Rangeland Health

Three perspectives, taken as a whole, are used in evaluating ecological status. The overall condition of the site is then determined by a process of “preponderance of evidence” considering these three perspectives:

• The first of these perspectives is the soils/watershed function. The basis of an ecological site's potential is its soil resources—the condition of the soil, particularly the upper horizons; its propensity toward erosion; and its ability to accept precipitation. Sites with their soils intact are not only productive in their ability to support plant growth and development, but also are able to capture raindrops where they fall (infiltration) to augment soil moisture, rather than allowing this precipitation to escape from the ecosystem. Overland flow—or runoff—not only fails to replenish the soil moisture on-site, but it may also erode soil from the site as it flows across the surface of the land.
   
• The second of these perspectives is the energy flow relationships on the site. Energy flow is a reflection of the sun's energy that has been captured and redirected through the process of photosynthesis. In evaluating this component, one must look at the existing plant communities, their life forms, and composition. For example, a site with a diverse mixture of perennial plants is capable of capturing sunlight over the entire growing season, whereas the same site occupied by alien, usually annual, species may see a positive energy flow only during a brief early spring period.
   
• The third of these perspectives is the site's ability to recover from a disturbance. Sites that have appropriate combinations of age classes, species composition, and plant vigor have the ability to withstand occasional disturbances from drought, fire, or herbivory (plant feeding). Those sites that are low in plant vigor, all of one age class, or lacking in community diversity are at risk of being eliminated if and when a disturbance occurs.