台灣北部樂佩山區暖溫帶雨林森林組成結構及植物樹種空間分佈型分析

Abstract

研究區域位於臺北縣三峽鎮，樂佩山及喀博山西北側坡面上，海拔介1135至1165公尺間。於1990年設立1公頃永久樣區，至1994年調查完畢。調查得31科、49屬、70種木本植物共12875株，其中以茶科(8種)、灰木科(7種)、薔薇科(6種)、冬青科(6種)所佔種類最多。以種的優勢度而官，錐果櫟為最優勢(17.08%)、次為紅花八角(13.80 %)、毽子櫟(11.68%)、紅楠(10.64 %)、綠樟(5.55%)等。優勢度集中於少數種類，排名前五名樹種累積重要值已達58.75％。並依雙向列表分析法(TWINSPAN)將整個樣區切分為四種生育地類型。 植株分佈與地形相關分析結果顯示：樣區之地形因數中，坡向與植株密度、植株平均胸高斷面積明顯相關；海拔則與植株密度呈明顯相關。趨勢大致為東北坡植株密度高於西坡、且東北坡植株平均胸高斷面積小於西坡，隨海拔增加兩坡面植株密度逐漸縮小。依不同物種進行分析，則可區分出東北面坡分佈型、西面坡分佈型及廣泛分佈型，並從分析數據可觀察各物種在空間上漸進變化。 空間分析法則以Ripley's K Analysis及L-function分析全樣區所有木本樹種，有80％以上呈現群聚分佈；而分別對四種生育地類型分析時，發現明顯有群聚型比例降低、隨機型比例升高現象。顯示生育地因數可能是影響植物空間分佈的主要因素之一。於各型生育地中發現冠層大樹間皆呈現顯著的規則分佈，顯示個體間存在排斥作用，其範圍約在2至5公尺間。從優勢種群體（前五優勢種綜合）來看，值株間4公尺內存在競爭排除的現象，並隨著徑級成長，其作用範圍及作用程度有逐漸增強的情形。以單樹種來說則個體間的競爭情形仍然存在，但不若與鄰樹之關係明顯；然而部分樹種大樹周邊2至7公尺內小樹有偏向規則分佈的情形，可能受到傳播機制與幼苗存活機率所造成。 就目前分析結果而吉，植物在本森林中的分佈受到多重因數的影響，且各因數影響的空間尺度各異。如大尺度生育地環境差異、鄰近植株成長過程中的資源競爭、以及同種個體間競爭與繁殖機制等。使植物個體的分佈呈現我們所觀察到的情形。

From 1990 to 1994, a permanent 1-ha plot of a warm-temperate rain forest was estabilished at Mt. Lopei, nothern Taiwan. All free-standing woody plants in this plot with DBH>=1cm were identified, tagged, and mapped. A total of 70 tree species (12875 stems), belonging to 31 families and 79 genera were recorded. The total basal area was about 47.53 m2/ha. The forest was dominant by Cyclobalanopsis longinux (17.58%), Illicium arborescens (13.79%), Cyclobalanopsis sessilfolia (11.68%), Machilus thunbergii (10.64%), and Meliosma squimulata (5.54%). The cumulative important value of these five species reached 58.75%. TWINSPAN analysis revealed four distinct groups of quadrats. Sites of the first and second group were located at the north-eastern hillside and the hilltop. These two groups were thought to be a windward community because of their high tree density, low canopy height and specific species composition; whereas the other two group were thought to be the oppsite. Tree species were divided into three types, north-eastern, western, and random, by their distribution. Most species were patchily distributed, showing high correlation with aspect and elevation. Spatial patterns of tree species were studied by Ripley's K analysis and L-function. Among the 44 species occuring with>=?15 individuals in the whole plot, 81.82% had an aggregated distribution, 15.91% were randomly distributed and just 2.27% showed regular distribution. But in each habitat, obviously, most species were randomly distributed. We suggest that habitat factors, such as wind and topography, played an important role in spatial distribution of tree species, and they may cause the difference between whole plot and each habitat. Spatial patterns of canopy trees showed a regular distribution between 2 to 5 meters. Adult trees of dominant groups also showed a regular distribution in 4 meters, and as tree individuals grew, this range became wider. It is revealed that tree individuals, especially adult ones, compete anainst each other for some recources, such as space or light, etc. Spatial relationships between conspecific adults and juveniles mostly showed a regular pattern between 2 to 7 meters, or longer. We are confident that adults affect the survival of juveniles. It could caused by some factors such as resource limiting, competition, herbivores, and pathogens, etc. This study suggest that this forest is subjected to multiple factors, eg., topography, wind, inter- and intra-specific competition, seed dispersal and germination. The importance of each factor changes across spatial and temporal scales.