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Managing the Forest for Fire Safety

Fire is a natural, cyclic occurrence in redwood forests. The favored management technique to avoid catastrophic fire is, therefore, regular low-intensity prescribed burns (Brown et al, 2004). But we cannot apply that technique in the Sea Ranch, because of proximity to housing. Moreover, in this age of excessive atmospheric carbon, it makes sense to avoid burning things except when absolutely essential.

Absent prescribed burning, thinning is required to reduce fuel loads. But the right kind of thinning is precisely the opposite of commercial logging. Investigations of post-fire survival in redwood forests have repeatedly found that redwoods of marketable size are precisely the ones that are very unlikely to burn. (A few large redwoods have been killed by fire in exceptional circumstances, but even when that happens they do not seem to contribute much fuel—they are killed by girdling caused by heat, as described in Box 4.3 of Sawyer et al.) Cutting down marketable trees has no appreciable impact on fuel loads. Worse: at least one set of researchers made the unexpected discovery that proximity to a large redwood has a sheltering effect on nearby hardwoods that would otherwise be fire-prone (Lazzeri-Aerts & Russell, 2014). Thus, cutting down the larger redwoods increases fire risk.

The kind of thinning that is effective in reducing fire risk is called by the descriptive names “understory thinning” or “low thinning” (Brown et al, 2004). As might be expected, this involves essentially removing some of the kinds of vegetation that would otherwise be consumed in the natural low-intensity fires we cannot afford, thus mimicking the effect of the natural fire cycle to some extent.

It is important to note that we should not remove all of the more flammable vegetation: hardwoods and shrubs are valuable both as wildlife habitat and as wildlife food sources (Tunheim 2009, p. 50). We can manage their density and distribution to typical post-fire levels, if we allow our fuel management to be guided by ecology rather than pecuniary concerns. For example, studies such as Lazzeri-Aerts & Russell (2014) or Douglas & Bendure (2012) provide post-fire survival information for varied vegetation types in wildfires in several rewood forests.

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