Terrestrial Rates and Amplitudes of Changes in Ecoclimate Systems (TRACES)

Science Center Objects

Vegetation changes caused by climatic variations and/or land use may have large impacts on forests, agriculture, rangelands, natural ecosystems, and endangered species. Climate modeling studies indicate that vegetation cover, in turn, has a strong influence on regional climates, and this must be better understood before models can estimate future environmental conditions. To address these issues, this project investigates vegetational response to climatic change, and vegetation-land surface impacts on climate change. The project involves calibration of the modern relations between the range limits of plant species and climatic variables, relations that are then used: 1) to estimate past climatic fluctuations from paleobotanical data for a number of time periods within the late Quaternary; 2) to 'validate' climate model simulations of past climates; 3) to explore the potential influences of land cover changes on climate change; and 4) to estimate the potential future ranges of plant species under a number of future climate scenarios. Project methodologies and data are also part of the national global change assessment of potential impacts of future climate changes.

Develop techniques and data sets to elucidate the modern relations among plant species distributions and climatic parameters in North America.

We developed a 25-km equal-area grid for modern climate for North America and compared the distributions of approximately 400 important plant species with these data (USGS Prof. Paper 1650). We also developed an analogue-based method of estimating past climate from these data and paleobotanical assemblages. This effort continues as we add additional species to the data set and as we devise new methods of portraying and transmitting the results to the scientific community.

Estimate past climatic conditions from paleobotanical data, based on the modern climate-vegetation relations identified using the methods described above.

We have worked with the NOAA paleoclimatology program and the University of Colorado to establish a packrat midden database and to augment the North American Pollen Database with pollen data from western North America. We have also taken a leading role in an international effort to document changes in biomes through the late Quaternary in North America. From these efforts we are preparing synoptic-scale reconstructions and regional lapse rate reconstructions for (initially) the Last Glacial Maximum at 21ka and the mid-Holocene at 6 ka. We will compare the results of different approaches to reconstructing climate based on both species-level and biome-level data, as well as implementing methods being developed by European colleagues.

Explore numerical model simulations of past climates by comparing simulated and observed past plant distributions.

The ability of climate models to simulate climates different from that of the present-day can be evaluated by comparing features of simulated past climates with geological data. We are using the relations identified from modeling using the gridded data described above to simulate the past ranges of selected plant species (based on numerical climate model simulations) for key past time intervals and will compare these with observed paleobotanical data. The results provide insights into both the direction and amplitude of errors in the model climate simulations, and are critical for modeling future climatic conditions.

Investigate the impacts of vegetation and other land-cover changes on climate.

Over the past 15 years climate modelers have become increasingly aware that changes in the land surface (as well as in the ocean) can strongly influence the direction and amplitude of climate changes. Project members will be develop landscape reconstructions for North America for (initially) the Last Glacial Maximum and 6 ka. These reconstructions will be used as boundary conditions for a series of numerical model simulations that will iteratively explore the role of land surface and ocean feedbacks in climate change.

Estimate potential changes in the distributions of plant species and biomes under a range of future climate scenarios.

Our initial approach was to use the modern climate/land surface relations with a selected numerical climate model simulation of a 2xCO2 climate to explore the potential impacts of future climate change on vegetation and hydrology in the western United States (USGS Circular 1153). As part of the national assessment of impacts of climate change, we are expanding this approach to include a range of simulations by different climate modeling groups, as well as to use information from the BIOME6000 effort to incorporate the effects of higher levels of atmospheric carbon dioxide on plant physiology and water utilization.