Influence of Vegetation Management on Yield and Quality Surface Runoff

Water requirements for the United States will triple by the year 2000 (Water Resources Council, 19689. In Texas and many western states about 75% of the total water used is from ground water and this source in many areas is rapidly being depleted. To meet future demands water will have to come from other sources (Runkles, 1972). A possible source is increased water yield from watersheds. The quantity and quality of this surface runoff is influenced by many factors which include precipitation pattern, vegetation-type, soil-type and land use. If surface runoff from watersheds is to be a potential water source, the impact of these factors on water quality and yield must be evaluated. Forests, grasslands and shrublands cover vast watersheds in Texas and North America. Many watershed studies have been conducted in forested regions, but rangeland areas have received only limited attention, particularly in Texas. The significance of these latter types cannot be overlooked since 40% of the land surface in the United States and 60% of Texas support this type of vegetation. The major use of rangeland is domestic livestock and wildlife production. The impact of this use on water yield and nutrient and sediment loss from watersheds requires investigation. The influence of various grazing systems and intensities must be determined in order to coordinate ranching practices with increased high quality runoff. The effect of brush control on runoff yield and quality has not been thoroughly investigated. The purpose of this study was to determine the influence of vegetation characteristics, grazing systems and precipitation on surface runoff from rangeland on the Edwards Plateau region of Texas. Water yield, organic-N, N03-N, NH4-N, N02-N, total and ortho-P, Ca, Mg, K, pH, conductivity, total and calcium hardness, turbidity and suspended sediment load were quantitively evaluated. Field sampling was conducted on small-gauged watersheds on the Texas A&M Agricultural Research Station at Sonora, Texas. These gauged watersheds, which have been established over the past 13 years by the Agricultural Research Service (ARS), represent a variety of grazing systems ranging from continuous heavy grazing with poor vegetation cover to fourpasture and seven-pasture deferred rotation systems with good cover. In addition several different techniques have been used for woody plant control on the watersheds. The Sonora Research Station, with over 25 years of grazing management research, provides a unique area for study of the effects of grazing management and brush control on surface runoff, nutrient load and sediment yield

Influence of Vegetation Management on Yield and Quality Surface Runoff

Water requirements for the United States will triple by the year 2000 (Water Resources Council, 19689. In Texas and many western states about 75% of the total water used is from ground water and this source in many areas is rapidly being depleted. To meet future demands water will have to come from other sources (Runkles, 1972). A possible source is increased water yield from watersheds. The quantity and quality of this surface runoff is influenced by many factors which include precipitation pattern, vegetation-type, soil-type and land use. If surface runoff from watersheds is to be a potential water source, the impact of these factors on water quality and yield must be evaluated. Forests, grasslands and shrublands cover vast watersheds in Texas and North America. Many watershed studies have been conducted in forested regions, but rangeland areas have received only limited attention, particularly in Texas. The significance of these latter types cannot be overlooked since 40% of the land surface in the United States and 60% of Texas support this type of vegetation. The major use of rangeland is domestic livestock and wildlife production. The impact of this use on water yield and nutrient and sediment loss from watersheds requires investigation. The influence of various grazing systems and intensities must be determined in order to coordinate ranching practices with increased high quality runoff. The effect of brush control on runoff yield and quality has not been thoroughly investigated. The purpose of this study was to determine the influence of vegetation characteristics, grazing systems and precipitation on surface runoff from rangeland on the Edwards Plateau region of Texas. Water yield, organic-N, N03-N, NH4-N, N02-N, total and ortho-P, Ca, Mg, K, pH, conductivity, total and calcium hardness, turbidity and suspended sediment load were quantitively evaluated. Field sampling was conducted on small-gauged watersheds on the Texas A&M Agricultural Research Station at Sonora, Texas. These gauged watersheds, which have been established over the past 13 years by the Agricultural Research Service (ARS), represent a variety of grazing systems ranging from continuous heavy grazing with poor vegetation cover to fourpasture and seven-pasture deferred rotation systems with good cover. In addition several different techniques have been used for woody plant control on the watersheds. The Sonora Research Station, with over 25 years of grazing management research, provides a unique area for study of the effects of grazing management and brush control on surface runoff, nutrient load and sediment yield

Decomposition of Common Curlymesquite Herbage on Edwards Plateau Rangeland, Texas

Decomposition of common curlymesquite herbage from a continuously, heavily grazed pasture and one pasture of a 4-pasture deferred rotation grazing system was investigated on the Edwards Plateau of Texas. Decomposition of herbage in litterbags was similar for both pastures. Approximately 40% of the original herbage weight was lost during the 345-day study. Average decomposition rate was 2.19 mg/g/day. Rate of decomposition during a 238-day period was significantly related to antecedent potential evaporation and precipitation since the preceding collection date and cumulative time. Percentage nitrogen and percentage ash content increased while percentage carbon and carbon/nitrogen ratio decreased over time in the decomposing herbage.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Herbage Dynamics and Forage Quality of Texas Cupgrass (Eriochloa sericea)

Herbage dynamics and forage quality of Texas cupgrass (Eriochloa sericea) were monitored during the 1977 and 1978 growing seasons on the Edwards Plateau, Texas. This species was dominant on a shallow rocky range site which had been excluded from grazing for 30 years. Average herbage production was low (527 kg/ha), and mulch constituted 85% of the total biomass. Peak live standing crop was only 145 kg/ha during the study. Green herbage production reflected the ability of this taxon to adjust phenological stage in response to precipitation. Litterbag studies showed decomposition rates of herbage held flat on the soil surface to be twice as rapid as herbage held upright in clumps of Texas cupgrass. This difference in decomposition illustrated the necessity for herbage removal to prevent dead centers and degradation of the stand. Crude protein content of live material averaged 9.8 and 10.7% during 1977 and 1978, respectively. Digestible energy of live herbage averaged 2300 kcal/kg and never went below 2,100 kcal/kg during the study. Forage quality parameters also reflected phenological stage of development.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Influence of spring burning on cattle diets and performance on the Edwards Plateau Rangeland

Immediately following spring burning of Edwards Plateau rangeland, steer diets had a higher percentage of grass and lower percentage of forbs than diets from unburned range. Intake of pricklypear cactus was greater on burned range than on unburned during the first summer and fall following the fire. Ash content of steer diets in the burn was generally higher, due primarily to increased use of pricklypear cactus on burned sites. Steer diets from burned range contained significantly higher in vitro digestible organic matter (IVDOM) during June. Increased use of pricklypear cactus contributed to a significantly higher IVDOM during September and October and lower percent crude protein from September to November in the burn. Heifers gained significantly more on burned range during June and August and also when averaged across the entire 5-month grazing period. Burning has potential as a useful tool to increase cattle production from Edwards Plateau rangeland.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Spatial Patterns of Grass Seedling Recruitment Imply Predation and Facilitation by Harvester Ants

Extended drought on the Edwards Plateau, TX, causes high mortality in grass species\u27 populations and their replacement by recruitment from the seeds of survivors. Harvester ant nests may act as refugia for perennial plants during drought, as evidenced by a high survivorship of plants directly adjacent to nests. Because grasses tend to disperse seeds short distances and drought eliminated seed banks, we hypothesized that the spatial pattern of grass seedlings and adults would be clumped at small scales around these refugia. In contrast, nests would be regular at small to moderate scales. We studied the spatial patterns of seedlings, adults, and ant nest locations using a modified Ripley\u27s K-function technique for transect data. Point data were collected along a 1-km transect. Spatially regular patterns were found for nests from 1.0- to 22.0-m scales. We found that two species\u27 seedlings and adults were significantly clumped with ant nests, and two species had significantly regular spatial patterns with nests. Surprisingly, patterns of clumped seedlings occurred up to 30-m scales with nests. Nests appear to affect seedling establishment at multiple scales. These results suggest that nests may facilitate colonization for some grass populations, but regular spatial patterns in other species imply that forager seed harvest may inhibit establishment

Vegetation of a 25-Year Exclosure on the Edwards Plateau, Texas

An evaluation was made of current species composition, production and 25-year vegetation trends within an exclosure on the Texas A&M University Agricultural Research Station at Sonora, Texas. Community composition was variable and most species responded individually to soil variables, particularly soil depth and degree and kind of stoniness. Common curlymesquite (Hilaria belangeri) was the most characteristic and widespread species of the area. Communities dominated by Texas cupgrass (Eriochloa sericea), on soils greater than 25 cm in depth, produced 4,330, 2,235, and 504 kg/ha in June and August 1972 and January 1973, respectively. Wright threeawn (Aristida wrightii) dominated communities with soil depths of 15 cm, produced 1,318, 1,349, and 413 kg/ha for the same dates; and hairy tridens (Erioneuron pilosum) sites with soil depths of 10 cm yielded 970, 1,456, and 84 kg/ha. Vegetation change over the past 25 years has been primarily adjustment in relative dominance of species rather than addition or loss of species. Following establishment of the exclosure some species adjusted to previous grazing history, and thereafter primary changes followed precipitation variation.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

State-and-Transition Models, Thresholds, and Rangeland Health: A Synthesis of Ecological Concepts and Perspectives

This article synthesizes the ecological concepts and perspectives underpinning the development and application of state-and-transition models, thresholds, and rangeland health. Introduction of the multiple stable state concept paved the way for the development of these alternative evaluation procedures by hypothesizing that multiple stable plant communities can potentially occupy individual ecological sites. Vegetation evaluation procedures must be able to assess continuous and reversible as well as discontinuous and nonreversible vegetation dynamics because both patterns occur and neither pattern alone provides a complete assessment of vegetation dynamics on all rangelands. Continuous and reversible vegetation dynamics prevail within stable vegetation states, whereas discontinuous and nonreversible dynamics occur when thresholds are surpassed and one stable state replaces another. State-and-transition models can accommodate both categories of vegetation dynamics because they represent vegetation change along several axes, including fire regimes, weather variability, and management prescriptions, in addition to the succession-grazing axis associated with the traditional range model. Ecological thresholds have become a focal point ofstate-and-transition models because threshold identification is necessary for recognition of the various stable plant communities than can potentially occupy an ecological site. Thresholds are difficult to define and quantify because they represent a complex series of interacting components, rather than discrete boundaries in time and space. Threshold components can be categorized broadly as structural and functional based on compositional and spatial vegetation attributes, and on modification of ecosystem processes, respectively. State-and-transition models and rangeland health procedures have developed in parallel, rather than as components of an integrated framework, because the two procedures primarily rely on structural and functional thresholds, respectively. It may be prudent for rangeland professionals to consider the introduction of these alternative evaluation procedures as the beginning of a long-term developmental process, rather than as an end point marked by the adoption of an alternative set of standardized evaluation procedures. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 2020Legacy DOIs that must be preserved: 10.2458/azu_rangelands_v58i1_smein

Browsing and tree size influences on Ashe juniper understory

Ashe juniper (Junius ashei, Buckholz) is increasing on most sites across the Edwards Plateau of Texas. It is the purpose of this investigation to document the influence of Ashe juniper tree size on understory vegetation and to evaluate how the interaction between tree size and browsing by domestic and white-tailed deer modifies overstory-understory relationships. Trees were randomly selected from 2 long-term treatments (browsed and unbrowsed) and analysed with univariate analysis of covariance and multivariate repeated-measures analysis. Without browsing, Ashe juniper is more abundant and its individual influence increases as the size of the tree increases; trees with a canopy diameter < 6.0 m expressed minimal influence on understory vegetation compared to larger trees. When browsers are present at sufficient stocking rates to create a browse line on large trees, encroachment of Ashe juniper is slowed, rate of increase of all woody speces is reduced, and large trees cause a shift in species composition directly under the canopy, however cover of all herbaceous species is not reduced. Immediately under the canopy of small browsed trees, herbaceous cover is lower than for unbrowsed trees. Environmental variables rpsponsible for these patterns were litter depth and light penetrating the canopy when the sun is at an angle (during the winter). The increased cover of several herbaceous species under the canopy of large browsed trees and at the canopy edge of browsed and unbrowsed trees, indicates the importance of the interaction between canopy cover and the presence of a browse line. Browse lines on large trees enhance growth and production of cool season species, such as Texas wintergrass (Stipa leucotricha Trin. & Rupr.) and reduce negative influences (low light, thick leaf litter, etc.) on other herbaceous species. At this level of browsing many other palatable species could be reduced or lost from the plant comunity.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

A Unified Framework for Assessment and Application of Ecological Thresholds

The goal of this synthesis is to initiate development of a unified framework for threshold assessment that is able to link ecological theory and processes with management knowledge and application. Specific objectives include the investigation of threshold mechanisms, elaboration of threshold components, introduction of threshold categories and trajectories, and presentation of an operational definition of ecological thresholds. A greater understanding of ecological thresholds is essential because they have become a focal point within the state-and-transition framework and their occurrence has critical consequences for land management. Threshold occurrence may be best interpreted as a switch from the dominance of negative feedbacks that maintain ecosystem resilience to the dominance of positive feedbacks that degrade resilience and promote the development of post-threshold states on individual ecological sites. Threshold categories have been identified to serve as ecological benchmarks to describe the extent of threshold progression and increase insight into feedback mechanisms that determine threshold reversibility. Threshold trajectories describe the developmental pathway that post-threshold states may follow once a threshold has been exceeded. These trajectories may produce a continuum of potential post-threshold states, but the majority of them may be organized into four broad states. This framework lends itself to management application by providing an operational definition of thresholds that is based on a probabilistic interpretation. Probabilities associated with 1) the occurrence of triggers that initiate threshold progression, 2) the trajectory of post-threshold states, and 3) threshold reversibility will provide an operational procedure for threshold assessment and application. If thresholds are to play a central role in rangeland ecology and management, then the rangeland profession must accept responsibility for their conceptual development, ecological validity, and managerial effectiveness. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 2020Legacy DOIs that must be preserved: 10.2458/azu_jrm_v59i3_brisk