南仁山亞熱帶雨林小苗動態及地被層植物組成之研究

Abstract

本研究的目的在瞭解南仁山亞熱帶雨林隨著海拔梯度小苗和地被層組成的變化，並探討其與環境因數間的關係。研究地點位於南仁山西北側稜線的樣帶上（東經120°50′，北緯22°05′），海拔295-480公尺處。在小苗的組成和分佈上，就1993年樹冠層調查所設立的89個10×10m2的樣區中，設立89個1×2m2的小苗樣區，由1995年一月至1996年三月間，對所有木本植物的小苗標定、鑑定及測量高度，並每隔一個月複查一次，藉以研究林下小苗的分佈和動態。此外並分別測量89個樣區的光度及土壤水分，作為環境因數的參考。在地被層植物方面，利用前已設定之89個小苗樣區，再加上每隔10公尺取2個1×2m2的系統取樣的樣區83個，共344m2，調查地被低於一公尺的草本及藤本植物的組成和覆蓋度。 結果共記錄木本小苗74種2797棵，分屬32科54屬，其中以樟科的紅楠656棵為最多（23.45％）、江某380棵次之（13.58％）、茄苳234棵第三（8.36％）。首次調查的966棵小苗存活率為68.18％，調查期間所有小苗的存活率為55.12％，密度受每月出生死亡的影響呈季節性的變化。出現在海拔較低的種類都以種子更新。海拔較高的種類則有萌蘗枝條更新的方式，佔全部小苗種數的43.87％，數目的7.58％。小苗的數量和同種成樹的數量有很大的差距，這是因為不同種類所進行的更新方式不同的緣故。在有小苗出現的樣區中，草本的覆蓋度相對的比較小，但小苗種類的分佈、出生量與死亡量皆與草本覆蓋度無關。小苗的分佈與海拔、坡度、土壤含水量、光度有相關，顯示小苗的出現和分佈受這些因素的影響。將小苗在一年之中的變化與氣候因數如溫度、雨量、雨日及相對濕度加以檢定，除小苗的出生量與溫度呈不明顯的正相關外，其他皆無相關，此表示氣候變化並非主要決定小苗季節性變化的限制因數，應另有其他重要的影響因數。 地被層共調查94種植物，以廣葉鋸齒雙蓋蕨所佔覆蓋度最大（13.04％），冷清草次之（10.55％）、莎勒竹第三（8.37％）。根據雙向列表比較法及降趨勢分析的結果，顯示草本植物及藤本植物在海拔高度的變化上，並無顯著的差異，此可能是由於稜線帶植被幹擾頻繁，地被草本植物的組成尚無海拔上的分化。其分佈與接近地面的光度有很弱的相關，與其他環境因數皆無顯著的相關，顯示地被層的分佈可能有其他的限制因數。

For study of seedlings and understory vegetation varied with elevation change and environmental condition, I established 89 small plots of 1 × 2 m2 in size. All seedlings in plots were tagged, identified, measured and recensused every month from Jan 1995 to Mar 1996. Soil water content and light intensity were recorded for every plot. For additional understory vegetation censuses, 83 plots of 1 × 2 m2 were located systematically along the transect. A total of 2798 seedlings in 74 species were followed over 15 censuses during a 15-month period. From the individuals calculated, Machilus thunbergii, Schefflera octophylla, Bischofia javanica, Litsea acutivena, were the most abundance species. The cohort tagged at the first census, comprising of 966 individuals of mixed ages and species, lost 31.8% during a 15-month period. Seedling density, germination and mortality showed seasonal in their distribution. 43.87% of the species produced sprout seedlings, with 7.58% individuals of total seedlings. The sprout seedlings ocurred mostly at higher altitude. Within some leading tree species, there were quantitative discordance between seedlings and adult conspecifics, it was possible due to different species regerneration processes. The understory coverage differed significantly between seedling plot and systematical plot, but its role in affecting seedling distributrion and composition was doubtful. Seedling distribution and composition were related to elevation, slope, soil water content, light intensity. Climate variation didn't significantly affect seedling density, germination, and mortality. The understory vegetation investigated included 93 species. The most abundant are Diplazium dilatatum, Elatostema lineolatum major, and Schizostachyum diffusum. The composition variation of the understory vegetation was related to light intensity, but didn't vary with elevation gradient. It seems that canopy disturbance may be the major determinant of the regional understory vegetation pattern.