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Pyric-Herbivory and Hydrological Responses in Tallgrass Prairie
Abstract
Pyric-herbivory is the spatial and temporal interaction of fire and grazing on area resources that results in site selection by animals on recently burned areas. Pyric-herbivory promotes heterogeneity by increasing bare ground on some patches and litter and aboveground biomass on other patches. The influences of this heterogeneity on hydrological properties and sediment transport are not well documented. We monitored the pattern of cattle occupancy on annually burned and patch burned pastures under moderate stocking rates of steers in the Tallgrass Prairie Preserve and quantified surface runoff and sediment transport for simulated rainfall of 10-year return storm intensity applied to different phases of the fire-grazing interaction in 2011 and 2012. Results showed that patch burn altered grazing distribution with cattle spending 70% of their time within the most recently burned areas. Our rainfall simulation results showed the high intensity grazing following a spring fire did not have a prolonged, ecologically meaningful detrimental impact on hydrological properties of the burned patch in comparison with annually burned grazing pasture. Instead, the increased spatial and temporal heterogeneity of hydraulic properties could potentially enhance resource conservation through runoff and runon interactions within the patch burned pasture. Further study focusing on quantifying pyric-herbivory effects on runoff and sediment transport at watershed scale will provide needed insights for managing tallgrass prairie for improving ecosystem services.
Key words: annual burn grazing, patch burn grazing, rainfall simulation, saturated hydraulic conductivity, sediment transport, surface runoff
... The current management regime in many tallgrass prairies consists of annually burning large patches and grazing with high stock densities (0Á8-1Á8 steer ha À1 ) for a full season (Owensby et al. 2008). In contrast, PBG reduces fire frequency and concentrates cattle impacts to smaller patches (West et al. 2016). Studies in other ecosystems suggested rest-rotation management could reduce riparian impacts (e.g. ...
... Future research could focus on required riparian buffer widths and understanding overland and subsurface flow paths to identify the mechanisms responsible and how these riparian fencing results apply to other geographical locations (West et al. 2016). We suspected that regions with deep soils and minimal overland flow would have the best riparian fencing results. ...
Fire and grazing are common in grasslands world‐wide to maintain grass cover and cattle production. The effects of fire, cattle grazing and riparian fencing efficacy on prairie stream ecology are not well characterized at catchment scales.
We examined alterations to stream water quality and biology from patch‐burn grazing (PBG) in tallgrass prairie during a five‐year, replicated, catchment scale experiment that used a Before‐After/Control‐Impact ( BACI ) design and was analysed by mixed‐effects models. Treatments included two patch‐burned control catchments (fire but no grazers) and PBG in two riparian‐fenced and two unfenced catchments. We assessed the effectiveness of riparian fencing for mitigating potential water quality impacts by monitoring water quality and riparian usage by cattle via Global Positioning System.
Riparian fences effectively excluded cattle; however, in unfenced pastures, cattle aggregated along streams 10–20% of the grazing season.
After initiation of PBG, we detected large increases in some nutrients, Escherichia coli , algal biomass, primary productivity and community respiration in all catchments with PBG. Some water quality variables, such as E. coli concentrations, recovered quickly after cattle were removed from pasture, which indicated resiliency.
Riparian fencing moderately reduced the impacts to stream variables, indicating either overland flow and/or subsurface flow allowed nutrients and bacteria to enter the streams.
Synthesis and applications . Patch‐burn grazing is a measurable disturbance that can alter the ecological condition of streams. Riparian fencing lessened the degree of impact, yet some water quality variables still exceeded regional reference conditions. Managers will need to assess the costs of riparian fencing compared to the moderate benefits that fencing provides to water quality.
... To prepare for potential shifts in land use, research focus should be placed on developing state-and-transition and social-ecological models that incorporate spatial and temporal heterogeneity and patterns to derive solutions that are focused on delineating and understanding the current and potential future placement of natural and novel landscapes and their effects on landscape processes and ecosystem services ( Turner 1989 ;Li and Mander 2009 ;Young et al. 2014 ;Wilcox et al. 2018 ). Restoring historical ecological processes such as pyric herbivory is beneficial to livestock production ( Fuhlendorf et al. 2009 ;Limb et al. 2011 ), wildlife ( Fuhlendorf et al. 2010 ;Doxon et al. 2011 ;Davis et al. 2016 ), and hydrological processes throughout much of the Ogallala ( West et al. 2016 ). ...
The Ogallala Aquifer region, located in the Great Plains of the central United States, is the largest freshwater aquifer in North America, supporting one of the most agriculturally productive regions in the world. In this paper, we discuss the history of settlement and water use in this region, from the Homestead Act and the Dust Bowl to modern irrigation systems. While many improvements to irrigation technology and water-efficient crops have helped to prolong the life of the Ogallala, continued use of this finite resource is leading to a tragedy of the commons, wherein difficult land management decisions will have to be made by this century's end. We posit that the art and science of rangeland management stands uniquely poised to tackle this challenge directly through creative integration, where appropriate, of native rangeland restoration, improved pasture management, integrated crop-livestock systems, and regen-erative agricultural practices aimed at preserving soil and rangeland health, thereby providing continuity in the ability of the Ogallala region to continue to provide food, fiber, and other ecosystem services both locally and globally. Furthermore, we provide discussion on future research, extension, and educational needs to consider as the exploration for adaptive solutions are developed and evaluated in the coming decades.
... The strong linear relationship for the event-based runoff depths and the sediment loads between the two watersheds during the calibration phase made it possible to detect the changes in the hydrological behavior after the conversion from prairie to a switchgrass production system. There was no change in the relationship between the Control and Impact Watersheds during the conversion phase for the runoff, but the large relative increase in the sediment indicated a greater sediment load per unit of runoff, which was due to the lack of vegetation cover [17,64,65]. The failure to find increased runoff from the Impact Watershed during the conversion phase could be related to the fact that most runoff generation occurs during the dormant season, when the ET is minimal, regardless of the vegetation cover. ...
The land systems between the humid and arid zones around the globe are critical to agricultural production and are characterized by a strong integration of the land use and water dynamics. In the southern Great Plains (SGP) of the United States, lakes and farm ponds are essential components in the land systems, and they provide unique habitats for wildlife, and critical water resources for irrigation and municipal water supplies. The conversion of the marginal grasslands to switchgrass (Panicum virgatum) biofuel feedstock for energy production has been proposed in the region. However, we have limited experimental data to assess the impact of this potential land-use change on the surface runoff, which is the primary water source for surface impoundments. Here, we report the results from a paired experimental watershed study that compared the runoff and sediment responses that were related to the conversion of prairie to a low-input biomass production system. The results show no significant change in the relationship between the event-based runoff and the precipitation. There was a substantial increase in the sediment yield (328%) during the conversion phase that was associated with the switchgrass establishment (i.e., the site preparation, herbicide application, and switchgrass planting). Once the switchgrass was established, the sediment yield was 21% lower than the nonconverted watershed. Our site-specific observations suggest that switchgrass biofuel production systems will have a minimum impact on the existing land and water systems. It may potentially serve as an environmentally friendly and economically viable alternative land use for slowing woody encroachment on marginal lands in the SGP.
... In contrast, native tallgrass prairie soils without cultivation history are highly permeable [35]. The saturated infiltration capacity of the well-managed native prairie was reported to be greater than the 10 yr return rainfall intensity of 68 mm h −1 for the tallgrass prairie region of the south-central Great Plains [36]. Vegetation impact on the streamflow generation mechanism might differ in native prairie without cultivation history. ...
The meteorological droughts in the climate transition zone of the Great Plains of the USA are projected to intensify, potentially leading to major shifts in water provisioning services in rangelands. To understand how meteorological drought interacts with vegetation to regulate runoff response, we collected precipitation, root zone soil moisture, and runoff data from experimental grassland and juniper (Juniperus virginiana L., redcedar) woodland watersheds for five years encompassing a drought year to pluvial year cycle. We contrasted the frequency distribution of precipitation intensities and applied wavelet analysis to reveal the coherence between precipitation and root zone soil moisture patterns. Compared with grassland, the root zone soil moisture in woodland had a narrower range, with the peak frequency skewed to lower soil moisture content. The conversion of herbaceous vegetation to evergreen juniper woodland results in a delayed response of runoff to precipitation due to reduced antecedent soil moisture. The reduction of streamflow from the woodland watershed was greater in the normal and pluvial years than in the drought year. Thus, conversion from grassland to evergreen woody vegetation prolongs the impact of meteorological drought on soil moisture and streamflow. Restoring prairie that is heavily encroached by woody species may serve as an adaptive measure to mitigate the climate change impact on water resources and other ecosystem services provided by rangeland.
... A few studies of this topic suggest that the sedimentation in the runoff from the well-managed tallgrass prairie is usually low [78], although grazing intensity could increase the sediment yield [31]. In general, we have limited information on redcedar encroachment impact on sediment yield in the tallgrass prairie in the Great Plains. ...
In the Great Plains of the central United States, water resources for human and aquatic life rely primarily on surface runoff and local recharge from rangelands that are under rapid transformation to woodland by the encroachment of Eastern redcedar (redcedar; Juniperus virginiana) trees. In this synthesis, the current understanding and impact of redcedar encroachment on the water budget and water resources available for non-ecosystem use are reviewed. Existing studies concluded that the conversion from herbaceous-dominated rangeland to redcedar woodland increases precipitation loss to canopy interception and vegetation transpiration. The decrease of soil moisture, particularly for the subsurface soil layer, is widely documented. The depletion of soil moisture is directly related to the observed decrease in surface runoff, and the potential of deep recharge for redcedar encroached watersheds. Model simulations suggest that complete conversion of the rangelands to redcedar woodland at the watershed and basin scale in the South-central Great Plains would lead to reduced streamflow throughout the year, with the reductions of streamflow between 20 to 40% depending on the aridity of the climate of the watershed. Recommended topics for future studies include: (i) The spatial dynamics of redcedar proliferation and its impact on water budget across a regional hydrologic network; (ii) the temporal dynamics of precipitation interception by the herbaceous canopy; (iii) the impact of redcedar infilling into deciduous forests such as the Cross Timbers and its impact on water budget and water availability for non-ecosystem use; (iv) land surface and climate interaction and cross-scale hydrological modeling and forecasting; (v) impact of redcedar encroachment on sediment production and water quality; and (vi) assessment and efficacy of different redcedar control measures in restoring hydrological functions of watershed.
Encroachment of woody plants into grasslands is a global phenomenon of environmental concern. Mechanical removal is often necessary to re-establish herbaceous dominance for heavily encroached watersheds, but its impact on water quality and quantity of runoff into streams and reservoirs has not been vigorously studied. The sediment concentration and load following mechanical removal of juniper (Juniperus virginiana, L.) woodland and subsequent re-establishment of tallgrass prairie or switchgrass (Panicum virgatum L.) biomass production were quantified at the experimental watershed scale in the south-central Great Plains, USA. Impact analysis was used to evaluate the effects of watershed treatment and phase of land use conversion. The annual sediment yield from juniper woodland watersheds averaged<0.10 t ha⁻¹ yr⁻¹ before treatment and increased to 0.28 t ha⁻¹ yr⁻¹ after juniper were cut and left on site. In the second year, removing the dried trees increased the annual sediment yield to 1.14 t ha⁻¹ yr⁻¹ in the prairie restoration watershed and 13.29 t ha⁻¹ yr⁻¹ in the switchgrass watershed that was sprayed with herbicide in preparation for no-till planting. The annual sediment loads averaged 0.44 t ha⁻¹ yr⁻¹ from the restored prairie and 0.29 t ha⁻¹ yr⁻¹ from the established switchgrass, comparable to 0.73 t ha⁻¹ yr⁻¹ from the intact juniper woodland during the third and fourth years after initiation of treatments. While restored grassland watersheds had elevated peak flows and longer flow duration leading to greater runoff, lower sediment yields were due to reduced mean and peak sediment concentration compared to the juniper watershed. Therefore, restoring juniper woodland to native prairie or switchgrass biomass production systems may increase water yield without increasing sediment yield, especially in years with extreme storm events.
Fire management around the world is now undergoing extensive review, with a move toward fire management plans that maintain biodiversity and other ecosystems services, while at the same time mitigating the negative impacts to people and property. There is also increasing recognition of the historical and anthropogenic dimensions that underlie current fire regimes and the likelihood that projected future climate change will lead to more fires in most regions. Concurrently, resilience theory is playing an increasingly important role in understanding social-ecological systems, and new principles are emerging for building resilience in both human and natural components. Long-term fire data, provided by paleoecological and historical studies, provide a baseline of knowledge about the linkages between climate, vegetation, fire regimes, and humans across multiple temporal and spatial scales. This information reveals how processes interacting over multiple spatial and temporal scales shape the local fire conditions that influence human and ecological response. This multiscale perspective is an important addition to adaptive fire management strategies that seek to build resilience, incorporate stakeholder perspectives, and support polycentric decision making.
Rainfall intensity and distribution has a great effect on soil erosion. In this study, a portable perforated steel tray is developed and calibrated to simulate artificial rainfall which can be used for investigation of soil erosion under a certain rainfall.The simulator's performance was compared with available tray and drip-type simulators as well as the natural rainfall. This is a drip-type simulator with the capacity of producing storms of up to 188 mm/h within 10 minutes. The higher value of D 50 (4.18 mm) of the rainfall simulator than the value of D 50 (3.25 mm) of natural rainfall indicates greater drop size distribution. The relatively lower height of the simulator to achieve the terminal velocity of natural rainfall was partially compensated by the greater drop size distribution. Fixing the perforated steel tray 3.3 m above ground surface generate a drop velocity of 4.2 m/s.The drop size distribution (D 50) was estimated using Flour Pellet Method. Christiansen's Uniformity (CU) Coefficient (86.2998% and 86.3143% for separate two runs) was determined for evaluation of Spatial Variability. Based on parameters such as raindrop size distribution, rain accumulation rate, spatial variability of rainfall and drop velocity, the simulator performs satisfactorily.
A portable perforated steel tray for artificial rainfall simulation is
designed and calibrated in this study. Its performance is also
evaluated compared to other conventional tray and spray-type
rainfall simulators as well as the natural rainfall. This simulator is
capable of producing storms up to 188 mm/h within 10 minutes
duration with a drop size distribution slightly greater than the
natural rainfall (D50 of simulated rainfall is 4.18 mm at 188 mm/h,
D50 of natural rainfall is 3.25 mm). This drop size partially
compensates for the relatively lower height of the simulator to
achieve the terminal velocity of natural rainfall. The perforated tray
was fixed at 3.3 m above the ground surface which generates a
drop velocity of 4.2 m/s. Flour pellet method was used to estimate
the drop size distribution of the simulated rainfall. Spatial variability
of the simulated rainfall was evaluated based on the Christiansen’s
Uniformity (CU) Coefficient (86.2998% and 86.3143% for separate
two runs). The rainfall simulator performs satisfactorily with respect
to rain drop size distribution, rain accumulation rate, spatial
variability of rainfall and drop velocity.
A regional frequency analysis was conducted to estimate the depth-duration frequency of precipitation for 12 durations in Oklahoma (15, 30, and 60 minutes; 1, 2, 3, 6, 12, and 24 hours; and 1, 3, and 7 days). Seven selected frequencies, expressed as recurrence intervals, were investigated (2, 5, 10, 25, 50, 100, and 500 years). L-moment statistics were used to summarize depth-duration data and to determine the appropriate statistical distributions. Three different rain-gage networks provided the data (15minute, 1-hour, and 1-day). The 60-minute, and 1-hour; and the 24-hour, and 1-day durations were analyzed separately.
Data were used from rain-gage stations with at least 10-years of record and within Oklahoma or about 50 kilometers into bordering states. Precipitation annual maxima (depths) were determined from the data for 110 15-minute, 141 hourly, and 413 daily stations.
The L-moment statistics for depths for all durations were calculated for each station using unbiased L-mo-ment estimators for the mean, L-scale, L-coefficient of variation, L-skew, and L-kur-tosis. The relation between L-skew and L-kurtosis (L-moment ratio diagram) and goodness-of-fit measures were used to select the frequency distributions. The three-parameter generalized logistic distribution was selected to model the frequencies of 15-, 30-, and 60-minute annual maxima; and the three-parameter generalized extreme-value distribution was selected to model the frequencies of 1-hour to 7-day annual maxima.
The mean for each station and duration was corrected for the bias associated with fixed interval recording of precipitation amounts. The L-scale and spatially averaged L-skew statistics were used to compute the location, scale, and shape parameters of the selected distribution for each station and duration. The three parameters were used to calculate the depth-duration-frequency relations for each station. The precipitation depths for selected frequencies were contoured from weighted depth surfaces to produce maps from which the precipitation depth-duration-frequency curve for selected storm durations can be determined for any site in Oklahoma.
Cattle grazing can enhance the loss of phosphorus (P) and suspended sediment (SS) in surface runoff, which can impair receiving water bodies. We tested the hypothesis that much of the particulate-bound P in surface runoff is carried in light, low-density aggregates that may enhance the transfer of P and SS to surface water. Four contrasting soil types were treated with combinations with or without treading by an artificial hoof to simulate a 24-h grazing event, and with or without dung return. A rainfall simulator was used to generate surface runoff.
This article examines the question of how well the rangeland management profession has served conservation of patterns and processes that support multiple ecosystem services. We examine the paradigms under which rangeland management operates and argue that our profession developed under the utilitarian paradigm with the primary goals of sustainable forage for livestock production. While optimization of multiple rangeland products and services has always been a consideration, a comprehensive set of principles have not be been developed to advance this concept. We argue that fire and grazing, often viewed as mere tools used for production goals, should rather be viewed as essential ecosystem processes. Rangeland management continues to operate under the utilitarian paradigm appropriate to societal values of the 20th century and by and large has failed to provide management guidance to reverse degradation of several highly valued ecosystem services. We support this argument with evidence that biodiversity has declined on rangelands in the past half century and that much of this decline is due to management goals that favor a narrow suite of species. The full suite of ecosystem services valued by society will only benefit by management for heterogeneity, which implies that there is no one goal for management and that landscape-level planning is crucial. Explicitly incorporating heterogeneity into state-and-transition models is an important advancement not yet achieved by our profession. We present new principles for rangeland management formed on the basis of conservation of pattern and process. While recognizing that many rangelands have significant deviations from historic plant communities and disturbance regimes, we suggest that management for conservation of pattern and process should focus on fire and grazing to the extent possible to promote a shifting mosaic across large landscapes that include patches that are highly variable in the amount of disturbance rather than the current goal of uniform moderate disturbance. Este artículo examina la pregunta de que tan bien los profesionales en manejo de pastizales han aplicado los patrones y procesos en la conservación de los servicios multiples que proveen los ecosistemas. Examinamos los paradigmas bajo los cuales opera el manejo de pastizales y discutimos el desarrollo de nuestra profesión bajo el paradigma utilitario con el principal objetivo de sustentabilidad forrajera para la producción de ganado. Mientras que la optimización de los múltiples productos y servicios de los pastizales han sido consideradas un paquete completo de principios no ha sido desarrollado para avanzar en este concepto. Discutimos que el fuego y el pastoreo a veces son vistos como simples herramientas usadas para objetivos de producción cuando deberían ser vistas como partes esenciales de los procesos del ecosistema. El manejo de pastizales continúa operando bajo el paradigma utilitario típico de los valores sociales del siglo XX y por mucho ha fallado en proveer directrices de manejo para revertir la degradación de varios servicios valiosos de los ecosistemas. Apoyamos este argumento con evidencia de que la biodiversidad ha decaído en los pastizales en la mitad del siglo pasado y mucho de esta disminución se debe a los objetivos de manejo que favorecen a un reducido número de especies. El juego completo de servicios valuados por la sociedad solo beneficiara con el manejo por heterogeneidad el cual implica que no hay un objetivo para el manejo y que la planeación a nivel paisaje es crucial. Incorporando de manera explícita modelos de estado y transición es un avance importante que no ha sido logrado por nuestra profesión. Presentamos nuevos principios para el manejo de pastizales desarrollados en base a procesos y patrones de conservación. Mientras reconozcamos que muchos pastizales tienen desviaciones significativas de históricas comunidades de plantas y regímenes de disturbio, sugerimos que el manejo por conservación de patrones y procesos deberá enfocarse en fuego y pastoreo en medida de lo posible para promover el cambio en un mosaico a través de grandes paisajes que incluyen parches que son altamente variables en la magnitud de disturbio en lugar de objetivos actuales de disturbio uniforme y moderado.
Many phion-juniper ecosystems in the western U.S. are subject to accelerated erosion while others are undergoing little or no era sion. Controversy has developed over whether invading or encroaching piiion and juniper species are inherently harmful to rangeland ecosystems. We developed a conceptual model of soil erosion in pi&on-juniper ecosystems that is consistent with both sides of the controversy and suggests that the diverse perspectives on this issue arise from threshold effects operating under very dii- ferent site conditions. Soil erosion rate can be viewed as a function of (1) site erosion potential (SEP), determined by climate, geomor- phology and soil erodibility; and (2) ground cover. Site erosion potential and cover act synergistically to determine soil erosion rates, as evident even from simple USLE predictions of erosion. In pifion-juniper ecosystems with high SEP, the erosion rate is highly sensitive to ground cover and can cross a threshold so that erosion increases dramatically in response to a small decrease in cover. The sensitivity of erosion rate to SEP and cover can be visuahxed as a cusp catastrophe surface on which changes may occur rapidly and h-reversibly. The mechanisms associated with a rapid shift from low to high erosion rate can be illustrated using percolation theory to incorporate spatial, temporal, and scale- dependent patterns of water storage capacity on a hillslope. Percolation theory demonstrates how hillslope runoff can under- go a threshold response to a minor change in storage capacity. Our conceptual mode1 suggests that piiion and juniper contribute to accelerated erosion only under a limited range of site condi- tions which, however, may exist over large areas.
Patterns of bison (Bison bison L.) grazing were examined in a 2-year study on a tallgrass prairie site in Oklahoma subjected to a seasonally and spatially variable burning regime. Mixed groups of bison, composed of cows, yearlings, calves, and young (< 5 years of age) bulls, comprised 90% of the study population and showed selectivity by using burned areas significantly more than expected 23 % of the time. Mixed groups avoided unburned areas 63% of the time. In contrast, bull groups of mature bulls > 5 years of age selected unburned areas for grazing 29% of the time and burned areas only 4% of the time. Temporal patterns in bison grazing were evident; selective use of burns persisted for only a short period during the first post-fire growing season, after which burns were grazed in proportion to availability and then selectively avoided as bison shifted grazing efforts to newer burns. Regression analysis verified that bison grazing was negatively related to burn age. Regression also showed that grazing patterns were positively related to burn patch size. Although burn types varied significantly in biomass and overall vegetative composition, bison exhibited only limited preference for any burn type, choosing those with higher relative cover of annual Bromus spp. and sedges. It appears that bison select recently burned areas with relatively low graminoid biomass for grazing, presumably choosing these areas based on forage quality rather than quantity.
The impact of short‐term, high intensity livestock trampling on selected properties of a silty clay soil was determined at the Texas Agriculture Experiment Station located near Sonora, TX. Intensive livestock trampling typical of multi‐pasture rotational grazing systems had a negative impact on soil physical properties. The deleterious effects tended to increase as stocking rate increased. Trampling on dry soil caused disruption of naturally occurring aggregates and compaction of the surface soil layer. Trampling on moist soil deformed existing aggregates and led to the creation of a flat, comparatively impermeable surface layer composed of dense, unstable clods.
Apparent, or effective, infiltration rates on grassland hillslopes vary with rainfall intensity and flow depth because of the interaction between rainfall, runoff, and vegetated microtopography. The higher parts of the microtopography are occupied by greater densities of macropores and therefore have much greater hydraulic conductivities than the intervening microdepressions. On short hillslopes and plots the apparent infiltration rate is simply the spatial average of the saturated and unsaturated conductivities of this surface. The proportion of the surface which is saturated and the value to which the unsaturated conductivity is raised depends on the rainfall intensity. On longer hillslopes the downslope increase in flow depth in microtopographic depressions progressively inundates more permeable, vegetated mounds so that the hydraulic conductivity of a greater proportion of the surface is raised to its saturated value. For this reason the apparent infiltration rate increases downslope, even in the absence of spatial trends in any of the surface characteristics that affect infiltration. Apparent, or effective, infiltration rate depends on hillslope length. Consequently, steady state discharge does not increase linearly with distance downslope. These two fundamental relationships between infiltration, rainfall intensity, and runoff are analyzed on the basis of sprinkling-infiltrometer measurements and a mathematical model.
Raindrop-impact-induced erosion is initiated when detachment of soil particles from the surface of the soil results from an expenditure of raindrop energy. Once detachment by raindrop impact has taken place, particles are transported away from the site of the impact by one or more of the following transport processes: drop splash, raindrop-induced flow transport, or transport by flow without stimulation by drop impact. These transport processes exhibit varying efficiencies. Particles that fall back to the surface as a result of gravity produce a layer of pre-detached particles that provides a degree of protection against the detachment of particles from the underlying soil. This, in turn, influences the erodibility of the eroding surface. Good understanding of rainfall erosion processes is necessary if the results of erosion experiments are to be properly interpreted. Current process-based erosion prediction models do not deal with the issue of temporal variations in erodibility during a rainfall event or variabilities in erodibility associated with spatial changes in dominance of the transport processes that follow detachment by drop impact. Although more complex erosion models may deal with issues like this, their complexity and high data requirement may make them unsuitable for use as general prediction tools. Copyright © 2005 John Wiley & Sons, Ltd.
The interactions between fire and grazing are widespread throughout fire-dependent landscapes. The utilization of burned areas by grazing animals establishes the fire-grazing interaction, but the preference for recently burned areas relative to other influences (water, topography, etc.) is unknown. In this study, we determine the strength of the fire-grazing interaction by quantifying the influence of fire on ungulate site selection. We compare the preference for recently burned patches relative to the influence of other environmental factors that contribute to site selection; compare that preference between native and introduced ungulates; test relationships between area burned and herbivore preference; and determine forage quality and quantity as mechanisms of site selection. We used two large ungulate species at two grassland locations within the southern Great Plains, USA. At each location, spatially distinct patches were burned within larger areas through time, allowing animals to select among burned and unburned areas. Using fine scale ungulate location data, we estimated resource selection functions to examine environmental factors in site selection. Ungulates preferred recently burned areas and avoided areas with greater time since fire, regardless of the size of landscape, herbivore species, or proportion of area burned. Forage quality was inversely related to time since fire, while forage quantity was positively related. We show that fire is an important component of large ungulate behavior with a strong influence on site selection that drives the fire-grazing interaction. This interaction is an ecosystem process that supersedes fire and grazing as separate factors, shaping grassland landscapes. Inclusion of the fire-grazing interaction into ecological studies and conservation practices of fire-prone systems will aid in better understanding and managing these systems.
Rangelands are globally extensive, provide fundamental ecosystem services, and are tightly coupled human-ecological systems. Rangeland sustainability depends largely on the implementation and utilization of various grazing and burning practices optimized to protect against soil erosion and transport. In many cases, however, land management practices lead to increased soil erosion and sediment fluxes for reasons that are poorly understood. Because few studies have directly measured both wind and water erosion and transport, an assessment of how they may differentially respond to grazing and burning practices is lacking. Here, we report simultaneous, co-located estimates of wind- and water-driven sediment transport in a semiarid grassland in Arizona, USA, over three years for four land management treatments: control, grazed, burned, and burned + grazed. For all treatments and most years, annual rates of wind-driven sediment transport exceeded that of water due to a combination of ongoing small but nontrivial wind events and larger, less frequent, wind events that generally preceded the monsoon season. Sediment fluxes by both wind and water differed consistently by treatment: burned + grazed > burned > grazed > or = control, with effects immediately apparent after burning but delayed after grazing until the following growing season. Notably, the wind:water sediment transport ratio decreased following burning but increased following grazing. Our results show how rangeland practices disproportionally alter sediment fluxes driven by wind and water, differences that could potentially help explain divergence between rangeland sustainability and degradation.
Prescribed burning is being used in the Conasauga River Watershed in southeastern Tennessee and northern Georgia by National Forest managers to restore degraded pine/oak communities. The purpose of these burns is to restore shortleaf pine (Pinus echinata Miller)/mixed-oak forests with more diverse understories, which include native bluestem grasses (Andropogon gyrans Ashe and Schizachyrium scoparium (Michx.) Nash). Although burning might be an effective tool for restoring these stands to a shortleaf pine/mixed-oak/bluestem grass community type, it is not known whether these restoration burns will have a negative impact on water quality. Six subwatersheds (similar in vegetation, soil type, stream size and location, and disturbance history) were located within the Conasauga River Watershed. Four of the sites were burned in Mar. 2001, and two sites were designated as controls. To evaluate initial effects of prescribed burning on water quality, we measured soil solution and streamwater nutrient concentrations and streamwater sediment concentration (TSS; total suspended solids) weekly over a 10-month period. Consistent with goals of the land managers, all the prescribed fires resulted in low- to moderate-intensity and low-severity fires. Soil solution and streamwater NO3 - - N and NH4+-N did not increase after burning on any of the sites. We found no differences in TSS between burn and control streams in any of the sample periods. In addition, we found no detectable differences between control and burned sites for concentrations of PO43-, SO42-, Ca2+, Mg2+, K+, or pH in soil solution or streamwater. Thus, these prescribed restoration fires did not have a significant effect on soil solution and stream chemistry or stream sediment (TSS) concentrations. Our results suggest that low-intensity, low-severity fires, such as those in this study, could be used as a tool to restore vegetation structure and composition in these mixed pine-hardwood ecosystems without negatively impacting water quality.
Selective grazing of burned patches can be intense if animal distribution is not controlled and may compound the independent effects of fire and grazing on soil characteristics. Our objectives were to quantify the effects of patch burning and grazing on wind erosion, soil water content, and soil temperature in sand sagebrush (Artemisia filifolia Torr.) mixed prairie. We selected 24, 4-ha plots near Woodward, OK. Four plots were burned during autumn (mid-November) and four during spring (mid-April), and four served as nonburned controls for each of two years. Cattle were given unrestricted access (April-September) to burned patches (<2% of pastures) and utilization was about 78%. Wind erosion, soil water content, and soil temperature were measured monthly. Wind erosion varied by burn, year, and sampling height. Wind erosion was about 2 to 48 times greater on autumn-burned plots than nonburned plots during the dormant period (December-April). Growing-season (April-August) erosion was greatest during spring. Erosion of spring-burned sites was double that of nonburned sites both years. Growing-season erosion from autumn-burned sites was similar to nonburned sites except for one year with a dry April-May. Soil water content was unaffected by patch burn treatments. Soils of burned plots were 1 to 3 degrees C warmer than those of nonburned plots, based on mid-day measurements. Lower water holding and deep percolation capacity of sandy soils probably moderated effects on soil water content and soil temperature. Despite poor growing conditions following fire and heavy selective grazing of burned patches, no blowouts or drifts were observed.
Ecologists are beginning to recognize the effect of heterogeneity on structure and function in arid and semiarid ecosystems. Additionally, the influences of temperature on ecosystems are widely documented, but landscape temperature patterns and relationships with vegetation are rarely reported in ecological studies. To better understand the importance of temperature patterns to the conservation and restoration of native ecosystems, we designed an experiment to investigate relationships among soil surface temperature, landscape heterogeneity, and grazing intensity. Grazing intensity did influence the vegetation structure and composition. Heavy treatments had the greatest bare ground and the least vertical structure. Ungrazed treatments had the most litter and live grass cover. However, average temperatures among the three grazing treatments were not different and ranged less than 2 degrees C during midday summer periods. The temperature difference between riparian and upland landscapes within grazing treatments was 21 degrees C. Landscape position (riparian vs. upland) did have a significant influence on soil surface temperature and produced a variation in temperature 11 times greater than grazing intensities. Thermal heterogeneity did not differ among grazing treatments. Lower soil surface temperatures (associated with riparian areas) may provide a critical thermal refuge for many animals in arid and semiarid ecosystems on hot summer days, when air temperatures can exceed 37 degrees C. Riparian zones, specifically riparian vegetation, are an important component in ecosystem management.
Rainfall simulators have a long history of successful use in both laboratory and field investigations. Many plot-scale simulators, however, have been difficult to operate and transport in the field, especially in remote locations where water or electricity is unavailable. This article describes a new rainfall simulator that is relatively easy to operate and transport to and from the field while maintaining critical intensity, distribution, and energy characteristics of natural rainfall. The simulator frame is constructed from lightweight aluminum pipe with a single 50 WSQ nozzle centered at a height of 3 m (9.8 ft). An operating nozzle pressure of 28 kPa (4.1 psi) yields continuous flow at an intensity of 70 mm h-1 (2.8 in. h-1) over a 1.5- × 2-m (4.9- × 6.6-ft) plot area with a coefficient of uniformity of 93%. Kinetic energy of the rainfall is about 25 J m-2 mm-1 (142.8 ft-lb ft-2 in.-1), approximately 87% of natural rainfall. The simulator can be easily transported by two field personnel and completely assembled or disassembled in approximately 10 min. Water usage is at a minimum as the simulator utilizes only one nozzle.
Resumen The objective of this study was to determine how rangeland hydrology of oak, juniper, bunchgrass and shortgrass vegetation types is altered by fire. The research was conducted at the Sonora Agricultural Experiment Station on the Edwards Plateau, Texas. Infiltration rate and interrill erosion were measured using a drip-type rainfall simulator. Terminal infiltration rates of unburned areas were significantly greater on sites dominated by oak (Quercus virginiana Mill.) (200 mm hour-') or juniper CJuniperus ashei Buchh.) (183 mm hour-') than on sites dominated by bunch-grass (146 mm hour-') or shortgrass (105 mm hour-'). Terminal infiltration rates on burned areas were significantly reduced on sites dominated by bunchgrass (110 mm hour-'), shortgrass (76 mm hour-'), and on oak sites that were cut and burned (129 mm hour-'). Soil organic matter content (r = .61), total organic cover (r = .59), and aggregate stability (r = 53) were the variables most strongly correlated with infiltration rate. Measured soil structure properties were not altered by fire, therefore, differences in infil-tration rate between unburned and burned treatments were attributable to variations in the amount of cover. The terminal infiltration rate of cut and burned juniper sites (162 mm hour-') was not changed significantly after the Rre because the associated good soil structure properties allowed rapid infiltration even after cover was removed. Good soil structure properties were also pre sent on the oak sites, but the infiltration rate significantly decreased as a result of the temporary hydrophobic nature of the soil on this site after burning. Prior to burning, interrill erosion was much lower under the tree sites (oak = 2 kg ha-'; juniper = 34 kg ha-') than on bunchgrass (300 kg ha-') or shortgrass (1,299 kg ha-') sites. After burning, interrill erosion significantly increased for all vegetation types (shortgrass = 5,766 kg ha-'; bunchgrass = 4,463 kg ha-'; oak = 4,500 kg ha-'; juniper = 1,926 kg ha-'). Total organic cover (r = -.74) and bulk density at O-30 mm (r = .46) were most strongly correlated with interrill erosion.
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The itiuences of continuous, rotationally deferred, and short-duration rotation grazing systems on soil compaction and water infiltration were assessed. Bulk density and water innltration were measured to evaluate the effects of the 3 grazing systems at moder-ate and heavy stocking rates. Measurements were made in the spring before grazing and at the end of the grazing season in 1983 and 1984. Bulk density was not affected by grazing systems or stocking rate; bulk density was greater in the fall than in spring of 1984, but not in 1983. Infiltration was significantly lower under the heavy stocking rate than under the moderate stocking rate at the end of the grazing season. The average water infiltration was significantly less in the fall than in the spring for the heavy stocking rate but showed no seasonal effect for the moderate stocking rate. Infiltration was significantly greater under continuous grazing than under rotational deferment but no different from that under short-duration grazing in 1983. However, in 1984 the relationship was reversed. The grazing systems evaluated did not affecct soil bulk density and water infiltration in a consistent manner; however, the stocking rate resulted in reduced infiltration during the grazing season.
A 2-year field experiment was undertaken to quantify the interacting effects of a late-spring prescribed burn and summer rainfall on seasonal runoff and erosin in a southern Arizona grassland. Six blocks with walled subplots (n = 24) were installed on a hillslope to measure changes to plant, soil, and hydrologic variables in response to treatments. Increased bulk density, erosion, and runoff volumes; and lowered plant cover and water intake rates were observed within the burned plots following the first summer season. In the second year, higher bulk density, runoff volumes, and erosion measures were again observed within the burned plots, as well as lower plant cover, aggregate stability, and water intake rates. The results of this study indicate that following late-spring burning, semi-desert grasslands are susceptible to greater summer runoff and erosion compared to unburned grasslands. /// Se condujo un estudio de campo de 2 años para cuantificar los efectos interactuantes del fuego prescrito a fines de primavera y la lluvia de verano en el escurrimiento estacional y erosión en un pastizal del sur de Arizona. En la ladera de la montaña se instalaron 6 bloques, subdivididos en subparcelas (n=24), para medir los cambios en planta, suelo y variables hidrológicas en respuesta a los tratamientos. En el primer verano después de la quema se observó en las parcelas quemadas una mayor densidad aparente del suelo, una mayor erosión y mayores volúmenes de escurrimiento así como una menor cobertura vegetal y menor tasa de infiltración. En el segundo año nuevamente se observo dentro de las parcelas quemadas mayores valores de densidad aparente, erosión y volumen de escurrimiento, así como menor cobertura vegetal, estabilidad de los agregados y consumo de agua. Los resultados de este estudio indican que después de un fuego a fines de primavera, los pastizales semidesérticos son susceptibles a una mayor erosión y escurrimiento en comparación con los pastizales sin quemar.
A central tenant of ecohydrology in drylands is that runoff redistribution from bare to vegetated patches concentrates the key limiting resource of water, which can then enhance vegetation growth and biomass. Conversely, a reduction in vegetation patches, particularly those associated with herbaceous plants, can lead to a threshold-like response in which bare patches become highly interconnected, triggering a large increase in hillslope runoff and associated erosion. However, generally lacking is an assessment of how maximization of run-on to herbaceous patches relates to minimization of hillslope-scale runoff. To illustrate how runoff redistribution potentially changes in response to conversion of herbaceous patches to bare ones, we used a spatially distributed model, SPLASH (Simulator for Processes at the Landscape Surface-Subsurface Hydrology), with an example of a semiarid piñon-juniper woodland hillslope with seven combinations of bare and herbaceous patch cover, culminating in complete loss of herbaceous patches, for a 1-yr design storm. As expected, the amount of hillslope runoff increased curvilinearly with reductions in herbaceous cover as runoff per cell increased from bare patches and run-on per cell increased for herbaceous patches. Notably, the total amount of run-on to all herbaceous patches was greatest when the amount of bare cover was intermediate, highlighting a trade-off between the source area for generating runoff and the sink area for capturing run-on. The specific nature of patch-hillslope runoff redistribution responses certainly depends on several site-specific conditions, but the general nature of the response exhibited in our example simulation may be indicative of a general type of response applicable to many rangelands. We suggest that a more robust suite of such relationships could be valuable for managing rangelands by enabling explicit accounting for optimality and trade-offs in biomass per herbaceous patch, total herbaceous cover, and prevention of hillslope-scale connectivity of bare patches that triggers a large increase in runoff and associated erosion. Un postulado central de la ecohidrología de tierras áridas es que la redistribución de la escorrentía desde parches de suelo desnudo hacia parches de vegetación concentra el recurso clave limitante, el agua, que a su vez puede mejorar el crecimiento y la biomasa de la vegetación. Por otro lado, una reducción en los parches de vegetación, particularmente aquellos asociados con plantas herbáceas, puede conducir a una dinámica de umbral en la que la interconexión de los parches de suelo desnudo incrementa de modo tal que se desencadena un incremento considerable en la escorrentía y la erosión asociada. Sin embargo, generalmente faltan evaluaciones de cómo la maximización de recepción de agua de escorrentía en parches de vegetación herbácea está relacionada con la minimización de la escorrentía a escala de ladera. A fin de ilustrar el modo en que la redistribución asociada a la escorrentía puede cambiar como consecuencia de la conversión de parches herbáceos a parches de suelo desnudo utilizamos el modelo espacialmente distribuido SPLASH (simulador para procesos de hidrología superficial-subsuperficial a escala de paisaje), con un ejemplo de una ladera con monte semiárido de Pinus sp. y Juniperus sp. con siete combinaciones de parches herbáceos y de suelo desnudo, culminando en una pérdida total de parches herbáceos, en un diseño de tormentas de 1 año. Como era de prever, la cantidad de escorrentía de ladera aumentó de modo curvilíneo con la reducción de cobertura herbácea; la escorrentía desde los parches de suelo desnudo de cada celda aumentó y la recepción del agua de escorrentía de los parches herbáceos también aumentóen cada celda del modelo. Llama la atención que la cantidad total de agua de escorrentía recibida por los parches herbáceos alcanzó valores máximos con valores intermedios de cobertura de suelo desnudo, hecho que resalta el compromiso existente entre el área de fuentes de agua escorrentía y las áreas de sumidero para la captura de dicha escorrentía. La naturaleza especifica de la relación entre parches y redistribución de la escorrentía sin dudas depende de varias condiciones sitio-especificas, pero la naturaleza de la respuesta exhibida en nuestro ejemplo de simulación podría ser indicativa de una respuesta de tipo general aplicable a muchos pastizales naturales. Sugerimos que un conjunto más robusto de dichas relaciones podría ser valioso para el manejo de pastizales naturales permitiendo tomar en cuenta la optimización y el compromiso entre la biomasa por parche herbáceo, la cobertura vegetal total, y la prevención de la conectividad de parches de suelo desnudo a escala de ladera que desencadena un aumento en la escorrentía y erosión asociada.
Management of rangelands has largely operated under the paradigm of minimizing spatially discrete disturbances, often under the objective of reducing inherent heterogeneity within managed ecosystems. This has led to a simplified understanding of rangelands and in many cases simplified rangelands. We argue that this type of management focus is incapable of maintaining biodiversity. An evolutionary model of disturbance (pyric-herbivory) suggests that grazing and fire interact through a series of feedbacks to cause a shifting mosaic of vegetation patterns across the landscape and has potential to serve as a model for management of grasslands with an evolutionary history of grazing. Our study demonstrates that the spatially controlled interaction of fire and grazing can be used to create heterogeneity in grassland ecosystems and the resulting heterogeneity in vegetation is expressed through other trophic levels, specifically small mammals in this study. Discrete fires were applied to patches, and patchy grazing by herbivores promoted a shifting vegetation mosaic across the landscape that created unique habitat structures for various small mammal species. Peromyscus maniculatus was about 10 times more abundant on recently burned patches (1–2 mo) than the uniform treatment or unburned patches within the shifting mosaic treatment. Chaetodipus hispidus was about 10 times greater in patches that were 15–20 mo post-fire in the shifting mosaic treatment than in the uniform treatment. Sigmodon hispidus, Microtus ochrogaster, and Reithrodontomys fluvescens became dominant in the shifting mosaic in patches that were more than 2 yr post-fire. This study, along with others, suggests that by managing transient focal patches, heterogeneity has the potential to be a new central paradigm for conservation of rangeland ecosystems and can enhance biological diversity and maintain livestock production across broad scales.
In this paper, a multiplication algorithm in extension field Fpm is proposed. Different from the previous works, the proposed algorithm can be applied for an arbitrary pair of characteristic p and extension degree m only except for the case when 4p divides m(p - 1) and m is an even number. As written in the title, when p > m, 4p does not divide m(p - 1). The proposed algorithm is derived by modifying cyclic vector multiplication algorithm (CVMA). We adopt a special class of Gauss period normal bases. At first in this paper, it is formulated as an algorithm and the calculation cost of the modified algorithm is evaluated. Then, compared to those of the previous works, some experimental results are shown. Finally, it is shown that the proposed algorithm is sufficient practical when extension degree m is small.
This is a comparison of two very different hydrology models, both designed to predict runoff from ungaged rural catchments. One is the commonly used and conceptually simple Soil Conservation Service curve number method. The other is a process oriented model based on the Green and Ampt equation. The Green and Ampt model employs newly developed techniques for parameterizing the Green and Ampt equation based on readily available soil and vegetation information. Annual, monthly and daily predicted runoff were compared to observed on six uncalibrated rangeland catchments located in Texas, Oklahoma, Arizona, Nebraska and Idaho. Model parameterization was based strictly on individual catchment characteristics. No model calibration was performed. Results indicate that the Green and Ampt model is a potentially useful tool for predicting runoff. These results are important because they demonstrate the utility of complex physically based models as management tools for predicting land use impacts to runoff and infiltration.
A portable, variable‐intensity, low‐cost rainfall simulator is described for use in small pan runoff‐erosion studies, and which can be adapted to larger plot studies for field use. Intensity is controlled by electrically operated solenoid valves into which wide square spray nozzles are fitted. The opening and closing of the solenoid valves, controlled via switches operated by a rotating cam or microcomputer, varies the intensity of rainfall from 0.0004 mm s ⁻¹ to approximately 0.024 mm s ⁻¹ , at 29 kPa water pressure. Coefficients of uniformity for 1 m ² plots under a single nozzle are 90 to 95%, and 85 to 90% for 1‐ by 3‐m field plots using a three nozzle system. Kinetic energy of the rainfall, determined from drop size distributions, is about 23 J m ⁻² mm ⁻¹ , which is within the range for natural rainfall.
After 56 years of grazing on shortgrass prairie and 13 years of grazing on mixed-grass prairie, surface runoff was estimated with a rotating boom rainfall simulator. Runoff was strongly and positively correlated with percent bare ground, and was strongly and negatively correlated with percent litter cover. Neither foliar nor basal plant cover were useful estimators of runoff.
Old World Bluestems, such as yellow bluestem (Bothriochloa ischaemum), have been seeded extensively in the Southern Great Plains because they are responsive to nitrogen fertilization and allow for higher stocking rates. From 1991 to 2005, we measured the effects of moderately grazing prairie species and heavily grazing fertilized yellow bluestem on runoff, sediment yield, leaf litter cover, and aboveground plant biomass for four adjacent watersheds located at the USDA-ARS Southern Plains Range Research Station in the sub-humid Rolling Red Plains of western Oklahoma. Here we show that factors other than leaf litter cover and biomass determine variation in runoff when leaf litter exceeds 70%. Runoff was related to grazing rate and storm size and inversely related to storm duration. Rainfall thresholds were similar between the moderately grazed prairie watersheds (15 mm) and the heavily grazed yellow bluestem watersheds (18 mm); however, the slope of the rainfall-runoff curve from heavily grazed yellow bluestem (0.242) was steeper than that of moderately grazed prairie (0.087). Slightly higher runoff from heavily grazed yellow bluestem relative to moderately grazed prairie may occur due to compaction of both the leaf litter and topsoil. Sediment yield was low from moderately grazed native prairie and heavily grazed yellow bluestem. Our findings indicate that both treatments assessed appear hydrologically sustainable. (c) 2012 Elsevier B.V. All rights reserved.
While most studies of heterogeneity have focused on describing patterns of species or communities, few have focused on the relationships between biotic and abiotic environmental landscape-level gradients. Our study was designed to determine relationships between grazing (heavy, moderate, ungrazed), topographic position (upland vs. riparian), vegetation structure and the thermal environment (i.e., soil-surface temperatures) and determine the influence on landscape patterns of heterogeneity. Biotic and abiotic patterns of heterogeneity were evaluated by establishing 200-m transects that were centered on and perpendicular to a riparian zone so that spatial patterns of variability could be determined along each transect which transcends the maximum level of landscape heterogeneity. Vegetation cover and structure and soil-surface temperatures were recorded at 1-m intervals along the transect. Bare ground increased and leaf litter, grass cover, vegetation heights and angle of obstruction decreased with grazing intensity. However, mean soil-surface temperatures did not differ between grazing treatments. Tree canopy cover associated with riparian areas generally reduced soil-surface temperatures 20 C below that of upland temperatures. In fact, 96% of observations of riparian soil-surface temperature were ≤ 39 C, while 94% of upland soil-surface temperatures were ≥ 40 C regardless of grazing intensity. Vegetation characteristics and soil-surface temperatures were correlated (P < 0.05), but correlation coefficients were small because soil-surface temperature was highly variable. Grazing influenced patterns of landscape heterogeneity, but effects were inconsistent among biotic and abiotic variables. Although grazing had little influence on moderating mean soil-surface temperatures, results suggest that grazing intensity influences thermal heterogeneity at a variety of spatial scales. For instance, thermal heterogeneity (in moderately grazed treatments) is highest at smaller (lag distances ≤ 20 m) and larger (lag distances ≥ 48 m) spatial scales but was lowest at moderate scales (lag distances 22–45 m). For all variables, other than soil-surface temperature and forb cover, semi-variances of moderately grazed sites generally lie intermediate between heavy and ungrazed sites. Nearly all ungrazed vegetation characteristics, except leaf litter, fit a spherical model that reached a sill at a lag distance ≤ 20 m and became spatially independent thereafter, while heavily and moderately grazed sites typically fit an exponential model, indicating a high degree of continuity. Patterns of thermal variability (on uplands) are not related directly to any one vegetation variable, hence, landscape patterns based on vegetation parameters alone are of limited value since patterns of thermal variability are effected by the integration of vegetation and environmental variables within the ecosystem.
The Automated Geospatial Watershed Assessment (AGWA) is an ArcGIS interface to support data organization, model parameterization, integration, and visualization for KINEROS2, RHEM, and the Soil Water Assessment Tool (SWAT) model. All of the required initial modeling parameters automatically are generated by AGWA from topography, soils, and land cover/land-use Geographic Information Systems (GIS) data layers. Built into AGWA are digitized and interpolated versions of the National Oceanographic and Atmospheric Administration (NOAA) technical publication 40 (TP40) rainfall frequency atlas maps. There are potential long-term implications of these results as well for overall plant productivity. The current RHEM and AGWA tools, as well as those in development, will support the analysis of alternative management systems as well as their placement in a watershed to reduce conservation investments and increase cumulative conservation benefits over a range of scales.
Prescribed burning is a forest management tool to reduce forest fire hazards. It is largely applied in the USA and is gaining importance worldwide, particularly in Europe. However, its effects on soils still have to be better understood. This study analyses the effects of two types of prescribed burnings (i.e. low and high burn severities of up to 200 °C and at or above 400 °C) on soil hydrophobicity, infiltration, and water storage capacity of top soils. Prescribed burnings were performed on four different plots in southern and western Catalonia, Spain. Soil samples were collected before and after burning to assess water repellency with the water drop penetration time (WDPT). Three rainfall simulations before burning and three after burning were executed on areas of 1 m2, and soil water contents at four to five depths were measured every 4 min during and after rainfall simulations using time domain reflectometry equipment (TDR). Following burning at both severities, water storage capacity of the top soil decreased between 1·7 and 5·4%vol on all four plots. No significant changes in volume flux density and velocity of the wetting fronts were discernible. Water drop penetration times increased moderately at the soil surface of the plots that were exposed to the high burn severity, and decreased slightly when burn severity was low. On two of the four plots the presence of partially moist organic litter prevented the underlying soil from excessive heating. Changes in hydrophobicity and water storage capacity of the top soil did not affect infiltration. Copyright © 2008 John Wiley & Sons, Ltd.
Fire and grazing are interactive disturbance processes that are important to the structure and function of grassland ecosystems. Studies of nitrogen (N) availability report different effects following grazing and fire. However, these studies have largely neglected the spatially controlled interaction between fire and grazing. The objective of our work was to evaluate an application of the fire-grazing interaction model on N availability in a tallgrass prairie. We compared patches within a shifting mosaic landscape where each patch varied in time since focal disturbance (fire and intense grazing disturbance). We also evaluated N availability on a burned and grazed landscape where fires and moderate grazing occurred annually and uniformly across the entire landscape. These treatments were both burned and grazed where the only difference was spatial and temporal variability in fire application and grazing disturbance. Samples were collected from upland sites in May of 2003 and 2004. Total soil inorganic N (NH4+-N + NO3--N) and a growth chamber experiment with hard red winter wheat (Triticum aestivum L. cv. Jagger) were used to evaluate potential N availability. Our study produced patterns of N availability that are more similar to studies of grazing lawns where N availability is enhanced by focal grazing than from studies of fire without grazing. Overall, our study demonstrates that fire and grazing are interactive. Unburned patches have minimal grazing pressure and low N availability. Fire-grazing interaction may provide a management alternative that enables sustainable livestock production, through increased carrying capacity in focally disturbed patches, concomitant with biological diversity in tallgrass prairie.
A comparative analysis of soils and vegetation from cultivated areas reseeded to native grasses and native prairies that have not been cultivated was conducted to evaluate restoration of southern mixed prairie of the Great Plains over the past 30 to 50 years. Restored sites were within large tracts of native prairie and part of long-term grazing intensity treatments (heavy, moderate, and ungrazed), allowing evaluation of the effects of grazing intensity on prairie restoration. Our objective was to evaluate restored and native sites subjected to heavy and moderate grazing regimes to determine if soil nutrients from reseeded cultivated land recovered after 30 years of management similar to the surrounding prairie and to identify the interactive influence of different levels of grazing and history of cultivation on plant functional group composition and soils in mixed prairies. For this mixed prairie, soil nitrogen and soil carbon on previously cultivated sites was 30 to 40% lower than in uncultivated native prairies, indicating that soils from restored sites have not recovered over the past 30 to 50 years. In addition, it appears that grazing alters the extent of recovery of these grassland soils as indicated by the significant interaction between grazing intensity and cultivation history for soil nitrogen and soil carbon. Management of livestock grazing is likely a critical factor in determining the potential restoration of mixed prairies. Heavy grazing on restored prairies reduces the rate of soil nutrient and organic matter accumulation. These effects are largely due to changes in composition (reduced tallgrasses), reduced litter accumulation, and high cover of bare ground in heavily grazed restored prairies. However, it is evident from this study that regardless of grazing intensity, restoration of native prairie soils requires many decades and possibly external inputs to adequately restore organic matter, soil carbon, and soil nitrogen.
Summary 1. Management of rangelands has long operated under the paradigm of minimizing spatially discrete disturbances, often under the objective of reducing inherent hetero- geneity within managed ecosystems. Management of grazing animals has focused on uniform distribution of disturbance, so that no areas are heavily disturbed or undis- turbed (i.e. management to the 'middle'). 2. A model of the fire-grazing interaction argues that grazing and fire interact through a series of positive and negative feedbacks to cause a shifting mosaic of vegetation pat- tern across the landscape. This interaction was important in the evolution of species in the North American Great Plains grasslands. This approach has the potential to serve as an ecological-based model for management of grasslands with a long evolutionary history of grazing. 3. We compared a heterogeneity-based approach, in which fire is applied to discrete patches, with typical homogeneity-based land management in the North American Great Plains, to determine if patch burning followed by focal grazing creates a shifting mosaic pattern of vegetation structure and composition. 4. Our data suggest that spatially discrete fires promote focal grazing, where grazing animals devote 75% of grazing time within the one-third of the area that has been burned within the past year. These focal disturbances cause local changes in the plant community and increase patch-level heterogeneity across landscapes. As the focal disturbance is shifted to other patches over time, successional processes lead to changes in local plant communities and the patchwork landscape can be described as a shifting mosaic. 5. A patch-dynamic approach can be accomplished in the tallgrass prairie through applying spatially discrete fires and allowing animals free access to a diversity of land- scape elements that vary in time since focal disturbance. This increases heterogeneity across the landscape, a variable that has been shown to be critical to some wildlife species as well as the structure and function of grassland ecosystems. 6. Synthesis and applications. Our study demonstrates that the fire-grazing model may be useful for generating heterogeneity in grassland management. Discrete fires are applied to patches, and patchy grazing by herbivores promotes a shifting vegetation mosaic across the landscape. Furthermore, application of the model has the potential of increasing the area of rangelands under management for conservation purposes, because livestock production is maintained at a level similar to traditional management. So, by managing transient focal patches that move through the landscape, heterogeneity has the potential to be a central paradigm for managing landscapes for multiple objec- tives, such as biodiversity and agricultural productivity.
An experimental watershed (Oskotz principal– Op –ca.1700 ha) covered with forest and pasture (cattle-breeding) with an equally experimental sub-watershed (Oskotz woodland – Ow – ca. 500 ha) almost entirely under forest was continuously monitored during 8 years (2001–2008). These watersheds were established by the Government of Navarre (Spain) in order to assess the impact of agricultural activities on different region of Navarre. The first results regarding exported sediment, runoff, nitrate and phosphate are presented herein. These results are compared with those from two grain-sown watersheds previously reported by the authors, elsewhere.The same as in the grain-sown watersheds, most runoff, sediment, nitrate and phosphate yields in Oskotz were generated during winter, though most erosive rainfalls occurred during summer. In Ow, average sediment, nitrate and phosphate yields were approximately: 700, 22, 0.35 kg ha year−1, respectively; for Op these figures were 550, 54 and 0.76 kg ha year−1, respectively.However, total sediment and solute yields were different depending on the prevailing land use: cereal crops > forest > pasture. Sediment yields in the forest were strongly affected by the logging moment, when exported sediment rocketed.Nitrate concentration and yields were lower (and under the critical threshold) in the forested/pastured watersheds than those recorded in the two intensively cultivated watersheds. However, phosphate yields were dramatically higher (and over the critical threshold) in the former watersheds due to the prevailing soil conditions and to the fertilization of pasture, mainly with slurry.The present work, along with that similar one recently reported by the authors, is an unprecedented and relevant piece of research for the region.
This study examined the importance of natural and manmade structural features on the avian community relative to management-induced vegetation dynamics. The study was conducted within the context of two alternative vegetation management treatments applied to pastures on a tallgrass prairie site in northcentral Oklahoma from 2001 to 2003. The brown-headed cowbird, a brood parasite, and the grasshopper sparrow, a common grassland obligate species, were most abundant in areas managed under a traditional treatment in which entire pastures were annually burned. Conversely, Henslow’s sparrow, a grassland obligate of conservation concern, was completely absent from traditional treatment pastures. Total bird species diversity and grassland obligate richness was highest in the patch-burn treatment, in which only discrete portions of each pasture were burned each year to create a mosaic of vegetation ‘patches’ in various stages of recovery from disturbance. Models of bird abundance reflected not only species-specific vegetation preferences, but also the often negative influence of structural features such as woody edges, roads, and ponds on breeding bird use of grasslands. Our study demonstrated that both disturbance-derived vegetation attributes and structural features contribute to heterogeneity and influence subsequent use by and composition of grassland bird communities.
Recent intensive grazing in Mongolia may be significantly reducing the infiltration rate of rangeland. This study measured infiltration rates using simulated rainfall with high raindrop impact for small plots established on steppe grassland, desert grassland, and shrubland sites in Mongolia. The response of the infiltration rate to short-term livestock removal was also investigated. On the steppe grassland, a high infiltration rate was measured on an ungrazed plot with relatively dense vegetation cover; a statistically significant correlation was found between the total surface cover and final infiltration rate, indicating that surface cover by rock fragments also increased the infiltration rate to some extent. For desert grassland and shrubland, however, the surface cover condition was not a major factor controlling the final infiltration rate. After 4 years of livestock removal, the surface vegetation cover of the ungrazed plot was greater than that of the grazed plot, but no appreciable change occurred in soil penetration resistance. These results suggest that the high infiltration rate on the ungrazed plot was maintained mainly by the recovery of surface vegetation cover after the short-term livestock removal; this may indicate a potential mechanism of recovery from desertification processes for Mongolian rangeland.
In the Mediterranean area, forest fires have become a first-order environmental problem. Increased fire frequency progressively reduces ecosystem recovery periods. The fire season, usually followed by torrential rains in autumn, intensifies erosion processes and increases desertification risk. In this work, the effect of repeated experimental fires on soil response to water erosion is studied in the Permanent Field Station of La Concordia, Valencia, Spain. In nine 80 m2 plots (20 m long×4 m wide), all runoff and sediment produced were measured after each rainfall event. In 1995, two fire treatments with the addition of different biomass amounts were applied. Three plots were burned with high fire intensity, three with moderate intensity, and three were unburned to be used as control. In 2003, the plots with the fire treatments were burned again with low fire intensities. During the 8-year interval between fires, plots remained undisturbed, allowing regeneration of the vegetation–soil system. Results obtained during the first 5 months after both fire experiments show the high vulnerability of the soil to erosion after a repeated fire. For the burned plots, runoff rates increased three timesmore than those of 1995, and soil losses increased almost twice. The highest sediment yield (514 gm−2)wasmeasured in 2003, in the plots of the moderate fire intensity treatment, which yielded only 231 gm−2 of sediment during the corresponding period in 1995. Runoff yield from the control plots did not show significant temporal changes, while soil losses decreased from 5 g m−2 in the first post-fire period to 0.7 g m−2 in the second one.
The effect of a repeated burning on soil hydrology and erosive parameters was studied on a Mediterranean forest soil (Rendzic leptosol) with the aim of identifying the effects of the fire and climatic parameters related to the post-fire runoff and soil loss. The study was carried out in an Experimental Permanent Field Station (La Concordia), close to Valencia (Spain). This field station is located on a calcareous hillside facing SSE, and is composed of nine erosion plots (20 × 4 m). Firstly, experimental fires were performed in June 1995 with two fire treatments (T1 or high severity fire and T2 or moderate severity fire) and a control one (unburnt, T3). The repeated fire (low severity) was carried out in July 2003. The studied period was focused from 18 months before the repeated fire (July 2003) until 18 months after it. Rainfall characteristics of each single event were recorded, which allowed us to statistically distinguish four time periods according to the rainfall intensity and duration: periods I (March 2002 to May 2003) and III (December 2003 to early May 2004) with low intensity and long duration rainfalls, and periods II (June 2003 to November 2003) and IV (late May 2004 to December 2004) with high intensity and short duration rainfalls. Before the 2003 fire, the partial recovery of soil and vegetation from the previous burning in 1995 led to a diminution in the runoff rates (6.5 L m− 2 in burned plots and 1.8 L m− 2 in unburnt ones). Six months later (period II), runoff increased in one order of magnitude (23.9 L m− 2 in burnt plots and 1.1 L m− 2 in the unburnt ones) due, in part, to the short time elapsed from fire until high intensity rainfalls. These differences in runoff production were maintained during the whole post-fire period.
Fire is a globally distributed disturbance that impacts terrestrial ecosystems and has been proposed to be a global "herbivore." Fire, like herbivory, is a top-down driver that converts organic materials into inorganic products, alters community structure, and acts as an evolutionary agent. Though grazing and fire may have some comparable effects in grasslands, they do not have similar impacts on species composition and community structure. However, the concept of fire as a global herbivore implies that fire and herbivory may have similar effects on plant functional traits. Using 22 years of data from a mesic, native tallgrass prairie with a long evolutionary history of fire and grazing, we tested if trait composition between grazed and burned grassland communities would converge, and if the degree of convergence depended on fire frequency. Additionally, we tested if eliminating fire from frequently burned grasslands would result in a state similar to unburned grasslands, and if adding fire into a previously unburned grassland would cause composition to become more similar to that of frequently burned grasslands. We found that grazing and burning once every four years showed the most convergence in traits, suggesting that these communities operate under similar deterministic assembly rules and that fire and herbivory are similar disturbances to grasslands at the trait-group level of organization. Three years after reversal of the fire treatment we found that fire reversal had different effects depending on treatment. The formerly unburned community that was then burned annually became more similar to the annually burned community in trait composition suggesting that function may be rapidly restored if fire is reintroduced. Conversely, after fire was removed from the annually burned community trait composition developed along a unique trajectory indicating hysteresis, or a time lag for structure and function to return following a change in this disturbance regime. We conclude that functional traits and species-based metrics should be considered when determining and evaluating goals for fire management in mesic grassland ecosystems.
Our understanding of fire and grazing is largely based on small-scale experimental studies in which treatments are uniformly applied to experimental units that are considered homogenous. Any discussion of an interaction between fire and grazing is usually based on a statistical approach that ignores the spatial and temporal interactions on complex landscapes. We propose a new focus on the ecological interaction of fire and grazing in which each disturbance is spatially and temporally dependent on the other and results in a landscape where disturbance is best described as a shifting mosaic (a landscape with patches that vary with time since disturbance) that is critical to ecological structure and function of many ecosystems. We call this spatiotemporal interaction pyric herbivory (literal interpretation means grazing driven by fire). Pyric herbivory is the spatial and temporal interaction of fire and grazing, where positive and negative feedbacks promote a shifting pattern of disturbance across the landscape. We present data we collected from the Tallgrass Prairie Preserve in the southern Great Plains of North America that demonstrates that the interaction between free-roaming bison (Bison bison) and random fires promotes heterogeneity and provides the foundation for biological diversity and ecosystem function of North American and African grasslands. This study is different from other studies of fire and grazing because the fires we examined were random and grazing animals were free to roam and select from burned and unburned patches. For ecosystems across the globe with a long history of fire and grazing, pyric herbivory with any grazing herbivore is likely more effective at restoring evolutionary disturbance patterns than a focus on restoring any large vertebrate while ignoring the interaction with fire and other disturbances.
In tallgrass prairie, disturbances such as grazing and fire can generate patchiness across the landscape, contributing to a shifting mosaic that presumably enhances biodiversity. Grassland birds evolved within the context of this shifting mosaic, with some species restricted to one or two patch types created under spatially and temporally distinct disturbance regimes. Thus, management-driven reductions in heterogeneity may be partly responsible for declines in numbers of grassland birds. We experimentally altered spatial heterogeneity of vegetation structure within a tallgrass prairie by varying the spatial and temporal extent of fire and by allowing grazing animals to move freely among burned and unburned patches (patch treatment). We contrasted this disturbance regime with traditional agricultural management of the region that promotes homogeneity (traditional treatment). We monitored grassland bird abundance during the breeding seasons of 2001-2003 to determine the influence of altered spatial heterogeneity on the grassland bird community. Focal disturbances of patch burning and grazing that shifted through the landscape over several years resulted in a more heterogeneous pattern of vegetation than uniform application of fire and grazing. Greater spatial heterogeneity in vegetation provided greater variability in the grassland bird community. Some bird species occurred in greatest abundance within focally disturbed patches, while others occurred in relatively undisturbed patches in our patch treatment. Henslow's Sparrow, a declining species, occurred only within the patch treatment. Upland Sandpiper and some other species were more abundant on recently disturbed patches within the same treatment. The patch burn treatment created the entire gradient of vegetation structure required to maintain a suite of grassland bird species that differ in habitat preferences. Our study demonstrated that increasing spatial and temporal heterogeneity of disturbance in grasslands increases variability in vegetation structure that results in greater variability at higher trophic levels. Thus, management that creates a shifting mosaic using spatially and temporally discrete disturbances in grasslands can be a useful tool in conservation. In the case of North American tallgrass prairie, discrete fires that capitalize on preferential grazing behavior of large ungulates promote a shifting mosaic of habitat types that maintain biodiversity and agricultural productivity.
Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web soil survey
Web Soil Survey, 2011. Soil Survey Staff, Natural Resources Conservation Service, United
States Department of Agriculture. Web soil survey [Available online at http://
websoilsurvey.nrcs.usda.gov/. Accessed 18 May 2011].
- A L West
A.L. West et al. / Rangeland Ecology & Management 69 (2016) 20–27
A canopy-cover method of vegetational analysis
- R F Daubenmire
Daubenmire, R.F., 1959. A canopy-cover method of vegetational analysis. Northwest Science 33, 43-46.
Mesonet Long-Term Averages—MapsAvailable at http://www.mesonet. org/index.php/weather/mesonet_averages_maps#y=average&m=12&p=rain&d= false
- Mesonet
Mesonet, 2014. Mesonet Long-Term Averages—MapsAvailable at http://www.mesonet.
org/index.php/weather/mesonet_averages_maps#y=average&m=12&p=rain&d=
false [Accessed 4 September 2014].
Pyric-herbivory to promote rangeland heterogeneity: evidence from small mammal communities
- S D Fuhlendorf
- I I Townsend
- D E Elmore
- R D Engle
Fuhlendorf, S.D., Townsend II, D.E., Elmore, R.D., Engle, D.M., 2010. Pyric-herbivory to promote rangeland heterogeneity: evidence from small mammal communities. Rangeland Ecology & Management 63, 670-678.