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Envirothon Current Issue Study Guide Notes NRCS Rangeland Health Interesting Information Rangelands = grazing for domestic animals, habitat for wildlife, and outdoor recreation Rangelands store carbon and reduce atmospheric greenhouses gases, store water, and filter impurities from water Are Our Rangelands Healthy? America’s rangelands deteriorated rapidly and significantly during latter part of 19th century Perennial species are disappearing and their place is being taken by less nutritious annuals Methods to Document “Change on the Range” The succession-retrogression model Developed in 1940s Succession theory = increasingly developed soils and more complex mixes of plants replace less developed soils and less complex mixes on the land Results in plant community in equilibrium with the environment (climate and soil) = “climax” plant community Disturbance leads to retrogress to an earlier stage of development Method: required rangelands to be classified into range sites—areas of land capable of producing a different kind or amount of climax vegetation Range sites are classified by soils, climate, topography, and other landscape characteristics of the site, and a description of the climax plant community Can be described as “excellent”, “good”, “fair”, or “poor” First used to help ranchers determine value of their land for livestock grazing Excellent = most productive for livestock use especially cattle Poor = degraded for both ecological and livestock production reasons 1960s classification system included ecological condition and values; tool to explain and predict how rangelands change with use and management Bad news: model not worked to describe ecological condition and value for livestock grazing in other parts of US Why are scientists re-examining this method? - climax plant community for a site is hard to define - two-attribute approach: plant species composition and production is inadequate to address the complexity of rangeland ecosystems - ecosystem change may not follow linear path suggested - succession or retrogression may not occur or occur slowly due to long-lived or dominant plants The state and transition model most valuable in explaining rangeland ecosystem change: - when system can evolve in several ways rather than follow single pathway - when change occurs rapidly when changes are near-permanent when detailed explanation of transitions that cause change is required vegetation types called states and processes that cause states to change from one to another called transitions steady states= states that are resistant to change (long-lived or otherwise dominant plant occur on a site); change only as result of transitions as long periods of above-average moisture or drought, fire, insect or disease outbreak, or human action thresholds = site factors that impose this high level of stability on a site - soil erosion and nutrient loss so severe that some plants cannot grow - invasion of a site by a plant that is so dominant that other plants cannot compete - change in water cycle such as rapid runoff because lower rate of water soaking into soilplant growth is restricted during part of growing season - change in plant community structure so that fire cannot occur or occurs in a more destructive way Ecological site descriptions provides extensive knowledge of existing and possible states, transitions, thresholds or other barriers to change, opportunities for management intervention, and what changes can occur through mismanagement range site became ecological site due to more knowledge gained in US site descriptions relate degree of soil development, hydrologic and ecosystem functions, and other ecological knowledge to the known plant communities description provides info needed for management of rangelands for many uses and values Rangeland Health model developed by National Research Council (NRC) Committee on Rangeland Classification; used to classify, inventory, and monitor rangelands Rangeland Health = the degree to which the integrity of the soil and ecological processes are sustained Healthy if an evaluation of the soil and ecological processes indicates that the capacity to satisfy values and produce commodities is being sustained At risk or unhealthy if degradation has resulted in an irreversible loss of capacity to provide values and commodities Healthy Rangeland = erosion not occurring at an accelerated rate, precipitation infiltrates into the soil and used on site for plant growth Loss of Rangeland Health = initiated by overgrazing which reduces productivity and competitiveness of plants desired by grazing animals; reduce plant cover and expose bare soil to erosion; woody shrubs and low-growing trees increase with overgrazing and lack of fire Site Conservation Threshold Assess sustainability of rangeland management by kind, amount, and/or pattern of vegetation needed as a minimum on a given site to prevent accelerated erosion Threshold is point where erosion rate increases greatly Early warning line = point where negative changes in ecosystem characteristics are first noticed