Different performing trees manifest varied scaling relationships at
individual and branch levels
Abstract
Competition is an important factor influencing the structure and
dynamics of plant communities, and understanding species coexistence.
Tree architectural traits, such as height-to-diameter (H-D) and branch
length-to-diameter (L-d) relationships influence species competitiveness
through affecting light capture by altering the occupation of space.
Unfortunately, little is known about how the H-D and L-d scaling
allometric exponent related to tree performance (growth vigour) in
competition. We surveyed 1739 (1642 living and 97 dead) individual trees
from an even-aged dense aerial seeding forest of Masson pine
(Pinus massoniana), in which 51 trees with 1087 first-order
branches were destructively sampled. Using the H-D and branch L-d
scaling data, we determined (1) whether the H-D scaling exponent
numerically differed across different levels of tree performance, and
(2) whether the L-d scaling relationship differed across tree
performance and branch vertical position in crowns. The results indicate
that (1) the H-D scaling exponent numerically decreased as tree
performance deteriorated; (2) the L-d scaling relationship differed
across tree performance, and the numerical value of the scaling exponent
of “inferior” trees was significantly larger than that of “moderate”
and “superior” trees; (3) the L-d scaling exponent declined as branch
position approached ground level, and it was significantly higher in
upper branches; and (4) overall, the branch scaling exponent numerically
decreased as tree vigour ameliorated in each canopy layer, but decreased
significantly only in the intermediate layer. This study highlights the
variation within (and linkage among) length-to-diameter scaling
relationships across tree performance at the individual and branch
levels. This linkage provides novel insights into tree competitive
strategies and potential mechanisms of tree mortality in the competition
of subtropical forests.