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 theH -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 branchL -d scaling data, we determined (1) whether theH -D scaling exponent numerically differed across different
levels of tree performance, and (2) whether the L -dscaling 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) theL -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.
Keywords: competition, height-diameter, intraspecific
variation, mortality, performance, scaling, Pinus