Assessing model performance in forecasting long-term individual tree diameter versus basal area increment for the primary Acadian tree species

作者：Russell Matthew B^*; Weiskittel Aaron R; Kershaw A Jr

来源：Canadian Journal of Forest Research, 2011, 41(12): 2267-2275.

DOI：10.1139/X11-139

Tree basal area (ba) or diameter at breast height (dbh) are universally used to represent tree secondary growth in individual tree based growth models. However, the long-term implications of using either ba or dbh for predictions are rarely fully assessed. In this analysis, Delta ba and Delta dbh increment equations were fit to identical datasets gathered from six conifer and four hardwood species grown in central Maine. The performance of Delta ba and Delta dbh predictions from nonlinear mixed-effects models were then compared with observed growth measurements of up to 29 years via a Monte Carlo simulation. Two evaluation statistics indicated substantial improvement in forecasting dbh using Delta dbh rather than Delta ba. Root mean squared error (RMSE) and percentage mean absolute deviation (MAD%) were reduced by 14% and 15% on average, respectively, across all projection length intervals (5-29 years) when Delta dbh was used over Delta ba. Differences were especially noted as projection lengths increased. RMSE and MAD% were reduced by 24% when Delta dbh was employed over Delta ba at longer projection lengths (up to 29 years). Simulations found that simulating random effects rather than using local estimates for random effects performed as well or better at longer interval lengths. These results highlight the implications that selecting a growth model dependent variable can have and the importance of incorporating model uncertainty into the growth projections of individual tree based models.

• 出版日期2011-12