Alpine tundra of the Rocky Mountains is subject to relatively little direct anthropogenic environmental change, and provides a good ecosystem for the detection of human effects associated with climate change and atmospheric pollution. The majority of the plants have patterns of vegetative development which limit the degree to which they can respond to variation in resource availability. Field experiments indicate that changes in the abundance of plant species is the predominant response of alpine tundra to simulated climate change (snow augmentation) and increased nitrogen deposition. This biotic change in turn influences ecosystem function, including the magnitude and variation in primary production, and nutrient cycling. These biotic responses may have a greater impact on changes in ecosystem function than the direct effects of environmental change.