Half of the earth's terrestrial surface is classified as rangeland and grassland. Rangeland and grassland ecosystems provide forage for livestock and native herbivores, habitat for native flora and fauna, watersheds for rural and urban uses; ecosystem goods and services; areas for recreation; and renewable and nonrenewable energy sources. NIFA seeks to ensure the sustainability of these resources through rangelands and grasslands programs.
Rangeland is land on which the potential plant cover is composed principally of native grasses, grass-like plants, forbs or shrubs suitable for grazing and browsing, and introduced forage species that are managed like rangeland. This would include areas where introduced hardy and persistent grasses might be planted and extensive practices, such as grazing management, targeted grazing, prescribed burning, and reseeding are used with little or no chemicals or fertilizer being applied. Grassland, savannas, many wetlands, some deserts, and tundra are considered rangeland. Certain shrub communities, dominated by mesquite, chaparral, mountain shrub, and pinyon-juniper, also are considered rangeland.
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous (non-woody) plants, such as forbs. Grasslands occur naturally on all continents except Antarctica, and in many other areas they have replaced the natural vegetation through human influence. In countries where modern agriculture has not destroyed wild grasslands, the greatest diversity of grazing animals and predators on the planet exists.
Rangeland health is the degree to which the integrity of soil, vegetation, water and air, as well as the ecological processes of the rangeland ecosystem, are balanced and sustained. Direct measures of site integrity and status of ecological processes are difficult or expensive to measure due to the complexity of the processes and their interrelationships. Therefore, biological and physical components are often used as indicators of the functional status of site integrity and ecological processes. Three quality components are assessed:
- Soil/Site Stability: the capacity of an area to limit redistribution and loss of soil resources (including nutrients and organic matter) by wind and water.
- Hydrologic Function: the capacity of an area to capture, store, and safely release water from rainfall, run-on, and snowmelt (where relevant), to resist a reduction in this capacity, and to recover this capacity when a reduction does occur.
- Biotic Integrity: the capacity of the biotic community (plants, animals, and microorganisms occurring both above and below ground) to support ecological processes within the normal range of variability expected for the site, to resist a loss in the capacity to support these processes, and to recover this capacity when losses do occur.
Rangelands and grasslands are in a variety of conditions ranging from degraded to fully functioning. They are managed by public and private land managers with an array of different management objectives for both production and conservation goals. Disturbances (e.g., grazing, fire, drought, global change), management practices and human activities (e.g. exurbanization, fragmentation) affect ecological processes that can trigger threshold mechanisms to alter plant-soil communities. The ecological and economic sustainability of rangeland and grassland ecosystems requires timely, proactive, and adaptive management based on a fundamental understanding of drivers and feedbacks that influence ecosystem composition, structure, and function. Science-based land management requires monitoring and analysis of rangeland and grassland landscapes to document ecological status relative to disturbances, assess management efficacy, and understand and quantify the environmental effects of conservation practices.
One of the most economically and ecologically significant changes in rangeland and grassland ecosystems is the arrival and spread of invasive species which can alter ecosystem structure, composition, and function and reduce biological diversity. Approximately 50,000 non-native species in the United States cause environmental damage and losses totaling $135 billion annually (Pimental et al. 2000, Bioscience 50:53-65). Weeds on rangelands encompass more than 300 species and account for $2 billion annually in losses (DiTomaso 2000, Weed Science 48:255-265). Effectively controlling invasive species requires understanding and, where possible, changing the processes driving invasion. Potential mechanisms of invasion in rangeland and grassland ecosystems are increases in resource availability (alterations by global changes and disturbances) and release from natural enemies and their interaction.
Today, rangeland and grassland activities reflect a growing interest in the ecosystem services that these lands provide, the relationships of humans to these landscapes, and the efforts required to keep these lands sustainable. Critical emerging issues include urban expansion, intense recreational impacts, catastrophic wildfire, and the potential for rangeland and grassland conversion to biobased fuel production. Continued interest exists to maintain watershed values-appropriate vegetation and soil conditions to sustain water availability, air quality, and wildlife populations while supporting the demands for agriculture, energy, and minerals production on the nation's rangelands and grasslands.