How Forest Yield works

Forest Yield has been developed for use in British forestry. Individual yield tables are specified by a combination of tree species, yield class and management prescription. More information on the Forest Yield software and the underpinning theory can be found in the user manual and supporting handbook.

Tree species

The Forest Yield tables can be applied to around 150 tree species currently growing in the British Isles (see Appendix 1 of the Forest Yield user manual for more information). Species that were historically considered to be ‘commercial’ generally have their own set of yield tables. Other species listed in Appendix 1 of the user manual, for which models have not been developed, are mapped to these more ‘commercial’ species on the basis of growth and silvicultural characteristics.

Forest Yield also includes new yield tables for Sitka spruce, which can be used as an alternative to the originals. These are based on the preliminary outputs of a dynamic growth and yield model which is being developed by the Forestry Commission and is currently in use as a research tool. The new tables may be particularly useful for application to Sitka spruce stands managed according to prescriptions not covered in the original yield tables, and in providing improved predictions for unthinned stands.

Yield class

Yield class is an index used in Britain of the potential productivity of even-aged stands of trees. It is based on the maximum mean annual increment of cumulative timber volume achieved by a given tree species growing on a given site and managed according to a standard management prescription.  It is measured in units of cubic metres per hectare per year.

Management prescription

In general, the Forest Yield tables represent one silvicultural system: even-aged, single species stand management. Within this system, a range of management prescriptions is considered. The management prescriptions are defined in terms of a combination of assumed initial tree spacing and a programme of thinnings. This is used to represent stands planted or established at different densities and thinned in various ways, including initial line thinnings, as well as stands that are left unthinned.