Long-term Vegetation and Climate Patterns in Yellowstone

Our research focuses on understanding the response and sensitivity of the Greater Yellowstone Area (GYA) to past climate change and natural disturbances. Information about past vegetation, climate, and fire activity in the Yellowstone region provides insights into how plant communities and fire regimes might respond to climate changes projected in the future. We examine the development of GYA vegetation since the last ice age and the ecological changes that have taken place since then as a result of past variations in climate. We also look at the history of fires in the region to get a better understanding of fire-climate linkages. The paleo-ecologic information comes from an examination of pollen, charcoal, and other fossils preserved in the sediments of lakes in the region. Radiocarbon dating indicates that most lakes in the region were formed 15,000 years ago, when glaciers retreated from the region. Our research has shown, for example, that Yellowstone experienced more fires between 10,000 and 7,000 years ago when summers were warmer and drier than today. At this time, fire-adapted and drought-tolerant species became more widespread, and areas that today experience fires every 300–400 years, burned every 50–100 years.  

Past variations of climate, vegetation, and fire do not provide analogies of what may happen in the future as a consequence of global climate change (because the controls of those changes differ), but they do illustrate how vegetation and fire respond as climate changes, and the past variations also provide a set of “natural experiments” that we can try to duplicate using vegetation and climate models. Once these models are able to accurately reproduce past climate patterns, they can be used to simulate the future. These simulations indicate that future climate changes will likely be spatially heterogeneous, with adjacent areas often experiencing opposing trends. It is also likely that novel climates—combinations of temperature and moisture that have not occurred since the last Ice Age—will develop in some parts of the GYA. Organisms will likely respond to these changes at different rates and new species can be expected to migrate into the region, creating novel plant and animal communities.