°N), included 681 native plains cottonwood (Populus deltoides subsp. monilifera) and introduced saltcedar (Tamarix ramosissima, T. chinensis and hybrids) collected from 15 sites ranging from Texas to Montana. In the common garden both species showed latitudinal variation in fall, but not spring, leaf phenology, demonstrating that the latitudinal gradient in fall phenology observed in the field reflects both genetic and climatic variation, while the latitudinal gradient in spring phenology observed in the field reflects climatic variation alone. In contrast, cold hardiness showed strong genetic variation in both fall and spring for both species. The latitudinal variation in fall phenology and cold hardiness of saltcedar appears to have evolved through hybridization and natural selection in the 150 years since introduction. Observed shifts in phenology and distribution of native and invasive species include the effects of both global change and evolution.