| Assessment Home | On-line Technical Reports | Overview of Maintenance of Forest Ecosystem Health and Vitality |

Chapter 3. Health

Overview of Maintenance of Forest Ecosystem Health and Vitality


October 2003


"Disturbance is part of the natural forest ecosystems. In fact, without disturbance, forests would eventually cease to function due to excessive buildup of biomass and the end of necessary nutrient cycling. In many cases, the combined occurrence of more than one disturbance produced the changes in forest composition that we observe today."

- Report of the United States on the Criteria and Indicators for the Sustainable
Management of Temperate and Boreal Forests (USFS, 1997)



Forest health and vitality of forest ecosystems refers to the ability to maintain biological diversity and ecosystem function when exposed to human and natural disturbance. The Montreal Process helps focus on an evaluation of the health and vitality with two indicators. These include:

  • Area and percentage of forest affected by processes and agents of disturbance beyond the range of historic variation (indicator 15);


  • Land and forest area susceptible to air pollutants (indicator 16); and


California’s population and economic prosperity have affected, both directly and indirectly, forest and rangeland health and vitality by altering the vegetation continuity and many natural processes. For example, fire suppression, timber harvesting, development, agriculture, exotic pests, and grazing have all altered the composition, structure, and processes that comprise the function of a forest ecosystem. Determining an overall assessment of “health” is challenging due to the complexity and interaction of disturbance agents to the many components of ecosystems. The primary objective of this chapter is to describe the current and projected status of several main disturbance agents and their resultant affect on forest and rangeland resources.

Gibson Meadow, Klamath/North Coast bioregion. Photo courtesy of Marc Hoshovsky, Department of Fish and Game.
Gibson Meadow, Klamath/North Coast bioregion. Photo courtesy of Marc Hoshovsky, Department of Fish and Game.

Assessment sections summarizing Chapter 3: maintenance of forest ecosystem health and vitality

In this Assessment, the Fire and Resource Assessment Program (FRAP) will address the criterion and indicators of maintaining ecosystem health and vitality with six sections focusing on the major agents of change affecting California’s forests and rangelands. Five of the six papers for Criterion 3 focus on Indicator 15, processes and agents of disturbance beyond the range of historic variation. Each section related to Indicator 15 is linked in a separate Adobe Acrobat pdf file below:

  • Habitat Loss and Alteration: This section describes historical and projected changes to the extent, land use characteristics, and vegetative cover of natural habitats within forest and rangelands. Direct estimates of the loss and alteration of habitats are made using the following: 1) census information on historical and projected housing development; 2) changes in land use as reported by the Natural Resource Conservation Service’s (NRCS) National Resource Inventory; and 3) recent changes (by cause) to vegetative cover using FRAP’s Land Cover Mapping and Monitoring Program


  • Trends in Wildland Fire: Historically, fire is at the root of most large-scale disturbances in California’s forests. Fire suppression has modified these patterns by increasing the length of time between fires and allowing the buildup of fuels. The historic and current trends of fire within the State’s forest and rangelands are examined. Estimates of fire threat based on current fuels and expected fire frequencies are presented.


  • Wildfire Risk to Assets: Fire causes change—both beneficial and detrimental—to a variety of assets important to the people of the State. For instance, many plant habitats have evolved under the presence of fire and their ecological stability is tied to specific fire effects on ecosystem components. Other assets, such as houses and timber values, are easily damaged by wildfire, and justify the need for a strong fire suppression system to minimize those losses. In this section the character of current and expected fire risks to a set of assets that span the social, economic, and natural resources of California is analyzed. These assets include people, ecosystem stability, range value, and watershed condition.


  • Forest Pests and Diseases: Insects and diseases are constantly shaping California’s forests. Native and introduced insects, fungi, and animals interact with other agents of stress such as drought, overstocking, and pollutants to shape the health and vitality of California’s forests and rangelands. Insects and disease perform a necessary role in forest ecosystem function through pollination of non-conifer species, nutrient cycling, and thinning over-mature and unhealthy trees. When these forces act in conjunction with natural influences such as fire, drought, and wind, they can have a significant effect on forests. This section focuses on the status of pest impacts on forest resources, emerging pests that are likely to impact resources in the future, and identifies forest locations at risk to pest damage.


  • Non-Native Invasive Species: Introduction of plant and animal species that are not native to California creates competition with native species and alters ecological processes. Although relatively few species introduced to new environments successfully establish themselves or become serious threats, those that do can have a significant influence. These influences include modifying fire frequency habitat value for rare species, and competition with native species through a variety of mechanisms. In addition, economic impacts continue to escalate and are also important. These include costs associated with control efforts and threats to the capability of the State’s forest and rangelands to produce desired products. The focus of this section is on the trends in extent and number of non-native invasive species within forest and rangelands.


Indicator 16 assesses the amount of forest land subjected to high concentrations of air pollutants and the consequent negative impacts. Only one Assessment document was needed to address this, and it is linked in an Adobe Acrobat pdf file below:

  • Air Quality Influences: Air pollutants have a significant cumulative impact on forest ecosystems. Pollutants can affect regeneration, productivity, and species composition over a wide area. When combined with other stresses such as drought or insects, air pollutants can contribute to damaging effects on forest vegetation including foliage discoloration, stunted growth, and mortality. The characteristics of the pollution levels within the air basins of Californian’s forest and rangelands are profiled. Additionally, trends and levels of damage to vegetation and aesthetic affects through reduction of visibility are analyzed.

Literature cited

USDA Forest Service International Programs. June 1997. Report of the United States on the Criteria and Indicators for the Sustainable Management of Temperate and Boreal Forests. First Approximation Report, USDA Forest Service. Washington, D.C.http://www.fs.fed.us/global/pub/links/report/candi.htm. Web site last accessed July 16, 2002.




back to top iconback to top