Vegetation Dynamics of a Lowland Rainforest at the Northern Border of the Paleotropics at Nanjenshan, Southern Taiwan

Long-term forest dynamic studies are vital for revealing how forests function. We conducted tree-by-tree censuses on 2 plots located in a valley of a lowland rainforest at Nanjenshan, southern Taiwan, which is located at the northern border of the Paleotropics. All free-standing trees ≥ 1 cm diameter at breast height (DBH) were identified, measured, and mapped for Nanjenshan plot I in 1993, 2000, and 2008, and for Nanjenshan plot II in 1999 and 2008. In 2008, 10,581 individuals in total were recorded in the 2 plots, belonging to 106 species, 75 genera, and 41 families. The community similarity index (Motyka’s index of similarity) showed that the 2 plots had 93~95% similarities to prior census. During 2000~2008, individuals in plot I increased by 10.0%, but the basal area decreased by 1.6%, and the plot was dominated by the broken mode of death (46.3%). During a similar period (1999~2008), individuals in plot II only decreased by 0.4%, the basal area increased by 2.6%, and the plot was dominated by the standing mode of death (66.7%). In addition, a higher proportion of large trees had died and more pioneer species were recruited in the same period in plot I. These results indicate that during the 2000~2008 census period, plot I might have experienced an increased frequency of disturbances, which could be caused by typhoons. In the meantime, the relatively low-elevation, small-sized plot II might have been better sheltered and less influenced by the gap-edge effect. Advanced studies of canopy gaps before and after typhoon seasons can help elucidate the disturbance mechanisms of lowland rainforests in Taiwan.

長期森林動態研究有助於瞭解森林運作的模式。本研究針對舊熱帶域邊緣，一座位於台灣南部溪谷邊的低地雨林（南仁山），設置兩調查樣區，定期進行每木調查。所有胸高直徑大於1公分的木本植物都加以測量直徑、鑑定物種以及繪製分布圖。至今，南仁山樣區Ⅰ已有3次調查紀錄，分別於1993、2000及2008年，而南仁山樣區Ⅱ則已有2次調查，分別於1999及2008年。於2008年時，此兩樣區植株數共計有10,581株，物種計有106種，分屬41科75屬。在物種組成方面，兩樣區變動不大，和其前一次調查的林分相似性(Motyka's index of similarity)皆達93~95%。但是，在2000~2008年間，樣區I增加了10.0%的個體，減少了1.6%的底面積，並且樹木死亡的方式主要方式為斷折(46.3%)。於近似的調查年間(1999~2008)，樣區Ⅱ則個體只減少了0.4%，底面積增加了2.6%，而樹木的主要死亡方式為立枯(66.7%)。除此之外，樣區I於2000~2008年間，有較高比例的大樹死亡，以及較多先驅物種進入。這些結果顯示，樣區Ⅰ於最近一期的調查年間(2000~2008)，曾遭遇到頻度較高的擾動，其有可能是颱風造成。在同一時期，樣區Ⅱ可能因為海拔較低和面積較小，而受到較良好的遮蔽效應和較低的林隙邊緣效應。因此，更進一步調查颱風前後樣區內的樹冠林隙變化，將有助於釐清此台灣低地雨林的干擾機制。

Abstract in English and Chinese; article in English only.