Balsam fir self-thinning relationship and its constancy among different ecological regions

The constancy of balsam fir (Abies balsamea (L.) Mill.) self-thinning relat ionship has been investigated among four study areas located in different e cological regions of Quebec's humid boreal forest. These four study areas c ontained respectively 348, 252, 146, and 55 observations (plots x measures) sampled over a period of up to 40 years. A self-thinning fitting method wa s developed to position objectively the self-thinning lines but, moreover, to allow comparisons among the different study areas. This method relies on principal component analysis to estimate the self-thinning line parameters and on the "jackknife" procedure to provide a standard error of these esti mates. Results demonstrate a concordance for the slope (p = 0.136) and the intercept (p = 0.148) among self-thinning relationships of those study area s. The combination of these four study areas in one large data set, to prov ide a general estimation of balsam fir self-thinning line, has given a slop e of -1.441 with a 4.114 intercept which is in agreement with the -3/2 powe r law of self-thinning. In this study, this law was able to describe the si ze-density relationship of stands of various ages and growing within differ ent conditions as expressed by the different ecological regions.