Brush Encroachment Research Articles

Grassland Resilience to Woody Encroachment in North America and the Effectiveness of Using Fire in National Parks

The grasslands of North America are threatened by woody encroachment. Restoring historical fire regimes has been used to manage brush encroachment. However, fire management may be insufficient due to the nonlinear and hysteretic responses of vegetation recovery following encroachment and the social–political constraints affecting fire management. We synthesized the fire thresholds required to control woody encroachment by typical encroaching species in North America, especially the Great Plains region, and identified the social–political constraints facing fire management in selected grassland national parks. Our synthesis revealed the resistance, hysteresis, and irreversibility of encroached grasslands using fire and emphasized the need for a combination of brush management methods if the impacts of climate change are to be addressed. Frequent fires alone may maintain grassland states, reflecting resistance. However, high-intensity fires exceeding fire-mortality thresholds are required to exclude non-resprouting shrubs and trees, indicating hysteresis. Fire alone may be insufficient to reverse encroachment by resprouting species, exhibiting reversibility. In practice, appropriate fire management may restore resistant grassland states. However, social–political constraints have restricted the use of frequent and high-intensity fires, thereby reducing the effectiveness of management actions to control woody encroachment of grasslands in national parks. This research proposes a resilience-based framework to manage woody encroachment in grassland national parks and similar protected areas.

Identification of Brush Species and Herbicide Effect Assessment in Southern Texas Using an Unoccupied Aerial System (UAS)

Cultivation and grazing since the mid-nineteenth century in Texas has caused dramatic changes in grassland vegetation. Among these changes is the encroachment of native and introduced brush species. The distribution and quantity of brush can affect livestock production and water holding capacity of soil. Still, at the same time, brush can improve carbon sequestration and enhance agritourism and real estate value. The accurate identification of brush species and their distribution over large land tracts are important in developing brush management plans which may include herbicide application decisions. Near-real-time imaging and analyses of brush using an Unoccupied Aerial System (UAS) is a powerful tool to achieve such tasks. The use of multispectral imagery collected by a UAS to estimate the efficacy of herbicide treatment on noxious brush has not been evaluated previously. There has been no previous comparison of band combinations and pixel- and object-based methods to determine the best methodology for discrimination and classification of noxious brush species with Random Forest (RF) classification. In this study, two rangelands in southern Texas with encroachment of huisache (Vachellia farnesianna [L.] Wight & Arn.) and honey mesquite (Prosopis glandulosa Torr. var. glandulosa) were studied. Two study sites were flown with an eBee X fixed-wing to collect UAS images with four bands (Green, Red, Red-Edge, and Near-infrared) and ground truth data points pre- and post-herbicide application to study the herbicide effect on brush. Post-herbicide data were collected one year after herbicide application. Pixel-based and object-based RF classifications were used to identify brush in orthomosaic images generated from UAS images. The classification had an overall accuracy in the range 83–96%, and object-based classification had better results than pixel-based classification since object-based classification had the highest overall accuracy in both sites at 96%. The UAS image was useful for assessing herbicide efficacy by calculating canopy change after herbicide treatment. Different effects of herbicides and application rates on brush defoliation were measured by comparing canopy change in herbicide treatment zones. UAS-derived multispectral imagery can be used to identify brush species in rangelands and aid in objectively assessing the herbicide effect on brush encroachment.

Grazing in California's Mediterranean Multi-Firescapes

The California landscape is layered and multifunctional, both historically and spatially. Currently, wildfire size, frequency, and intensity are without precedent, at great cost to human health, property, and lives. We review the contemporary firescape, the indigenous landscape that shaped pre-contact California's vegetation, the post-contact landscape that led us to our current situation, and the re-imagined grazing-scape that offers potential relief. Vegetation has been profoundly altered by the loss of Indigenous management, introduction of non-native species, implantation of inappropriate, militarized, forest management from western Europe, and climate change, creating novel ecosystems almost always more susceptible to wildfire than before. Vegetation flourishes during the mild wet winters of a Mediterranean climate and dries to a crisp in hot, completely dry, summers. Livestock grazing can break up continuous fuels, reduce rangeland fuels annually, and suppress brush encroachment, yet it is not promoted by federal or state forestry and fire-fighting agencies. Agencies, especially when it comes to fire, operate largely under a command and control model, while ranchers are a diverse group not generally subject to agency regulations, with a culture of autonomy in decision-making and a unit of production that is mobile. Concerns about potential loss of control have limited prescribed burning despite landowner and manager enthusiasm. Agriculture and active management in general are much neglected as an approach to developing fire-resistant landscape configurations, yet such interventions are essential. Prescribed burning facilitates grazing; grazing facilitates prescribed burning; both can reduce fuels. Leaving nature “to itself” absent recognizing that California's ecosystems have been irrecoverably altered has become a disaster of enormous proportions. We recommend the development of a database of the effects and uses of prescribed fire and grazing in different vegetation types and regions throughout the state, and suggest linking to existing databases when possible. At present, livestock grazing is California's most widespread vegetation management activity, and if purposefully applied to fuel management has great potential to do more.

The role of brush encroachment in Mediterranean ecosystems: a review

Abstract Encroachment of woody plants into grasslands and subsequent brush management are among the most prominent changes occurring in arid and semiarid ecosystems over the past century. The reduced number of farms, the abandonment of marginal land and the decline of traditional farming practices have led to encroachment of the woody and shrubby components into grasslands. This phenomenon, specifically in the Mediterranean region, which is followed by a reduction in herbage production, biodiversity and increased fire risk, is generally considered an undesirable process. Sarcopoterium spinosum has had great success in the eastern Mediterranean as a colonizer and dominant bush species on a wide variety of sites and climatic conditions. In the Mediterranean dehesa, the high magnitude and intensity of shrub encroachment effects on pastures and on tree production were shown to be dependent on temporal variation. Accordingly, there are attempts to transform shrublands into grassland-woodland matrices by using different techniques. The main management interventions that are commonly used include grazing, woodcutting, shrub control with herbicides or by mechanical means, amelioration of plant mineral deficits in the soil, and fire. However, the effects of these various treatments on the shrubs under diverse environmental conditions were found to be largely context-specific. As such, the most efficient option for suppressing encroachment of shrubs is combining different interventions. Appropriate management of grazing, periodic control of the shrub component, and occasional soil nutrient amelioration can lead to the development of attractive open woodland with a productive herbaceous understory that provides a wider range of ecological services.

The role of prescribed burn associations in the application of prescribed fires in rangeland ecosystems

Risk and liability concerns regarding fire affect people's attitudes toward fire and have led to human-induced alterations of fire regimes. This has, in turn, contributed to brush encroachment and degradation of many grasslands and savannas. Efforts to successfully restore such degraded ecosystems at the landscape scale in regions of the United States with high proportions of private lands require the reintroduction of fire. Prescribed Burn Associations (PBA) provide training, equipment, and labor to apply fire safely, facilitating the application of this rangeland management tool and thereby reducing the associated risk. PBAs help build networks and social capital among landowners who are interested in using fire. They can also change attitudes toward fire and enhance the social acceptability of using prescribed fire as a management practice. PBAs are an effective mechanism for promoting the widespread use of prescribed fire to restore and maintain the biophysical integrity of grasslands and savannas at the landscape scale. We report findings of a project aimed at determining the human dimensions of using prescribed fire to control woody plant encroachment in three different eco-regions of Texas. Specifically, we examine membership in PBAs as it relates to land manager decisions regarding the use of prescribed fire. Perceived risk has previously been identified as a key factor inhibiting the use of prescribed fire by landowners. Our results show that perceived constraints, due to lack of skill, knowledge, and access to equipment and membership in a PBAs are more important factors than risk perceptions in affecting landowner decisions about the use of fire. This emphasizes the potential for PBAs to reduce risk perceptions regarding the application of prescribed fire and, therefore, their importance for restoring brush-encroached grasslands and savannas.

To Burn or Not to Burn: Ecological Restoration, Liability Concerns, and the Role of Prescribed Burning Associations

F ire suppression in ecosystems that have evolved in the presence of fire, together with the occurrence of other natural and anthropogenic processes, has resulted in the conversion of many grasslands and savannas to woodlands. From an ecological perspective, eliminating fire in areas that evolved with fire inhibits natural processes that limit woody plant expansion and, con- sequently, promotes ecosystem degradation. From an eco- nomic perspective, brush encroachment associated with fire suppression has led to reduced livestock carrying capacity and destruction of property by catastrophic fires that occur when accumulated fuel loads ignite under hot dry conditions. By contrast, research results suggest many ecological and economic benefits to using prescribed fire. 1,2 This leaves social constraints as the primary hurdle to applying periodic fire on the landscape. 3 Prescribed fire has not been adopted widely as a management and/or restoration tool primarily because of perceived safety and legal concerns. 4,5 In this paper we discuss the benefits and risks of using prescribed fire and how prescribed burn asso- ciations have mitigated these risks, resulting in an increase of prescribed fire application, including extreme restoration burns that are ignited under wildfire-like conditions. DOI: 10.2458/azu_rangelands_v34i2_toledo

A fecal near-infrared reflectance spectroscopy-aided methodology to determine goat dietary composition in a Mediterranean shrubland1

An ecologically sound approach to the problem of brush encroachment onto Israeli rangeland might be their utilization by goats, but better knowledge of the feeding selectivity and ability of goats to thrive in encroached areas is required to devise viable production systems. Direct observation of bites could provide precise and accurate estimates of diet selection, but construction of a sufficiently large database would require too much time. The present study describes the first attempt to construct fecal near-infrared reflectance spectroscopy (NIRS) calibrations of the botanical and nutritional composition of the diet, and of the total intake of free-ranging goats, based on reference values determined with bite-count procedures. Calibration of fecal NIRS was based on 43 observations encompassing 3 goat breeds and 4 periods (spring, summer, and fall of 2004, and spring of 2005). Each observation comprised 242 min of continuous recording of the species and bite-type category selected by a single animal, on each of 2 consecutive days. The mass and chemical quality of each species and bite-type category-a total of more than 200,000 bites-were determined by using the simulated bite technique. Associated feces were scanned in the 1,100- to 2,500-nm range with a reflectance monochromator. Fecal NIRS calibrations had reasonable precision for dietary percentages of the 3 main botanical components: herbaceous vegetation (as one category; R(2) = 0.85), Phillyrea latifolia (R(2) = 0.89), and tannin-rich Pistacia lentiscus (R(2) = 0.77), with SE of cross-validation (SECV) of 7.8, 6.3, and 5.6% of DM, respectively. The R(2) values for dietary percentages of CP, NDF, IVDMD, and polyethylene glycol-binding tannins were 0.93, 0.88, 0.91, and 0.74, respectively, with SECV values of 0.9, 2.1, 4.3, and 0.9% of DM, respectively. The R(2) values for intakes of herbaceous vegetation, P. latifolia, and P. lentiscus were 0.80, 0.75, and 0.65, with SECV values of 71, 64, and 46 g of DM/d, respectively. The R(2) values for the daily nutrient intakes were below 0.60. Fecal NIRS data can be used to expand the databases of botanical and nutritional dietary composition when observed and resident animals graze simultaneously, but intakes should be calculated from fecal NIRS-predicted dietary DM composition and an independent evaluation of DMI.

Foraging behaviour of the newly introduced Boer goat breed in a Mediterranean woodland: A research observation

Brush encroachment is reducing pasture and amenity values of rangelands in the upper Galilee, Israel. Local Mamber goats are efficient at preventing brush encroachment, but their low prolificacy and slow growth of their kids prevent profitable farming. Boer goats from southern Africa are deemed to be prolific and rapidly growing, but their ability to exploit Mediterranean woodland and scrubland in Israel was unknown. Simultaneous observations ( n = 604) on the eating behaviour of Boer goats imported from Namibia and of local Mamber goats were recorded from May 1997 to January 1998. Socialization between breeds was prevented by keeping them in distinct flocks in two similar paddocks. Boer goats spent less time than Mamber goats in grazing herbaceous species (22 and 44%, respectively), which suggests that Boers would be potentially less competitive to cattle than Mambers in mixed grazing systems. Boers allocated 90% of their eating time to eight species, compared with only four species for Mambers. Browse use on the main encroaching species differed between goat breeds: Mambers spent more time browsing on Sarcopoterium spinosum whereas Boers spent more time on Cistus creticus and Cistus salvifolius. No difference between breeds was observed with regard to Calycotome villosa, the main encroaching species on the range. Boers exhibited a 10% lower bite rate than Mambers, but no difference between breeds was noted in their mass per bite of browse species. Results of this study suggest that Boer goats have the potential to control brush encroachment more than Mamber goats, especially when they are associated with cattle.

The Legacy of Bobwhite Research in South Texas

More than a half century of research on northern bobwhites (Colinus virginianus) in south Texas has provided a legacy of information for ecologists and managers. South Texas is a semiarid and subtropical environment with highly variable weather, a land base consisting of large private ranches devoted to livestock production, a perennial problem of brush encroachment on rangelands, and a strong tradition of fee-lease hunting. These physical, biotic, and social conditions focused research efforts on descriptive natural history (ca. 1930-1980) and evaluation of grazing and brush management practices (ca. 1980-1990). By natural evolution of knowledge, these efforts led to the development of unified theory that synthesized descriptive and applied information about bobwhite management (ca. 1990-2000). In the context of grazing on rangeland subject to encroachment by woody plants, descriptive studies focused on bobwhite home ranges, mobility, flight behavior, nesting cover, resting cover, and whistling posts, among other aspects of habitat use and behavior. The purpose of these studies was to determine how different plant structures and communities should be dispersed in space and time to maximize their value as bobwhite habitat. South Texas studies revealed that the dogmatic principle, bobwhites are early successional species, holds poorly in semiarid, subtropical environments. Research in south Texas led to formalization of the usable-space-in-time hypothesis on bobwhite density. The hypothesis states that, within ordinary limits, mean abundance of bobwhites on an area is correlated more strongly with the quantity of permanent cover to which they are adapted and less strongly with (human) perceptions of habitat quality (foods, interspersion, edge, diversity). Space-time seems to be an omnibus variable that can be assessed in a variety of management and ecological settings. In association with highly variable rainfall patterns and amounts in south Texas, bobwhite populations exhibit boom-bust population behavior. Research on the cause-effect process governing booms and busts has led to rejection of hypotheses on phosphorus, calcium, phytoestrogens, vitamin A, macronutrition, water, and stress-related hormones as causally involved in the phenomenon. Heat-mediated variation in productivity remains a viable hypothesis that is, of course, open to challenge. The information legacy from research on bobwhites in south Texas has led to revision of knowledge emanating from the southeastern United States; the revised knowledge better fits bobwhites and other quails that inhabit semiarid environments.

Habitat Selection by the Texas Tortoise in a Managed Thornscrub Ecosystem

Brush encroachment on semiarid shrublands resulting from livestock grazing has created global concern. Southern Texas is dominated by Prosopis-Acacia mixed brush communities typical of the Tamaulipan Biotic Province, and the geographic range of the state-threatened Texas tortoise (Gopherus berlandieri) is nearly identical to the boundaries of this biotic province in Texas. In light of the perceived threat to Texas tortoises because of habitat change caused by brush encroachment, we monitored 36 Texas tortoises by radiotelemetry during 1994-1996 to assess habitat selection on a site containing grazed and ungrazed pastures. Tortoises did not exhibit habitat selection at the level of locations within home ranges. Differential habitat selection at the level of home ranges within study areas was not apparent for sex, but was evident for treatment (grazed or ungrazed). Analysis of pooled data indicated that tortoises exhibited broad-scale selection for home ranges within study areas. Selection was expressed as preferential avoidance of old-field and riparian habitats, which represented vegetational extremes of canopy cover. However, tortoises tolerated the broad continuum of other brush communities on the study site. Apparent treatment differences may be an artifact of our inability to adequately pair study areas given the scale of tortoise movement. Our data indicate that increases in the extent of woody canopy cover resulting from grazing-induced brush encroachment will not be detrimental to Texas tortoises. Furthermore, large-scale range improvement practices, such as root-plowing, create unsuitable habitats for this species.

Shrub Invasions of North American Semiarid Grasslands

▪ Abstract The composition and structure of the semiarid or desert grasslands of southwestern North America have changed over the past 150 y. Brushy or woody species in these communities have increased in density and cover. This increase in density of woody species is called brush encroachment because most of these species have been present in these communities at lower densities for thousands of years. The brushy or woody species were not introduced from other continents or from great distances. They are indigenous species that have increased in density or cover because of changes in local abiotic or biotic conditions. The brushy and woody plants are not the cause of these changes, but their increase is the result of other factors. The causes of changes that have led to the present woody-brushy composition of these semiarid grasslands has been difficult to determine. Warming of the climate seems to be a background condition, but the driving force seems to be chronic, high levels of herbivory by domestic animals. This herbivory has reduced the aboveground grass biomass, leading to the reduction of fine fuel and a concomitant reduction or complete elimination of grassland fires. This combination of factors favors the encroachment, establishment, survival and growth of woody plants. Less competition from grasses, dispersal of seeds of woody plants by domestic animals, and changes in rodent, lagomorph, and insect populations seem to modify the rate of change. Elevated levels of atmospheric CO2are not necessary to explain shrub encroachment in these semiarid grasslands. The direction of future change is difficult to predict. The density of brushy and woody plants will probably increase as will the stature and number of species. However, if soil nutrients increase, woody legumes may be replaced by other brushy or woody species. Reversing the changes that have been going on for 150 y will be a difficult, long-term, and perhaps impossible, task.

Characterization of Sympatric or Adjacent Habitats of 2 Deer Species in West Texas

Fourteen vegetative parameters and a Land Surface Ruggedness Index (LSRI) were quantified on 306,000 ha of rangeland in western Texas and eastern New Mexico that differentially supported high and low densities of desert mule deer (Odocoileus hemionus crooki) and white-tailed deer (0. virginianus texanus). Percent woody cover was the only parameter measured that was significantly different (P 75%. Increases in white-tailed deer densities were positively correlated (r = 0.69, P < 0.001) with increases in percent woody cover. Using the measurement of percent woody cover, we correctly classified 83 and 65% of the 17 study areas into high and low density classes, respectively, for white-tailed deer and desert mule deer. It is apparent that desert mule deer populations on rangelands in this region could be enhanced by limiting woody plant canopy cover in their habitats to about 40%. Conversely, white-tailed deer populations would be favored by encouraging brush encroachment above this level. J. WILDL. MANAGE. 50(1):129-134 The Trans-Pecos and Panhandle regions of west Texas accommodate ranges of both desert mule deer and white-tailed deer. Landowners, spo smen, and biologists are concerned about an apparent population decline in desert mule deer and an increase in white-tailed deer in areas traditionally considered desert mule deer range (Harwell and Gore 1981). Although no substantive data are available, it is thought that this situation resulted from brush infestation 'Present address: School of Forestry, Fisheries, and Wildlife, 112 Stephens Hall, University of MissouriColumbia, Columbia, MO 65211. 2 Present address: Caesar Kleberg Wildlife Research Institute, P.O. Box 218, Texas A&I University, Kingsville, TX 78363. This content downloaded from 157.55.39.236 on Tue, 11 Jul 2017 17:51:06 UTC All use subject to http://about.jstor.org/terms 130 DEER IN WEST TEXAS * Wiggers and Beasom J. Wildl. Manage. 50(1):1986 (Humphrey 1958, Johnston 1963, U.S. Dep. Agric. 1964) that has altered habitat conditions to favor white-tailed deer (Harwell and Gore 1981). Krfimer (1972) reported similar patterns of white-tailed deer encroachment in the westcentral United States and southern Canada. He suggested that the increasing densities of woody vegetation along water channels may have influenced a shift in species ratio favoring whitetailed deer. Habitat requirements for either deer species in west Texas are not well defined, especially on sympatric and adjacent ranges. This knowledge is essential before concerns regarding the future status of the desert mule deer can be addressed. Further, the lack of habitat information restricts the formulation of management guidelines for possible habitat improvement for either species. Our objective was to determine if selected habitat attributes differentially influenced population levels of desert mule deer and white-tailed deer. Support for this work was provided by the U.S. For. Serv., Rocky Mt. For. and Range Exp. Stn., and the Dep. Range and Wildl. Manage., Texas Tech Univ. We thank the many private ranchers in west Texas and personnel of the Tex. Parks and Wildl. Dep., the U.S. Soil Conserv. Serv., the U.S. Natl. Park Serv., and the U.S. Bur. Land Manage. (BLM) for their support in this project. STUDY AREAS AND METHODS Study areas were selected that were known to support or previously have supported populations of both deer species. They included all or parts of 30 private ranches, 1 state and 1 federally administered park in west Texas, and the Mescalero Sands area in southeastern New Mexico (Fig. 1). These areas totaled 306,000 ha of habitat where desert mule deer and whitetailed deer populations are sympatric or contiguously allopatric. Overlapping populations of desert mule deer and white-tailed deer in Texas occur in the Panhandle and Trans-Pecos geographic regions (Harwell and Gore 1981, Russ 1981). In the Panhandle Region, including the Mescalero Sands in southeastern New Mexico, deer are associated primarily with the Rolling Plains Physiographic Area. The Rolling Plains occupies a zone between the arid, desert regions to the southwest and the more humid regions to the east. Precipitation averages about 52 cm NEW MEXICO

Economic Impact of Brush Encroachment in Texas

Range livestock is important to the economy of the state of Texas. Over 4.2 billion lbs. of beef were produced in Texas with a value of over $1.2 billion in 1971, which was the greatest for any of the 50 states. Sheep and lamb production in Texas for 1971 exceeded 200 million lbs. and was valued at $43.4 million which was the highest of all 50 states. Cash receipts from cattle, calves, sheep, and lambs marketed in Texas in 1971 were estimated at $1.6 billion.Texas' production of range livestock is limited by the availability of rangeland. In 1967, over 53 percent of the land area in Texas was classified as rangeland. Undesirable woody plants which compete with favorable grasses for moisture and sunlight have infested 82 percent of the grasslands in the state.

Forest Management Practices as Related to and Influenced by Forest Soil Differences in Western Washington

AbstractIn developing correlations between soil and site quality for Douglas fir, observations were made on other forest management factors which appeared to be related to the soil. Presence or absence of windfall was noted on each plot. Nearby cutover areas of the same soil were checked for abundance of regeneration and for encroachment of hardwoods. On soils with cemented or compacted subsoils, checks were made for occurrence of natural seedlings and for their proximity to old stumps as an indication of micro‐site differences in seedling receptivity. In addition to site quality, susceptibility or resistance to wind‐throw, susceptibility to hardwood brush encroachment, abundance of conifer regeneration, seasonal use limitations and other management factors are strongly influenced by the soil profile properties.Management should be varied to capitalize on the good or desirable factors and to eliminate or minimize the undesirable ones. Forest growth patterns are described for widely different soils, and specific forest management recommendations are given to illustrate the tailoring of management to fit individual soils.