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)

High impact NIPS species are capable of having significant impacts on biological diversity, productive capacity, soil and water, and social well being. These impacts include out-competing native species, slowing timber regeneration and forage production, altering riparian shading and streambank morphology, and altering fire regimes affecting public heath and safety. (from the 2003 Forest and Rangeland Assessment)

Efficient and effective weed control programs and strategies are characterized by efforts that prevent invasions and quickly detect new occurrences so the species may be removed or contained before spreading. The California Department of Food and Agriculture’s (CDFA) Noxious Weed Prevention and Control Program works under the assumption that it is more cost effective to keep pests out of California than to address potentially widespread and ongoing infestations. The strategy for pest prevention is similar for all kinds of pests. There are four major parts: 1) keep a foreign pest from getting into California in the first place (exclusion); 2) if a pest does get in, find it while the population is still small (detection); 3) when such a population is found, remove it so California is once again free of the pest (eradication); and 4) inform the public of the importance of keeping California free of new pests. (from the 2003 Forest and Rangeland Assessment)

American agricultural policy has long recognized the threat to domestic farming and ranching from diseases introduced from other countries. Concerns over homeland security have heightened efforts to monitor the food supply chain. California’s livestock industry has undergone a variety of changes making it more susceptible to the spread of diseases such as foot-and-mouth disease and anthrax. These changes include factors such as greater concentrations of cattle in feedlots and nearby areas, and use of dairy related by-products as cattle feed. (fromt eh 2003 Forest and Rangeland Assessment)

In forest ecosystems, insects naturally consume living and dead vegetation. Climate change, fire suppression, land management activities, and other influences can cause outbreaks of insects outside the normal range. Much of California’s forests are at high risk to mortality from native and non-native pest damage (greater than 25 percent tree mortality expected). Given current management regimes and fire suppression tactics, stocking levels on many forests are very high. With increased stocking levels, host materials accumulate making some areas susceptible to insect and disease attacks. accumulate making some areas susceptible to insect and disease attacks. (adapted from 2003 Forest and Rangeland Assessment)

Non-native animal species are also increasingly recognized as one of the principal threats to the maintenance of biological diversity. Overall, approximately 14 percent of California’s animal species (terrestrial and aquatic vertebrates) are established non-natives.

Trends in air pollution have shown improvements due to new laws and regulations as well as improved technologies. These results show decreasing numbers of non-attainment days (days in which state air pollution maximums are exceeded) in several air basins for ozone and particulate matter greater than ten microns in size (PM10). Ozone levels remain a concern to forest and rangeland resources within the Sierra Nevada mountains and east of the San Joaquin Valley and South Coast air basins. Wide variations in air quality are found throughout these air basins. The primary source of ozone that drifts east into the Sierra Nevada mountains has been linked to the agricultural activity in the Sacramento and San Joaquin valleys via westerly air flows. (from the 2003 Forest and Rangeland Assessment)