Pre-fire fuel treatments impact fuel loadings 9 years after a large wildfire

Background/Question/Methods

Increasing size and severity of wildfires has lead to an interest in the effectiveness of forest fuels treatments on reducing fire severity and post-wildfire fuels. We sampled 7 sites within the Rodeo Chediski fire, the second largest fire in Arizona’s history, which burned 189,000 ha in 2002. We studied adjacent treated and untreated plots on the Apache-Sitgreaves National Forest to determine the effectiveness of treatments on reducing post-wildfire fuels.  These sites were measured in 2004 and again in 2011, to observe long-term changes in the fuels structure. We measured stand structure and surface fuel characteristics.

 

Results/Conclusions

In 2004 downed woody fuel only marginally varied between treated and untreated plots, however in 2011 treated areas had substantially lower fuel loadings in nearly all fuel categories.  In 2011, coarse woody debris (CWD; woody material >7.62cm) was 257% higher and fine woody debris (FWD; woody material <7.62cm) was 152% higher on untreated sites than treated sites. Yet, in spite of higher levels of CWD on untreated sites, loadings did not exceed recommended ranges based on published literature. We do not predict that the CWD loadings will increase above recommended ranges in the future. There are few fire-killed trees still standing, thus there is little material that will continue to contribute to surface fuel loadings. This finding is in contrast with immediate post-fire analyses that predicted CWD loadings greatly in excess of the mean of 30.2 Mg/ha observed on our untreated sites. Thus, whereas pre-fire treatments did reduce fuel accumulations post-wildfire, the accumulations in untreated areas do not exceed upper limits of coarse woody debris recommended for dry forest types.