Henry A. Wright

Effects of fire, ash, and litter on soil nitrate, temperature, moisture and tobosagrass production in the rolling plains.

Removal of litter by burning or clipping in tobosagrass communities increased soil temperature and the rate of nitrogen mineralization. Ash had no effect on either of these soil properties in 1972, but did appear to stimulate production in 1974. With adequate soil moisture, the higher soil temperatures on burned or clipped plots stimulated plant growth and concomitantly reduced soil moisture and nitrates. By contrast, suboptimal soil temperatures on control plots limited plant growth, even though soil nitrate and moisture were ample. During dry years, soil moisture is the limiting plant growth factor and burning has no beneficial effects.

Effect of fire on honey mesquite.

Highlight: Based on this research and other work that has been reported, honey mesquite is very difficult to kill with fire on the High Plains and along river bottoms in the Rolling Plains. On upland sites in the Rolling Plains, 27% of the mesquite trees were killedfollowing single fires. Using repeated fires on upland sites at 5 to 10 year intervals, the potential exists to kill 50% of the older mesquite trees. Seedlings of honey mesquite were easy to kill with moderate fires until they reached 1.5 years of age, severely harmed at 2.5 years of age, and very tolerant of intense fires after 3.5 years of age.

Temperatures of Headfires in the Southern Mixed Prairie of Texas.

Maximum soil surface temperatures varied from 182 F to 1260 F for fuels that varied from 1546 to 7025 lb/acre Tempil card data correlated well with these data-r = 0.919. The duration of temperatures above 150 F varied from 0.9 to 5.4 minutes. The data from this study can be used to simulate approximate intensities of natural fires with a portable burner. Fires with soil surface temperatures above 1000 F show potential to kill mesquite trees.

Effects of cattle grazing and Juniperus pinchotii canopy cover on herb cover and production in western Texas.

Effects of redberry juniper (Juniperus pinchotii) on species composition and biomass production of the herbaceous layer were evaluated for 3 yr on an ungrazed site and a site with past cattle grazing in western Texas. Herb production and grass production decreased as juniper cover increased. Species composition differed between ungrazed and formerly grazed sites, and the formerly grazed site produced less grass biomass than the ungrazed site during each year. The inverse relationship between juniper cover and grass production was linear on the ungrazed site and logarithmic on the formerly grazed site during all 3 yr of the study, suggesting that grazing resulted in a competitive advantage to the overstory species. This relationship persisted for at least 5 yr following release from grazing. Nearly all studies of overstory-understory relations in pinyon-juniper woodlands have shown an inverse logarithmic relationship between overstory cover of pinyons (Pinus spp.) and junipers (Juniperus spp.) and herb production (Arnold et al., 1964; Jameson, 1967; Short et al., 1977; Clary, 1987). In closed-canopy stands, junipers can exclude virtually all herbaceous vegetation (Buechner, 1944; Burkhardt and Tisdale, 1969). The impact of cattle grazing on the juniper-herb relationship has not been studied, probably because ungrazed sites are rare in pinyon-juniper communities. The influence of grazing on production and composition of grasslands has been the subject of considerable research (see Sims et al., 1978; Sims, 1988), but woodlands have received considerably less attention. In general, the competitive balance among herbaceous species is shifted by grazing (Harper, 1977), and grazing often reduces grassland productivity (Sims, 1978). Compensatory growth in response to grazing may overcome losses in productivity (McNaughton, 1979). The latter phenomenon has been the focus of considerable discussion, primarily as a population-level process (McNaughton, 1986; Belsky, 1986). Juniperus pinchotii (redberry juniper) is an important overstory species on semiarid Texas grasslands (Scifres, 1980). It is capable of sprouting following top removal (Correll and Johnston, 1970). Woody plant response to cattle grazing and environmental factors has been described for redberry juniper-mixed grass communities (McPherson et al., 1988). However, overstory-understory relations and herb response to grazing have not been addressed. The objective of this study was to quantify the relationship between redberry juniper cover and herbaceous vegetation under contrasting precipitation and livestock grazing regimes. I Present address: Forest-Watershed Sciences Program, School of Renewable Natural Resources, University of Arizona, Tucson 85721

Patterns of Shrub Invasion in Semiarid Texas Grasslands

-Patterns of woody plant invasion and establishment were investigated in western Texas on three landscapes with different soils and grazing histories. Rate of Juniperus pinchotii encroachment was facilitated by the presence of Prosopis glandulosa on southern High Plains sites with shallow soil but not on a relatively mesic Rolling Plains site. Cattle grazing accelerated Juniperus invasion. Large juniper plants on the High Plains site apparently facilitated establishment of three woody species (Berberis trifoliolata, Rhus microphylla and Mimosa biuncifera).

Effects of fire on an ashe juniper community.

Highlight: In an ashe juniper (Juniperus ash& community n minimum of 1,000 kg/ha of fine fuel was needed to carry a fire fo kill juniper seedlings and burn piles of dozed juniper. Grasses recovered quickly and soil erosion was minimal when burning was done during a wet winter and spring. During a dry winter and spring, however, burning increased drouth S~ESS on plants, reduced herbaceous yields, and exposed soil to wind and wafer erosion for a long period of time when soil moisture was low.

Fire in medium fuels of west Texas.

Highlight: Chained and unchained mesquite in medium fuels were burned to measure the effect of prescribed burning on noxious brush species and on the production and utilization of major forage species. The fire did not kill any living mesquite trees. Very few standing dead mesquite stems burned down. Chained mesquite stems were easily consumed by fire with 2,000 lb/acre of fine fuel. Pricklypear and cholla mortality exceeded 50% by the end of the second growing season. Burning greatly increased production and utilization of tobosa grass; production of buffalograss was unaffected. Most annual forbs were harmed by burning.

Soil Loss, Runoff, and Water Quality of Seeded and Unseeded Steep Watersheds following Prescribed Burning

Seeding of steep slopes (37 to 6lg)after burning on the Edwards Plateau in central Texas reduced soil losses 78 to 93%. Moreover, the major impact of burning on soil losses was significantly reduced in 3 months on burned and seeded watersheds, but not for 15 to 18 months on unseeded watersheds. Stability (soil losses comparable to pretreatment levels) was reached in 6 months on burned and seeded watersheds. Soil loss rates stabilized when cover (live vegetation plus litter) reached 64 to 72% during normal to wet years or 53 to 60% during dry years. Thus, amount of precipitation and cover are closely tied to soil losses. Overland flow stabilized in 4 to 5 years on unseeded watershed and in 1 to 2 years on seeded watersheds. Water quality, lowered slightly by burning, returned to preburn levels within 2 years after seeding. Without seeding it took 4 years to reach preburn levels. Overall, water quality change following burning was not considered to be serious. Ashe juniper (Juniperusashei) has invaded extensive areas of the mixed prairie in central Texas and reduced grazing capacities from I animal unit/6 ha to 1 animal unit/20 ha. A recommended range management practice is to remove the tall green junipers by knocking the trees down individually with a tractor (dozing) or dragging an anchor chain over them that is attached between two tractors (chaining). This allows the native grasses to recover, but it leaves piles of debris over 22% of the land area (devoid of grass), enhances germination of Ashe juniper seed, and does not kill the young trees (Wink and Wright 1973). Prescribed burning removes the piles of debris, kills the young Ashe juniper trees, and creates an unfavorable environment forthe establishment of Ashe juniper seedlings (Wright 1978), but before recommendation to use by ranchers, we needed to know whether soil losses following burning were significant. In 197 1 we initiated a study to determine how long it would take for runoff, soil loss, vegetative cover (live vegetation plus litter), and water quality to return to preburn status on level (0 to 4%), moderate (8 to 20%), and steep (37 to 6 1%) slopes. The study revealed that soil losses and changes in water quality were not serious on level and moderate slopes (Wright et al. 1976). However, adverse effects lasted for 15 to 30 or more months on steep slopes. Soil losses are influenced by intensity of storms (Orr 1970), size and frequency of bare areas (Packer 1951), and soil, topography, and plant cover (Smith and Wischmeier 1962). Among these factors vegetative cover and slope are the most important (Meeuwig The authors are Chairperson and Horn professor, Department of Range and Wildlife Management, Texas Tech University, Lubbock; and professors, Department of Biology, Abilene Christian University, Abilene, Texas. This research was supported in part by the Forest Service, U.S. Department of Agriculture, through the Eisenhower Consortium for Western Environmental Forestry Research, and is published as Eisenhower Consortium Journal Series No. 36, and as Texas Tech University, College of Agricultural Sciences Publication No. T-9-212. The authors would like to thank S.C. Bunting, D.M. Engle, M. Baker, E. Miller, and T. Fulbright for their many hours of work on various phases of this study. We also wish to thank Mr. Bob Beckham, on whose ranch this study was conducted, and personnel of the Abilene Water Treatment Plant, who provided facilities todo the soil

Effect of fire on southern mixed prairie grasses.

Highlight: The long-term effect of fire was studied on the major grass species of west Texas when the winter-spring precipitation was 0 to 40% above normal. This and other studies indicate that sideoats grama and Texas wintergrass are harmed by fire. Buffalograss, blue grama, and sand dropseed were neither harmed nor benefited by fire. Vine-mesquite, Arizona cottontop, little bluestem, plains bristlegrass, and Texas cupgrass increased after burning for 1 or 2 years.

Response of big sagebrush and three-tip sagebrush to season of clipping.

An 80% clipping treatment reduced yields of big sagebrush (Artemisia tridentata) most when applied during July, moderately when applied during spring, and least when applied during late summer through winter months. Three-tip sagebrush (Artemisia tripartita) responded similarly during July, but it was most tolerant to clipping during April and May. During the fall and winter months, three-tip sagebrush appears less tolerant to clipping than big sagebrush.