Definitions

Current forest cover:

estimated closed forest cover within the last 10 years or so (this date varies by country). Only closed moist forest is depicted for tropical Africa and Asia. Woodlands and shrublands are not included in this category.

Original forest cover:

is the estimated extent of closed forest about 8,000 years ago, assuming current climatic conditions.

Frontier Forests:

are defined as being primarily forested; of sufficient size to support viable populations of the full range of indigenous species associated with that particular forest ecosystem given periodic natural disturbance episodes (fire, hurricanes, pests & disease, etc.), (note that this implies that frontier forests provide habitat for these species, not that they actually contain these species); and exhibiting a structure and composition shaped largely by natural events, as well as by limited human disturbance from traditional activities (such as shifting cultivation). De facto they are relatively unmanaged (natural disturbance regimes such as fire are permitted to occur), are home to most if not all of the species associated with that ecosystem type, are dominated by indigenous tree species associated with that ecosystem type, and are characterized by mosaics of forest patches representing a range of seral stages, in areas where such landscape heterogeneity would be expected to occur under natural conditions.

Forested areas must meet all of the following 7 criteria to qualify as frontiers. They must:

1. Be of sufficient size to support ecologically viable populations of the largest carnivores and herbivores associated with that particular forest ecosystem, although they may not actually contain these species.

(Rationale: range requirements of umbrella species are believed to be large enough to provide for habitat requirements of most other species within a given ecosystem).

2. Be of sufficient size to support ecologically viable populations of these species in the face of a major natural disturbance episode such as one would predict to occur once in a century, within the ecosystem in question (fire, hurricanes, pests & disease, etc.).

(Rationale: If frontiers are supposed to serve as forest refugia during the next extinction crises, they must be large enough to maintain their resident species in the face of periodic natural disturbance. The “once in a century” cutoff, although arbitrary, is a yardstick used by engineers and others in designing bridges, buildings, dams etc. that can weather catastrophic natural events.)

3. Exhibit a structure and composition shaped largely by natural events, as well as by limited human disturbance from traditional activities (such as shifting cultivation).

4. Be relatively unmanaged (natural disturbance regimes such as fire are permitted to occur across most of the area in question).

5. Be characterized by mosaics of forest patches representing a range of seral stages, in areas where such landscape heterogeneity would be expected to occur under natural conditions.

6. Be home to most if not all of the species associated with that ecosystem type.

7. Be dominated by indigenous tree species associated with that ecosystem type.

Many temperate frontier forests do not strictly qualify according to all seven criteria, primarily due to size constraints and to fire suppression and other management. For example, Clayquot Sound in British Columbia may be too small to qualify as a frontier forest, and all sites in Scandinavia may be too disturbed to meet WRI criteria. After consultation with temperate experts we decided to include those temperate areas: (i) that are large enough to maintain ecologically viable populations of indigenous species when the surrounding non-frontier forest matrix is considered; and: (ii) where fires are generally allowed to burn across at least half of the frontier site (although fire suppression may have been practiced in the past). Most temperate sites in North America and Europe consist of a mix of old growth and secondary forest. Frontier sites that would not otherwise qualify using a strict interpretation of the WRI criteria are automatically listed as threatened due to lack of buffering capacity and disturbance of surrounding forest.

Threatened frontier forests are areas assessed by experts as under “medium” or “high” threat, where ongoing or planned human activities will likely result in the eventual violation of one of the seven frontier forest criteria listed above (e.g. cause declines in or local extinctions of plants and animals or large-scale changes in the forest’s age and structure). In some cases, sites listed as threatened are currently undisturbed but are slated for logging or other development activity, likely to affect the ecosystem integrity of the forest. Note that many threatened frontier forests include large areas of protected forest. While the core areas of these sites may be undisturbed, these frontiers are considered threatened because human activity in surrounding forest is likely to impact the integrity of the ecosystem as a whole.