1) Efforts to assess and monitor forests, which previously focussed primarily on area and timber supply, are being expanded to reflect the full range of goods and services that forests provide, including the preservation of biological diversity.
2) In providing habitat for more than half of the world’s species, forests play a major role in maintaining global biodiversity. Species richness varies among forest types and locations, but the capacity of any given forest to retain its original complement of biodiversity is a crucial factor in biodiversity trends.
3) Human activity is affecting the capacity of forests for biodiversity preservation through reduction in overall forest area (deforestation), changes in the spatial configuration of forests (forest fragmentation) and changes to forest structure and composition. While the first of these is already being monitored at global scales, this paper proposes approaches for monitoring changes in forest configuration at similar scales and for evaluating the magnitude of human influence as an indicator of other ecological changes
4) The impacts on biodiversity of alteration of forest spatial configuration by deforestation and fragmentation are primarily through:
• Area effects – the tendency of small forest patches to support only subsets of the biodiversity complement of large areas and to be more vulnerable because of their size;
• Edge and gradient effects – the impact of the interface with non-forest ecosystems, which affects environmental variables and biotic interactions;
• Isolation effects – the separation of populations of forest organisms from similar populations and other forest areas, reducing genetic change and diversity and resource availability.
5) Measuring forest configuration and spatial integrity at broad geographic scales can be done using geographic information systems (GIS) to quantify indices that address each of these impacts:
§ Patch size – the area of each contiguous unit of forest cover;
§ Spatially weighted forest density – the % of cells within a given radius that are occupied by forest;
§ Connectivity – the from each forest cell to ‘core’ forest distance along a forested route.
These indices can all be presented in both mapped and statistical form to support decision-making. Constraints on their measurement include the coarse resolution of the land-cover data available for global and regional scale analyses.
6) A single summary index of forest spatial integrity, which combines the three basic indices is proposed as a useful indicator of forest capacity to retain a full biodiversity complement. It can be displayed in mapped form to support decision making with biologically meaningful information. It can also be summarised statistically to provide a baseline for monitoring.
7) Other ecological changes brought about by human activity are better investigated by measuring the driver of change, human activity itself. This can best be assessed by combining spatial information about settlements, infrastructure and land use in relation to ecosystem distribution.
8) A well-developed example of this approach is the Australian Wilderness Index, which evaluates remoteness from human influence in terms of distance and land use intensity.
9) This approach is illustrated applied at the global scale, and proposed as the basis for a measure of forest naturalness. The forest naturalness index would be derived by overlaying the wilderness index with forest cover and assigning a wilderness index score to each forest unit.
10) The resulting data on forest naturalness could be displayed in both mapped and statistical forms, and baselines could be established for monitoring work.
11) The implementation of baseline assessments and subsequent monitoring of forest spatial integrity and naturalness as proposed in this paper would be a significant advance over current periodic forest assessments. It would ensure that they addressed biodiversity preservation as one of the multiple benefits included in the periodic assessment of the world’s forest resources.