Excerpt:
The more than 100 million trees that died in California after being weakened by drought and insect infestations have transformed large swaths of the Sierra Nevada into browned-out tree cemeteries. In some areas more than 90 percent of trees are dead.
This week a group of scientists warned in the journal BioScience that the dead trees could produce wildfires on a scale and of an intensity that California has never seen.
Coming in the aftermath of the deadly and destructive fires last year both in wine country and Southern California, the warning is sobering because the scientists say they cannot even calculate the damage the dead-tree fires might cause; it exceeds what their current fire behavior modeling can simulate.
The authors of the study say the fire risk will ratchet up in the coming years, as the dead trees fall to the forest floor and form a tangled pile of timber resembling something like a giant bonfire.
Why do the researcher say we’ve never seen this before in California?
Mark A. Finney, an expert in fire behavior for the U.S. Forest Service and an author of the study, says California forests are much more vulnerable now because, paradoxically, they have been better protected. In their natural state, forests were regularly thinned by fire but the billions of dollars that the state spends aggressively fighting wildfires and restrictions on logging have allowed forests to accumulate an overload of vegetation.
How might the dead-tree forests affect California? One of the most striking concerns is the damage the fires might do to watersheds. Intense, hot-burning fires could disrupt forests’ ability to channel water into the Sierra reservoirs that provide cities like San Francisco with drinking water. That’s a scenario that could nudge the state into rethinking its forest management.
A theoretical depiction of vegetation and fuel dynamics following severe pine mortality due to bark-beetle attack in a mixed-conifer forest. Initially (1–2 years following mortality), the primary change would be reduced moisture content of canopy fuels (a). In the intermediate time period (3–10 years), there would be an overall loss of canopy fuels as dead foliage and branches are deposited on the forest floor, and there would be a corresponding increase in dead and live surface fuels as tree seedlings and shrubs establish (b). The longer-term changes (11–20 years) would include continued low canopy fuels—although this could be offset by the growth of residual overstory trees taking advantage of the available growing space—and considerable increases in large surface fuel (c). Increased surface fuels would be in both the dead (primarily fallen snags) and live (regenerating trees and shrubs) pools (c).