Comparison of indicator variables for estimating growth reduction associated with Phellinusweirii root rot in Douglas-fir plantations

Abstract

Total height, annual height increment, annual diameter at breast height (dbh) increment, ratio of total height to dbh, and ratio of annual height increment to annual dbh increment were assessed as indicator variables for estimating growth reduction associated with Phellinusweirii root rot of Douglas-fir (Pseudotsugamenziesii). Generally, height variables were more sensitive indicators than dbh. Total height by 2-cm-dbh classes, ratio of total height to dbh, and ratio of annual height increment to annual dbh increment were more sensitive and less variable than the other indicators. Ratio of total height to dbh was a more consistent and sensitive indicator of growth reduction than all other variables. Application of this ratio in estimating height growth reduction in three plantations indicated reductions in infected trees of 1 to 8 m over periods of 2 to 24 years, averaging 0.9 to 1.7% annually.