Assessing Structural Diversity in Managed Forests

Abstract

Many spatial scales are recognised within multi-objective forest management, but relatively little is known about the effects of current management regimes on biodiversity at a stand level in British forests. This is important, as most management operations are carried out at this level within commercial forests. This paper describes one aspect of a project to assess forest biodiversity at the stand level, namely the description of vertical stand structure. The Project aims to assess levels of biodiversity associated with plantation stands, through the evaluation of new field assessment methods, the collection of baseline data, and an appraisal of the effects of management through the complete range of structural classes generated by clearfelling and replanting silvicultural methods. In other countries, chronosequences have been examined for this purpose.

A three-year project has been initiated to collect baseline ecological data for major plantation forest types in the UK — Sitka spruce (Picea sitchensis), Norway spruce (Picea abies), Scots pine (Pinus sylvestris), Corsican pine (Pinus nigra var. maritima), and oak (Quercus robur and Quercus petraea). This information will then be compared with data obtained from analogous semi-natural and high conservation value forests, to help define appropriate target levels of biodiversity that should be achievable within plantations. In addition to generating these baseline data, the project aims to identify key biodiversity indicators for validation and use in future assessment programmes, and the development and monitoring of biodiversity standards. These are standards which are relevant to the site type in question, which are ecologically robust, are clearly understood and acceptable to forest managers and other stakeholders, and which use methodologies which are repeatable and easy to use.

A standardised series of assessments are being undertaken in target sampling areas, comprised of one hectare plots (one within each structure class), and using methods which take account of patterns and processes at larger spatial scales. It is intended that this work be extended to assess landscape scale variation and to incorporate additional forest types and management regimes across Europe, along a forest exploitation and climatic continuum.

This work aims to provide a baseline against which the impacts of changes in management to achieve desired future conditions (targets) can be compared. These targets are defined in terms of structural, compositional and functional attributes of biodiversity, as applied to plantation forest ecosystems. Appropriate levels for these need to take into consideration factors such as pre-afforestation habitat types, physio-chemical site limitations, and the ecological uniqueness of plantation forests in the United Kingdom.