3: Maintenance of forest ecosystem health and vitality

The historically high levels of mortality seen in the early 1990s in the Sierra and Modoc bioregions have declined in recent years, although new pests are beginning to become established that threaten forest and rangeland resources. Several pests and diseases are of particular interest including sudden oak death (Phytophthora ramorum), eucalyptus borer (Phoracantha sp.), white pine blister rust (Cronartium ribicola), and pitch canker (Fusarium subglutinans). Sudden oak death is spreading through a variety of tree and shrub species in 12 coastal counties of California and is continuing to be found in new hosts. Eucalyptus borer and related exotic Australian defoliators cause significant damage to urban southern California eucalyptus trees. White pine blister rust, a disease with a long history in California, continues to threaten sugar and other pine species by affecting regeneration and size class distributions. Pitch canker, which affects coastal pine species, is in decline although no remedy for eradication of the disease has been identified. (from the 2003 Forest and Rangeland Assessment)

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.

Invasive, non-native plant species can change the structure an function of ecosystems. As they invade, they will increase their cover of forest and rangeland ground.

Tree crowns are both sites of primary production and habitat for arboreal species. Crowns may be damaged by human activity and pollution (e.g., ozone), as well as disease, insects, storms and fire.

Artificial and natural disturbance is usually followed by regeneration of species removed by the disturbance. Ideally the number of regernating native woody species will be close to expected, after disturbance.

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 will produce tabular and graphical information on the spread of selected invasive species and on the success in controlling new invasive species introductions. Invasive species constitute a major threat to the integrity of native forest ecosystems. Mild climate coupled with increases in commerce and influxes of new people have facilitated the introduction and spread of invasive pests. Invasive species reduce the diversity found in native forests and adversely affect populations of native species through predation, competition, altered fire regimes, or destruction of habitat.

Population growth and increased land consumption per household jointly lead to increases in urban and other developed surfaces in watersheds. Increases in population often indicates increased land and resource consumption and reduction in natural and agricultural lands. Changes in land cover can include changes in extent of different types and appearance of new types in a watershed. Forest cover can increase with restoration or afforestation of previously agricultural or barren areas. Impervious cover includes any paved or developed surface that prevents surface water penetration into the ground.

Evaluate changing climate conditions on large fire activity. Trends in climate patterns impact the length of fire season and consequently the duration of fire threat conditions. Impacts of increasing fire season length are reflected in trends in fire activity and in costs of manning fire stations for longer periods. We will evaluate this indicator by looking at frequency of fires greater than 10 acres by date.

There are many sources of stress on forests, including climatic, human, and biotic. Naturally occurring and introduced insect pests and diseases can kill large numbers of trees in contiguous areas of forest until natural limits curtail the insects or diseases. Introduced (weeds) or naturally-occurring plants can stress trees, for example, mistletoe is a parasitic plant that can create structural and nutritional pressure on individual trees. Over-browsing or grazing by animals can reduce succession or seedling recruitment rates in forests (e.g., cattle consumption of seedling oak trees).