Carbon recovery rates following different wildfire risk mitigation treatments

Sequestered forest carbon can provide a climate change mitigation benefit, but in dry temperate forests, wildfire poses a reversal risk to carbon offset projects. Reducing wildfire risk requires a reduction in and redistribution of carbon stocks, the benefit of which is only realized when wildfire occurs. To estimate the time needed to recover carbon removed and emitted during treatment, we compared the 7-year post-treatment carbon stocks for mechanical thinning and prescribed fire fuels reduction treatments in Sierra Nevada mixed-conifer forest and modeled annual carbon accumulation rates. Within our 7-year re-sample period, the burn only and understory thin treatments sequestered more carbon than had been removed or emitted during treatment. The understory thin and burn, overstory thin, and overstory thin and burn continued to have net negative carbon stocks when emissions associated with treatment were subtracted from 7-year carbon stock gains. However, the size of the carbon deficit in the understory thin and burn 7 years post-treatment and the live tree growth rates suggest that the remaining trees may sequester treatment emissions within several more years of growth. Overstory tree thinning treatments resulted in a large carbon deficit and removed many of the largest trees that accumulate the most carbon annually, thereby increasing carbon stock recovery time. Our results indicate that while there is an initial carbon stock reduction associated with fuels treatments, treated forests can quickly recover carbon stocks if treatments do not remove large, fire-resistant overstory trees.

Research highlights▶ Reducing fire risk requires a reduction in carbon stocks. ▶ Carbon stock reduction increases with increasing treatment intensity. ▶ 7-years of tree growth resequestered the C emitted in the burn and understory thin. ▶ The understory thin/burn will recover in as few as nine more years. ▶ The overstory thin treatments will require a much longer period of time to recover.