Abstract
The self-thinning exponent of stems, branches and leaves of the subtropical mangrove Kandelia obovata stands was investigated over seven years. According to Weller's allometric model, the slope of the self-thinning exponent alpha(x) of a partial organ "x" is calculated from the allometric constants theta(x) and delta(x) obtained from the allometric relationships between mean tree height (H) over bar (m) and organ mass density (d) over bar (kg m(-3)) with mean organ mass (w) over bar (x) (kg). The self-thinning exponent, alpha(x), was estimated to be 1.509 for stem, 1.647 for branch, 1.090 for leaf, and 1.507 for aboveground. The phi(x)-value which is the allometric coefficient between (s) over bar (mean occupied area per tree) and (w) over bar (x) (kg) was 0.6629 +/- 0.0250 for stem, 0.6072 +/- 0.0229 for branch, 0.9167 +/- 0.0356 for leaf, and 0.6637 +/- 0.0297 for aboveground. The value did not significantly differ from 2/3 but did significantly differ from 3/4 for stem, branch, and aboveground, indicating that the self-thinning exponents for woody parts did not significantly differ from 3/2. Our result suggests that the self-thinning exponent is closer to 3/2 than to 4/3. In contrast, the phi(L)-value for leaf significantly differed from both 2/3 and 3/4 but did not significantly differ from 1.0, indicating that stand leaf biomass was constant regardless of population density. The self-thinning exponent for leaf had a negligible effect on that for aboveground mass due to the combined mass of all woody organs. Our data support the 3/2 power law for aboveground self-thinning. For overcrowded K. obovata stands, self-thinning could be explained by a simple geometric model rather than a metabolic model. (C) 2014 Elsevier B.V. All rights reserved.