A recent study shows that trees on old growth forests across the West are dying at a small, but increasing rate. Scientists blame it all on longer and hotter summers from a changing climate. The death rate is doubling every 17 to 29 years, according to the 52-year study published in the Friday edition of the journal Science. The trend was apparent in trees of all ages, species, and locations.

It is clear that this will eventually lead to decreasing tree size. In addition, this is an indicator that future forests might store less carbon than present. Old growth forests store large amounts of carbon, making them a resource in the fight against global warming. As trees die, they decompose and give off carbon dioxide, contributing to the amount of greenhouse gases.

Scientists have also thought of other causes for the higher death rate: air pollution, overcrowding of young trees, the effects of logging, large trees falling on small ones, and a lack of forest fires, which keep forests healthy. However, the data they collected shows that the trend affects trees young and old, in polluted and clean air, in crowded and sparse stands and at different elevations.

This death rate could produce a cascading decline in forests, which may lead to fewer habitats for fish and wildlife, an increased risk of wildfires and a vulnerability to sudden forest die-offs. The study examined data between 1955 and 2007 in 76 research plots in British Columbia, Washington, Oregon, California, Idaho, Colorado and Arizona. The average age of the forests examined was about 450 years, with some even 1,000-years old. Of the 59,736 trees counted, 11,095 died over the study period. The death rate increase varied, with the highest in California's Sierras, from about 0.9 percent in 1980 and rising to about 1.3 percent.