Photo Series for Quantifying Fuels and Assessing Fire Risk in Giant Sequoia Groves

Photo Series for Quantifying Fuels and Assessing Fire Risk in Giant Sequoia Groves David R. Weise, Aaron Gelobter, Sally M. Haase, and Stephen S. Sackett Introduction he giant sequoia (Sequoiadendron giganteum Lindl. Taylor 1979). Fuel reduction has been accomplished using TBuchholz.) of the Sierra Nevada is among the most prescribed fire and thinning (Benson 1986, Harrison 1986, highly valued tree species in North America. Parsons and Nichols 1986, Rogers 1986). These treatments Approximately 75 giant sequoia groves exist throughout have resulted in a wide range of stand and fuel conditions the natural range, a 420- by 24-km belt in central that affect the fire hazard potential as well as the esthetics California. Groves occupy a combined area of 14,410 ha of the groves. (Weatherspoon 1990). Fire is an important part of the giant Fire hazard analysis requires an inventory of the sequoia/mixed conifer forest type. Fire is essential to the combustible natural fuels present in each grove. This continued vigor of this type and plays many roles ranging inventory can be costly and time consuming even though from fuel reduction and nutrient cycling to seedbed the total area occupied by the giant sequoia type is small preparation and serotinous cone opening (Barbour and compared to other forest cover types. Photo series are others 1980). However, effective fire exclusion in this often used to quickly provide rough estimates of the century has caused dead and live fuel loadings to increase amount of fuel in a stand (Maxwell and Ward 1976) by in many groves. Fire-free intervals ranged from 5 to 18 providing a series of photographs that can be used to years during the time period 1700 to 1875 for a 4,500-acre estimate the loading of each fuel component separately. area in the giant sequoia-mixed conifer type (Kilgore and Thus a composite loading for the site could be derived by USDA Forest Service Gen. Tech. Report PSW-GTR-163. 1997. 1 USDA Forest Service Gen. Tech. Report PSW-GTR-163. 1997. 2 summing the components from different photographs. burned, logged and burned, or undisturbed were located Standard procedures to ensure compatibility of photo in Sequoia National Forest, Sequoia-Kings Canyon series have been developed (Maxwell and Ward 1980). National Parks, and Mountain Home Demonstration State Photo series have been developed for a wide variety of Forest. Because multiple activities have occurred in many forest cover types and fuels. Most photo series have been groves, a description of the activities that resulted in the developed for western cover types; however, a small present fuel condition accompanies each photo. number have been developed for eastern forest types. Photo points were located at each site and Recent photo series have included stereo photographs permanently identified with reinforcing bar. Locational (Ottmar and Hardy 1989, Ottmar and others 1990). The information such as distance and bearing from a photo series developed by Blonski and Schramel (1981) prominent landmark or latitude and longitude determined and Maxwell and Ward (1979) illustrate fuels created by with a global positioning system was collected for each natural processes (natural fuels) and active management photo point. This information can be used to reestablish (activity fuels), respectively, and are applicable to the the photo point in the future to monitor the long-term Sierra Nevada of California. Other photo series may also changes associated with various management activities. A be applicable to California fuels. 6-foot (1.8-m) pole with 1-foot (0.30-m) increments was placed near the center of the field of view. The design of the inventory plot followed the guidelines developed by Development of Photo Series Maxwell and Ward (1980). The photo series presented in this report was developed as Five equally spaced lines 150 feet long (45.7 m) an aid to determine fire hazard potential caused by natural radiating from the photo point were established at each and activity fuels in giant sequoia groves; it also illustrates location. Dead and downed fuels were inventoried along the esthetic impacts of the various treatments used in the each line at five sample points. At each sample point, dead selected groves. Nineteen sites representing the range of and down woody material was sampled and classified fuel loading conditions generated by various management along a 30-ft (horizontal distance) sample plane (Brown activities were identified by Sequoia National Forest staff 1974). A 3-ft (0.91-m) sample plane was used for 0- to 0.25- in cooperation with Sequoia-Kings Canyon National Park inch (0 to 0.64-cm) material, 6-ft (1.83-m) for 0.25- to 1-inch and Mountain Home Demonstration State Forest staffs. (0.65- to 2.54-cm), 10-ft (3.05-m) for 1- to 3-inch (2.54- to Sites that were easily accessible and had been logged, 7.62-cm), and 30-ft (9.15-m) for greater than 3-inch (> 7.62-cm) material. A 0.15-acre (0.06 ha) triangular plot was centered photo point data sheet (Haase and others 1996). Forest in the field of view. The apex of the equilateral triangular floor fuels accounted for as much as 80 percent of the total plot (150 ft on a side, 90 ft base) was located at the photo dead fuel loading at some of the photo points. point. Diameter at breast height, total height, and crown For 15 of the 19 photo points, a depth was measured in height (height to crown base) were estimated for all trees the center of each side for each undisturbed square-foot and all snags greater than 8 inches dbh (20.3 cm). Trees forest floor sample because Haase and others (1996) have less than 8 inches dbh were sampled in six 1/300th-acre shown a direct relationship between depth and loading (13.5 m2) circular plots, and shrub and grass data were for undisturbed forest floors in giant sequoia/mixed collected using twelve 1/4,000th-acre (1-m2) circular plots. conifer stands. An equation to predict forest floor weight The small plots were located along the 150-ft lines (see as a function of depth was successfully developed (R2 = 0.91) Brown 1974 for exact plot configuration). Because of the (Haase and others 1996). The general equation to predict nature of the sampling scheme, prominent fuels in the forest floor weights is photo may or may not have been measured. Loading = 12.3(depth) − 2.9, Organic material (litter, fermentation, and humus where loading is in tons/acre and depth is in inches. layers) that has accumulated for many years in the groves This equation may be used to easily estimate forest floor is quite deep and a significant percentage of the total fuel loading in giant sequoia groves with undisturbed forest load. Research has shown that prescribed fires often floors. The accuracy of this estimate depends on the total remove most if not all accumulated organic material. The percentage of the area that has undisturbed forest floor resulting temperature increase in the mineral soil below material. the organic layers has been found to be quite significant Information on overstory and understory was (Sackett and Haase 1988). Current photo series often list collected using various-sized plots. All stems greater than only the depth of the accumulated organic material—not 2 inches were inventoried. Diameter at breast height, total the weight. To determine the actual forest floor loading height, and height to live crown (crown height) were (all organic material and woody material up to 1-inch measured. Because giant sequoia is a component of the 2 diameter) for each photo, twenty-five 1-ft (0.09-m2) forest Sierra Nevada mixed-conifer type (Society of American floor samples were systematically located within each field Foresters 1980), the stand description lists the major of view. Mean forest floor loadings were determined and species for each photo point. No dominant species is are included in the Other Measurements section of the assigned. A dominant brush and grass were determined USDA Forest Service Gen. Tech. Report PSW-GTR-163. 1997. 3 USDA Forest Service Gen. Tech. Report PSW-GTR-163. 1997. 4 by selecting the brush type and grass type that occurred are desired in an inventory, they must be derived from an most frequently in the sample plots. Mean height and independent sampling or observations. If forest floor ground cover were calculated from data for all brush and loading is desired, use the equation developed to estimate grass species. forest floor loading for this photo series (Haase and others 1996), or develop an equation that follows procedures Using the Photo Series outlined in Haase and others (1996). Visual inventory of downed woody fuels using the photo series can be made as follows. Each fuel characteristic Fire Behavior Prediction should be considered separately. It is possible that the Fire behavior can be predicted using the fuels information composite fuel loading for the site will be derived from in the photo series combined with appropriate weather several different photos. and environmental variables. A table containing rate of 1. Observe each characteristic of the woody fuel on the spread and fireline intensity predictions for a single set of ground, such as size, arrangement, and amount of decay, environmental conditions is included in the photo series by walking the site. (table 1). This table was developed using the BEHAVE fire 2. Select a photo that nearly matches the observed behavior prediction system, the fuels information for each characteristic or two photos that appear to bracket it. photo point, and three sets of weather data—the 10th, 3.

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