NASA satellites spy on forests

A NASA funded study is using satellites to monitor forests, with the aim of measuring the impact of climate change on their growth and health.

The research should help scientists better understand the interplay of the factors that contribute to the composition and health of a forest. This in turn may help them forecast how forests could change as weather patterns shift.

The research is based on the so-called "vegetation index" from the MODerate-resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra and Aqua satellites. This is a measure of forest productivity - a measure of photosynthesis and the ability of the forest of absorb carbon dioxide and convert that into new planet tissue.

The scientists found a strong link between the diversity of a forest's trees and its overall productivity in different weather conditions.

Richard Waring, professor emeritus of forest science at Oregon State University and lead author of the study, said: "These new data help us better predict how forests may change so officials can implement environmental plans or regulations to lessen the impact in advance. The data...may be helpful in sorting out changes in forest health caused by land conversion or pollution rather than climate change."

According to NASA, the vegetation index can also be used to estimate the number of tree species in a region.

Previously, tracking forest diversity was a very laborious process, involving lots of expensive field work and sample analysis. This project compared the predictions from the vegetation index against the last forest "census" and found that the predictions are usually very accurate.

There was an anomaly, however, in the Pacific North West. Here, the vegetation index correlated with about double the actual number of tree species.

The researchers suggest that an abrupt climate shift during the Pliocene, when the region became much cooler and drier, is responsible. Many species died out during this period and have not recovered. However, the data suggests the region could support as many as 60 additional species, were it not for this shift.

"It is unclear how forests will respond in the future, when climate change is likely to accelerate," said Waring.

The work does suggest a couple of scenarios. If evergreen conifers move into new, previously treeless areas, for example, they could actually accelerate local warming because they would reflect less of the sun's heat than the snow they'd be replacing.

Alternatively, a shift in climate could increase diversity in some forests, making the forest more resistant to disease or infestations of insects. It could also make areas vulnerable to invasion by "alien" species, the researchers said. ®