Title: Validation of NE-TWIGS for tolerant hardwood stands in Ontario

Author: Bankowski, Jacek; Dey, Daniel C.; Boysen, Eric; Woods, Murray; Rice, Jim

Year: 1996

Publication: Forest Research Information Paper. Issue 130. 1996. pp. 1-21

Abstract: The individual-tree, distance-independent stand growth simulator NE-TWIGS has been tested for Ontario's tolerant hardwood stands using data from long-term permanent sample plots. NE-TWIGS provides reliable short-term (5-year) predictions of stand basal area (modelling efficiency from 77% to 99%), but in longer projections the efficiency of the model drops significantly. Basal area is underestimated an average of 2% to 5% for 5-year projections (with exception of the data set representing low-productivity sites). The error of basal area for individual stands ranges from -22% to 37%. NE-TWIGS is not reliable for predicting basal area by timber size classes, particularly those for medium and large sawlogs. In over 51% of stand projections, the predicted diameter distribution is significantly different from the actual distribution, primarily due to the ingrowth function. Thus, calibrating the ingrowth model is recommended for Ontario conditions. NE-TWIGS uses Site Index as ameasure of site productivity, but this data was not available for this analysis. Inclusion of site productivity data may have improved the performance of NE-TWIGS.