The proportion of all forest types that are considered under some kind of threat, in decline, or relatively rare compared to historic forests provides useful information about the level of threat to biodiversity in the region of interest.

This is green-leaf area (one side of leaves) per unit area of ground. For conifers, the leaf area is half of the surface area per needle. The LAI can be used to predict primary productivity.

The mountain pine beetle is a native species, populations of which can occupy large forested areas in the Western US. Large numbers of beetles can kill individual trees and whole swaths of forest during an outbreak. It is normal to have some proportion of forest killed by beetle outbreaks, but climate change and other stressors can increase the likelihood of occupation and spread of the beetle.

This index measures the economic well-being of forest communities. The condition of many forest communities is heavily dependent on the forest sector. As the mountain pine beetle outbreak has spread in Western forests, the economic and social impact will be greatest on communities with a high level of dependence on the forestry sector.

This index is also called the evenness index and compares calculated and maximum biodiversity (evenness = (calculated diversity - minimum diversity)/(maximum diversity - minimum diversity)).

Herbaceous plants on the forest floor and in rangelands are habitat an forage for many animal species. They are light/shade-sensitive, usually lost during fire, and recover quickly from disturbance, assuming climatic conditions and seeds are available. Their presence, abundance and diversity indicate a healthy forest or rangeland.

In some areas, one would expect to find a wide range of woody species, in other areas, less diversity might be expected. The number of observed species relative to expected is a common measure of ecosystem condition.

The IUCN "Red List" includes plants and animals that are threatened with further endangerment or extinction. Presence on this list is an indication of serious rarity or threats to a species.

Ideally, 100% of a forest or rangeland area would be covered with native species. As weeds invade, the area covered by native species may decline, resulting in simplification of plant communities, loss of habitat, and change in ecosystem structure and function.

Artificial and natural disturbance can eliminate plants form an area. Natural regeneration occurs when seeds, or remaining root masses sprout and create new plant cover. This will vary with species due to variation in number of propagules, rate of regeneration, climatic conditions, severity of disturbance, and competition with other species.