3.2 The branch L-d scaling exponent among tree performance and branch position
The branch L -d scaling exponent of all individuals was 1.31 (95 % CIs = 1.27 - 1.35, p< .001; Table 2; Fig 3A). Likewise, the branch scaling exponent showed significant differences across tree performance (p < .01). The L-d scaling exponent significantly decreased from 1.50 (95 % CIs = 1.42 - 1.59, p < .001) for inferior trees to 1.33 (95 % CIs = 1.25 - 1.41, p< .001) for moderate trees, and 1.34 (95 % CIs = 1.27 - 1.41,p < .001) for superior trees (Table 2; Fig 3B). TheL -d exponent also numerically decreased as branches deepened within the crown (p < .001), i.e., from 1.34 (95 % CIs = 1.25 - 1.44, p < .001) for upper branches, to 1.09 (95 % CIs = 1.04 - 1.14, p < .001) for intermediate branches, and 1.02 (95 % CIs = 0.97 - 1.08, p< .001) for lower branches (Table 2; Fig 4A).
In the intermediate and lower canopy layers, the branchL -d scaling exponent decreased as tree performance deteriorated (Table 2, Fig 4CD). Furthermore, numerical differences in the branch L -d exponent of trees among different growth vigour were significant only in the intermediate canopy layer (p < .001, Fig 4BCD). Specifically, theL -d scaling exponent of inferior trees (a = 1.34, 95 % CIs = 1.23- 1.46, p < .001) was significantly numerically larger than that of moderate trees (a = 1.08, 95 % CIs = 0.97- 1.20, p < .001) or superior trees (a= 1.04, 95 % CIs = 0.98-1.14, p < .001) (Table 2; Fig 4C).