Dynamics of seedling populations and tree species coexistence in a forest: a simulation study |
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Authors: | Akio Takenaka |
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Institution: | (1) National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan |
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Abstract: | Theoretically, temporal variation of reproduction promotes species coexistence of sessile and polycarpic organisms when the
reproduction is synchronized within species but independent among species. Monopoly of vacant sites and high relative population
growth rate of minor species in the absence of propagules of other species is the essence of this mechanism. The mechanism
is expected to work in forests, but persistent populations of seedlings may affect the promotion of coexistence. Using a tree-based
simulation model of forest dynamics, it was demonstrated that the number of coexisting tree species was sensitively affected
by the seedling establishment rate. The coexistence was not enhanced by temporal variation of reproduction when seedling establishment
rate was low. This is because the reproducing minor species fail to monopolize vacant sites and allow the establishment of
seedlings of other species in later years. High mortality of established seedlings under shade also suppressed coexistence.
This is likely to be the result of a reduced storage effect of the population of seedlings. A forest structure and dynamics
pattern that appears when tree species coexistence is promoted by fluctuating reproduction was searched for, and the number
of coexisting species was varied by manipulating the seedling establishment rate. No distinct difference other than the species
number itself was found between species-rich and species-poor forests. For example, the seedling population size varied, reflecting
the temporal variation of reproduction, irrespective of the seedling establishment rate. Further strategy development is needed
to validate the proposed mechanisms of species coexistence. |
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Keywords: | Forest Reproduction Seedling Simulation Species coexistence |
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