William E. Pinchak

Economics of managing mesquite in north Texas: a sensitivity analysis.

This paper presents a comparative simulation analysis of the economics of prescribed fire and aerially applied root-killing herbicide treatment as methods for maintaining livestock productivity on rangeland in the Texas Rolling Plains. A “no-treatment” scenario is used as the base for comparison. In almost all the simulated scenarios both herbicide application and prescribed burning were economically feasible since net present values were > 0 and benefit/cost ratios were >1. However, the net present values for prescribed fire were much higher that those for the herbicide treatment even with a lower increase in carrying capacity with burning. The cost of herbicide would have to be less than half the current cost of

Effects of stocking rate on quantity and quality of available forage in a southern mixed grass prairie.

57 ha -1 before it would be economically competitive with fire in controlling mesquite. If cattle numbers were not increased after treating brush, burning had an even greater net present value and benefit/cost ratio advantage over herbicide treatment than if cow numbers were increased after treatment. Even if fences have to be constructed to implement adequate deferment for burning, the net present value and benefit/cost ratios of the fire option were higher than those for herbicide scenarios. This analysis indicates that there is an economic advantage to using fire wherever possible, and use of herbicides is restricted to those instances when fine fuel amount is < 1,700 kg ha -1 yr -1 when fire is not a viable option. The analyses indicate the economic response is most sensitive to the treatment effect on wildlife income.

Integrated Grazing and Prescribed Fire Restoration Strategies in a Mesquite Savanna: I. Vegetation Responses

The objective of this study was to quantify the long-term (25 years) effects of heavy (HC) and moderate (MC) rates of stocking on quantity and quality of forage available. Study design required frequent harvest of standing crop on 5 range sites in twice replicated, 244 ha treatment pastures. Results from the 20-month study showed aboveground standing crop dynamics were similar in both treatments, quantity of available forage was greater in the MC than HC treatment, quality of available forage was greater generally in the HC than MC treatment, and that heavy stocking favored a dominance of warm-season shortgrasses as opposed to a dominance of warm-season midgrasses. Averaged across dates and adjusted for differences among pastures in range site composition, aboveground herbaceous standing crop averaged 1,341 kg/ha in the HC pastures as compared to 1,816 kg/ha in the MC treatment pastures. Crude protein and organic matter digestibility averaged 8.6% and 49.3%, respectively, in the HC pastures and 7.7% and 46.7%, respectively, in the MC pastures. It is concluded that the greater variation among years in cow/calf production in the HC than in the MC treatment is primarily because forage availability in the HC treatment is less than in the MC treatment.

Sideoats Grama Growth Responses to Seasonal Fires and Clipping

Abstract This study evaluated the efficacy of prescribed fire applied within landscape-scale rotational grazing treatments to reduce mesquite (Prosopis glandulosa Torr.) encroachment and restore herbaceous productivity and cover. One-herd, multiple-paddock rotational grazing was used to accumulate herbaceous fine fuel for fires via prefire deferment and to provide periodic postfire deferment for grass recovery. Treatments were an unburned continuous-grazed control, a four-paddock-1 herd system with fire (4:1F), and an eight-paddock-1 herd system with fire (8:1F), with two replicates per treatment (1u200a294–2u200a130 ha per replicate). The management plan was to burn 25% of each system (one paddock in the 4:1F; two paddocks in the 8:1F treatments) and defer grazing during all or portions of the 9 mo (May to January) prior to burning. Deferral was “internalized” by grazing on the remaining 75% of each treatment without reducing stocking rate determined for the entire system. Mesquite cover increased on clay-loam soils from 22% to 40% in unburned paddocks over 7 yr (1995–2001). This increase, coupled with extended drought, reduced fine fuel amounts for fire and limited the number and intensity of fires that were applied. It was possible to burn one paddock in the 8:1F treatment (12.5% of total area), but not in the 4:1F treatment (25% of total area) during drought. Fires reduced mesquite and cactus (Opuntia spp.) cover by 25–79% and 24–56%, respectively, but cover of these species increased to prefire levels within 6 yr. All fires reduced (Pu200a≤u200a0.05) total herbaceous biomass for 1 yr postfire. The 8:1F treatment increased (Pu200a≤u200a0.05) grass biomass on loamy-bottom soils and reduced (Pu200a≤u200a0.05) bare ground on clay-loam and loamy-bottom soils in unburned paddocks compared to the unburned continuously grazed control. The 8:1F treatment, through internalized grazing deferment, facilitated the application of fire to reduce woody cover during extended drought without degrading the herbaceous understory.

Effect of long-term, year-long grazing at moderate and heavy rates of stocking on diet selection and forage intake dynamics.

Abstract There is increased interest in the use of summer-season fires to limit woody plant encroachment on southern prairie grasslands, but collateral effects of these fires on grasses are poorly understood. We quantified effects of repeated winter fires, repeated summer fires, simulated grazing (clipping), and their interaction on yields of the C4 midgrass, sideoats grama (Bouteloua curtipendula) in northern Texas. Monoculture patches of sideoats grama were exposed to 1 of 3 fire treatments: 1) no burn, 2) 2 winter fires in 3 years, or 3) 2 summer fires in 3 years; and to 1 of 2 clip treatments (no clip or clip once each spring). Total yield (liveu2009+u2009standing dead), live yield, percent live tissue, and foliar cover were measured in spring and late-growing season (late-season) over a 7-year period. In unclipped plots, late-season total yield did not fully recover until 2 growing seasons after winter fires and 3 growing seasons after summer fires. By 5 years postfire, total yield was greater in both fire treatments than in the no burn. Live yields recovered more quickly than total yields following summer fires but never exceeded the no burn. Percent live tissue was greater in both fire treatments than in the no burn for up to 2 years postfire. Clipping reduced total and live yields in the no burn and winter-fire treatments but not in the summer-fire treatment. By 5 years postfire, total and live yields were greater in the summer fireu2009+u2009clip than the no burnu2009+u2009clip or winter fireu2009+u2009clip treatments. Results suggest that 1) sideoats grama is tolerant of summer fires but full recovery may require at least 3 years, and 2) in the long-term, summer fireu2009+u2009clipping may stimulate sideoats grama production more than winter fireu2009+u2009clipping or clipping alone.

Interannual Herbaceous Biomass Response to Increasing Honey Mesquite Cover on Two Soils

A 2-year experiment was conducted to determine the effect of 27 years of continuous grazing at moderate (7 ha/cow/yr) (MC) and heavy (5 ha/cow/yr) (HC) rates of stocking on seasonal diet selection and forage intake dynamics. Nine trials were conducted to determine differences between treatments in botanical composition and quality of diets and forage intake. Proportion of Texas wintergrass (Stipa leucothrica Trin. and Rupr.) in diets was greater (P<.05) in the MC than HC treatment whereas amounts of warmseason shortand midgrasses were less. Differences between treatments in botanical composition of diets were related to differences in seasonal availability and live:dead tissue ratios of forages. However, such differences did not generally affect diet quality. Supplementation of HC cattle with 20%/o CP breeder cube either replaced forage organic matter intake (January 1986) or substituted for insufficient forage availability (February 1987). Supplementation never stimulated forage intake. Forage organic matter intake was restricted at forage standing crops below 700 kg/ha.

Effects of incubation time and sodium sulfite upon in-vitro digestibility estimates and sample filtering time.

Abstract This study quantified herbaceous biomass responses to increases in honey mesquite (Prosopis glandulosa Torr.) cover on two soils from 1995 to 2001 in north central Texas. Vegetation was sampled randomly with levels of mesquite ranging from 0% to 100%. With no mesquite covering the silt loam soils of bottomland sites, peak herbaceous biomass averaged (±SE) 3u200a300u200a±u200a210 kgu2009·u2009ha−1 vs. 2u200a560u200a±u200a190 kgu2009·u2009ha−1 on clay loam soils of upland sites (Pu200au200a=u200au200a0.001). A linear decline of 14u200a±u200a2.5 kgu2009·u2009ha−1 in herbaceous biomass occurred for each percent increase in mesquite cover (Pu200au200a=u200au200a0.001). The slope of this decline was similar between soils (Pu200au200a=u200au200a0.135). Herbaceous biomass with increasing mesquite cover varied between years (Pu200au200a=u200au200a0.001) as did the slope of decline (Pu200au200a=u200au200a0.001). Warm-season herbaceous biomass decreased linearly with increasing mesquite cover averaging a 73u200a±u200a15% reduction at 100% mesquite cover (Pu200au200a=u200au200a0.001) compared to 0% mesquite cover. Cool-season herbaceous biomass was similar between soils with no mesquite, 1u200a070u200a±u200a144 kgu2009·u2009ha−1 for silt loam vs. 930u200a±u200a140 kgu2009·u2009ha−1 for clay loam soils, but averaged 340u200a±u200a174 kgu2009·u2009ha−1 more on silt loam than on clay loam soils at 100% mesquite cover (Pu200au200a=u200au200a0.004). Multiple regression analysis indicated that each centimeter of precipitation received from the previous October through the current September produced herbaceous biomass of 51 kgu2009·u2009ha−1 on silt loam and 41 kgu2009·u2009ha−1 on clay loam soils. Herbaceous biomass decreased proportionally with increasing mesquite cover up to 29 kgu2009·u2009ha−1 at 100% mesquite cover for each centimeter of precipitation received from January through September. Increasing mesquite cover reduces livestock forage productivity and intensifies drought effects by increasing annual herbaceous biomass variability. From a forage production perspective there is little advantage to having mesquite present.

Effect of restricted forage intake in confinement on estimated fecal output from a sustained release bolus.

We conducted 2 experiments to quantify the effects of incubation time, filtering method, forage type, and associated interactions on the precision and accuracy of in-vitro digestibility as estimates of in-vivo digestibility. Experiment I used 10 incubation times and alfalfa (Medicago sativa L.), kleingrass (Panicum coloratum L.), prairie grass, and wheat straw (Triticum aestivum L.) hays to determine whether a single incubation time should be employed to estimate digestibility of a variety of forages. Additionally, 2 second stage neutral detergent extraction methods were evaluated to determine sodium sulfite effect on fiber recovery and filter time. An interaction existed between incubation time and in-vitro estimates of digestibility. The use of sodium sulfite increased (P<0.05) digestibility estimates (1.3 units) across all hays and decreased filtering times by as much as 9.5 min/sample. Experiment II utilized 3 hays (alfalfa, kleingrass, and wheat straw), 4 incubation times and 4 neutral detergent extraction methods in an effort to isolate where the changes in neutral detergent fiber (NDF) estimates due to sodium sulfite occurred and if a method could be developed to maximize filtering speed without compromising the accuracy of digestibility estimates. Use of sodium sulfite in the rinse water did not affect apparent NDF recovery and decreased filtering time by approximately 10 min. when compared to no sulfite additions. Results of this study confirm previous observations that a single incubation period should not be used to estimate in-vivo digestibility. Addition of sodium sulfite to the rinse water provides a viable means to decrease sample analysis time without jeopardizing the accuracy of digestible NDF estimates.

Assessing accuracy of a laser rangefinder in estimating grassland bird density

Two experiments were conducted to investigate the effects of restricted forage intake on patterns of chromium excretion to determine sample window duration and the accuracy and precision of fecal output estimates derived from the Captec Chrome sustained release bolus. In Experiment 1, 8 crossbred steers (mean = 243 +/- 14 kg) were assigned randomly to receive prairie hay (PH) at intake levels of either 1.12% body weight (BWT) or 0.75% BWT while maintained in individual metabolism crates and(or) pens. In Experiment 2, steers from Experiment 1 were rerandomized and assigned to receive PH at either 1.12% BWT or alfalfa hay (AH) at 1.30% BWT. The average post-dosing bolus failure rate across experiments exceeded 30%. Estimated fecal output exceeded actual fecal output under all experimental conditions (P 0.60). Treatment effects were similar for estimated fecal output, corrected estimated fecal output, and actual fecal output. Under conditions of pen feeding and restricted forage intake, estimated fecal output exhibited treatment differences similar to those of total fecal collection. However, unless adjusted for average marker recovery, these estimates were significantly greater than actual fecal output.