樂佩山森林動態樣區30年之植群變化

Abstract

長期觀測植群變化有助於釐清亞熱帶森林的生態運作與動態過程。本研究依 ForestGEO 標準，在相隔 30 年後重新調查位於新北市三峽區的 1 公頃樂佩山森林動態樣區，評估植株密度、胸高斷面積、物種多樣性與群落組成的長期變化。樣區內可區分為四種依據第一次調查資料得到的物種組成劃分、並以坡位命名的植群類型，分別為迎東側坡型、稜脊型、西側坡型與河谷型。2024 年共記錄 2,011 株個體，其中包含 1,344 株存活個體、 667 株新生個體及1921株死亡個體，整體族群呈現負成長。雖然四種植群的植株密度皆下降，但胸高斷面積總量反而上升，顯示森林結構正朝向「樹木變少但變粗」的方向發展，亦反映大型個體的生長或存活相對較佳。四種植群類型的多樣性皆呈現下降趨勢，Shannon 與 Simpson 多樣性在稜脊型與西側坡型下降顯著反映物種多樣性減少。群落組成亦發生明顯變動，不僅小喬木族群下降，部分在先前調查中屬部分優勢種的物種也呈現明顯衰退，顯示競爭層級與長期環境過濾作用皆產生廣泛影響。綜合而言，樂佩山森林在過去 30 年呈現植株密度下降、胸高斷面積增加、以及植群類型間差異化的多樣性變化，反映森林結構逐漸朝大型個體主導、物種組成有所變動的方向發展，這些變化可能部分與東北季風逐漸減弱有關，因風力暴露減低可能降低了長期機械性過濾作用並改變了群落內的競爭動態。

Understanding long-term vegetation change is essential for revealing the processes that shape subtropical forest dynamics. We resurveyed the 1-ha Lopeishan Forest Dynamics Plot in northern Taiwan after 30 years, following standard ForestGEO protocols. We examined changes in stem dynamics, species diversity, and species composition across four vegetation community types defined by species composition data from the first census; the types are named after their corresponding slope positions (east-facing slope, ridge, west-facing slope, and valley). In a subset of 25 10 × 10 m subplots, a total of 2011 living individuals were recorded in 2024, including 1344 survivors and 667 recruits, and 1921 dead individuals, indicating a negative population growth rate, whereas total basal area increased, indicating a structural shift toward fewer but larger stems. This pattern suggests improved growth or survival of large trees despite overall population decline. Diversity in general declined in all vegetation types, while Shannon and Simpson diversity declined significantly in the ridge and west-facing slope types. Community composition also shifted markedly. Not only did small trees decline, but several species previously identified as dominant showed reductions in abundance, suggesting broader changes in competitive hierarchies and long-term filtering processes. Overall, the forest exhibited declining stem density, increasing basal area, and vegetation-type–specific loss of diversity, pointing to a long-term transition toward a structure dominated by larger individuals and altered species assemblages. These changes may be partly driven by a gradually weakening northeastern monsoon, which reduces chronic mechanical filtering and alters competitive dynamics within the community.