Assessing the Accuracy of TWIGS and STEMS85 Volume Predictions: A New Approach
Computer based growth projection systems can help foresters evaluate the effect of management prescriptions. However, using projection systems wisely requires information about how accurate they are. Both parts of accuracy, bias and precision, are estimated for volume predictions from a Lake States projection system using data from 822 remeasured plots. Volume tends to be underpredicted for four locations in the northern part of the Lake States but overpredicted for one location in Lower Michigan. The bias is large for dense stands and for northern hardwood and lowland hardwood stands in Lower Michigan. Forests are highly variable, however, and the precision of a projection system must be estimated as well as its bias. Prediction intervals are computed that help estimate the likely range for a given prediction. The interval that has a 90% probability of containing the true volume can be quite large. North. J. Appl. For. 6:109-114, September 1989.
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Document Type: Journal Article
Affiliations: North Central Forest Experiment Station, 1992 Folwell Ave., St. Paul, MN 55108
Publication date: 01 September 1989