3: Maintenance of forest ecosystem health and vitality

The maintenance of forest health and vitality is dependent upon the ability of the ecosystem’s functions and processes to recover from or adapt to disturbances. While many disturbance and stress events are natural components of forest ecosystems, some may overwhelm ecosystem functions, fundamentally altering their patterns and processes and reducing ecological function. Decline in forest ecosystem health and vitality may have significant economic and ecological consequences for society including a loss of forest benefits and the degradation of environmental quality. Information gained on the impacts of biotic and abiotic processes and agents may inform management strategies to minimize and mitigate risk. The maintenance of forest ecosystem health and vitality is the foundation of sustainable forest management.

Associated Indicators

Forest structure: Number of large, dead standing and fallen trees per hectare

This indicator is a measure of the large snag production of an area. Large standing and fallen dead trees are critical habitat for birds and mammalian predators, store carbon, and contribute eventually to soil carbon and nutrient cycling.

Forest structure: Number of vegetation layers

Multi-layered canopies and ground cover contribute to habitat quality and cover for cryptic animal species, and indicate a healthy forest, though one with potentially low rates of severe disturbance.

Forest structure: Percentage of surface area consisting of dead standing trees

Dead standing trees provide habitat for various birds, insects, and mammals. These benefits increase with the size of the trees and to some degree the number of dead trees in an area. Dead standing trees store carbon, but will gradually release it to the soil after falling, or more rapidly during a fire.

Forest structure: Percentage open spaces

Most forests have naturally-occurring openings among stems. Sometimes this is caused by localized disturbance (fire, disease). Openings provide habitat for species tolerant of openings and edges and reduce habitat for species preferring the cover of closed forests. Logging tends to create more openings (thinning), or larger openings (clear-cutting).

Forest structure: Stem distribution

The distribution of tree stems will help to determine horizontal forest structure. Depending on scale, the more heterogeneous the distribution, the more likely the provision of habitat for a wide range of species. Natural disturbance will tend to maximize heterogeneity because many random forces may come into play. Logging and re-planting strategies may make the distribution homogeneous, depending on how it is carried out.

Forestry: Percent of forested area disturbed in last 20 years

Frequent disturbance of forested areas by logging can limit forest productivity, reduce biodiversity, increase soil compaction and erosion, and change nutrient and fire dynamics. Long cycles of artificial disturbance (>100 years) are less likely to negatively impact natural processes and characteristics.

Forests and forestry: Area of forest affected by the Mountain Pine Beetle

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.

Forests and forestry: Forest Vulnerability Index

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.

Forests and parks: Area (in ha) of each forest type

Forests encompass a wide variety of environments (from inland to coast, to alpine) and a range of natural disturbances (for example fire regimes). (California’s) forests are vitally important for maintaining watershed health, biodiversity, and social values and services. This indicator measures the amount of forest of each of the diverse types.

Frequency of severe fire weather days

Evaluate changing climate influences on daily fire conditions that are associated with large fire development. The pattern and occurrence of severe fire weather directly influences the likelihood of large fires. We will evaluate a reconstructed 10-year climate data set expressed at 2km grids for patterns and trends in frequency of severe fire days as expressed in terms of the modified Fosberg Weather Index (mFWI) that accounts for a drought correction.