A comparison of two yield forecasting methods used in Ireland.

Abstract

A comparison was made between two methods for forecasting the growth and yield of five conifer species growing in even-aged stands in Ireland: the Forestry Commission (FC) Yield Tables and the dynamic yield modelling system Growfor (GF). The goal of the study was to examine and compare the outputs of each system as both are used in forest management planning and decision making in Ireland. A typical regime used in the FC yield tables was adopted and the details of this regime were used as inputs into GF. The cumulative volume was examined under a no-thin scenario and also under a scenario that involved thinning to the marginal thinning intensity (MTI). Using the GF system, volumes were significantly lower than with the FC system, for both the no-thin and the thinning scenarios, for most species. In the no-thin scenario, Norway spruce, lodgepole pine and Douglas fir showed deviations from the FC trend while Sitka spruce and Scots pine showed similar patterns to the FC volumes. Under the thinning scenario, Sitka spruce showed a similar trend to the FC volume while the GF volumes for the other species deviated from the FC ones. The MTI proved too severe and resulted in a loss in the productive capacity of the stands. Cumulative volume production was increased by reducing the thinning intensity.