Present Forest Structure

Some aspects of an area's fire history are evident in the present-day structure and composition of forest stands (Arno and Sneck 1977, Agee 1996). For example, a large stand of similarly aged trees, also known as an “even-aged” stand, probably originated after a major disturbance like a severe fire, windstorm, insect outbreak, or timber harvest. If the stand originated after fire, we should find both charred remains within the stand and fire scars in older, adjacent stands.

Tree-ring analyses can be used to determine the age of such a stand and to verify the occurrence of a major, tree-killing fire just prior to its origin (e.g., Tande 1979, Barrett et al. 1991, Winter et al. 2002). A similar analysis can reveal evidence of an insect outbreak just prior to stand initiation (e.g., Speer et al. 2001, Girardin et al. 2002). Stumps can be used to date stand initiation in heavily logged forests.

These analyses can yield information about the size and location of severe, stand-replacing fires. However, boundaries of only the most recent events can be gleaned from the age-structure of present-day forests (Rollins et al. 2001).

In contrast to fire-scar studies, analyzing the age class of stands throughout a region via dendrochronology is most instructive when the fire history consists of infrequent, high-severity fires (Agee 1990).



LITERATURE CITED:

Agee, J. K. 1996. Fire regimes and approaches for determining fire history. Pp. 12-13 In C. C. Hardy and S. F. Arno, editors, The use of fire in forest restoration. USDA Forest Service Intermountain Forest and Range Experiment Station, General Technical Report, INT-GTR-341. Available online.

Arno, S. F., and K. M. Sneck. 1977. A method for determining fire history in coniferous forests of the mountain west. USDA Forest Service Intermountain Forest and Range Experiment Station, General Technical Report, INT-42.

Barrett, S.W., S. F. Arno, and C. H. Key. 1991. Fire regimes of western larch-lodgepole pine forests in Glacier National Park, Montana. Canadian Journal of Forest Research 21:1711-1720.

Girardin, M.-P., J. Tardif, and Y. Bergeron. 2002. Dynamics of eastern larch stands and its relationships with larch sawfly outbreaks in the northern Clay Belt of Quebec. Canadian Journal of Forest Research 32: 206-216.

Rollins, M. G., T. W. Swetnam, and P. Morgan. 2001. Evaluating a century of fire patterns in two Rocky Mountain wilderness areas using digital fire atlases. Canadian Journal of Forest Research 31:2107-2123.

Speer, J.H., T. W. Swetnam, B. E. Wickman, and A. Youngblood. 2001. Changes in Pandora moth outbreak dynamics during the past 622 years. Ecology 82:679-697.

Tande, G. F. 1979. Fire history and vegetation pattern of coniferous forests in Jasper National Park, Alberta. Canadian Journal of Botany 57: 1912-1931.

Winter, L. E., L. B. Brubaker, J. F. Franklin, E. A. Miller, and D. Q. DeWitt. 2002. Initiation of an old-growth Douglas-fir stand in the Pacific Northwest: a reconstruction from tree-ring records. Canadian Journal of Forest Research 32: 1039-1056.

ADDITIONAL AVAILABLE LITERATURE:

Agee, J. K. 1990. The historic role of fire in Pacific Northwest forests. Pp. 25-38 in J. D. Walstad, S. R. Radosevich, and D. V. Sandberg, Editors, Natural and prescribed fire in Pacific Northwest forests. Oregon State University Press, Corvallis.

Arno, S. F., and S. Allison-Bunnell. 2002. Flames in our forests: Disaster or renewal? Island Press, Washington DC.



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