An increase in the number of wildfires and summer droughts caused by climate change is drastically changing a globally unique bio-region of northern California and southwestern Oregon, according to new research funded by the National Science Foundation and published today in the journal Scientific Reports.
Ecologists from Harvard University focused their research on the Klamath region because it is one of the most biophysically complex areas in North America and a huge carbon sink. There are 29 species of conifers and a number of rare plants that are not found in any other part of the world.
Because of its unique geological features, the rugged mountains of the Klamath harbors a rich biodiversity, with several distinct plant communities, including temperate rain forests, moist inland forests, oak forests and savannas, high elevation forests, and alpine grasslands.
Wildfires in the Klamath
The forest landscape of the Klamath has become well adapted to wildfires, but more severe fires, like the region’s record-breaking Biscuit Fire of 2002, which burned 500,000 acres, have a much greater impact on the biodiversity of the region.
This is because as plants begin to recover from a fire, the iconic conifers must compete with fast-growing shrubs and other species that are more fire-resistant.
Jonathan Thompson, HF Senior Ecologist and co-author on the study, explains, “If the fire-free interval is too short or if the growing conditions are too dry, the shrubs can persist indefinitely, and the iconic conifers are squeezed out.”
The research method used in the study
To study the dynamics of Klamath forest landscape, Thompson and his colleagues from the Harvard Forest, Smithsonian Conservation Biology Institute, and Portland State University simulated the next 100 years of forest dynamics in the Klamath according to five potential climate futures, reports ZME Science.
The projected shifts ranged from conservative to extreme, in warming and seasonal precipitation. Interestingly, every climate change scenario led to increased summer drought, which reduced plant survival overall, according to the authors.
“The Klamath is a challenging place to model future forests because the global models of future climate change (the Global Circulation Models) don’t agree about future precipitation in the region. The models agree that it will be warmer, but some predict wetter and some drier. So we ended up running all the analysis with four different climate change projections. Not surprisingly, the drier climate scenarios were associated with the largest losses of conifer forests,” Thompson told ZME Science.
Because climate change will increase the frequency and intensity of wildfires, fast-growing shrubs will take over the forests – and because they can regenerate quickly when subjected to high-intensity wildfires, they will squeeze out the conifers. “This is often referred to as a shrub trap,” Thompson said.
“These forests are among the most carbon dense in the world. So, the replacement of old conifer forests with shrubs will mean much more carbon in the atmosphere. It is also a major shift in the fire regime. This region has always supported a low to mixed-severity fires, meaning that frequent fires would perpetuate the forest condition,” said Thompson,
Harvard researchers are now working with the U.S. Forest Service and other forest managers in the Klamath “to develop regional scenarios of land management that might prevent the loss of forests or produce other outcomes the stakeholders see as favorable,” according to Thompson.
This research, “Disequilibrium of fire-prone forests sets the stage for a rapid decline in conifer dominance during the 21st century,” was published in the journal Scientific Reports April 30, 2018.