南仁山區低地雨林之樹冠結構

Abstract

森林樹冠的層次結構是很早已前就存在的概念，研究植物社會的垂直結構有助於我們瞭解該森林內物種間的相互關係。過去在南仁山溪谷地區所進行的研究是以整個社會內的組成，以及植株在樣區內的分佈位置為討論的重點，本研究欲以各樹冠在立體空間上的分佈狀況為研究對象，討論樣區內的樹冠在垂直方向與水準方向上的結構差異。 本研究以南仁山溪穀0.64公頃樣區為研究對象，測量樣區內胸徑大於1公分以上所有植株之樹高、枝下高、葉下高、主幹傾斜之角度與方向、樹冠八方位半徑，以及樹冠葉片覆蓋密度級數等項目，標定每一株樹的根在樣區內的分佈位置，可將每一株樹冠在樣區內的空間分佈呈現出來。 就垂直高度的方向來看，較高的區域樹冠面積較大、植株數量較少、物種豐富度亦較少，逆之則反，但是樹冠覆蓋面積最大也最密集的區域則是出現在高度5至12公尺之間，乃因樹冠在面積大小與植株數量的變化曲線在此區間產生交集之故。在水準的方向上，根據樹冠頂的高度可將樣區劃分為林隙期、建造期與成熟期三個更新時期，在這三個更新時期的植株密度和樹冠覆蓋面積比例皆以成熟期最高、建造期居中、林隙期最低。 垂直方向的樹冠分層結果顯示，在種類的組成上可分做六個層次，在層次之間不乏兩層次共同出現的種類。但就樹冠結構的分層結果卻是無法分層，整個樣區的樹冠結構是一個大集合體，在垂直高度的區間內並沒有一個明顯的分層界線可以切分出上、下兩個分別的層次。原因可能在於本研究樣區的樹冠頂高度較矮且組成複雜，故垂直結構上無法分層。

Stratification is an old concept in forest architecture. Study in vertical stratification in the plant community can help us know more about interactions among species. In the Nanjenshan area, we study the structure of species and the patterns of tree distribution in the past, and now we want to know about how these crowns distribute in the 3-D space. Our research was done in a 0.64-ha plot. For all trees with stem DBH > 1.5 cm were measured. We collect records of each tree with tree height, height of the lowest stem, height of the lowest leaf, tilt angle and direction of the main stem, crown radius of 8 directions, and coverage index of leaves in each crown. Root location was combine with its crown characters, and then we knew about the location of each crown in space. In the higher level, there are fewer crowns but with bigger area, and in the lower level are more crowns with smaller area. From 5 to 12 meters height, crowns are densely placed, and the coverage projections are bigger than all the other levels. We adapt three regeneration phases (gap phase, building phase, mature phase) from height of canopy-top, and delimit boundaries of these three phases on the map of our plot. The area of mature phase has the greatest stem density and greatest percent of crown coverage, and the area of gap phase is the lowest. For the vertical stratification of species, we can divide it into 6 strata. Among these strata, there are species with highest CIV (crown important value) in 2 strata. It means that dominant species change gradually among these strata. But we cannot stratify it with individual crowns. It may because of the complex structure of the lower level, or the shorter maximum height (comparing to other rain forest plot, 20.5 meters is much shorter) of our plot.