Live Fast, Die Young

Trees in the world's most productive forests are a lot like James Dean - they live fast and die young.

A new study by the U.S. Geological Survey suggests that trees in forests that add the most new growth per year tend to die young. This finding could help scientists predict how forests will respond to environmental changes, both today and in the future.

"One implication of this fast turnover rate is that the world's most productive forests may be those likely to respond most quickly to such things as climatic change," said Nate Stephenson, a USGS research ecologist and lead author of the study.

"You can view a forest like a bank account," Stephenson said. "As long as deposits and withdrawals are similar, your balance remains stable. But if the deposits or withdrawals are disrupted, the balance changes."

Changes in productive forests can cause the most dramatic effects. In a tropical forest growing on rich soils, the rates of both tree birth and death are high. If either of these rates were significantly altered, the tree population of one of these forests would be cut in half in 30 years. According to Stephenson, if similar alterations occur in a less productive, slower growing coniferous forest, the same population changes may take more than a century.

Stephenson and his colleagues pointed out that increased dominance by younger trees could also lead to changes in the amount of carbon stored in forests, though size and type of such potential changes are currently unknown and require more research. Atmospheric carbon dioxide, a heat-trapping gas implicated in climatic warming, increases as carbon storage in forests decreases, and decreases as carbon storage in forests increases. Information regarding such potential changes is therefore needed to reduce uncertainties in predicting future climatic changes.

This study was published in a recent issue of the journal Ecology Letters.