Development of current stand structure in dry fir-pine forests of eastern Washington

Journal of the Torrey Botanical Society, Apr-Jun 2007 by Everett, Richard, Baumgartner, David, Ohlson, Peter, Schellhaas, Richard, Harrod, Richy

Conclusions. Under the National Fire Plan (2001) and subsequent Healthy Forest Restoration Act (2003), significant effort and funding has been directed to restoring fire and fire-dependent structure of fir-pine forests in the western United States. Accurate information on historical forest conditions has been needed to guide this effort. Our results indicated that historic stands varied greatly in tree densities, had a well-represented tree-understory, and dead and down fuels were scarce prior to the cessation of fire events.

Several centuries of forest structural record have documented the forests innate resilience to change. Given these forests have repeatedly demonstrated self-thinning adjustments to overstocked conditions, we need to insure ongoing and planned thinning projects to reduce fire hazard (Vissage and Miles 2003) compliment what has already occurred naturally. Forest management may be made more efficient by working with ongoing mortality processes to reduce tree densities while treating accumulated dead and down fuels to lower the fire hazard.

Morgan et al. (1994) suggested "Historical Range of Variation" in forest structure as a guide in managing for sustainable forests. However, change in fire cycles, ubiquitous post-fire recruitment, and deadwood accumulations indicated estimates of historical range of variability should be based on forest conditions around 1860 in these dry fir-pine forests. Both live tree and deadwood were needed to estimate historic stand density; using only current living trees under-estimated historic tree density by 20 to 86%.

Amounts of live and dead forest structures in 2000 exceeded historical levels; land managers have an abundance of biomass to work with in their restoration efforts. Restoration efforts will be constrained by the continued aging of these stands with the mortality of historical trees, and the decay loss of historical snags and logs. The broadened age-class structure and the increase in older age-classes indicated better opportunities for creating "historical-like" stand structure than preserving all its current remnants. However, as a high proportion (up to 86%) of trees that established prior to 1860 now reside in the dead wood component, conservation of the remnant live trees is warranted. Numerous peaks in tree establishment and mortality over several centuries have created a complex live and deadwood structure that cannot be duplicated rapidly following a stand replacement fire or timber harvest. Also, much of the forest structure history in current stands was found to be at risk given the already welldecayed snags and logs, and the increased potential for stand replacement fire events.

Literature Cited

AGEE, J. K. 1994. Fire and weather disturbance in terrestrial ecosystems of the eastern Cascades. Gen. Tech. Rep. PNW-GTR-320. USDA, Forest Service, Pacific Northwest Research Station, Portland, OR. 52 p.

AGEE, J. K. 1998. The landscape ecology of western forest fire regimes. Northwest Sci. 72: 24-34.