南仁湖低地雨林動態樣區之樹種分佈類型

Distribution Patterns of Tree Species in a Lowland Rainforest at Nanjen Lake, Southern Taiwan

本研究利用Ripley’s K指數來探討臺灣南端的南仁湖低地雨林1.61公頃樣區之樹種分佈類型。在整個樣區中，植株數量多於15株的植物種類有91種，以四公尺的尺度來看，有90.1%的種類呈現聚集分佈，8.8%呈現隨機分布；以1-30公尺的距離尺度來看，有71.4%的種類在這尺度範圍下維持群聚分佈類型，只有一種保持隨機分佈。以植株數量而言，株數較少的較株數多的種類更為聚集。至於不同徑級大小，40.9%的種類隨著徑級增加而由高度群聚的分佈類型逐漸偏向較低強度的群聚分佈或是隨機分佈，但有9.1%的物種呈現相反的結果。單純考慮胸徑大於等於8公分的大樹時，68.2%的種類為隨機分佈，只有29.6%的種類仍呈現群聚分佈。在整個樣區中沒有規則分佈的種類。本研究顯示南仁湖樣區的植物分佈和生育地的異質性有關，某些植物僅分佈於山頂或是南仁湖邊。另外大樹隨機比例偏高，顯示樣區中可能有種內競爭導致天然疏伐作用的現象。

Spatial patterns of trees in a lowland rainforest at Nanjen Lake, southern Taiwan were evaluated. Among the 91 species with more than 15 individuals in the 1.61-ha plot, 90.1% species showed an aggregated distribution pattern, and 8.8% species were randomly distributed at the 4 m scale. Along the distance scales, 71.4% species kept aggregated distribution pattern, and only one species remained randomly distributed at all distance scales. Rare species tended to be more aggregated than the common species. As for trees in different size classes, 40.9% highly aggregated species became less aggregated or even randomly distributed with the increase of tree size, while 9.1% species had an inverse pattern. As for trees in the size class ≥ 8 cm diameter, 68.2% species were randomly distributed and only 29.6% species were aggregated. No species displayed a regular pattern in any size class. There were four major habitat types in the study plot, including ridge, mid-slope, valley and streamside types. Our results suggested that the distribution patterns of most species within the Nanjen Lake plot were related to habitat heterogeneity, such that some species were only distributed along the streamside and some species could only be found on the ridge top. Other factors, such as dispersal limitation, might also play a role in determining the distribution patterns of trees.