Northward displacement of optimal climate conditions for ecotypes of Eriophorum vaginatum L. across a latitudinal gradient in Alaska.

Plants are often genetically specialized as ecotypes attuned to local environmental conditions. When conditions change, the optimal environment may be physically displaced from the local population, unless dispersal or in situ evolution keep pace, resulting in a phenomenon called adaptational lag. Using a 30-year-old reciprocal transplant study across a 475 km latitudinal gradient, we tested the adaptational lag hypothesis by measuring both short-term (tiller population growth rates) and long-term (17-year survival) fitness components of Eriophorum vaginatum ecotypes in Alaska, where climate change may have already displaced the optimum. Analyzing the transplant study as a climate transfer experiment, we showed that the climate optimum for plant performance was displaced ca. 140 km north of home sites, although plants were not generally declining in size at home sites. Adaptational lag is expected to be widespread globally for long-lived, ecotypically specialized plants, with disruptive consequences for communities and ecosystems.

Interactive effects of resource availabilities and defoliation on photosynthesis, growth, and mortality of red oak seedlings.

Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to site and from individual to individual. To determine whether some of this variation could be explained by variation in other stress factors, red oak (Quercus rubra L.) seedlings were exposed to low and high light, water, mineral nutrient, and defoliation treatments, in a complete factorial design in a greenhouse. Significant interactions were observed among factors for photosynthesis, growth, and mortality, indicating that the response to defoliation was influenced by other stresses. Defoliation increased the photosynthetic capacity per unit leaf area of seedlings grown in the low-water, but not in the high-water, regime. In response to defoliation, growth of seedlings in a low-mineral-nutrient, or low-light, regime was depressed less than that of seedlings grown in a high-mineral-nutrient, or high-light, regime. However, defoliation resulted in a similar percent reduction in biomass in all seedlings in both the high and the low light, water, and mineral nutrient treatments. Defoliation-induced mortality of shaded plants was twice that of plants grown in full sun.