Ecological Sites
By Jeffrey P. Repp, State rangeland management specialist, and Craig M. Ziegler, State forester, Natural Resources Conservation Service.
During this survey, the relationship between the soils and vegetation was established. Each detailed soil map unit component was correlated to an ecological site, a distinctive kind of land with specific physical characteristics that differs from other kinds of land in its ability to produce a distinctive kind and amount of vegetation. An ecological site is the product of many environmental factors—soils, climate, hydrology, landscape position, time, and living organisms. Each ecological site is recognized and described on the basis of the characteristics that differentiate it from other sites in its ability to produce and support a characteristic plant community.
Most ecological sites evolved with a characteristic kind of herbivory (kinds and numbers of herbivores, seasons of use, and intensity of use) and a characteristic fire regime. The frequency and intensity of fires contributed to the characteristic plant community of each site. Soils with similar properties that support a similar native plant community are grouped in an ecological site.
The ecological site descriptions are provided in the Natural Resources Conservation Service Ecological Site Inventory Information System (ESIS)- Ecological Site Inventory (ESI) database. (http://plants.usda.gov/esis)
Each detailed soil map unit component in this survey has been correlated to a rangeland or forestland ecological site. This information is given in table 5.
Vegetative information about the historic climax plant community for each ecological site is also given in table 5. The table includes the characteristic vegetation for each ecological site, species composition, and for the rangeland sites only, total dry-weight production. The historic climax plant community is the plant community that is best adapted to the unique combination of factors associated with an ecological site. It is a natural dynamic equilibrium with the historic biotic, abiotic, and climatic factors on an ecological site in North America at the time of European immigration and settlement.
Total dry-weight production is the amount of vegetation that can be expected to grow annually on well managed rangeland that is supporting the climax natural plant community. It includes all vegetation, whether or not it is palatable to grazing animals. It includes the current year’s growth of leaves, twigs, and fruits of woody plants. It does not include the increase in stem diameter of trees and shrubs. It is expressed in pounds per acre of air-dry vegetation for favorable, normal, and unfavorable years. In a favorable year, the amount and distribution of precipitation and the temperatures make growing conditions substantially better than average. In a normal year, growing conditions are about average. In an unfavorable year, growing conditions are well below average, generally because of low available soil moisture. Yields are adjusted to a common percent of air-dry moisture content.
Characteristic vegetation—the grasses, forbs, and shrubs that make up most of the historic climax plant community on each soil—is listed by common name. Under range composition, the expected percentage of the species is based on annual production of vegetation (air-dry weight). Under forest composition, the expected percentage of the species is based on canopy cover.
The characteristic overstory vegetation for the forested ecological sites is shown in table 6. This table includes the ecological site name, overstory vegetation, and composition. Under composition, the expected percentage of the species is based on canopy cover.
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