Download Envirothon Current Issue Study Guide Notes

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 soilplant 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