'' `` If in your hometown where you live , the death rates of your friends and neighbors doubled and there are no compensating birth rates , would n't you want to figure out what 's going on ? '' said Nathan Stephenson , research ecologist with the U.S. Geological Survey and one of the authors of the report . The study primarily focused on three types of coniferous trees : pines , firs and hemlocks . Older-growth forests -- some up to 500 years old -- have trees of all ages , and researchers found that mortality rates have increased for all age groups . Since mortality rates went up across the board , scientists ruled out a number of other possible causes , including ozone-related air pollution , long-term effects of fire suppression and normal forest dynamics . In the end , California had the highest tree death rate . Of the three types of coniferous trees studied , pines were found to be dying at the fastest rate . Ultimately , higher tree mortality may lead to significant shifts in forest structure and function , the report states . `` Much of the world 's population in
-LRB- CNN -RRB- -- Forests in the Pacific Northwest are dying twice as fast as they were 17 years ago , and scientists blame warming temperatures for the trend , according to a new study . This photo of Rocky Mountain National Park in Colorado shows dying pines and firs among healthy trees . The study , to be released Friday in the journal Science , is the first large-scale analysis of environmental changes as contributing factors in the mortality of coniferous forests . The data for this research was gathered by generations of scientists over a 50-year period at multiple sites in Oregon , Washington , California , Arizona , Colorado , New Mexico and southwestern British Columbia . Seventy-six forest plots , all more than 200 years old , were monitored by scientists doing some of the most rudimentary research -- counting trees . `` It 's not a happy story , but , an important one , '' said Phillip van Mantgem , a research ecologist with the U.S. Geological Survey and the lead author of the study . `` These are beautiful places . They do change and respond to their environment , sometimes quickly .