No abstract

ver 147 million dead trees were detected in California by the U.S. Forest Service Aerial Detection Survey (USFS ADS) from 2010 to 2018 (USDA 2019). The massive tree mortality, mostly in the Sierra Nevada and evident in swaths of conifers with red needles, resulted from the 2012-2016 drought and subsequent explosions in native bark beetle populations. While levels of mortality have declined in the last 2 years, the consequences will last for decades to come. Trees that died will fall over and surface fuel loads will increase-already the accumulation of millions of tons of dead material on forest floors is vastly outpacing the resources of local, state and federal jurisdictions to remove it. Urgent dialogue has started among UC scientists, forest managers, and public agencies to manage the consequences of the unprecedented tree die-off and increase the resiliency of forests to future droughts. To accomplish these goals, we need data on the rates of ongoing tree mortality and dead tree fall, surface fuel build-up, wildfire hazard, forest renewal patterns, and the course of bark beetle outbreaks. Data are also needed to understand the long-term impacts of the wave of tree mortality on ecological services such as carbon storage and water quality.

No abstract

Mortality and reduced growth rates due to raking accumulated basal duff were evaluated for old, large-diameter ponderosa and Jeffrey pine trees on the Lassen National Forest, California. No fire treatments were included to isolate the effect of raking from fire. Trees were monitored annually for 5 years after the raking treatment for mortality and then cored to measure basal area increment. Results showed that raking basal duff and litter to mineral soil from the bole out to 60 cm had no effect on basal area increment or mortality for 5 years posttreatment. Results are pertinent to managers who question whether raking basal duff will decrease tree vigor or increase tree mortality of large and old ponderosa and Jeffrey pine trees in northern California.