USA –The size and frequency of wildfires in the northern Rocky Mountains will increase so much with global warming that it will profoundly alter the landscape of Yellowstone National Park and its environs, predicts a new study.
The conifer forests of spruce, pine and Douglas fir that grow at elevations from 6,000 to 8,000 feet could give way to open woodlands, grass and shrubs, transforming the greater Yellowstone ecosytem that includes parts of Wyoming, Montana and Idaho.
The large, severe wildfires that have historically occurred infrequently will grow more common as rising temperatures hasten spring snowmelt, lengthening the fire season and drying out the region’s mid-elevation forests. It’s really by mid-century that it’s going to happen, said the study’s lead author, UC Merced environmental engineering and geography professor Anthony Westerling.
Westerling and four coauthors examined climate and fire data from 1972-1999 and then used projections from three global climate models to predict wildfire trends for the rest of the century. The results were dramatic: The fire rotation — the amount of time it takes to burn an area the size of the entire landscape — would drop to 30 years or less from the historical 100 to 300 years.
“Continued warming could completely transform [greater Yellowstone ecosystem] fire regimes by the mid-21st century, with profound consequences for many species and for ecosystem services including aesthetics, hydrology and carbon storage,” concludes the paper, which will be published online this week in the Proceedings of the National Academy of Sciences. “The conditions associated with extreme fire seasons are expected to become much more frequent, with fire occurrence and area burned exceeding that observed in the historical record or reconstructed” for the past 10,000 years.
The interval between big wildfires would be so short that the dense mountain forests typical of much of the northern Rockies would not have enough time to regenerate. Westerling cautioned that when that vegetation shift occurs, it will alter wildfire patterns in a way models can’t predict.
But he doubted fire conditions would be worse than projected. I think all the surprises will tend to be pleasant ones,” he said. For instance, if the climate is wetter than expected, that could partially counter the effects of rising temperatures.