USA — Humboldt State University researchers have confirmed that prolonged invasion of coastal woodlands by sudden oak death poses an acute new forest fire threat to portions of Southern Humboldt, Marin and Sonoma counties, according to a university press release.
The onset of sudden oak death is imminent in the watersheds of the Van Duzen and Mattole River basins, and unfortunately we expect they (tanoaks) will die very quickly as the disease spreads, warned wildland fire science professor Morgan Varner in the release. Portions of the Kings Range, Eel, Mad, Klamath and Trinity river riparian regions are also at risk.
Sudden oak death is well-known in many San Francisco Bay Area suburbs, where hillside landscapes in Marin and Sonoma counties are brown with large patches of exceptionally dry dead leaves, according to the release.
HSU’s new threat assessment stems from fresh field research, laboratory burnings and mathematical modeling by Varner and graduate student Howard Kuljian, who is pursuing a master’s degree in wildland fire management.
A non-native disease first detected in the Bay Area in 1995, sudden oak death infects tanoak, one of the five most flammable oaks in California and the hottest-burning hardwood in North America. The disease drastically reduces the moisture content of leaves and foliage. The missing moisture in dead trees poses a high risk of crown fires, the HSU scientists say. Crown flames burn with exceptional heat and speed, and inflict grave ecological damage, according to the release.
Owing to their height, crown fires are also more likely than ground blazes to be whipped up by prevailing winds.
The danger is intensified by a specific characteristic of sudden oak death: Deceased tanoaks experience prolonged leaf retention for up to two years. That means crowns bear heavy fuel loads for extended periods, primed for ignition by extreme dryness.
Eventually, prolonged dead-leaf retention adds to the litter fuel on the forest floor, further compounding the threat.
The energy released is so great you can’t combat (crown fires) with standard firefighting practices, Varner said in the release. You just have to move back, and let them die down.
The death of tanoak confronts Native American communities with particular dilemmas because acorns and the food products derived from them, like flour, have been a staple of tribal diets since time immemorial, according to the release. The species also has sacred religious and spiritual significance to indigenous peoples.
As Varner and Kuljian started their research a year ago, they were hearing from many land and forest managers about sudden oak death’s spread and how to deal with it.
Kuljian said the best interim countermeasure is pruning a dead tree’s lower limbs.
That raises the height of the fuel so that, even if you had a moderate surface fire, it might not reach the crown, he said in the release. Some land owners have tried whole tree removal. It can be very expensive, but it can still be a good option. They’ve also made the mistake of dropping the tree, hoping it would decompose on the site quickly. But, in fact, it can take several years and, in the meantime, you’ve got a huge surface fire potential there.