Invasions of non-indigenous species can threaten native biodiversity, ecosystem functions, animal and plant health, and human economies. Plant invasions are a serious threat to natural and managed ecosystems. The optimal solution regarding invasive and non-native species is to prevent the introduction of these species into the ecosystem. However, in many rangeland situations, this option has already been lost, and a system must be developed to manage invaded areas, monitor exotic organisms, and attempt to minimize their impacts on other ecosystems. The proposed indicator is designed to track the area of infestation and the presence or absence of invasive or nonnative species on rangeland over time.

This indicator deals with plants that are invasive to the area of interest. These plants may or may not be noxious and may or may not be exotic. Generally they are invaders or increasers to the site that can, and often do, continue to increase regardless of the management of the site and may eventually dominate the site. Invasives can include noxious plants (i.e., plants that are listed by a state because of their unfavorable economic or ecological impacts), non-native, and native plants.

Certain invasive species (e.g., certain grass species) have long accompanied rangeland because they were planted as feed for domestic animals. Other species have done well in the disturbed environments that can accompany grazing (e.g., in meadows or riparian areas). Because some domestic animals find a wide range of plants palatable, they have also been used to non-chemically control certain weeds.

This indicator measures the numbers and geographic ranges of rare or “at-risk” species that occupy rangeland habitats for a significant portion of their life cycle, as well as the presence and extent of rangeland plant communities of concern. Trends in the number of at-risk species and communities help identify potential loss of historical and natural rangeland ecological functioning, as well as the loss of associated values and benefits. There are several metrics that could be used to describe the indicator. For species, metrics include the number of species, the number of populations per species, the abundance (number of individuals) per population, and the geographic range. For communities, metrics include the presence and number of at-risk communities, the number of stands of each community, the size of the stands, and the geographic range of the community.

The importance of this indicator lies in its relation to watershed conditions and natural biological diversity. To estimate rangeland condition and trend in condition, plant composition existing at a given moment in time is compared with the plant composition that the given area is capable of supporting at its potential. Downward trends in rangeland condition can also be associated with declines in water quality, aquatic and riparian habitats, and the ability of aquatic habitats to support native biota. These changes can cause aquatic native biota assemblages to shift away from that which would be expected to occur under natural, unimpaired hydrologic conditions.

This indicator measures the population levels (abundance) and the current geographic ranges of rangeland-dependent plant and animal species, monitored across their known range. It is not possible to monitor the population levels and ranges of all species of animals, plants, and microorganisms, so some species must be selected for monitoring. If the selected species include keystone species and those that are sensitive to particular threats, such as overgrazing, irreversible soil erosion, or fire, and if the species are diverse with respect to their taxonomy, habitats, trophic levels, ranges, and life strategies, the indicator will have a higher likelihood of detecting trends in range ecosystems.

This indicator measures both presence and density of representative species within functional groups of wildlife and within ecoregions or physiographic regions. Examples of functional groups for purposes of measuring this indicator may be: large herbivores, small herbivores, large predators, small predators, avian foragers, avian predators, burrowing reptiles, surface reptiles, insect grazers, amphibians, fish, and pollinators. Rangeland ecosystems provide all or a critical portion of many wildlife species annual habitat requirements. Habitat components include mating components, rearing young components, forage or food components, and resting components. Depending on the species, these may or may not be available or required in the same space. Grazing practices can impact the presence and well-being of wildlife functional groups.

Rangelands provide certain ecosystem services, the type and degree of which vary with intensity and type of domestic animal grazing. Ecosystem services are processes or attributes of ecosystems that result in benefits for humans. For example, maintenance and enhancement of flowering plants in rangelands could maintain pollinator species that then pollinate nearby flowering crops.