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.