A Method For Landscape-Scale Vegetation Assessment: Application to Great Basin Rangeland Ecosystems

The growth of landscape-scale land management necessitates the development of methods for large-scale vegetation assessment. Field data collection and analysis methods used to assess ecological condition for the 47 165-h North Spring Valley watershed are presented. Vegetation cover data were collected in a stratified random design within 6 Great Basin vegetation types, and the probability of detecting change in native herbaceous cover was calculated using power analyses. Methods for using these quantitative assessment data are presented to calculate a departure index based on reference condition information from LANDFIRE (an interagency effort to map and model fire regimes and other biophysical characteristics at a mid-scale for the entire United States) Biophysical Setting models for the mountain big sagebrush (Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle) vegetation type. For mountain big sagebrush in the North Spring Valley landscape, we found that the earliest successional classes were underrepresented and that mountain big sagebrush moderately invaded by conifers was more abundant than predicted by the LANDFIRE reference based on the historic range of variability. Classes that were most similar to the reference were mountain big sagebrush with the highest conifer cover and late development mountain big sagebrush with perennial grasses. Overall, results suggested that restoration or approximation of the historic fire regime is needed. This method provides a cost-effective procedure to assess important indicators, including native herbaceous cover, extent of woody encroachment, and ground cover. However, the method lacks the spatial information that would allow managers to comprehensively assess spatial patterns of vegetation condition across the mosaics that occur within each major vegetation type. The development of a method that integrates field measurements of key indicators with remotely sensed data is the next critical need for landscape-scale assessment.     

Incorporating Plant Mortality and Recruitment Into Rangeland Management and Assessment

Rangeland management is largely focused on managing vegetation change. Objectives may include managing against change if the desired vegetation is in place, or attempting to create a shift in vegetation if the desired plant community is not present. There is a rich body of research documenting influences of disturbance and management on rangeland vegetation. However, in many cases the information is largely observational and does not identify mechanisms driving change. We propose using the regeneration niche concept to more effectively predict when vegetation change is possible and to suggest successional direction. Simply stated, as plants die and leave gaps in the community, recruitment of new individuals will dictate successional direction. Recruitment requires that propagules are present, that the propagules find safe sites in which to establish, and that the seedlings and young plants are able to compete with existing vegetation and survive. In many rangeland communities, perennial bunchgrasses are a key to stability and invasion resistance. Existing literature shows that most rangeland bunchgrasses have average life spans of 10 yr or less, so periodic recruitment is necessary to maintain communities in which they are a major component. Disturbance can influence plant population dynamics, and we suggest classifying disturbances based on how they influence mortality and recruitment. We also suggest that more emphasis be placed on the concept of critical transitions and less on the degree of disturbance per se. In other words, a small disturbance at the wrong point in community composition (low plant density and high gap size for example) can cause a transition, whereas major disturbance in a high condition community may yield little risk of transition. We suggest that a focus on mortality and recruitment will provide a mechanistic approach for predicting vegetation change and making management decisions. We refer to this approach as recruitment-based management.     

政府决策和管理体制在草地健康发展中的作用

草地资源退化不能仅仅归谬于全球变化、人口压力和放牧强度的增加,政府的决策和现行的体制对草地的健康发展同样起到决定性的作用。如果没有合理的政策法规和有效的实施体制,单纯的技术管理往往不能根本改变目前草地退化的现状。从中国草地管理的发展历程及主要存在问题、草地科研体制与方向对草地生态系统的影响与作用、草地管理的组织机构以及美国草地管理政策启示等几个方面,系统分析了政府决策和体制对草地健康发展的影响,提出了促进草地可持续发展的一系列政策建议。     

Adaptive,Multipaddock Rotational Grazing Management: A Ranch-Scale Assessment of Effects on Vegetation and Livestock Performance in Semiarid Rangeland

A comprehensive understanding of multipaddock, rotational grazing management on rangelands has been slow to develop, and the contribution of adaptive management (Briske et al. 2011) and sufficient scale (Teague and Barnes 2017) have been identified as key omissions. We designed an experiment to compare responses of vegetation and cattle in an adaptively managed, multipaddock, rotational system with that of a season-long, continuous system at scales comparable with those of a working ranch. We hypothesized that 1) year-long rest periods in the adaptively managed, rotational pastures would increase the density and productivity of perennial C₃ graminoids compared with continuously grazed pastures and 2) adaptive management, supported with detailed monitoring data, would result in similar cattle performance in the rotational as in the continuously grazed pastures. However, we found little supporting evidence for grazing management effects on C₃ graminoid abundance or production under either above-average or below-average precipitation conditions during the 5-yr experiment. Furthermore, adaptive rotational grazing resulted in a 12–16% reduction in total cattle weight gain relative to continuous grazing each year. Our work shows that the implementation of adaptive management by a stakeholder group provided with detailed vegetation and animal monitoring data was unable to fully mitigate the adverse consequences of high stock density on animal weight gain. Under adaptive rotational grazing, C₃ perennial grass productivity and stocking rate both increased following above-average precipitation. But when adaptive rotational management was directly compared with continuous grazing with the same increase in stocking rate, continuous grazing achieved similar vegetation outcomes with greater cattle weight gains. We suggest that managers in semiarid rangelands strive to maintain cattle at stock densities low enough to allow for maximal cattle growth rates, while still providing spatiotemporal variability in grazing distribution to enhance rangeland heterogeneity and long-term sustainability of forage production.     

The Elusive Promise of Social-Ecological Approaches to Rangeland Management

Resilience-based frameworks for social-ecological systems (SES) are prominent in contemporary scientific literatures, but critics suggest these approaches may promise more than they deliver. A fundamental premise underlying the SES approach is that, because of the scope of human activities worldwide, we cannot separate ecological and human elements of nature when tackling our biggest challenges. Proponents argue that managers should not seek optimal solutions, but instead build capacity to adapt and transform systems to thrive within unpredicted or novel ecological states. If the range profession is to take advantage of resilience ideas, we need better tools and concepts for understanding interconnected systems. SES research and management strategies will pose practical difficulties, most notably finding ways to bridge differences between the methods of social and natural sciences. Also needed are institutions that involve scientists, managers, and stakeholders in analysis and informed governance, thereby addressing a key tenet of “resilience thinking” while accounting for the “wicked” nature of problems that, like many facing rangeland managers today, do not have a single best solution but only more or less feasible responses. In hopes of guiding managers toward more feasible options, I offer a model of rangeland social-ecological systems describing how management choices are influenced by, and may affect, human and natural systems at local and regional-to-global scales through both top-down and bottom-up processes.     

Assessing Transportation Infrastructure Impacts on Rangelands: Test of a Standard Rangeland Assessment Protocol

Linear disturbances associated with on- and off-road vehicle use on rangelands has increased dramatically throughout the world in recent decades. This increase is due to a variety of factors including increased availability of all-terrain vehicles, infrastructure development (oil, gas, renewable energy, and ex-urban), and recreational activities. In addition to the direct impacts of road development, the presence and use of roads may alter resilience of adjoining areas through indirect effects such as altered site hydrologic and eolian processes, invasive seed dispersal, and sediment transport. There are few standardized methods for assessing impacts of transportation-related land-use activities on soils and vegetation in arid and semi-arid rangelands. Interpreting Indicators of Rangeland Health (IIRH) is an internationally accepted qualitative assessment that is applied widely to rangelands. We tested the sensitivity of IIRH to impacts of roads, trails, and pipelines on adjacent lands by surveying plots at three distances from these linear disturbances. We performed tests at 16 randomly selected sites in each of three ecosystems (Northern High Plains, Colorado Plateau, and Chihuahuan Desert) for a total of 208 evaluation plots. We also evaluated the repeatability of IIRH when applied to road-related disturbance gradients. Finally, we tested extent of correlations between IIRH plot attribute departure classes and trends in a suite of quantitative indicators. Results indicated that the IIRH technique is sensitive to direct and indirect impacts of transportation activities with greater departure from reference condition near disturbances than far from disturbances. Trends in degradation of ecological processes detected with qualitative assessments were highly correlated with quantitative data. Qualitative and quantitative assessments employed in this study can be used to assess impacts of transportation features at the plot scale. Through integration with remote sensing technologies, these methods could also potentially be used to assess cumulative impacts of transportation networks at the landscape scale.     

Grazing Management in Tropical Savannas: Utilization and Rest Strategies to Manipulate Rangeland Condition

Grazing management is important for sustaining the productivity and health of rangelands. However, the effects of grazing management on herbage growth and species composition in the tropical savannas of northern Australia are not well known. In this eight-year study the influences of utilization rate and resting pastures from grazing on vegetation dynamics were measured at three sites in northeast Queensland, Australia. The sites had high, medium, and low soil fertility, and there were two land condition classes (States I and II) at each site. Severe drought occurred during the first four years, but above-average rainfall was received in the second half of the study. High utilization rates reduced biomass, perennial grass basal area, and ground cover. The reduction in biomass was due to both higher consumption and decreased primary production. State I condition plots at the high and medium soil fertility sites were initially dominated by decreaser perennial grasses, but these declined at all utilization levels, particularly the high rate. They were largely replaced by exotic perennial grasses. At the low fertility site there were no exotic grasses, and the decreaser grasses increased in all treatments, with the increases greatest in plots with low utilization or medium utilization plus resting. In the State II condition plots at the high and medium fertility sites, low or moderate utilization, led to an increase in both decreaser and exotic perennial grasses; with high utilization the decreaser perennial grasses declined and were replaced largely by exotic perennial grasses. This study clearly demonstrated that either conservative stocking with year-round grazing or a grazing system that includes some wet-season resting will help maintain land in a desirable state or help facilitate the transition from a less desirable ecological state to one more desirable for pastoral production and rangeland condition.