台灣中部山區森林林木多樣性與林分結構在海拔上的變化趨勢

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2013

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生物多樣性、森林內林木的結構與葉面積指數等乃是森林生態研究上的重要參數,隨著森林生態研究尺度逐漸擴大,生態學者進一步比較不同緯度或海拔梯度森林之上述各參數所產生的變化與造成的機制。此類研究早期多在中南美洲等熱帶地區或生物多樣性熱點進行,且生物多樣性、生物量累積、樹冠高度、葉面積指數等在大部分的研究都顯示出統一的趨勢,即隨海拔高度而逐漸下降。由於台灣目前少有在海拔梯度上的比較,本研究於台灣中部尋找未受擾動的原生林或次生天然林進行調查,調查記錄樣區內所有高於1.3 m、胸高直徑(DBH)大於1 cm的林木之樹種、樹高與胸高直徑。生物多樣性以豐富度表示,研究並利用二種方法估算估算生物量。此外亦整理有關各個樣區之氣候背景資料,包括歷年之各月平均降雨量、年均溫、蒸發散量與颱風擾動的資料等,並嘗試利用上述資料來解釋生物多樣性、生物量、樹冠高度和葉面積指數在海拔梯度上的趨勢。研究結果顯示生物多樣性隨海拔梯度下降且主要應受到溫度的影響。生物量與樹高皆有隨海拔梯度而增加的趨勢,本研究推測(1)水份(隨海拔上升而增加) (2)颱風擾動(隨海拔而減弱) 可能為主要造成此特殊趨勢之機制。葉面積指數在海拔梯度上呈現駝峰狀,於中海拔最高而在低海拔最低,前人推論該趨勢可能與低海拔冬季時有乾旱有關,然而統2 計結果無法支持該項推論;而上述影響冠層高度與生物量累積之颱風擾動或許亦可適用於解釋葉面積指數在海拔梯度上的變化趨勢。
Biodiversity, forest structure and leaf area index (LAI) are important parameters in forest ecological research. Forest ecologists are interested in understanding changes in these parameters along latitudinal and altitudinal gradients. Early altitudinal studies were conducted in tropical regions (ex. Central and South America) or biodiversity hotspots (ex. Costa Rica) in 1970, and most studies reported a general decreasing trend in biodiversity, biomass accumulation, canopy height, and LAI along the altitudinal gradient. There are very few altitudinal studies in Taiwan, I investigated undisturbed forests in the central Taiwan to examine the patterns of biodiversity, canopy height, biomass, and LAI along the altitudinal gradient. All stem > 1cm and higher than 1.3m in plots were identified to species and diameter at breast height (DBH), and tree height were measured. Biodiversity is presented as species richness. Further, we utilized two equations to biomass estimate. We also collect information of important weather parameters including mean monthly precipitation, annual mean temperature, evapotranspiration and typhoon disturbance to explore their role on controlling the altitudinal pattern of forest structure. The results indicate that biodiversity decreased with increases in altitude and may be influenced by temperature. Biomass and tree height both decreases along the altitudinal gradient. Water availability (increases with elevation) and typhoon disturbance (decreases with elevation) probably contributed to the decreasing trend. LAI showed a “hump-shape” along the altitudinal gradient. Previous research infers that this tendency might be related to occasional drought at low altitude in winter and low temperature at highest altitude. However, statistical result is unable to suppose this inference. We propose that typhoon disturbance may also be important in causing low LAI value at lower elevations in addition to its effects on biomass and tree height.

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海拔梯度, 生物多樣性, 物種豐度, 生物量, 葉面積指數, 樹冠高度, altitudinal, species richness, biomass, typhoon, LAI, canopy height

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