Vegetation Classification and Potential Climate-induced Altitudinal Shifts of Tree Species on a Pacific Tropical Island

• Main Authors: Jian-Hong Yang, 楊建宏
• Other Authors: Yea-Chen Liu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/36026735526600459876

碩士 === 國立嘉義大學 === 生物資源學系研究所 === 103 === Researches on plant distribution help us understand the responses and the extinction risk of plants under climate change, and predict compositional and structural changes of vegetation in the future. Tropical islands have high biodiversity and endemism. However, environmental heterogeneity on tropical islands is lower than that of continents, so that ecosystems on tropical islands are likely more sensitive to impacts of climate change. This study site located on Kolombangara, Solomon Islands (8°S, 157°E). The presence of saplings (Diameter at Breast Height (DBH) ≦2.5 cm, distribution of these individuals are affected by more severe impacts of climate change) and adult trees (DBH≧10 cm, distribution of these individuals are affected by less severe impacts of climate change) were recorded at a 25 m interval from 500 m to 1,700 m (the submit of Mt. Tapalemenggutu) a.s.l. Through comparing the distribution range of saplings and adult trees to (1) identify distribution shift patterns of tropical-island tree species under climate change; and (2) predict the compositional change and extinction risk of overstroy trees in the future. Results showed that 35.14% of species exhibited range contraction and 27.03% shifted downwards; while only 13.51% of species showed upward shift patterns. The shift patterns of the upper altitudinal boundaries were influenced by the cloud belt (which altitudinal distribution ranging from 1,000 m a.s.l to highest peak of this island). That is, for species which upper boundaries were in the cloud belt, their upper boundaries showed few signs of shift. In contrast, upper boundaries of species which were not the cloud belt shifted upward. Lower boundaries of majority species shifted downwards, regardless of their location related to the cloud belt. I speculate that there are two main possible reasons causing unexpected shifting directions. Firstly, the rate of warming in Solomon Islands (ca. 0.15℃∙decade-1) is slower than world average (ca. 0.2-0.3℃∙decade-1). Secondly, the environmental stresses strengthen and competitive release at lower boundaries of studies species due to climate change. The likelihood of mass extinction on tops of mountain is expected to be low. However, the lowland species probably tend to shift downwards and shift to habitats with high human disturbances. Therefore, the local forest management agencies should develop strategies to protect these lowland species.