PS 25-81
Tree population structure and spatial pattern in an ecotone of Abies-Tsuga upper-montane conifer forest of subtropical Taiwan
A temperature-based ecotone in altitudinal vegetation seems well-suited for measuring dynamic responses of vegetation to climate change. In subtropical Taiwan, Abies-Tsuga upper-montane coniferous forest appears along elevations from 2,500 to 3,600 m. Abies kawakamii and Tsuga chinensis var. formosana are separated spatially by climatic conditions in winter. The purpose of this study is to explore spatiotemporal patterns of both species in their ecotone. A 3-ha plot with Abies-Tsugaforest was established along a 3,000 m zone on Hehuanshan East Peak. All stems with DBH ≥ 1 cm were identified, mapped, tagged and measured. Multiple regression trees, Berman test, tree size structure and spatial bivariate pair-correlation analysis were used to measure their spatiotemporal patterns.
Results/Conclusions
Abies kawakamii (532 stems) was more abundant than T. chinensis var. formosana (337 stems) in this plot. Relative abundances of the different life stages of both species differed between gentle (slope < 27.81 °) and steep (slope ≥ 27.81 °) regions. Size structure of T. chinensis var. formosana showed reverse J shape, while A. kawakamii was bell shaped in the gentle region, but both species were reverse J shaped in the steep region. Poles and saplings of T. chinensis var. formosana were correlated with slope and convexity of variables, respectively. Bivariate pair-correlation showed that adult A. kawakamii are correlated negatively with saplings of both species. Although this ecotone was dominated by A. kawakamii, T. chinensis var. formosana had a stable regeneration mode and sapling distributions were not negatively associated with adult. These observations suggest that the Tsuga chinensis var. formosana is expanding in this ecotone. Moreover, the Tsuga zone is moving upwards, which relates to the observed reductions of snowfall in Hehuanshan area over the last 30 years.