Time-trajectory of mean component weight and density in self-thinning <Emphasis Type="Italic">Pinus densiflora</Emphasis> stands |
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| Authors: | Li Xue Hui-fang Feng Feng-xia Chen |
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| Institution: | (1) College of Forestry, South China Agricultural University, Guangzhou, 510642, People’s Republic of China |
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| Abstract: | The allometric relationships between mean weights of components, such as stems, branches and leaves and tree weight as well
as their time-trajectories, were studied with data of self-thinning Pinus densiflora stands with different densities. The allometric relationships existed between the weights of stems, branches and leaves and
the tree weight during the course of self-thinning. The stem weight ratio increased with increasing tree weight because the
allometric coefficient in stem was higher than unity, whereas the branch weight ratio and the leaf weight ratio decreased
because the allometric coefficients in branches and leaves were less than unity. An allometric power relationship existed
between mean component weight and mean tree weight during the course of self-thinning. The time-trajectory of mean component
weight (w
o) and density (ρ) in the early growth stage was expressed as a mathematical model which incorporates the allometric power
relationship into the Tadaki’s model, whereas the model for describing w
o-ρ trajectory in the later growth stage was derived by combining the allometric power relationship with 3/2 power law. The
two models, Tadaki’s model and 3/2 power law, showed a good fit to data from P. densiflora stands. The time-trajectories of mean tree weight (w)-density (ρ) or w
o-ρ initially almost moves nearly vertically in the low-density stand, moves along a steep curve and an inclined curve in the
medium- and high-density stands, respectively, and gradually approaches self-thinning line in the early stage of stand development,
whereas they reached and moved along the self-thinning line in the later stage of stand development. The self-thinning exponents
were determined to be 1.71, 1.19 and 1.13 for the trees, 2.38, 1.33 and 1.20 for the stem, 3.16, 1.55 and 1.46 for the branches,
2.66, 1.39 and 1.35 for the leaves in the low-, medium- and high-density stands, respectively. The 3/2 power law of self-thinning
is derived on the basis of simple geometric model of space occupation by growing trees, but allometric growth of tree and
components can make the slope of the self-thinning line being different from −3/2. The reasons that the self-thinning exponents
of components in the low-density stand were greater than those in the medium- and high-density stands were discussed. |
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