The Heat Is Online

Vastly Different Vegetation Results from Climate Changes

Climate Change Likely to Produce Novel Plant Communities

SANTA BARBARA, Calif., Feb. 13 – The forests we see today may not exist in the future, if the past is any guide. Composition of forests likely will change in the future, as they have in the past, according to research into the fossil record, published by University of California, Santa Barbara post-doctoral fellow John W. Williams and co-authors in a recent edition of the journal Ecology.

Research shows that climate change over the past 25,000 years was responsible for vastly different and constantly changing assemblages of types of trees, said lead author Williams, based at the National Center for Ecological Analysis and Synthesis (NCEAS) at UC Santa Barbara.

"A lot of trees are dying right now -- oaks in California, chestnut, elm and spruce in the East – and while the direct causes are pests and fungal attacks, the indirect cause could be climate change, making the trees more stressed out," said Williams. "It becomes harder for them to defend against other causes of mortality."

In developing his report, Williams and co-authors did not look at a single tree, twig, or leaf. Instead, they analyzed data from computerized data sets accessible by the internet. Using the North American Pollen Database, a collection of fossil pollen records collected from lake sediments over the past 30 years, and climate model simulations, the authors were able to independently track vegetation change and climate change in Eastern North America during the past 25,000 years.

From this sediment scientists have been able to match up the assemblages of trees that were present during a variety of climatic periods. The results showed short lag times and large changes in vegetation in response to rapid climate change. Plant communities that are unlike any today grew under climates also unlike any today, suggesting that future climate change may also produce novel plant communities.

The authors note that vegetation composition has changed rapidly in the past 100 to 200 years (the life span of a single tree) and may change similarly rapidly in the future. "There is the potential for very rapid changes in forest composition," said Williams. The Intergovernmental Panel on Climate Change projects a rise in temperature of 2.7 to 9.9 degrees Fahrenheit over the next century which would cause major changes in trees and other vegetation. "The implications of change are large," said Williams. "They include things like water availability, habitat for endangered species and use of recreational areas."

(University of California at Santa Barbara News Office)

PALEOECOLOGY: Living in Harmony

Editor's Choice Section of Science

The sedimentary fossil pollen record has allowed paleoecologists to make detailed reconstructions of the changes in vegetation composition that have taken place across the Northern Hemisphere during the Pleistocene.

Frequently, they have found that plant species were grouped into communities and assemblages with no counterparts in the present day, and they have debated whether these "no-analog" communities signify vegetation that was at equilibrium with its corresponding climate or instead reflect disequilibrium owing to the effects of rapid climate fluctuations.

Williams et al. have analyzed pollen assemblages from North America at intervals since the last glacial maximum and have tested their correspondence with simulated no-analog climates. They find good spatial and temporal relationships with the simulated climates, as well as synchronicity between climate change and vegetational change, supporting the idea that no-analog vegetation was at equilibrium with its surroundings. Thus, not only are fossil pollen assemblages a useful source of information about past climatic conditions, but they show that new idiosyncratic assemblages of plant species will likely develop in response to future climate change. – AMS