Faced with climate change, where will trees go?

Two web-based systems help forestry professionals and landowners understand the potential impact of climate change on tree species.

All forest tree species have a natural range – broad geographic areas that include a combination of climate and environmental conditions that favor reproduction and growth. With changing climatic conditions, those ranges may change – some areas that are currently suitable for a given species will no longer be, some places will stay the same and others will become more favorable.

In response to those changes tree species have several responses: 1) they adapt to the new environment in that area, 2) their natural range shifts to areas with conditions most similar to their current range, and/or 3) species disappear from areas no longer suited to their growing requirements. All of these outcomes have significant consequences for tree and forests.

So, just what will those changes be? Two research efforts by the US Forest Service and other partners are trying to answer just that question.

The Forecasts of Climate-Associated Shifts in Tree Species project (ForeCASTS) evaluates 17 environmental variables to predict the future geographic ranges resulting from global climate change of more than 200 tree species.

Researchers analyzed data from approximately 125,000 existing forest inventory plots to identify eco-regions and created maps of current acceptable habitat for most of the studied species, and future locations of acceptable habitat in 2050 and 2100, based on two global change models. Finally, maps were generated that depict present and future ranges. Another analysis shows the minimum distances from current suitable habitat for species to future favorable areas. The longer that distance is, the more likely that a species will no longer be found in portions of its current range.

The Climate Change Atlas uses the same inventory data and a somewhat different modeling approach to evaluate tree abundance and distribution for 134 eastern forest species using several general climate circulation models. The resulting maps predict importance values (a measure of abundance) under a variety of scenarios. This site also includes a similar analysis for bird species.

The two models predict somewhat different outcomes, but tell a similar story – a northern shift in suitable habitat for many species, and loss of habitat in some areas currently occupied by them.

The maps developed through these projects are interesting to look at, especially by forestry professionals and forest owners, and a good tool to help managers think about potential impacts of climate change in Michigan. They don’t predict what will happen; rather provide a picture of possible future tree habitats, based on climate models. Many other factors, such as competition with other species and forest fragmentation also influence how tree species will be distributed in the future.

While providing a rapid assessment of future conditions, the information is not sufficient to make specific decisions about what landowners should do on their property. These models predict change over a long time period. The best approach for landowners is still to use well-established stewardship techniques to keep forests healthy and productive.

For more information about climate change topics, visit the Michigan State University Extension Climate Change and Variability website

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