Forest biodiversity is influenced by a wide range of factors including environmental, geographical, cultural, biological, social and economic factors. In order to assess biodiversity a series of indicators that include more general forest quality factors are necessary.
Biodiversity can be measured at a number of different levels, depending on the time, resources and expertise available. For simple surveys to determine forest management practices, conservation strategies and areas requiring further study, very broad-scale survey techniques are probably adequate. At the other end of the scale, detailed surveys of local provenance and genetic variation may be needed for studies of genetic biodiversity.
Five general levels of assessment can be identified: (1) National – to monitor issues of compliance with international agreements; (2) Landscape – to identify areas worthy of further study; (3) Structural – to identify ground-level forest authenticity and composition; (4) Indicator – to summarily indicate biodiversity using specialised indicators; (5) Genetic – to detail the genetic variation within a stand.
No single series of indicators is adequate to summarise information on all aspects of forest biodiversity. Instead, a picture has to be built up from a range or portfolio of different indicators which together provide an approximate picture of forest biodiversity status. The decision on which series of indicators will be used for any one biodiversity assessment has to be made before developing the indicators in detail.
The following elements of forest quality form a basis for developing indicators:
(1) Authenticity: composition of trees; spatial variation pattern of trees with respect to age and size; continuity of forest function, proportion and type of dead timber; natural disturbance patterns, regeneration processes and strategies; management practices, mimicking natural processes, landscape approaches; (2) Forest Health: health of trees; health of other flora and fauna; robustness to changing environmental conditions; (3) Environmental benefits: biodiversity and genetic resource conservation; soil and watershed protection; impacts on other natural and semi-natural habitats; climatic stabilisation; (4) Social and economic values: wood products; non-wood products; indirect employment and subsistence activities; recreational activities; forest as homeland for people; historical value; educational and scientific research value; cultural and aesthetic values; spiritual and religious values; and (5) Local distinctiveness.
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The UN Food and Agriculture Organisation co-ordinates an international survey of forests working with the UN Economic Commission for Europe. The UN Forest Resource Assessment reports every 10 years with interim reports in between. The International Tropical Timber Organisation, the African Timber Organisation, the World Resources Institute and the OECD are each involved in developing indicator and criteria processes. Their processes feature the following factors; forest cover and quality, protected areas, forest dependent species and forest health.