More and more trees in Western U.S. and Canada forest are dying as a consequence of the warming of the region and, according to a recently-released study, if the trend continues, this change will lead to a drop in the quality of wildlife and, more importantly, in the forests’ capability to store carbon.

The forests will basically become thinner and weaker and thus more vulnerable to wildfires. The weakening of the forests will contribute to the global warming process because less carbon dioxide will be absorbed by forests.

The study is based on data collected over a period of almost 50 years during which researchers gathered documentation on trees in old-growth forests. The die-off of the forests in Western U.S. and Canada is beginning to outpace the replacement with young threes which means the situation is critical. The death rate may grow even more as the warm temperatures lead to a climate which is encouraging for pine beetles and similar organism that attack trees, the study said. This may accelerate the death rates.

The temperature in the region rose by more than 1 degree F (half a degree C) over the last few decades. Although it doesn’t seem much, it was just enough to reduce winter snowpack, cause earlier snowmelt, and lengthen the summer drought, said Phillip van Mantgem of the U.S. Geological Survey.

This caused the death rate to more than double in old-growth forests over the same period of time. All species and sizes of trees are affected including the most wide-spread species such as pine, fir and hemlock.

"Wherever we looked, mortality rates are increasing," said Nathan Stephenson, a study coauthor and USGS research ecologist.

The regions most affected by the deaths of old-growth forests are the U.S. Pacific Northwest and southern British Columbia, Canada. The highest mortality rate was in California where more than 1.5% of the state’s forests died each year due to drought and devastating bushfires.