Brush Management Research Articles

Spatial and temporal changes in ecosystem carbon pools following juniper encroachment and removal

Proliferation of woody plants is a predominant global land cover change of the past century, particularly in dryland ecosystems. Woody encroachment and its potential impacts (e.g., livestock forage, wildlife habitat, hydrological cycling) have led to widespread brush management. Although woody plants may have substantial impacts on soils, uncertainty remains regarding woody encroachment and brush management influences on carbon (C) pools. Surface C pools (shallow soils and litter) may be particularly dynamic in response to encroachment and brush management. However, we have limited understanding of spatiotemporal patterns of surface C responses or how surface pools respond relative to aboveground C, litter, roots, and deep soil organic C. Spatial variability and lack of basic ecological data in woody-encroached dryland ecosystems present challenges to filling this data gap. We assessed the impact of western juniper (Juniperus occidentalis) encroachment and removal on C pools in a semi-arid sagebrush ecosystem. We used spatially-intensive sampling to create sub-canopy estimates of surface soil C (0–10 cm depth) and litter C pools that consider variation in tree size/age and sub-canopy location for live juniper and around stumps that were cut 7 years prior to sampling. We coupled the present size distribution of junipers with extensive existing allometric information about juniper in this region to estimate how landscape-level C pools would change through time under future management and land cover scenarios. Juniper encroachment and removal leads to substantial changes in C pools. Best-fit models for surface soil and litter C included positive responses to shrub basal diameter and negative responses to increasing relative distance from the bole to dripline. Juniper removal led to a net loss of surface C as a function of large decreases in litter C and small increases in surface soil C. At the landscape scale, deep soil C was the largest C pool (77 Mg C ha−1), with an apparent lack of sensitivity to management. Overall, encroachment led to substantial increases in C storage over time as juniper size increased (excluding deep soil C, ecosystem C pools increased from 13.5 to 30.2 Mg C ha−1 with transition from sagebrush-dominated to present encroachment levels). The largest pool of accumulation was juniper aboveground C, with important other pools including juniper roots, litter, and surface soil C. Woody encroachment and subsequent brush management can have substantive impacts on ecosystem C pools, although our data suggest the spatiotemporal patterns of surface C pools need to be properly accounted for to capture C pool responses. Our approach of coupling spatially-intensive surface C information with shrub distribution and allometric data is an effective method for characterizing ecosystem C pools, offering an opportunity for filling in knowledge gaps regarding woody encroachment and brush management impacts on local-to-regional ecosystem C pools.

Effects of Brush Management on the Reproductive Ecology of Endangered Black-capped Vireos

Terrestrial habitats are frequently managed to improve perceived economic or aesthetic value of the land and to improve habitat quality for wildlife species. In central Texas, removal of native Juniperus asheii (Ashe Juniper) is a common landscape-management practice due to the species' propensity for invasion of rangeland, vigorous growth leading to dominance of habitats, and reputation for high water-use. Ashe Junipers provide habitat for wildlife species of economic (e.g., Odocoileus virginianus [White-tailed deer], Meleagris gallopavo [Wild Turkey]) and conservation concern (e.g., the endangered Setophaga chrysoparia [Golden-cheeked Warbler]); however, the relationship between Ashe Junipers and the federally endangered Vireo atricapilla (Black-capped Vireo) is less clear. Blackcapped Vireos breed in early successional shrublands where Ashe Junipers are often able to invade, grow quickly, and shade out the deciduous shrubby vegetation preferred by vireos. Although Ashe Juniper removal in Black-capped Vireo habitat is common practice, relatively little is known about the impacts of brush management on Black-capped Vireo use and reproductive success. Here we present results of a study on the effects of an Ashe Juniper removal treatment, in which juniper trees were removed but surrounding deciduous vegetation was largely left intact, on Black-capped Vireo habitat use and reproductive success. Comparing before and after Ashe Juniper removal, we found that the number of Blackcapped Vireos settling in manipulated habitats remained similar, and we saw no significant changes in the size of the average territory or reproductive success. We conclude that, when the amount of damage to the surrounding deciduous vegetation is limited, selective Ashe Juniper removal is unlikely to negatively affect Black-capped Vireos.

Evaluating outcomes of management targeting the recovery of a migratory songbird of conservation concern.

BackgroundAssessing outcomes of habitat management is critical for informing and adapting conservation plans. From 2013–2019, a multi-stage management initiative aims to create >26,000 ha of shrubland and early-successional vegetation to benefit Golden-winged Warblers (Vermivora chrysoptera) in managed forested landscapes of the western Great Lakes region. We studied a dense breeding population of Golden-winged Warblers at Rice Lake National Wildlife Refuge (NWR) in Minnesota, USA, where shrubs and young trees were sheared during the winter of 2014–2015 in a single treatment supported in part by the American Bird Conservancy (ABC) and in part by other funding source(s) to benefit Golden-winged Warblers and other species associated with young forest [e.g., American Woodcock (Scalopax minor)] and as part of maintenance of early successional forest cover on the refuge.MethodsWe monitored abundance of Golden-winged Warblers before (2013–2014) and after (2015–2016) management at the treatment site and a control site, and we estimated full-season productivity (i.e., young recruited into the fall population) on the treatment site from predictive, spatially explicit models, informed by nest and fledgling survival data collected at sites in the western Great Lakes region, including Rice Lake NWR, during 2011 and 2012. Then, using biologically informed models of Golden-winged Warbler response to observed and predicted vegetation succession, we estimated the cumulative change in population recruitment over various scenarios of vegetation succession and demographic response.ResultsWe observed a 32% decline in abundance of Golden-winged Warbler breeding pairs on the treatment site and estimated a 27% decline in per-pair full-season productivity following management, compared to no change in a nearby control site. In models that ranged from highly optimistic to progressively more realistic scenarios, we estimated a net loss of 72–460 juvenile Golden-winged Warblers produced from the treatment site in the 10–20 years following management. Even if our well-informed and locally validated productivity models produced erroneous estimates and the management resulted in only a temporary reduction in abundance (i.e., no change in productivity), our forecast models still predicted a net loss of 61–260 juvenile Golden-winged Warblers from the treatment site over the same time frame.ConclusionsOur study sites represent only a small portion of a large young-forest management initiative directed at Golden-winged Warblers in the western Great Lakes region; however, the brush management, or shearing of shrubs and small trees, that was applied at our study site is a common treatment applied by contractors funded by ABC and its partners on public lands across Minnesota with the expressed intent of benefiting Golden-winged Warblers and related species. Furthermore, the resulting vegetation structure at our treatment site is consistent with that of other areas managed under the initiative, and ABC documents include our study site as successful Golden-winged Warbler management based on observations of ≥1 Golden-winged Warbler at the treatment site since the management. Our assessment demonstrates that, at least for the only site for which pre- and post-management data on Golden-winged Warblers exist, the shearing of shrubs and small trees has had a substantial and likely enduring negative impact on Golden-winged Warblers. We suggest that incorporating region-specific, empirical information about Golden-winged Warbler—habitat relations into habitat management efforts would increase the likelihood of a positive response by Golden-winged Warblers and also suggest that management directed generically at young forest may not benefit Golden-winged Warblers.

Understanding Management Decisions of Absentee Landowners: More Than Just Presence-Absence

Ownership and management of North American rangelands has become increasingly diverse, prompting a need to better understand how changing demographics and values relate to individual land management decisions and land cover. Absentee landowners, who reside away from their rural property, are a growing segment of this changing social landscape. The implications of absentee ownership are not clearly understood, perhaps because the absentee concept is ambiguously defined and inconsistently specified. We introduce the construct of involvement with one’s land to clarify and reframe the absentee landowner concept. We analyzed data from a mail survey of rangeland owners in central Texas to explore the relationship between absentee land ownership and the use of brush management to restore woody-plant invaded grasslands. We employed an information-theoretic approach to compare candidate models using indicators of absenteeism (permanent residence on land and distance of permanent residence from land) and involvement. We measured involvement with one’s land as hours per week operating or working one’s land. We conducted path analysis to examine the relationship between absenteeism and brush management as a function of involvement. Involvement in land management was the best predictor of brush management behavior. Absenteeism, as measured through presence-absence or as distance from land, had no relationship with brush management unless mediated by the involvement construct. Segmenting landowners based solely on the location of their full-time residence provides little information on brush management behavior because it neglects the relationship that landowners may have with their land, regardless of residency. The absentee landowner concept is central to understanding the dynamics of rangeland management and important to get right. Our analysis suggests that getting it right means knowing more than the location of the residence of the landowner.

Wildlife Responses to Brush Management: A Contemporary Evaluation

Wildlife-associated recreation and biodiversity are important management considerations on public and private rangelands, making it imperative that rangeland professionals explicitly take wildlife conservation into account in vegetation management planning and implementation. Here, we synthesize the literature reporting effects of brush management on wildlife and make recommendations for applying brush management to accomplish wildlife conservation objectives. Key observations arising from our synthesis are that habitat-related terminology is often misused in brush management literature. Recommending brush management as a “wildlife habitat improvement” tool is a non sequitur because habitat is species specific and brush management has different consequences for different species of wildlife and plants. Communication between resource managers and stakeholders can be improved by making it clear that habitat is species specific and then identifying what constitutes a benefit of brush management. Changes in resources resulting from brush management may not benefit targeted wildlife species unless these changes overcome some limiting factor or factors. Wildlife responses to brush management treatments are too complex to make broad generalizations because they are mediated by environmental factors and depend on the plant community, size and configuration of the area manipulated, type of treatment applied, and time since application. Prescriptions aimed at improving habitat for wildlife generalists may have relatively modest positive effects on that group but have potentially detrimental effects on specialists. Given this potential trade-off, an idea to consider is that it may be best to err on the side of using brush management as a tool to manage habitat for specialists. Brush management plans and recommendations should take into account trade-offs such as benefiting grassland wildlife at the expense of woodland species. Taking a broader “systems” perspective that balances needs of wildlife in conjunction with other ecosystem services affected by woody plant encroachment and brush management should be a goal of natural resource managers.

The importance of parameterization when simulating the hydrologic response of vegetative land-cover change

Abstract. Computer models of hydrologic systems are frequently used to investigate the hydrologic response of land-cover change. If the modeling results are used to inform resource-management decisions, then providing robust estimates of uncertainty in the simulated response is an important consideration. Here we examine the importance of parameterization, a necessarily subjective process, on uncertainty estimates of the simulated hydrologic response of land-cover change. Specifically, we applied the soil water assessment tool (SWAT) model to a 1.4 km2 watershed in southern Texas to investigate the simulated hydrologic response of brush management (the mechanical removal of woody plants), a discrete land-cover change. The watershed was instrumented before and after brush-management activities were undertaken, and estimates of precipitation, streamflow, and evapotranspiration (ET) are available; these data were used to condition and verify the model. The role of parameterization in brush-management simulation was evaluated by constructing two models, one with 12 adjustable parameters (reduced parameterization) and one with 1305 adjustable parameters (full parameterization). Both models were subjected to global sensitivity analysis as well as Monte Carlo and generalized likelihood uncertainty estimation (GLUE) conditioning to identify important model inputs and to estimate uncertainty in several quantities of interest related to brush management. Many realizations from both parameterizations were identified as behavioral in that they reproduce daily mean streamflow acceptably well according to Nash–Sutcliffe model efficiency coefficient, percent bias, and coefficient of determination. However, the total volumetric ET difference resulting from simulated brush management remains highly uncertain after conditioning to daily mean streamflow, indicating that streamflow data alone are not sufficient to inform the model inputs that influence the simulated outcomes of brush management the most. Additionally, the reduced-parameterization model grossly underestimates uncertainty in the total volumetric ET difference compared to the full-parameterization model; total volumetric ET difference is a primary metric for evaluating the outcomes of brush management. The failure of the reduced-parameterization model to provide robust uncertainty estimates demonstrates the importance of parameterization when attempting to quantify uncertainty in land-cover change simulations.

Patterns of woody plant-derived soil carbon losses and persistence after brush management in a semi-arid grassland

Woody encroachment and subsequent brush management aimed at reducing woody plant cover can alter soil organic carbon (SOC) pools. However, brush management influences on the sources and stability of SOC is unknown. Using a space-for-time approach in a site with closely co-located patches representing unencroached grassland, woody encroachment, and brush management, we coupled stable isotopes and plant-derived biomarkers to quantify how woody encroachment alters input sources and stability of SOC and how these patterns change with brush management. Stable isotopes, lignin-derived phenols, substituted fatty acids, and carbon content of density fractions were measured in soils collected in shrub canopy interspaces, under live shrubs, and under shrubs killed 8 or 52 y previously. Bulk SOC and C3-derived SOC were higher in shallow soil (0–5 cm) under live shrubs than in interspace soil. Long-term brush management showed a decline in total SOC stocks, substituted fatty acids, and C3-derived SOC that were associated with the soil light fraction. Despite declines in bulk SOC following brush management, accumulated C3-derived SOC pools in the dense fraction remained largely stable following brush management. Woody encroachment increases the proportion of poorly-protected light fraction and loosely-mineral associated SOC derived from leaf litter, which is lost within several decades after brush management. However, woody encroachment produced a stabilized mineral-bound pool of C3- and C4-derived SOC that remained 52 years after brush management, suggesting that woody encroachment has the potential for long-term SOC stabilization.

Informal Rangeland Monitoring and Its Importance to Conservation in a U.S. Ranching Community

Effective natural resource management relies on accurate and timely information on the natural environment, which may be obtained by formal (“scientific”) or informal (“local” or “traditional”) methods. Formal monitoring methods are well documented and widely accepted among the rangeland science community, yet adoption by U.S. ranchers is inconsistent. In contrast, informal monitoring appears to be widely used by ranchers, but its practice and importance have rarely been documented or assessed. By interviewing ranchers and government agency personnel, we evaluated informal monitoring in and around the Altar Valley, Arizona, United States. Informal monitoring techniques included qualitative visual appraisals of forage quantity, indicator species and erosion, and incorporated local environmental history. The environmental knowledge embedded in informal monitoring was generally compatible with natural science. Informal monitoring was conducted continuously throughout the year and provided near real-time assessments that integrated observations of most land in individual pastures and ranches. In contrast, formal monitoring was generally performed only once per year, in a limited number of areas and with a delay of a few months between observation and completion of analysis. Thus informal monitoring had higher spatial coverage and temporal resolution and provided assessments faster than formal monitoring. Consequently, ranchers generally considered informal monitoring to be more relevant than formal monitoring to formulating yearly grazing plans and responding rapidly to unpredictable changes in the natural environment. Ranchers incorporated informal monitoring into assessments of rangeland trends and outcomes of conservation measures and thereby into choices of grazing system and planning of brush management and erosion control. Thus informal monitoring was foundational to long-term conservation, annual rangeland management planning, and adaptive natural resource management on subyearly timescales. If informal monitoring is of comparable utility in other rural communities, it would appear advantageous to document and evaluate informal approaches and to incorporate them into formal conservation planning.

Errata: Development of an integrated multiplatform approach for assessing brush management conservation efforts in semiarid rangelands

Millions of dollars have been spent on brush management, or removal of unwanted woody vegetation, as a conservation practice to control the presence of woody species. Land managers need an inexpensive means of monitoring the effects of brush management conser- vation methods for decreasing degradation in rangeland systems. In this study, free, publically available, high-resolution (1 m) imagery from the National Agricultural Imagery Program (NAIP) and moderate-resolution (30 m) Landsat-5 Thematic Mapper (TM) imagery were com- bined to produce a large-scale technique for mapping woody cover. High-resolution imagery- based estimates of woody cover were found to be reasonable (RMSE ¼ 3.8%, MAE ¼ 2.9%) surrogates for ground-based woody cover. An equation for TM-derived woody cover was developed. TM scenes of woody cover (TMWC) were produced and validated using NAIP and ground-based data. Results showed that the developed relation produced viable (RMSE ¼ 8.5%, MAE ¼ 6.4%) maps of woody cover that could be used to successfully track the occurrence of brush removal, as well as monitor the presence or lack of subsequent reemergence. This work provides land managers with an operational means of determining where to allocate resources to implement brush management, as well as a cost-effective method of monitoring the effects of their efforts. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.9

Development of an integrated multiplatform approach for assessing brush management conservation efforts in semiarid rangelands

Millions of dollars have been spent on brush management, or removal of unwanted woody vegetation, as a conservation practice to control the presence of woody species. Land managers need an inexpensive means of monitoring the effects of brush management conservation methods for decreasing degradation in rangeland systems. In this study, free, publically available, high-resolution (1 m) imagery from the National Agricultural Imagery Program (NAIP) and moderate-resolution (30 m) Landsat-5 Thematic Mapper (TM) imagery were combined to produce a large-scale technique for mapping woody cover. High-resolution imagery-based estimates of woody cover were found to be reasonable (RMSE=3.8%, MAE=2.9%) surrogates for ground-based woody cover. An equation for TM-derived woody cover was developed. TM scenes of woody cover (TMWC) were produced and validated using NAIP and ground-based data. Results showed that the developed relation produced viable (RMSE=8.5%, MAE=6.4%) maps of woody cover that could be used to successfully track the occurrence of brush removal, as well as monitor the presence or lack of subsequent reemergence. This work provides land managers with an operational means of determining where to allocate resources to implement brush management, as well as a cost-effective method of monitoring the effects of their efforts.

An ecosystem services perspective on brush management: research priorities for competing land‐use objectives

Summary The vegetation of semi‐arid and arid landscapes is often comprised of mixtures of herbaceous and woody vegetation. Since the early 1900s, shifts from herbaceous to woody plant dominance, termed woody plant encroachment and widely regarded as a state change, have occurred world‐wide. This shift presents challenges to the conservation of grassland and savanna ecosystems and to animal production in commercial ranching systems and pastoral societies. Dryland management focused on cattle and sheep grazing has historically attempted to reduce the abundance of encroaching woody vegetation (hereafter, ‘brush management’) with the intent of reversing declines in forage production, stream flow or groundwater recharge. Here, we assess the known and potential consequences of brush management actions, both positive and negative, on a broader suite of ecosystem services, the scientific challenges to quantifying these services and the trade‐offs among them. Our synthesis suggests that despite considerable investments accompanying the application of brush management practices, the recovery of key ecosystem services may be short‐lived or absent. However, in the absence of such interventions, those and other ecosystem services may be compromised, and the persistence of grassland and savanna ecosystem types and their endemic plants and animals threatened. Addressing the challenges posed by woody plant encroachment will require integrated management systems using diverse theoretical principles to design the type, timing and spatial arrangement of initial management actions and follow‐up treatments. These management activities will need to balance cultural traditions and preferences, socio‐economic constraints and potentially competing land‐use objectives. Synthesis. Our ability to predict ecosystem responses to management aimed at recovering ecosystem services where grasslands and savannas have been invaded by native or exotic woody plants is limited for many attributes (e.g. primary production, land surface–atmosphere interactions, biodiversity conservation) and inconsistent for others (e.g. forage production, herbaceous diversity, water quality/quantity, soil erosion, carbon sequestration). The ecological community is challenged with generating robust information about the response of ecosystem services and their interactions if we are to position land managers and policymakers to make objective, science‐based decisions regarding the many trade‐offs and competing objectives for the conservation and dynamic management of grasslands and savannas.

Grass–woodland transitions: determinants and consequences for ecosystem functioning and provisioning of services

Summary A large fraction of grasslands world‐wide is undergoing a rapid shift from herbaceous to woody‐plant dominance, while in other parts of the world, the opposite transition from woodland to grassland is the dominant phenomenon. These shifts have received increasing attention in the ecological literature during the last two decades due to their global extent and their impacts on ecosystem functioning. This Special Feature includes a series of contributions on key topics within the study of grass–woodland transitions, including three articles addressing the drivers of these vegetation shifts and another three evaluating their ecological consequences. These articles, which include reviews, modelling and empirical studies, highlight the multiplicity of approaches and spatial scales being currently used when studying grass–woodland transitions. The first articles focus on the role of fire in driving the dynamics of mesic grasslands in the USA, on the effects of climate change on the transition zones between treeless vegetation, savanna and forest in tropical and subtropical Americas and on the role of the internal structure of vegetation as a determinant of grassland–woodland transitions. The articles devoted to exploring the consequences include a modelling study on the ecohydrological consequences of shrub removal in western North America and an empirical study aiming at understanding how abiotic and biotic attributes influence above‐ground net productivity across Patagonian grasslands and shrublands, as well as a review of the consequences of brush management on the provision of ecosystem services. Synthesis. Identifying the best actions to avoid or take advantage of grass–woodland transitions requires a mechanistic understanding of both the drivers of these shifts and their ecological consequences. The collection of reviews, empirical and modelling studies included in this Special Feature contributes to forecasting how ongoing global change will affect grass–woodland transitions and their consequences for the provisioning of ecosystem services from drylands, which account for a large fraction of Earth's surface.

Long-term results of tebuthiuron herbicide treatment on creosote bush (Larrea tridentata) in southeast Arizona, USA

Creosote bush (Larrea tridentata) is native to the southwestern United States and central Mexico. Experimental plots of creosote bush treated with tebuthiuron herbicide in southeast Arizona in the early 1980s were rediscovered in 2010. The response over the 30-year period was monitored, revealing creosote bush was effectively controlled by tebuthiuron; however, the anticipated recolonization by native grasses was not realized. Reducing the overall vegetative canopy cover of the site may leave the soil more susceptible to erosion, negatively affecting its hydrologic function. Land management strategies should more thoroughly consider shrub treatments in ecosystems receiving less than 254 mm of annual rainfall and inadequate seed source, such as this study site. Low and inconstant precipitation are typical of the American Southwest. This study demonstrates that, while brush management techniques are effective for long periods of time, the reduction of shrub cover does not directly stimulate recolonization of the site with native grasses.

Rangeland CEAP: An Assessment of Natural Resources Conservation Service Practices

The Conservation Effects Assessment Project (CEAP) is a multi-agency effort to quantify the environmental effects of conservation practices and programs and develop the science base for managing the agricultural landscape for environmental quality. The rangeland CEAP review evaluated the scientific literature on seven core NRCS conservation practices: prescribed grazing, prescribed burning, brush management, range planting, riparian herbaceous cover, upland wildlife habitat management, and herbaceous weed control. The scientific literature “broadly supports” the reviewed rangeland conservation practices standards; however, there is a disjunct in integrating science and field-based knowledge so that managers and conservationists can fully understand the individualistic dynamic aspects of rangeland conservation practices. The CEAP synthesis establishes a precedent for partnerships among scientists, land managers, conservation specialists, and policymakers to provide NRCS with useful, current, science-based information for rangeland conservation practices.

Long-Term Effects of Aeration and Fire on Invasion of Exotic Grasses in Mixed-Brush Plant Communities

Abstract Invasion of exotic grasses into grasslands dominated by native plants changes fire cycles and reduces biodiversity. Brush management practices that create soil disturbance, such as aeration, may potentially result in invasion of exotic grasses and replacement of native vegetation. We tested the hypothesis that a long-term effect of aeration and prescribed burning is an increase in exotic grasses. The study was conducted at the Chaparral Wildlife Management Area in the western south Texas plains where four treatments were evaluated: aeration, warm-season burn, aeration followed by a warm-season burn, and no treatment (control). The experimental design was a randomized complete block with four replicates. We estimated percentage canopy cover of exotic grasses, native grasses, forbs, litter, bare ground, and woody and succulent plants in 2007. There was a multivariate main effect among treatments for the dependent variables absolute canopy cover of exotic grasses, native grasses, forbs, litter, and ...

Does Shrub Removal Increase Groundwater Recharge in Southwestern Texas Semiarid Rangelands?

Abstract Evapotranspiration (ET) is a key component limiting groundwater recharge past the root zone in semiarid regions. Vegetation management may alter groundwater recharge if ET is altered due to changes in vegetation type or cover. This study quantifies changes in groundwater recharge following vegetation cover change from native woodland to pasture in a semiarid region of southwest Texas. The Carrizo–Wilcox aquifer is a valuable groundwater resource in this area, where overuse by dependent farming practices has lowered aquifer levels significantly in the last 85 yr. Combining data from short-term (30 mo) monitoring of the changes in soil moisture and long-term (5–30 yr) changes in total soil chloride indicated deep drainage increased slightly where land had been cleared of vegetation. Annual recharge rates below rooting depths (standardized to 155 cm) averaged only 0.72 ± mm · yr -1 (mean ± SE) in areas not cleared of woody vegetation, as estimated by chloride mass balance. Upon clearing, 72% of the total chloride naturally occurring in the soil profile was flushed away within 30 yr, leading to an estimated 2.59 ± mm · yr -1 additional recharge. Deep soil moisture in recently cleared land increased by up to 17% during the growing season of wet years (double the average rainfall) but did not increase in dry or normal precipitation years, providing supporting evidence that more water penetrated below the roots under certain environmental conditions. These results demonstrate that brush management can increase recharge by modest, but measurable, amounts depending on site-specific soil characteristics and degree of reduction in vegetation.

Juniper Consumption Does Not Adversely Affect Meat Quality in Boer-Cross Goats

Goat browsing can be used as an alternative brush management option for redberry (Juniperus pinchotii Sudw.) and ashe (Juniperus asheii Buch) juniper instead of more expensive and invasive brush control methods, assuming consumption of juniper does not adversely affect the marketability of offspring. Some wildlife species reportedly retain juniper flavor when consumed. We determined if juniper consumption affected meat quality or flavoring of Boer-cross kid carcasses. Twenty recently weaned, Boer-cross wethers were randomly assigned to one of four treatments with treatments fed different amounts of juniper (0%, 10%, 20%, 30% juniper in the diet). All goats were fed juniper for 28 d at the Angelo State University (ASU) Management, Instruction, and Research Center. All goats were also fed a feedlot ration to meet maintenance requirements (2% body weight). Juniper intake varied (P < 0.05) between all treatments (0%, 10%, 20%, 30%) primarily because treatments were fed different amounts of juniper. Following a 28-d trial, goats were harvested at the ASU Food Safety and Product Development Laboratory. Carcass characteristics including live weight, hot carcass weight, dressing percentage, loineye area, body wall fat thickness, and leg circumference were similar (P > 0.05) among treatments. Sensory characteristics including tenderness, juiciness, flavor intensity, off-flavor, and overall acceptability were also similar (P > 0.05) among treatments. Landowners can utilize goats as a biological management tool without adversely affecting goat meat quality or flavoring. El ramoneo con cabras puede ser usado como una opción alternativa de manejo de arbustivas de junípero rojo (Juniperus pinchotii Sudw.) y junípero cenizo (Juniperus asheii Buch) en lugar de métodos de control de arbustivas más caros e invasivos, asumiendo que el consumo de junípero no afecta el mercado del cabritos. Algunas especies de fauna silvestre se ha reportado, que mantienen el sabor de junípero cuando son consumidas. Determinamos sí el consumo de junípero afecta la calidad y el sabor de la carne de cabritos de la cruza con Boer. Veinte cabritos recién destetados cruzados con Boer fueron asignados aleatoriamente a 1 de 4 tratamientos con alimentación con diferentes cantidades de junípero (0%, 10%, 20%, 30% de junípero en la dieta). Todos los cabritos fueron alimentados con junípero por 28 d en el Centro de Manejo, Instrucción e Investigación de Angelo State University (ASU). Todos los cabritos también recibieron una ración de engorda para cubrir los requerimientos de mantenimiento (2% PV). El consumo de junípero varió (P < 0.05) entre todos los tratamientos (0%, 10%, 20%, 30%). Principalmente, por que los tratamientos suministraban diferentes cantidades de junípero. Después de 28 d de experimentación los cabritos fueron sacrificados en el Laboratorio de Seguridad de los Alimentos y Desarrollo de Productos de ASU. Las características de la canal, incluyendo peso vivo, peso caliente de la canal, porcentaje de rendimiento, área de la Costilla, grosor de la grasa dorsal y circunferencia de la pierna fueron similares (P > 0.05) entre tratamientos. Características sensoriales incluyendo suavidad, jugosidad, intensidad y duración del sabor y en general la aceptación fueron similares (P > 0.05) entre tratamientos. Propietarios de predios ganaderos pueden usar cabras como una herramienta de control biológico sin afectar de manera adversa la calidad y el sabor de la carne.

Commentary on "Effect of brush control on evapotranspiration in the North Concho River watershed using the eddy covariance technique" by Saleh et al. (2009)

I n a paper “Effect of brush control on evapotranspiration in the North Concho River watershed using the eddy covariance technique,” published in the September/October 2009 issue of the Journal of Soil and Water Conservation , Saleh et al. argue that clearing mesquite has “great potential” for increasing water yield in the North Concho River watershed near San Angelo, Texas. The clear implication is that shrub removal is a viable strategy for increasing water supply to the city of San Angelo. The authors make this argument mainly on the basis of the small differences in evapotranspiration rates they measured between pastures with mesquite and those without mesquite. We do not dispute the fact that the timing and amount of evapotranspiration may be affected by differences in tree cover and density, but we do not agree that these modest differences will translate to meaningful changes in water supply. There is already overwhelming evidence that brush management in the North Concho watershed will not lead to increases in water flow in the North Concho. A brush control project was begun in the North Concho watershed 10 years ago, and even though this period included one of the wettest years on record (2007), there has…

Simulation of Conservation Practices Using the APEX Model

Information on agricultural Best Management Practices (BMPs) and their effectiveness in controlling agricultural non-point source pollution is crucial in developing Clean Water Act programs such as the Total Maximum Daily Loads for impaired watersheds. A modeling study was conducted to evaluate various BMPs including pasture planting, nutrient management, brush management, clearing and range planting, prescribed grazing, critical area planting, conservation cropping, contour farming, terrace, ponds, grade stabilization structures, and grassed waterways implemented in a 280-km2 Mill Creek Watershed in north-central Texas. The main objective of this study was to assess the long-term impacts of BMPs, at both field and subwatershed levels, on surface runoff, sediment, and nutrient losses using the Agricultural Policy/Environmental eXtender (APEX) model. Considering all BMPs, average annual reductions in runoff, sediment, total nitrogen (TN), and total phosphorus (TP) at the field level ranged from 0 to 52%, 36% to 99%, 0 to 96%, and 15% to 92%, respectively, reflecting the variability in topography, soils, landuse, climate, and relative magnitude of these constituents entering the field from upstream contributing area. However, at the subwatershed level, the reductions only ranged from 2.9% to 6.5% in runoff, 6.3% to 14.8% for sediment, 11% to 15.1% for TN, and 6.3% to 8.6% for TP. The impacts of BMPs on water quality varied depending on the type of practice and its location in the landscape. This study also showed that reduction in sediment at the watershed outlet was proportional to the area treated with BMPs.

Influence of Rainfall, Type of Range, and Brush Management on Abundance of Northern Bobwhites (Colinus virginianus) in Southern Texas

Assessing numerical response of northern bobwhites (Colinus virginianus) to habitat improvement in semi-arid rangeland often is confounded by responses of populations to highly variable patterns of rainfall. During 2 years of above-average rainfall, we investigated abundance of northern bobwhites relative to type of range and treatments to reduce brush on seven ranches in southern Texas. We expected response of populations to treatment of land to be more evident when northern bobwhites were released from constraints of low precipitation. However, main factors dominating abundance were rainfall during the previous growing season and type of range. Greatest numbers of calls were in mid-productivity rangeland (potential production of forage 2,000–3,900 kg/ha), especially sandy loam, clay loam, sandy, and gravelly ridge. Treatments to reduce brush increased abundance of northern bobwhites to a limited extent and were most effective when large blocks of land were treated. Techniques that kill brush (root-plowing) were more successful in increasing populations than top-removal methods (roller-chopping). Leaving strips or mottes (large clumps of living brush and trees) in cleared areas did not enhance populations, although we caution that retaining some brush cover may be important to survival of northern bobwhites in drier years and in situations where herbaceous cover is less abundant.