Sequoia and Kings Canyon National Parks are located in Tulare and Fresno Counties, California, in the southern Sierra Nevada encompassing some 864,383 acres. The Parks' prescribed fire program, begun in 1969, was created in response to the growing recognition that fire played an important role in many Sierra Nevada ecosystems. In the giant sequoia-mixed conifer forest, pre-Euroamerican fires burned at intervals ranging from 2-30 years, as evidenced by fire scars in the giant sequoia annual ring record dating back nearly 2,000 years (Kilgore and Taylor 1979; Swetnam 1993).
As in many other areas of California and the Western US, heavy surface fuels had accumulated in many forest types in the Parks as a result of a century-long disruption of the natural fire regime (Parsons 1978, van Wagtendonk 1985). In addition, an increase in small trees in the understory, limited by fire in the past, resulted in an unusually high density of young trees (Vankat and Major 1978). These altered fuel and vegetation conditions increase the risk of unusually severe wildland fires that may result in undesirable fire effects. Reproduction has also been limited for species that depend on fire for regeneration, such as giant sequoia (Sequoiadendron giganteum [Lindley] Buchholz) (Kilgore 1972). To begin to address these changes, fire reintroduction was needed.
The Parks' long-term goals include restoring and maintaining the natural fire regime to the maximum extent possible. For the past three decades, the Parks' fire management program has focused first on using fire to reduce heavy surface fuel loads, in part because of the extent of the fuel hazard problem. The primary objective of the prescribed fire program, therefore, is to reduce heavy surface fuels that expose Park developments and cultural and natural resources to damage from severe wildland fire. The first fire planned in an area, called a restoration burn, has an objective of 60-80 percent total surface fuel consumption.
While fuel reduction objectives were assessed using short-term fuel load measurement, the prescribed fire program was in place for over ten years before a long-term monitoring program was initiated in 1982. This monitoring program was designed to assess objective achievement as well as to document short- and long-term changes in fuel and vegetation in areas where prescribed fire is used.
With further evolution of the program, the Park staff began to address issues in addition to fuel reduction. While large changes in forest stand structure occurred following prescribed fire (Keifer 1998), there were no specific targets for stand structure, making it difficult to assess goals related to forest structural restoration. The Park staff has recently developed preliminary targets for structural conditions in all vegetation types where stand structure is likely to have been greatly altered over the past century. These target conditions have been determined using the best available information, including research data, historic photographs, written accounts and expert opinion.
To determine whether the prescribed fire program is making progress toward achieving forest structural goals, stand density results from the Parks' fire effects monitoring program were compared with the newly developed targets. If these and other structural target conditions are attained, the program can progress more readily toward restoring and maintaining the natural fire regime, where appropriate. If the target conditions are not achieved, changes to the prescribed fire treatment or reanalysis of the target conditions may be needed before natural fire regimes can be readily restored. The stand-level structural target for the giant sequoia-mixed conifer forest is to maintain the density of trees >80 cm DBH (trees established almost exclusively prior to Euroamerican settlement) between 10-75 trees/ha and to restore the density of trees <80 cm DBH to 50-250 trees/ha.
Three broad vegetation zones dominate the parks: the foothills (1600 to 5000 ft), composed of annual grasslands, oak and evergreen woodlands, and chaparral shrubland; the mixed-conifer forest (5000 to 10000 ft), with ponderosa pine and white and red fir dominated forests; and the high country (10,000 to 14,000 ft), composed of subalpine and alpine vegetation, and unvegetated landscapes. While prescribed fire effects monitoring takes place in seven different vegetation types, results from just one vegetation type, the giant sequoia-mixed conifer forest, are presented here.
The giant sequoia-mixed conifer forest is located at elevations from 1,650-2,200 meters (5,400-7,200 feet), on all aspects, in drainage bottoms, broad upland basins and, occasionally, on steep slopes and ridgetops. Soils are coarse-textured and acidic, and soil depth ranges from shallow to very deep. The giant sequoia-mixed conifer forest is dominated by mature white fir (Abies concolor [Gordon & Glend.] Lindley), red fir (A. magnifica Andr. Murray) and giant sequoia (Sequoiadendron giganteum [Lindley] Buchholz), but also includes sugar pine (Pinus lambertiana Douglas), ponderosa pine (P. ponderosa Laws.), Jeffrey pine (P. jeffreyi Grev. & Balf.) and incense cedar (Calocedrus decurrens [Torrey] Florin) in small, varying amounts. Understory trees are primarily composed of white fir and incense cedar. The understory vegetation is typically sparse, with few herbs and <20 percent shrub cover.
Monitoring data were collected from a network of permanently marked 20 x 50 meter plots established using a stratified-random sampling design within the Park areas designated for prescribed fire. Fuel load was measured using the planar transect method (Brown and others 1982). Total fuel load included: duff (the consolidated, decomposing organic layer above mineral soil), 1-hour (0-0.24 inches in diameter), 10-hour (0.25-0.99 inches), 100-hour (1.0-2.99 inches), and 1,000-hour (3 inches and greater) TLFM woody fuels. To obtain overstory tree density, all trees >1.37 meters (4.5 feet) in height were tagged, mapped, identified to species, measured for diameter, and recorded as live or
dead. Tree seedling (trees <1.37 meters in height) and brush density, as well as herbaceous vegetation cover were also measured (U.S. Department of Interior, National Park Service 1992a). In each plot, measurements were taken pre-burn, immediately post-burn, and 1-, 2-, 5-, and 10-years post-burn. All areas monitored were burned within the same range of burning conditions specified for each fuel/vegetation type (U.S. Department of Interior, National Park Service 1992b).
For post-burn fuel reduction and tree mortality, 28 plots that burned in 17 different prescribed fires between 1982 and 1995 were analyzed. To examine long-term post-burn fuel accumulation and changes in tree density over time, 12 plots that reached the 10-year post-burn stage were evaluated. These plots burned in seven separate prescribed fires.
Mean total fuel load ± one standard error was 63.6 tons/acre ±5.8 pre-burn and 18.3 tons/acre ±3.1 immediately post-burn, a 71 percent reduction in mean total fuel load (Figure 1). This result indicates that the fuel reduction objective for the initial prescribed burn (60-80 percent total fuel reduction) was achieved in the giant sequoia-mixed conifer forest using the current burn prescriptions.
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Figure 1: Post-burn fuel reduction from
prescribed fires in Sequoia-Kings Canyon National Parks, 1982-1995
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Pre-burn mean density for trees <80 cm DBH was 625 trees/ha, which is two and a half times the maximum target value (Figure 2). The pre-burn mean density of trees >80 cm DBH was 46 trees/ha, well within the target range of 10-75 trees/ha. Tree density was reduced one-year post-burn, with 53% mortality of trees <80 cm DBH but only 4% mortality of trees >80 cm DBH. While large tree post-burn density remained within the target range, the density of trees <80 cm DBH (292 trees/ha) was still higher than the target maximum of 250 trees/ha (Figure 2).
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Figure 2: Comparison of post-burn tree
densities with program targets, Sequoia and Kings Canyon Natioanl Parks
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By five years post-burn, the mean density of trees <80 cm DBH was further reduced to 222 trees/ha, which falls within the target range (Figure 2). The larger trees are only slightly reduced to 42 trees/ha by five years post-burn. Most of the density reduction occurred in the smaller trees, indicating that prescribed fire may reduce the potential for spread of crown fire in these forests by thinning smaller trees and ladder fuels, while minimizing effects on larger trees (8% reduction in density from pre-burn to 5-years post-burn). All large giant sequoia trees within the monitoring plots survived the prescribed fires (Keifer and others, in press).
Although the Parks' preliminary target conditions do not yet include species composition, one of the indicators of successful fire regime restoration is the regeneration of fire-adapted species. Giant sequoia establishment and recruitment rely heavily on exposed mineral soil and canopy openings resulting from fire. Results from 12 giant sequoia-mixed conifer forest monitoring plots indicate that the relative density of giant sequoia has tripled 10 years after prescribed fire (Figure 3). This increase is primarily attributed to the successful recruitment of giant sequoia post-burn regeneration into the smallest tree diameter class, along with the fire-induced mortality of many of the small white fir (Keifer 1998). This regeneration of giant sequoia is in stark contrast to areas that have not burned, where giant sequoia regeneration is almost entirely absent (Stephenson 1994). Demographic models suggest that the amount of sequoia regeneration following prescribed fire may be roughly comparable to that prior to Euroamerican settlement (Stephenson, unpublished data).
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Figure 3: Tree density changes for individual
species by size class, 10 years after prescribed fire, Sequoia and Kings
Canyon National Parks
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The results from this monitoring program provide an example of prescribed fire being successfully used both to reduce fuel load and to restore forest structure in the giant sequoia-mixed conifer forest of Sequoia and Kings Canyon National Parks. Whether forest structure can be restored in other vegetation communities using prescribed fire depends on many site-specific factors, including the number of fire-return intervals missed and history of other disturbance. In some areas, several prescribed fires may be needed to completely restore fuel load and forest structure before natural fire regimes can be returned.
Development of target conditions is ongoing, and any new knowledge gained about past conditions will be used to further refine target conditions. Additional information that will be useful in this process includes quantitative analysis of historic photography and examination of existing Park databases that contain information, by species, on the density of large trees (those present prior to Euroamerican settlement). Also, additional targets for landscape-scale conditions that cannot be measured at the plot level (such as forest patch size and distribution) are being developed.
In addition to monitoring areas burned once, areas where repeated prescribed burning has occurred is especially interesting to fire and resources managers. Long-term monitoring results indicate that mean total fuel load reached 63 percent of pre-burn levels 10 years after fire (Keifer and Manley, in press). Woody fuels (most of which are >1 inch in diameter) accumulated much faster than duff, reaching 80 percent of pre-burn levels after 10 years, compared to only 37 percent of pre-burn levels for duff. The relatively rapid accumulation of woody fuels demonstrates that a second burn after about 10 years may be needed to reduce both the fuels not consumed by, and the fuels accumulated as a result of, the initial fire.
Many areas in the parks treated initially by restoration burns have reached or exceeded the 10-year post-burn phase. For the past 30 years, the park staff has focused on initial restoration burns and so many of the areas burned early in the program did not get further attention after receiving the first fire application. Although the intention was to return to many of these areas for subsequent burns, areas that had not been burned took precedence. The park staff is concerned that neglecting areas initially burned could result in fuel hazards that the initial burns were intended to mitigate. More attention is now being paid to plan and execute 'repeat' burns so as not to lose the benefit accrued from the initial prescribed fire. Monitoring in these areas will be critical to help address the many questions that have been raised that more repeated burns and long-term monitoring of these reburns will help address.
Once fuels are restored to more natural levels, some areas of the Parks may then be returned to a natural fire regime where lightning ignitions are allowed to burn within the usual constraints of safety and environmental conditions. Other areas, especially those located near developments and some Park boundaries, may need to be managed under perpetual prescribed fire regimes. In these areas, the consequences of various fire return intervals must be determined (using models) and decisions about fire application frequency must be made. The effects of repeated fires on giant sequoia regeneration must also be well understood to ensure the perpetuation of the giant sequoia-mixed conifer forest. Long-term monitoring is critical for understanding the consequences of our land management actions
and for providing feedback to managers. The results from this ongoing adaptive management program may be especially interesting to managers of other parks or wilderness areas where fire is considered the most appropriate means for the restoration and management of natural ecosystems. -
You can reach MaryBeth at 559-565-3128/marybeth_keifer@nps.gov
Brown, J.K., R.D. Oberhue, and C.M. Johnston. 1982. Inventorying surface fuels and biomass in the Interior West. Gen. Tech. Rep. INT-129. Ogden, Utah: Intermountain Forest and Range Experiment Station, U.S. Department of Agriculture, Forest Service.
Keifer, M. 1998. Fuel load and tree density changes following prescribed fire: the first 14 years of fire effects monitoring. In: Brennan, Leonard A.; Pruden, Teresa L., editors. Proceedings of the Tall Timbers fire ecology conference, No. 20. Fire in ecosystem management: shifting the paradigm from suppression to prescription. Tallahassee, Florida: Tall Timbers Research Station.
Keifer, M. and J. Manley, in press. Beyond initial fuel reduction in the giant sequoia-mixed conifer forest: Where do we go from here? In: Proceedings, Fire in California Ecosystems: Integrating Ecology, Prevention, and Management, November 17-20, 1997, Bahia Hotel, San Diego, CA.
Keifer, M., N.L. Stephenson, and J. Manley, in press. Prescribed Fire as the Minimum Tool for Wilderness Forest and Fire Regime Restoration: A Case Study from the Sierra Nevada, CA. In: Cole, David N.; McCool, Stephen F. 2000. Proceedings: Wilderness Science in a Time of Chance. Proc. RMRS-P-000. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Kilgore, B.M. 1972. Fire's role in a sequoia forest. Naturalist 23(1):26-37.
Kilgore, B.M. and D. Taylor. 1979. Fire history of a sequoia-mixed conifer forest. Ecology 60(1):129-142.
Parsons, D.P. 1978. Fire and fuel accumulation in a giant sequoia forest. Journal of Forestry 76:104-105.
Stephenson, N. L. 1994. Long-term dynamics of giant sequoia populations: Implications for managing a pioneer species. Pages 56-63 in P. S. Aune, technical coordinator. Proceedings of the Symposium on giant sequoias: their place in the ecosystem and society, 23-25 June 1992, Visalia, California. USDA Forest Service General Technical Report PSW-151.
Swetnam, T.W. 1993. Fire history and climate change in giant sequoia groves. Science 262: 885-889.
U.S. Department of Interior, National Park Service. 1992a. Western Region Fire Monitoring Handbook. Available from Pacific West Regional Office, San Francisco, CA.
U.S. Department of Interior, National Park Service. 1992b. Sequoia and Kings Canyon National Parks fire management plan. Available from Sequoia and Kings Canyon National Parks. Three Rivers, CA.
Vankat, J.L., and J. Major. 1978. Vegetation changes in Sequoia National Park, California. Journal of Biogeography 5:377-402.
van Wagtendonk, J. W. 1985. Fire suppression effects on fuels and succession in short-fire-interval wilderness ecosystems. Pages 119-126 in J. E. Lotan, B. M. Kilgore, W. C. Fischer, and R. W. Mutch, editors. Proceedings - symposium and workshop on wilderness fire, 15-18 November 1983, Missoula, MT. USDA Forest Service General Technical Report INT-182.
