ObjectiveBased on the data of planted Larix olgensis trees in Heilongjiang Province of northeastern China, the height of effective crown (HEC) was respectively determined from the principle of photosynthate allocation and the vertical distribution of the trunk basal area increment and the leaf mass. The influencing factors of HEC were also analyzed.

MethodFirst, HEC was determined according to the contribution of carbon from branches in each pseudo-whorl to trunk, based on the data of three photosynthetic sample trees during the growing season. The relationship between HEC and the vertical distribution of cumulative leaf mass was analyzed, and the rule for determining HEC was defined according to the vertical distribution of cumulative leaf mass. Then, HEC was also judged by comprehensive analysis of the vertical distributions of the trunk basal area increment and the leaf weight by adopting traditional method. Finally, according to the data of 133 branch analysis sample trees in 19 standard plots from different stand conditions, the difference of HEC determined by above two methods was compared, and consequently the judgment basis for HEC was determined. The main influencing factors and changing rules of HEC were analyzed.

ResultThe net carbon contribution of branches in each pseudo-whorl exhibited an " unimodal” curve with the increment of relative depth into crown (RDINC). The effective crown was consisted of the branches having positive contribution to trunk. The HEC of three photosynthetic samples were 2.84 m, 4.73 m and 4.38 m, respectively. But the relative cumulative leaf mass corresponding to HEC was 87%, 90% and 86%, which were close to 90%. Thus, it could be the principle of HEC determination. Comparted to above method, although there were some differences of the HEC determined according to the vertical distributions of the trunk basal area increment and the leaf weight, the differences between the two were not significant. Stand age (Age) showed the strongest correlation with HEC among all stand factors, it was linearly and positively correlated with HEC and the correlation coefficient was up to 0.8. The mean crown contact height of neighboring trees (CH) and tree height (H) exhibited a significant linear and positive correlation with HEC, and their correlations were about 0.9. Stand density (SD) and competition index (CI) were negatively correlated with HEC, but these were mainly diven by Age, CH and H.

ConclusionIt was feasible to use the height of the adjacent pseudo-whorl above the position that relative cumulative leaf mass was up to 0.9 from treetop to the base of crown as HEC. The mean and minimum values of the ratio of effective crown length to whole crown length were 3/4 and 1/2, respectively. Our results provide a scientific basis for artificial pruning of young Larix olgensis forest.