We have been funded by the Department of Energy to study how the recent deaths of pine trees in the mountains of the Western US are likely to affect regional and global carbon budgets. An unprecedented outbreak of mountain pine beetle populations has caused widespread mortality, especially in lodgepole pine forests. We hypothesized that by removing the photosynthetic potential of these forests, and producing abundant litter in the form of dead needles and fallen branches, the pine beetle outbreak would cause these forests to shift from being carbon sinks (providing a service to society by removing carbon dioxide from the atmosphere) to being carbon sources (providing a challenge to society by emitting more carbon dioxide to the atmosphere). Our studies have shown that indeed the forests will shift from being a carbon sink to being a carbon source. However, the magnitude of the source will not be as great as we originally hypothesized. There are natural limits on the rate of carbon emission to the atmosphere in these 'dead' forests, which have not yet been resolved.
