臺灣南部南仁山亞熱帶雨林林下物種的空間自相關格局

Spatial Autocorrelation Patterns of Understory Plant Species in a Subtropical Rainforest at Lanjenchi, Southern Taiwan

許多研究描述外在環境及內部因子與植物種類分布的關連，但鮮少定量物種的空間尺度。本文章使用定量的方法，如：空間自相關及軌跡方差法，來估計物種的空間尺度；並以其反映的尺度來探討影響物種分布的可能因子。我們於台灣南部南仁山保護區欖仁溪樣區進行林下小苗（即胸高直徑小於1公分的灌木、冠層及次冠層樹種）及草本植物（即高度小於1公尺的草本植物、小型灌木和樹蕨）的帶狀取樣。共建立樣七條樣線並選取其中三條進行小苗普查，央5公尺×300公尺樣線分為60個5公尺×5公尺樣方進行調查。利用相連樣方中草本植物覆蓋度及小苗數量來計算各物種的空間尺度。各物種呈現不同的空間尺度及相尺寸。草本植物較木本植物的小苗有較大的空間尺度。個體大及具有延伸性莖葉的物種傾向擁有較大的空間尺度。然而，在我們的研究尺度中種子傳播方式與果實種類並未能呈現與空間尺度的相關。在約180公尺的尺度下，物種呈現顯著的空間自相關，剛好反應欖仁溪樣區兩個山頭的距離，顯示物種豐富度反映地形的重複。由上總結，欖仁樣區林下層物種的空間尺度反映出地形變化及物種本身的特性。

Many studies described relationships between plant species and intrinsic or exogenous factors, but few quantified spatial scales of species patterns. In this study, quantitative methods were used to explore the spatial scale of understory species (including resident and transient species), in order to identify the influential factors of species distribution. Resident species (including herbaceous species, climbers and tree ferns < 1 m high) were investigated on seven transects, each 5-meter wide and 300-meter long, at Lanjenchi plot in Nanjenshan Reserve, southern Taiwan. Transient species (seedling of canopy, subcanopy and shrub species < 1 cm diameter at breast height) were censused in three of the seven transects. The herb coverage and seedling abundance were calculated for each 5 × 5 m quadrat along the transects, and Moran’s I and Galiano’s new local variance (NLV) indices were then used to identify the spatial scale of autocorrelation for each species. Patterns of species abundance of understory layer varied among species at fine scale within 50 meters. Resident species showed a higher proportion of significant autocorrelation than the transient species. Species with large size or prolonged fronds or stems tended to show larger scales in autocorrelation. However, dispersal syndromes and fruit types did not relate to any species’ spatial patterns. Several species showed a significant autocorrelation at a 180-meter class which happened to correspond to the local replicates of topographical features in hilltops. The spatial patterns of understory species at Lanjenchi plot are mainly influenced by species’ intrinsic traits and topographical characteristics.