臺灣森林地上部生物量與環境因子的關係

Abstract

自過去半世紀以來，氣候變遷及全球暖化等環境議題備受關注。為瞭解全球碳循環的運作機制及過程，估算森林生物量成為瞭解森林生態系碳含量多寡的重要方式。而森林生物量的空間模式是環境因子綜合影響下的結果。由於臺灣全島海拔變化大，加上中央山脈與兩大氣候系統（季風及颱風）交互作用，造就許多環境因子的高空間異質性。本研究目的為探討臺灣重要環境因子（氣候、地形、人為干擾）與全島天然林地上部生物量之間的關係。以「國家植群多樣性調查及製圖計畫」中共計2,813個樣區之木本植物調查資料為基礎，估算各樣區的森林地上部生物量。並透過廣義線性模式（Generalized Linear Models），找出環境因子與生物量相關性。研究結果顯示，各因子依影響生物量空間變化的強弱程度，依序為年均溫、冬季降雨量、乾季時間長度、實際蒸發散量、地形凸出程度、距離主要道路最短距離、東北季風迎風指數，以及坡度。其中，實際蒸發散量、地形凸出程度、距離主要道路最短距離及東北季風迎風指數，皆與生物量正相關；而年均溫(平方項)、冬季降雨量、缺水月份數與坡度，則和生物量負相關。生物量隨溫度降低而增加的可能原因，溫度上升不僅提高植物生長速率，也加強個體間的競爭而提高了死亡率。實際蒸發散量較少與缺水月份數較多，皆使生物量減少，表示水分多寡及降雨的時空分布均勻度為影響生物量空間分布的重要因子。人為干擾越嚴重的森林，生物量越小。在越凸出或坡度越陡的地形上累積的生物量越高，則顯示了土石流為颱風影響臺灣森林生物量空間變化的可能機制。東北季風對帶來充沛的雨量，將使森林生物量減少；但整體而言，東北季風對臺灣生物量空間變化的影響，仍可能因各地受季風影響的程度不同而有差異。

In recent years, since the growing concerns of climate change and global warming, estimation on forest biomass has become one of the main methods to understand the carbon cycle. Due to the large range of variation in elevations, and the interactions between the Central Mountain Range and two major climate systems (monsoon and typhoon), Taiwan is an island with high spatial heterogeneity of environment factors. As an overall realization of AGB and its relationship between environmental factors were still unavailable in Taiwan, the aim of this study was to identify the relationships between above-ground biomass (AGB) and different types of environmental factors (such as climatic, topographic, and human disturbance factors) in Taiwan. A total of 2,813 plots in the database of The National Vegetation Diversity Inventory and Mapping Project (2003 – 2008) were analyzed by generalized linear models (GLMs). The most influential factor was mean annual temperature, followed by winter precipitation, length of dry season, actual evaportranspiration, convexity, distances to major roads, the windwardness index. Among the eight influential factors, mean annual temperature (as quadratic term), winter precipitation, length of dry season and slope were negatively related to AGB, whereas actual evaportranspiration, convexity, distances to major roads and the windwarness index were positive correlated with AGB. For climatic factors, higher stem turnover rate appeared to limit AGB accumulation in warmer forests, while both adequate water balance and temporal evenness of precipitation distribution contributed to enhance AGB accumulation. The island-wide spatial patterns of AGB showed the mechanism related to convexity and slope might regulate the quantity of AGB reduction. Both human- and natural-induced disturbances would result in decreasing AGB. Considering with the interactions of typhoons and topographic factors, landslides followed with intensive rainfall were the potential impact of typhoons on AGB in Taiwan. The intensity of the winter monsoons were not evenly distributed at island-widei, which might be one reason of unexpected relationships between AGB and the windwardness index and winter precipitation which both were used to evaluate the impacts of the northeast monsoons in winter.