海上の森における絶滅危惧種シデコブシの当年生実生の消長
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概要
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The relationship between urban environments and changes in suburban secondary forest must be understood. To elucidate the effects of forest fragmentation and succession on the disappearance of plant species that continued adapting to the environment in secondary forests, we need to clarify the population characteristics (e.g., local distribution, demography, and reproduction) of the threatened species. Therefore, we examined regeneration traits at the initial stage, i.e., the emergence, initial growth, and survival of seedlings, of a threatened tree species, Magnolia stellata Maxim., in secondary forests dominated by Pinus densiflora in Kaisyo Forest, near the city of Nagoya. In 2001, we established a 10×660-m transect (0.66-ha in area) along a narrow stream in the forest. From June to October 2006, we conducted a bi-weekly census of current-year seedlings of Magnolia stellata along the study transect. Photosynthetic photon flux densities (PPFDs) for emerged seedlings on the forest floor were measured in September. Seedling emergence in the upper stream area or on slope sites along the stream tended to be delayed by about two weeks. More seedlings emerged in the swampy middle stream area than did in upstream or downstream areas. The survival rate of the seedling cohort that emerged before early June was higher than that of the cohort that emerged after late June. The forest floor in the upstream area had significantly lower PPFD values than the downstream area, and the mortality rate of current-year seedlings was higher in the upstream area than in the downstream area. We analyzed the effect of light intensity (relative PPFD) on seedling survival using a generalized linear model (GLM). The probability of seedling survival increased significantly with light intensity (P<0.05). The results of this study suggest that the establishment of Magnolia stellata seedlings is influenced by soil moisture and forest floor light conditions.
- 2007-03-31