Climate change impacts on community and ecosystem properties: Integrating manipulations and gradient studies in montane meadows

In high elevation/latitude regions, anthropogenic climate change is likely to alter ecosystem structure and function substantially. Models predict that warming will be greater than at low elevations/latitudes, and cooler regions often have seasonal snow cover that is highly sensitive to temperature shifts. Snowpack characteristics and timing of snowmelt affect the length of the growing season and soil moisture availability, important factors that constrain biological activity.; I explored effects of climate variability and climate change on sagebrush-dominated subalpine meadow plant phenology, community composition, production, and nitrogen availability through a novel combination of gradient and experimental approaches. I expanded a year-round warming experiment at the Rocky Mountain Biological Laboratory in Gunnison County, CO, by adding three nearby sites along an elevational climate gradient. At the warming meadow, infrared radiators increased downward heat flux as predicted for a doubled CO2 atmosphere, resulting in early snowmelt plus warmer and drier soils during the growing season. At the elevational sites, a spring snow removal manipulation induced early snowmelt. I compared and integrated results from the manipulations with observations from three natural climate gradients by also monitoring ecological responses to microclimate variability within a site, across sites, and across years.; Flowering phenology responded consistently to both natural and manipulated climate variation. In particular, dramatically earlier flowering resulted from earlier snowmelt and warmer soil temperatures. Vegetation composition and nitrogen availability displayed less consistent responses. Shrub aboveground biomass was greater and forb biomass lower due to experimental warming but not snow removal, with strong evidence for soil moisture and snowmelt controls on biomass. Soil nitrogen availability did not respond to experimental warming but was altered by snow removal. In this ecosystem, responses of plant phenology and aboveground biomass to changing climate appear strongly mediated by direct effects of microclimate rather than effects of climate on nutrient cycling.; My research contributes to the growing body of evidence that anthropogenic climate change will have dramatic impacts on community and ecosystem properties. I have also demonstrated how integration of multiple experimental and gradient approaches can provide ways to distinguish among consistent, dynamic, and context-dependent ecological responses to global warming.