Increasing Fire Activity in Idaho Forests
Since 1986, longer, warmer summers in the western United States have resulted in four times as many major wildfires and six times as much area of forest burned, compared to 1970-1986 (13). The length of the wildfire season (when fires are actively burning) has increased by 78 days. The average time-span of large fires has increased from 7.5 to 37.1 days. Earlier snowmelt, higher summer temperatures, and a longer fire season have contributed to these changes in fire activity (13). In Idaho, 12.36 million acres of forests burned in the past century [6; 1900-2009], affecting roughly 22.5% of the total forested area in the state (Figure 1). The most area burned was during the early (1910-1935) and later part of the century (1985-2008; Figure 1). In addition, 8.17 million acres of non-forested lands burned between 1984 and 2009 (Figure 1).
Managers and scientists use satellite imagery to classify fires into four severity classes post-fire; unburned, low, moderate, and high severity. The classifications are divided by the percent of the overstory trees that are killed in the fire. In general, a low severity fire refers to less than 25% tree mortality, moderate severity fire can be between 25-75% tree mortality and high severity fires are above about 75% tree mortality. Burn severity has been monitored using satellite imagery for large fires (greater than 1000 acres) since 1984. In this time period, no trend in the area burned severely has been observed in forested and non-forested areas of Idaho. To access up-to-date information on the area burned in each state, the amount of area burned in prescribed fires, and where active fires are currently burning, go to: http://www.nifc.gov/fireInfo/fireInfo_main.html.
The northern Rockies region is at risk of more forest fires due to drier and longer summers [13]. If Idaho experiences more drought, more lightning, and more human-caused ignitions, fires in Idaho may become more common and larger than those in the past [14]. Forests have also become denser with the lack of natural fire over the past century [15]. In combination with a warming climate, this could lead to more severe, stand-replacing fires in Idaho.
References:
1. Agee, J. K. Fire Ecology of Pacific Northwest Forests. (Island Press, 1993).
2. Stephens, S. L. & Ruth, L. W. Federal Forest-Fire Policy in the United States. Ecological Applications 15, 532-542, doi:10.1890/04-0545 (2005).
3. Flannigan, M. D., Krawchuk, M. A., de Groot, W. J., Wotton, B. M. & Gowman, L. M. Implications of changing climate for global wildland fire. International Journal of Wildland Fire 18, 483-507 (2009).
4. Parisien, M.A. & Moritz, M. A. Environmental controls on the distribution of wildfire at multiple spatial scales. Ecological Monographs 79, 127-154, doi:10.1890/07-1289.1 (2009).
5. Heyerdahl, E. K., Morgan, P. & Riser, J. P. Multi-season climate synchronized historical fires in dry forests (1650-1900), Northern Rockies, USA Ecology 89, 705-716, doi:10.1890/06-2047.1 (2008).
6. Morgan, P., Heyerdahl, E. K. & Gibson, C. E. Multi-season climate synchronized forest fires throughout the 20th century, northern Rockies, USA. Ecology 89, 717-728 (2008).
7. Littell, J. S. & Gwozdz, R. B. in The Landscape Ecology of Fire Vol. Ecological Studies 213 (eds Donald McKenzie, Carol Miller, & Donald A. Falk) Ch. 5, 117-139 (Springer Science + Business Media B.V. 2011, 2011).
8. Heyerdahl, E. K. et al. Climate drivers of regionally synchronous fires in the inland Northwest (1651–1900). International Journal of Wildland Fire 17, 40-49, doi:http://dx.doi.org/10.1071/WF07024 (2008).
9. Hessl, A. E., McKenzie, D. & Schellhaas, R. Drought and Pacific Decadal Oscillation Linked to Fire Occurrence in the Inland Pacific Northwest Ecological Applications 14, 425-442, doi:10.1890/03-5019 (2004).
10. Schoennagel, T., Veblen, T. T., Romme, W. H., Sibold, J. S. & Cook, E. R. ENSO and PDO variability affect drought-induced fire occurrence in Rocky Mountain subalpine forests Ecological Applications 15, 2000-2014, doi:10.1890/04-1579 (2005).
11. Kitzberger, T., Brown, P. M., Heyerdahl, E. K., Swetnam, T. W. & Veblen, T. T. Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over Western North America. Proceedings of the National Academy of Sciences 104, 543-548 (2007).
12. Sibold, J. S. & Veblen, T. T. Relationships of subalpine forest fires in the Colorado Front Range with interannual and multidecadal-scale climatic variation. Journal of Biogeography 33, 833-842 (2006).
13. Westerling, A. L., Hidalgo, H. G., Cayan, D. R. & Swetnam, T. W. Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. Science 313, 940-943, doi:10.1126/science.1128834 (2006).
14. Littell, J. S. et al. Forest ecosystems, disturbance, and climatic change in Washington State, USA. Climatic Change 102, 129-158, doi:10.1007/s10584-010-9858-x (2010).
15. Keeling, E. G., Sala, A. & DeLuca, T. H. Effects of fire exclusion on forest structure and composition in unlogged ponderosa pine/Douglas-fir forests. Forest Ecology and Management 237, 418-428, doi:10.1016/j.foreco.2006.09.064 (2006).
Managers and scientists use satellite imagery to classify fires into four severity classes post-fire; unburned, low, moderate, and high severity. The classifications are divided by the percent of the overstory trees that are killed in the fire. In general, a low severity fire refers to less than 25% tree mortality, moderate severity fire can be between 25-75% tree mortality and high severity fires are above about 75% tree mortality. Burn severity has been monitored using satellite imagery for large fires (greater than 1000 acres) since 1984. In this time period, no trend in the area burned severely has been observed in forested and non-forested areas of Idaho. To access up-to-date information on the area burned in each state, the amount of area burned in prescribed fires, and where active fires are currently burning, go to: http://www.nifc.gov/fireInfo/fireInfo_main.html.
The northern Rockies region is at risk of more forest fires due to drier and longer summers [13]. If Idaho experiences more drought, more lightning, and more human-caused ignitions, fires in Idaho may become more common and larger than those in the past [14]. Forests have also become denser with the lack of natural fire over the past century [15]. In combination with a warming climate, this could lead to more severe, stand-replacing fires in Idaho.
References:
1. Agee, J. K. Fire Ecology of Pacific Northwest Forests. (Island Press, 1993).
2. Stephens, S. L. & Ruth, L. W. Federal Forest-Fire Policy in the United States. Ecological Applications 15, 532-542, doi:10.1890/04-0545 (2005).
3. Flannigan, M. D., Krawchuk, M. A., de Groot, W. J., Wotton, B. M. & Gowman, L. M. Implications of changing climate for global wildland fire. International Journal of Wildland Fire 18, 483-507 (2009).
4. Parisien, M.A. & Moritz, M. A. Environmental controls on the distribution of wildfire at multiple spatial scales. Ecological Monographs 79, 127-154, doi:10.1890/07-1289.1 (2009).
5. Heyerdahl, E. K., Morgan, P. & Riser, J. P. Multi-season climate synchronized historical fires in dry forests (1650-1900), Northern Rockies, USA Ecology 89, 705-716, doi:10.1890/06-2047.1 (2008).
6. Morgan, P., Heyerdahl, E. K. & Gibson, C. E. Multi-season climate synchronized forest fires throughout the 20th century, northern Rockies, USA. Ecology 89, 717-728 (2008).
7. Littell, J. S. & Gwozdz, R. B. in The Landscape Ecology of Fire Vol. Ecological Studies 213 (eds Donald McKenzie, Carol Miller, & Donald A. Falk) Ch. 5, 117-139 (Springer Science + Business Media B.V. 2011, 2011).
8. Heyerdahl, E. K. et al. Climate drivers of regionally synchronous fires in the inland Northwest (1651–1900). International Journal of Wildland Fire 17, 40-49, doi:http://dx.doi.org/10.1071/WF07024 (2008).
9. Hessl, A. E., McKenzie, D. & Schellhaas, R. Drought and Pacific Decadal Oscillation Linked to Fire Occurrence in the Inland Pacific Northwest Ecological Applications 14, 425-442, doi:10.1890/03-5019 (2004).
10. Schoennagel, T., Veblen, T. T., Romme, W. H., Sibold, J. S. & Cook, E. R. ENSO and PDO variability affect drought-induced fire occurrence in Rocky Mountain subalpine forests Ecological Applications 15, 2000-2014, doi:10.1890/04-1579 (2005).
11. Kitzberger, T., Brown, P. M., Heyerdahl, E. K., Swetnam, T. W. & Veblen, T. T. Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over Western North America. Proceedings of the National Academy of Sciences 104, 543-548 (2007).
12. Sibold, J. S. & Veblen, T. T. Relationships of subalpine forest fires in the Colorado Front Range with interannual and multidecadal-scale climatic variation. Journal of Biogeography 33, 833-842 (2006).
13. Westerling, A. L., Hidalgo, H. G., Cayan, D. R. & Swetnam, T. W. Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. Science 313, 940-943, doi:10.1126/science.1128834 (2006).
14. Littell, J. S. et al. Forest ecosystems, disturbance, and climatic change in Washington State, USA. Climatic Change 102, 129-158, doi:10.1007/s10584-010-9858-x (2010).
15. Keeling, E. G., Sala, A. & DeLuca, T. H. Effects of fire exclusion on forest structure and composition in unlogged ponderosa pine/Douglas-fir forests. Forest Ecology and Management 237, 418-428, doi:10.1016/j.foreco.2006.09.064 (2006).