Forest Yield is a PC-based yield model for forest management in Britain. The software provides the user with estimates of various aspects of tree growth, for a range of tree species, yield classes and management prescriptions. The software and user manual are supported by a handbook on forest growth and yield tables, for those who would like to know more about the theory underpinning yield modelling. Forest Yield will be of use to forest and woodland managers and practitioners, researchers and students.
How to order Forest Yield
Forest Yield (version 1.0) can be downloaded from this site using a unique access code.
Individual access codes can be purchased for £50 + VAT.
Multiple single-user licences are discounted as follows:
Number of copies Price per copy 1-5 £50 6-10 £47.50 (5%) 11-25£45 (10%) 26-50£42.5 (15%) 51-100£40 (20%)
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.
Yield tables
What the yield tables show
The Forest Yield tables present values for all the main growth and yield variables for a sequence of stand ages. There are two table formats. The first format is for displaying yield tables involving thinning as part of the management prescription. The format is designed to show results for both standing trees and thinnings. The second format is for displaying yield tables for unthinned stands, and only shows values for standing trees and a summary for volume lost to mortality.
Yield tables for thinned and unthinned stands display values for:
stand age
top height
number of trees per hectare
mean diameter at breast height (dbh)
basal area per hectare
mean volume per tree
volume per hectare
per cent mortality (applies to unthinned stands only)
mean annual increment (MAI).
Yield tables for thinned stands display values for standing trees and thinnings separately and also show cumulative production of basal area and volume. For unthinned stands, values for cumulative volume production are not displayed and values for mean annual increment are based on standing volume rather than cumulative volume, i.e. not including volume effectively lost due to mortality.
When displaying a yield table, the values for number of trees, basal area and volume are normally expressed for a stand area of one hectare so that they represent per-hectare results. However, a different stand area can be specified in Forest Yield if required, in which case, values will be displayed that relate to the specified area.
Limitations of the yield tables
The yield tables are designed mainly for application to even-aged silvicultural systems. They have limited application to forest stands with more complex structure and silvicultural practice, for example uneven-aged stands of trees – this is a subject of ongoing research and development. A characteristic stand growth pattern and a particular management prescription have been assumed in the construction of each yield table. Any deviation from the assumed growth pattern or management prescription will result in different stand characteristics compared with predictions. Direct comparisons of the results for an actual stand with predictions from a yield table may not be meaningful because it is inevitable that the growth of an individual stand will vary in some way from the patterns assumed in a yield table. However, the trends of growth which are given in a yield table can be used to estimate the probable development of any particular stand.
About yield models
Yield models are one of the foundations of forest management. They provide information about the patterns of tree growth and potential productivity that can be expected in forest stands of different tree species, with varying growth rates, when managed in different ways.
Yield models are in daily use by forest managers and practitioners when making decisions about the future management of a forest – whether it is an individual stand of trees or a whole estate. They are also applied when forecasting future levels of production, when making commitments to supply timber markets, and for planning and scheduling forest operations. Yield models are essential for demonstrating that ongoing and intended management is consistent with the principles of sustainable forestry.
The outputs of yield models support many other calculations and models relevant to the evaluation of forests and forestry. These include analyses of the development of forest structure at the stand and landscape scales, the modelling of timber and wood properties, the estimation of forest biomass and carbon stocks, the modelling of forest greenhouse gas balances and the economic evaluation of forest policies and forest management options.
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