20 Jan 2009, 7:32pm
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Fuel treatment effects on tree-based forest carbon storage and emissions under modeled wildfire scenarios

Matthew Hurteau and Malcolm North. 2009. Fuel treatment effects on tree-based forest carbon storage and emissions under modeled wildfire scenarios. Front Ecol Environ 2009; 7, doi:10.1890/080049

Full text [here]

Selected excerpts:


Forests are viewed as a potential sink for carbon (C) that might otherwise contribute to climate change. It is unclear, however, how to manage forests with frequent fire regimes to maximize C storage while reducing C emissions from prescribed burns or wildfire. We modeled the effects of eight different fuel treatments on tree-based C storage and release over a century, with and without wildfire. Model runs show that, after a century of growth without wildfire, the control stored the most C. However, when wildfire was included in the model, the control had the largest total C emission and largest reduction in live-tree-based C stocks. In model runs including wildfire, the final amount of tree-based C sequestered was most affected by the stand structure initially produced by the different fuel treatments. In wildfire-prone forests, tree-based C stocks were best protected by fuel treatments that produced a low-density stand structure dominated by large, fire-resistant pines. …

As trees grow, C is sequestered, and these additional tons of C can be used to offset emissions in other sectors. In fire-prone forests, however, tree-based C storage may lead to large releases of C if trees are killed and partially consumed by a high-severity fire (Breshears and Allen 2002; Hurtt et al. 2002; Kashian et al. 2006; Hurteau et al. 2008). …

Beginning in the mid-1900s, US forested lands became a net sink for CO2, as a result of forest regrowth and fire suppression (Hurtt et al. 2002). Fire suppression has increased forest density and stand-replacement fire risk in forests that were historically characterized by frequent, low-severity fire regimes (McKelvey and Busse 1996). …

In fire-prone forests of the western US, there are three common management practices for reducing forest biomass and the risk of catastrophic fire: prescribed fire, mechanical thinning, and both treatments combined. …

Our objective was to model the amount of live- and dead-tree-based C stored and released over a century with and without wildfire in Sierra Nevada mixed-conifer forests, after fuel reduction treatments. Our hypotheses were:

(1) in the absence of wildfire, the no-fuels treatment alternative will store the most live- and dead-treebased C;
(2) with wildfire, treatments that develop and retain large trees will store the greatest amount of livetree C;
(3) pre-settlement forest structure will maximize tree-based C storage while minimizing C release during wildfire;
(4) with wildfire, prescribed fire treatments will have a lower total C release than unburned treatments; and
(5) reducing stand density and concentrating live tree C stocks in larger individuals will decrease the post-wildfire mortality, reducing the drop below the baseline.

Here, we use current CCAR FSP (2007) accounting methods to evaluate changes in C stocks using the Forest Vegetation Simulator (FVS) and track fire emissions using the Fire and Fuels Extension (FFE) of FVS (Crookston and Dixon 2005). Although FVS does not account for soil C, it is regionally calibrated, widely used by managers to model forest response to different treatments and disturbances, and one of the CCAR-approved models for establishing baselines. …

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