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Wildlife, Animals, and Plants |
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FIRE CASE STUDIES
1st CASE STUDY:
Effects of fall and spring fires on woody vegetation on the pine-grassland ecotone of the southern Black Hills REFERENCES: Bock, C. E.; Bock, J. H. 1983 [47] Bock, J. H.; Bock, C. E. 1984 [48] FIRE CASE STUDY AUTHORSHIP: Howard, Janet L. 2001. SEASON/SEVERITY CLASSIFICATION: Not stated STUDY LOCATION: The study was conducted on Wind Cave National Park and adjacent Black Hills National Forest lands in Custer County, South Dakota. PREFIRE VEGETATIVE COMMUNITY: Slopes above the study sites were forested with interior ponderosa pine (Pinus ponderosa var. scopulorum); lower slopes were mixed plains grasslands composed of sedges (Carex spp.), big bluestem (Andropogon gerardii var. gerardii), little bluestem, (Schizachyrium scoparium), Sandberg bluegrass (Poa secunda), blue, hairy, and sideoats grama (Bouteloua gracilis, B. hirsuta, B. curtipendula), and western wheatgrass (Pascopyrum smithii). The study site was a mosaic of interior ponderosa pine savanna and interior ponderosa pine forest with an understory of graminoids and shrubs. Important shrubs on the study site were western snowberry (Symphoricarpos occidentalis), currant (Ribes spp.), chokecherry (Prunus virginiana), leadplant (Amorpha canescens), and Saskatoon serviceberry (Amelanchier alnifolia). Based upon dendrochronological analysis, presettlement fire return interval at the Park was 13 to 21 years. Before prescribed fire treatments, mean interior ponderosa pine density on study plots was 3.2 stems/17 m2; most of those trees were saplings less than 4 inches (10 cm) dbh [47,48]. TARGET SPECIES PHENOLOGICAL STATE: Interior ponderosa pine was probably dormant during both the fall and early spring fires. SITE DESCRIPTION: elevation: 4,900 feet (1500 m) FIRE DESCRIPTION: The purpose of the study was to determine the effects of cool-season fires on woody vegetation at the interior ponderosa pine-grassland ecotone. Objectives were: (1) determine if prescribed fire increases understory shrub and tree density, (2) quantify mortality of immature interior ponderosa pine on the ecotone, and (3) determine if prescribed fires had consistent and predictable results throughout the study area. Two cool-season fires were conducted. The fall fire was a 157-acre (63 ha) burn on 17 October 1979. The fire was set at mid-day and passed over the area in 4 hours. A few snags smoldered until the next morning, when it started raining. Fire weather conditions were [47]: windspeed 10 miles/h (16 km/h)temperature 57.9 oFahrenheit (14.4 oC) relative humidity: 45% soil/fuel moisture: 4-29% The spring fire was an 815-acre (326 ha) burn on 14 April 1980. The fire was set at 10:30 a.m. and burned most of area within control lines within 36 hours. It was declared out on 15 May 1980. Fire weather conditions were [47]: windspeed: 5 miles/h (8 km/h)temperature: 57 oFahrenheit (14 oC) relative humidity: 32% soil/fuel moisture: 21-36% The 2 fires were similar, so pre- and postfire litter and vegetation data were pooled for the 2 sites. Litter depth averaged 1.61 inches (4.02 cm) before fire [47]. FIRE EFFECTS ON TARGET SPECIES:Interior ponderosa pine canopies, trunks, and saplings were reduced through the 2 postfire years of the study. Nearly all pines less than 4.6 feet (1.4 m) tall were killed. Among taller trees, most mortality was in trees less than 2 inches (5 cm) dbh. Pine canopy was reduced 12% by the fires. Changes in percent interior ponderosa pine cover over the study period are given below. Chi-square values were calculated using actual numbers.
Litter depth was significantly reduced (p < 0.01) to a 0.76-inch (1.89 cm) depth by burning [47]. FIRE MANAGEMENT IMPLICATIONS:The study demonstrates that prescribed spring or fall fire can control interior ponderosa pine encroaching plains grasslands. Outcome of the study objectives, listed by number above, follow. (1) A single fire treatment had little effect on the density of shrubs and deciduous understory trees. Overall shrub cover was reduced in the 1st but not the 2nd postfire year [47]. Density of currants was reduced and leadplant increased, but density of other shrubs was unaffected by fire. Overall graminoid cover was also unaffected by burning, although species showed different responses. (2) The prescribed fires reduced fuels and dramatically slowed interior ponderosa pine invasion and recruitment. (3) The prescribed fires gave consistent and predictable results across the study areas. Grassland fires are more predictable than fires in woody vegetation [48]. The Bocks' hypothesis of consistent and predictable results was also borne out in an earlier Wind Cave National Park study by Gartner and Thompson [121]. 2nd CASE STUDY:
CASE NAME: Interior ponderosa pine mortality from seasonal prescribed fires in southwestern Colorado REFERENCES: Harrington, M. G. 1985 [139] Harrington, M. G. 1987 [142] FIRE CASE STUDY AUTHORSHIP: McMurray, Nancy. 1988. SEASON/SEVERITY CLASSIFICATION: fall (20 Oct. 1977)/light-severity spring (12 June 1978)/light- to moderate-severity summer (18 Aug. 1978)/light- to moderate-severity STUDY LOCATION: The study site is on the San Juan National Forest. PREFIRE VEGETATIVE COMMUNITY: The study sites were in an interior ponderosa pine/Gambel oak (Pinus ponderosa var. scopulorum/Quercus gambelii) stand. A fire history study showed that the last fire occurred in the stand in 1877. Prior to 1877, fires burned at 1- to 16-year intervals [139], and stand structure was presumably open. Pretreatment stand structure in 1977 was a dense overstory of pole-sized pines, and a dense understory of shrubby oaks. Herbaceous species and shrubs other than Gambel oak were sparse. Tree density was 300 per acre (750 trees/ha); basal area averaged 124 square feet per acre (28 m2/ha). Size class distribution of interior ponderosa pine was [139,142]:
TARGET SPECIES PHENOLOGICAL STATE: fall: dormant - buds set; seeds ripe spring: active growth beginning - buds broken; stems expanding; needles 1 to 2 inches (2.5-5 cm) long and expanding summer: active growth - stem diameter growth; cones and seeds developing [142] SITE DESCRIPTION: Elevation: 7,600 feet (2317 m) Aspect: south slope: < 5% [139,142] Precipitation was above the 16.8-inch (427 mm) annual mean 3 months preceding each burn, ranging from 2.8 inches (710 m) above normal before the spring burn to 0.4 inch (102 mm) above normal for the summer burn (fall ppt. not stated). The study site received about 2.2 inches (560 mm) of rain the July prior to summer burning, which probably encouraged tree growth. Precipitation following the fire treatments was 0.5 inch (130 mm), 3.8 inches (965 mm), and 3.5 inches (890 mm) above average for fall, spring, and summer treatments, respectively [142]. FIRE DESCRIPTION:Backing fires were used until 15- to 20-foot (4.5-6 m) strips had burned inside firelines. Strip headfires were then ignited at 15- to 30-foot-wide (4.5-9 m) strips, depending upon weather and fuel conditions. Weather, fuel* moisture, and fire behavior during prescribed burning were [139]:
FIRE EFFECTS ON TARGET SPECIES: The study objective was to compare interior ponderosa pine mortality resulting from crown scorch incurred during fall, spring, and summer prescribed surface fires. Tree scorch classes, defined as the percentage of total crown height on all sides of the tree in which foliage was killed, were 10-30%, 34-66%, 67-89, 99%, and 100%. Study trees were monitored for 5 postfire years. In order to avoid the interactive effects of cambium and crown scorch damage, tree with boles that were charred enough to sustain damage to the cambium were not included in the study [139]. The management objective was to reduce the density of understory Gambel oak with 2nd-year reburns. Treatment effects to Gambel oak are summarized in the Fire Case Studies section of the FEIS report on that species. At the end of 5 years, overall interior ponderosa pine mortality from fall crown scorch was significantly less (p=0.05) than that from spring or summer. Tree mortality equaled 12, 26, and 29% for fall, spring, and summer fires, respectively. Differences in mortality between seasons were most substantial during the 1st postfire season: only 5% of fall-scorched trees died, compared with 17% of spring-scorched trees and 21% of summer-scorched trees. Subsequent mortality for all seasons was relatively similar over the length of the study, suggesting good survival potential for those trees not killed outright by scorching. Generally mortality decreased as d.b.h. increased regardless of season. Trees less than 7 inches (17.5 cm) d.b.h. accounted for approximately 85% of the observed mortality. Mortality from fall burns was comparable to that recorded on the control plots. Mortality in trees in the < 4-inch and 7 to 10.9-inch d.b.h. classes was significantly greater on spring and summer burn plots than on fall burn and unburned plots. Percent mortality of scorched trees by diameter class and season of fire is given below. Means in rows followed by different letters differ at the 5% significance level. Means in columns followed by different numbers differ at the 5% level [142].
Scorch damage of up to 90% produced minimal mortality regardless of season of burn. When more than 90% of the crown was scorched, fall burning caused only 1/3rd the mortality produced by spring or summer burning. Percent mortality of scorched trees by scorch class and season of burn is presented below. Means in rows followed by different letters differ at the 5% significance level. Means in columns followed by different numbers differ at the 5% level [142].
Trees subjected to dormant-season burning were resistant to severe crown scorch damage. Of those trees sustaining 100% damage, only 10 of 28 (39%) ultimately died. All 8 trees sampled in the 7 to 10.9-inch (17.5-27.3 cm) category survived. Harrington [139] cautioned that this resistance to fire mortality is demonstrated for trees where crown scorch was the only type of fire damage recorded; such extensive damage would probably be fatal when combined with bole damage. FIRE MANAGEMENT IMPLICATIONS:Fall burning is the best option if minimizing mortality in the smaller size classes is a management objective; this is particularly true in burn units where fuel concentrations are heavy. If management objectives include large reductions in fuels or the elimination of undesirable understory brush species, growing-season fire may be the most effective. Although trees are generally more susceptible to fire damage during the growing season, most mortality due exclusively to crown scorch occurs in the smaller size classes. Such mortality can be beneficial if thinning from below is desired. 3rd CASE STUDY:
CASE NAME: Natural interior ponderosa pine regeneration following prescribed fire in north-central Arizona REFERENCES: Sackett, S. 1980 [247] Sackett, S. S. 1984 [248] Sackett, S. S.; Haase, S.; Harrington, M. G. 1993 [252] Sackett, S. S.; Haase, S.; Harrington, M. G. 1996 [251] FIRE CASE STUDY AUTHORSHIP: Howard, Janet L. 2001. SEASON/SEVERITY CLASSIFICATION: fall/moderate STUDY LOCATION: The study took place on the Fort Valley Experimental Forest near Flagstaff, Arizona. PREFIRE VEGETATIVE COMMUNITY: The study site was in an interior ponderosa pine/Arizona fescue (Pinus ponderosa var. scopulorum/Festuca arizonica) forest. Interior ponderosa pine was the only overstory tree species. Stand structure was small, even-aged groups in an uneven-aged stand. Site index was 82, based on 100 years. Mean density of interior ponderosa pine on study sites was 39 per acre (96/ha). Size class distribution is presented below [248]: Seedlings: < 4.5 feet tall, 395
stems/acre (< 1.4 m, 975 stems/ha) Relative tree cover on the experimental plots consisted of the following: sapling 17%; pole 62%, sawtimber 17.3%; small openings comprised the remaining 3.7%. Irregular distribution of the pine understory resulted in numerous grass-dominated openings [248]. Fendler's ceanothus (Ceanothus fendleri), mountain muhly (Muhlenbergia montana), bottlebrush squirreltail (Elymus elymoides), pine dropseed (Blepharoneuron tricholepis), Cainville thistle (Cirsium calcareum), groundsel (Senecio spp.), and goldenrod (Solidago spp.) were understory associates [252]. TARGET SPECIES PHENOLOGICAL STATE:dormant SITE DESCRIPTION: Elevation: 7,200 to 7,400 feet (2195-2255 m) Slope: 0 to 5% Mean annual temperature: 43 degrees Fahrenheit (6 oC) Average annual precipitation: 22 inches (570 mm); bimodal distribution; summer drought is common Soils: Brolliar stony clay loam, tentatively classified as a fine, montmorillonitic, frigid, typic Argiboroll; depth to basalt flow rock usually 8 to 40 inches (20-100 cm) [248] Results of fire scar analysis indicate that the study area had not burned since 1876; prior to that time, mean fire return interval was 2 years [252]. FIRE DESCRIPTION:Rainfall was below normal during the late summer and fall. The following precipitation amounts were recorded at the fire site just prior to prescribed burning on November 5, 1976: October 21 - 0.27 inch (69 mm) October 25 - 0.03 inch (8 mm). Ignition began at 5:30 p.m. and continued until 11:00 p.m. Backing fires were used initially, but later in the evening when these ceased to carry effectively, short strip headfires with 30 to 40 feet (9-12 m) between strips were utilized. Although rate of spread approximated 4 to 6 feet per minute (1.2-1.8 m/min), it sometimes increased to as much as 12 feet per minute (3.7 m/min). Flame lengths in surface needles rarely exceeded 16 inches (40 cm). Air temperature dropped from 59 degrees Fahrenheit (15 oC) at 5:30 p.m. to 37 degrees Fahrenheit (3 oC) at 12:00 a.m., when most of the flaming combustion was complete. Measured surface needle moisture content increased from 8 to 12% during the night as temperatures fell; similarly, ground fuel (F & H layers) moisture content of the forest floor increased from 10 to 19%. Glowing combustion in deep duff fuels continued for 2 to 3 days; some large woody debris and stumps smoldered for up to 4 weeks. Forest floor material less than 1 inch (2.5 cm) in diameter was reduced 63%; material greater than 1 inch (2.5 cm) was reduced 69%. Mineral soil was exposed on about 19% of the area, mostly around large mature trees and rotten logs. Pre- and postfire fuel loads were as follows [248]:
FIRE EFFECTS ON TARGET SPECIES: Seedlings appeared soon after summer rains started in mid-July, 1977. High seedling concentrations occurred under large, mature pines and near heavy fuel accumulations where the forest floor layers had been completely consumed. Although partial shade was provided by the overstory, charcoal chunks, and unburned debris, seedlings appeared to be most frequent on the northeast side of seed trees. Needles cast over the period from November to July covered seeds with a fresh litter layer of 300 to 475 pounds/acre (268-424 kg/ha). In comparison to unburned controls, burned areas produced better germination and stocking; burns had approximately 2,600 seedlings/acre, with 38% of sample quadrats stocked versus control plots where seedlings equaled 833 seedlings/acre with a 17% stocking. Germination was most successful in areas where fire disturbance was most pronounced, and correlation between quadrat bare area (feet2) for each burning treatment and quadrats stocked with interior ponderosa pine seedlings was high (r=0.92). Number of seedlings in relation to seedbed is presented below:
Germination and initial establishment were excellent on burned areas despite below normal precipitation during the spring and summer of 1977. The enhanced survival under these conditions may have resulted from the improved moisture relations, increased nutrient availability, and more favorable soil temperatures associated with mineral soil seedbeds. However, subsequent mortality was quite high due to the combined effects of drought, frost heaving, animal damage, and interval burning (see below). By the fall of 1981, only 12% of tagged seedlings (25 on each of 18 plots treatment plots and 8 on controls) remained. Survival of 4-year-old tagged seedlings on plots subjected to interval burning was 6%; 19% of tagged seedlings survived on plots receiving the initial treatment only. Probable cause of death (by %) of seedlings selected 1 year after 1977 postfire germination is presented below [251].
22 fires after seedling selection 31 fire after seedling selection 4No fires after seedling selection Although very few sample seedlings were still alive by the fall of 1980, many 1977 seedlings remained on treatment plots. As a result, prior to interval burning in the fall of 1980, all seedlings on the 1-, 2-, and 4-year rotation plots were inventoried; a 100% inventory of 1977 seedlings on projected 6-, 8-, and 10-year rotations was done in the spring of 1981. Dry burning conditions in the fall of 1980 created more intense fires than had previously occurred during the study. Fireline intensities ranging between 260 to 650 btu/sec/fireline foot were produced on 4-year rotation plots, killing 94% of 3-year-old seedlings. Reduced fuel accumulations on annual and biennial plots produced less intense fires that resulted in 50 and 87% seedling mortality, respectively. Regardless of interval treatment, most surviving seedlings were located in areas of sparse or discontinuous fuels. Number of seedlings remaining from 1977 germination is presented below by treatment [251].
2one fire after seedling selection 3No fires after seedling selection FIRE MANAGEMENT IMPLICATIONS: Prescribed fire represents an effective means of site preparation for interior ponderosa pine establishment in the Southwest, especially when regeneration is needed in dispersed, small openings where hand planting is not cost effective. Despite abundant initial establishment on mineral soil seedbeds created by burning, drought, frost heaving, and animal damage still constituted obstacles to long-term establishment. Seedbeds remained favorable for natural regeneration for at least 4 years after fire, allowing managers some leeway in attempting to coordinate site preparation with good seed crop years. Burning can be deferred for several years after germination so interior ponderosa pine seedlings are large enough to resistant to surface fire damage. Sackett and others [251] concluded that 4-year interval burning was most effective for fire hazard reduction while protecting the overstory. Annual burning or 2-year interval burning was not feasible because conditions were too damp for fire (scarcity of fuels was not limiting). Six-year rotations allowed fuels to build up to the point that overstory could be damaged, and wildfires may be difficult to control under extreme fire weather conditions. They noted that mullein (Verbascum thapsus), Dalamation toadflax (Linaria dalmatica), and Cainville thistle (Cirsium calcareum) were most likely to invade severely burned sites, favoring bases of large, old-growth snags as microsites [252]. OTHERS: There are several other fire cases studies on interior ponderosa pine. Studies that may be of particular interest are listed below. Contact your local agency, university, or public library for copies of these articles.
Related categories for SPECIES: Pinus ponderosa var. scopulorum | Interior Ponderosa Pine |
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