Controlling Mature Ashe Juniper in Texas with Crown Fires

Dozed plots and windrow plots were evaluated during 1979 and 1980 with respect to their effectiveness in igniting a crown fire in an adjacent live juniper stand. Dozed plots were ineffective in igniting a crown fire. However, if herbaceous fuel is less than 500 kg/ha, windspeed is less than 10 km/hr, humidity is above 45% and air temperature is less than 3O”C, recently chained or dozed juniper (<lOO days since treatment) can be burned with minimal risks. Windrowed plots produced the best results for igniting the adjacent crowns. Correlation coefficients and coefficients of determination indicated that air temperature, maximum windspeed, and leaf moisture would best predict the area the fire would burn per 6 m of windrow length. Crown fires usually stopped where distance between trees exceeded 7 to 10 m. For optimum results, average windspeed should exceed 16 km/hr, canopy cover should exceed 35% relative humidity should be between20 and 401, air temperature should be between 2 and 32OC, and leaf moisture should be below 60%. Although potential for broad application is limited, this technique could reduce the total cost of juniper control or could be used in wildlife habitat management. Ashe juniper (Juniperus ushei). a non-sprouting species, is a major brush problem on the Edwards Plateau region of Texas (Wink and Wright 1973, Wright 1978) because it suppresses growth of understory herbaceous vegetation and lowers forage availability to domestic livestock and wildlife. The economical control of mature stands has become an increasing concern to rangeland managers. Costs of total chemical or mechanical treatment of stands of woody plants are becoming prohibitive. Prescribed burning can control small Ashe juniper if a minimum of 1,123 kg/ ha of fine fuel is available (Wink and Wright 1973). With windspeed of 16 km/h, air temperature of 23O C, and relative humidity of 28%, almost all trees less than 1.8 m tall were killed. Under cooler burning conditions in Oklahoma, Dalrymple (1969) obtained 100% kill of trees less than 0.6 m and 1.8 m. However for trees over 1.8 m tall in Oklahoma, less than 25% were killed by fire. Other researchers also have reported this inverse relationship between tree size and mortality due to fire (Dwyer and Pieper 1967). While burning of individual trees has been used to control mature juniper (Arnold et al. 1964, Jameson 1966), only Schroeder (1966) and Bruner and Klebenow (1979) have attempted crown fires in pinyon (Pinus edulis) and juniper (Juniperus sp.) woodlands. Schroeder (1966) predicted that a nearly pure stand of juniper would be impossible to burn and suggested that there is a positive relationship between the percentage of pinyon in the stand and the success of fire spread. Bruner and Klebenow (1979) recommended that canopy cover must be at least 23-3570 for a successful The authors were assistant professor, research assistant, and research associate, Department of Range and Wildlife Management, Texas Tech University, Lubbock 79409. Launchbaugh currently is with the Texas Agricultural Experiment Station, Uvalde, while Koerth is with the Texas Agricultural Experiment Station, Corpus Christi. We are indebted to Charles Schriener IV of the YO Ranch for financial and logistical support. We also thank Dr. Henry A. Wright for his help throughout the study, and especially his helpful criticism of the manuscript. Support from the Noxious Brush and Weed Control Program, Texas Tech University, is gratefully acknowledged. Technical Article T-9-269 from the College of Agricultural Sciences, Texas Tecli University. Manuscript received July 29, 1981. JOURNAL OF RANGE MANAGEMENT 36(2), March 1963 burn in Nevada. They advised against burning closed stands (>35% canopy cover of trees) because the tire might be difficult to control and understory shrubs would need to be present to carry the fire. In certain areas of the Edwards Plateau, several problems arise that have before precluded the use of prescribed burning: (I) the mature age class of a stand that supports trees 1.8 to 4.6 m in height, (2) the lack of fine fuel or understory shrubs to carry a fire, and (3) the fear of hazardous conditions necessary to carry a fire. Another salient limitation was that crown fires may not allow for site selection and treatment control without dozed firelines (Aro 1971). The objectives of this study were to evaluate prescribed burning in dense stands of tall mature juniper trees which lacked a continuous understory of herbaceous or shrubby vegetation and to establish the conditions necessary for a successful burn without the need for dozed firelines. Study Area and Methods Approximately 250-ha of a dense Ashe juniper community with very little understory was selected on the YO Ranch, 48 km SE of Junction, Texas, on the Edwards Plateau. The Edwards Plateau of west-central Texas covers about 1 X 107 ha of rangeland (Aukenet al. 1980). The Plateau boundaries on the south and east were formed by the Balconies Escarpment, but on the north and west, they blend with the Rolling Plains and Trans-Pecos regions, respectively (Gould 1969). Across the Edwards Plateau from east to west, rainfall varies from 84 to 38 cm/yr. Peaks in rainfall occur in April and May and again in September or October. Mean annual treatment is 200 C. Soils usually are shallow, underlain by caliche or limestone (Gould 1969). The study site was classified as a low, stoney hill range site with Tarrant stoney clay soils. Ashe juniper dominated the vegetation. Plateau oak (Quercus virginianus varfusiformes), Vasey shin oak (Q. vuseyanu), and Texas persimmon (Diospyros texana) also were common woody plants. Grass species included Texas grama (Bouteloua texanu), threeawn (Aristida sp.), curly mesquite (Hilaria berlangeri), and occasionally little bluestem (Schizachyrium scoparium). In June 1978, a fireline 61 m wide was established in a horseshoe fashion on the north, east, and west sides of the 250-ha study site. The fireline was cleaned by pushing trees into piles in the middle of the fireline. These piles were burned in June 1978. This insured that a crown fire could be contained if strong, southerly winds occurred during ignition. Color infra-red photographs (I :4,800) were used to select sites of varying canopy cover among plots to be burned, since cover was an important criterion in evaluating the success of crown fires in Nevada (Bruner and Klebenow 1979). Thirty-five plots, 30 X IS m, were dozed in February 1979. Ashe juniper trees were pushed down, thus increasing the quantity of ground-level fuel. This was done to allow the fire front to gather intensity prior to entry into the adjacent standing juniper. In the summer of 1979, 20 additional plots were dozed into windrows adjacent to live standing trees. This allowed ignition of an intense