The Klamath-Siskiyou (KS) region hosts mixed evergreen forests consisting of fire-adapted plants that include conifers, hardwoods and chaparral. Wildland fire is an important natural disturbance in mixed evergreen forests, influencing their structure, composition, soil nutrient cycles, wildlife habitat and hydrology. Indigenous species evolved with fire, indeed, the life history of many requires fire.

Natural fire disturbances historically exhibit gentle combustion as well as intense conflagrations. Such varied fire effects yield a mixed fire regime (Agee 1993). The mixed fire regime produces patchy mosaics of forest stands with different tree densities, ages and species mixtures that constantly changes over space and time (Willis & Stuart 1994). Patches now exhibiting “old-growth” character survived relatively frequent fires of low and moderate severity. However, in most places, very severe fires eventually interrupt this pattern and initiate new forest patches that enhance the landscape mosaic (Taylor & Skinner 1998). 

The mixed fire regime is a key contributor to KS forests’ unusual biodiversity (Martin & Sapsis 1992). It follows that biodiversity conservation depends on the active function of wildland fire throughout the ecosystem.

Ecological value of severe fires

Politicians and industry capitalize on a myth that forests blackened by highly severe fires are dead and wasted. In fact, stand-replacing fires create valuable patches of young shrub and forest communities that include physical legacies of the prior stand (fire killed trees). Naturally regenerated forests rich in coarse woody structure may be the rarest of all wild habitats in the Pacific Northwest due to widespread fire suppression, post-fire logging and planting of burned areas with nursery stock (Lindenmayer & Franklin 2002). Severe wildland fires should be accommodated to some degree because they positively contribute to ecosystem diversity and health (Smucker et al. 2005).  

Fire regimes are locally unique

Fire regimes vary across regions, and this variation contributes to regional differences in forest structure, pattern and biodiversity. Likening fire regimes across regions is problematic, even among similar floristic communities, because fire regimes differ by seasonal timing along the Pacific slope of North America.

For example, forests in the KS region and the Sierra Nevada tend to burn at different times in the growing season. The former mainly experience dormant season burns late in summer through autumn (Taylor & Skinner 2003), but the latter encounter more fire earlier in the summer as well as through autumn (Caprio & Swetnam 1995). In contrast, the Sierra San Pedro Martir of Baja, Mexico, forests routinely burn in the spring and early summer (Stephens et al. 2003).
The burning season influences ecosystem responses to fire (Brown 2000).  Therefore, fire ecology information extrapolated from other regions to KS forests may not reliably support ecosystem management (Frost & Sweeney 2000, Odion et al. 2004).

REFERENCES

Agee, J.K. 1993. Fire Ecology of Pacific Northwest Forests. Island Press: Covelo, CA.

Brown, J.K.  2000.  Ecological principles, shifting fire regimes and management considerations. Pp. 185-203 in: J.K. Brown and J.K. Smith, eds. Wildland Fire in Ecosystems, Vol. 2: Effects of Fire on Flora. USDA For. Serv. Gen. Tech. Rep. RMRS-42-vol.2: Ogden, UT.

Caprio, A.C. and T.W. Swetnam. 1995. Historic fire regimes along an elevational gradient on the west slope of the Sierra Nevada, California. Pp. 173-179 in: J.K. Brown, R.W. Mutch, C.W. Spoon and R.H. Wakimoto (tech. cords.). Proc. Symp. on Fire in Wilderness and Park Management. USDA For. Serv. Gen. Tech. Rep. INT-320: Ogden, UT.

Franklin, J.F., T.A. Spies, R. Van Pelt, A.B. Carey, D.A. Thornburgh and others. 2002. Disturbances and structural development of natural forest ecosystems with silvicultural implications, using Douglas-fir forests as an example. Forest Ecology and Management 155: 399-423.

Frost, E.J. and R. Sweeney. 2000. Fire Regimes, Fire History and Forest Conditions in the Klamath-Siskiyou Region: An Overview and Synthesis of Knowledge. Unpubl. report to World Wildlife Fund. Ashland, OR. 

Lindenmayer, D.B. and J.F. Franklin. 2002. Conserving Forest Biodiveristy: A Comprehensive Multiscale Approach. Island Press: Washington, D.C.

Martin, R.E. and D.B. Sapsis. 1992. Fires as agents of biodiversity: pyrodiversity promotes biodiversity. Pp. 150-157 in H.M. Kerner (ed.). Proc. Symp. on Biodiversity of Northwestern California. Santa Rosa, CA: 28-31 Oct. 1991. Ctr. Wildland Res. Rep. No. 29. Univ. of California: Berkeley. 

Odion, D.C., E.J. Frost, J.R. Strittholt, H. Jiang, D.A. DellaSala and M.A. Moritz. 2004. Patterns of fire severity and forest conditions in the western Klamath Mountains, northwestern California, U.S.A. Conservation Biology 18: 927-936.

Smucker, K.M., R.L. Hutto and B.M. Steele. 2005. Changes in bird abundance after wildfire: importance of fire severity and time since fire. Ecological Applications 15: 1535-1549.

Stephens, S.L., C.N. Skinner and S.J. Gill. 2003. Dendrochronology-based fire history of Jeffrey pine-mixed conifer forests in the Sierra San Pedro Martir, Mexico. Canadian Journal of Forest Research 33: 1090-1101.

Taylor, A.H. and C.N. Skinner. 2003. Spatial patterns and controls on historical fire regimes and forest structure in the Klamath Mountains. Ecological Applications 13: 704-719.

_____. 1998. Fire history and landscape dynamics in a late-successional reserve, Klamath Mountains, California, USA. Forest Ecology and Management 111: 285-301. 

Willis, R.D. and J.D. Stuart. 1994. Fire history and stand development of a Douglas-fir/hardwood forest in northern California. Northwest Science 68: 205-212.

Fire Regimes, Fire History and Forest Conditions in the Klamath-Siskiyou Region:
An Overview and Synthesis of Knowledge
Evan Frost, Rob Sweeney, Wildwood Environmental Consulting