瑞岩溪紅檜林型組成及其徑級分布之研究

Composition and DBH Class Distribution of the Stands of Chamaecyparis formosensis Type in the Jui-Yen Nature Reserve

於瑞岩溪自然保護區中的紅檜林型選擇不同林分設置樣區，林分I樣區中的紅檜僅出現巨木，全無中、小徑木，全林分的密度偏低，除豬腳楠外，其它樹種的更新均不良，此一林分可稱為老熟期林分。林分II之紅檜及其它優勢闊葉樹種的徑級頻度均呈現反J型分布，顯示主要優勢樹種均有更新，但紅檜的幼苗常在倒木上或倒木的周圍出現，分析此林分中紅檜小徑木之連年直徑生長，可發現其生長有明顯壓抑之現象，顯示本林分之紅檜小徑木具前生苗之特性，此一林分可視為森林發育階段之成熟期。林分III之樣區取自水管路兩側，可視為次級演替之建造期階段，紅檜幼苗於此林分中大量出現，並有其它先驅樹種相伴發生，各主要樹種之徑級頻度分析顯示仍持續有幼苗發生。由紅檜在本地區之狀況研判其兼具孔隙種與先驅種之特性，即其幼苗可於成熟林下以前生苗的形態存在，以等待孔隙形成後晉升至冠層，而在新形成的裸露地中也可更新良好，可與其它先驅植物共同競爭；但在過於老熟之紅檜林分中，由於上層鬱閉破裂導致林床之地被植物過度繁盛，將會影響包括紅檜等木本植物的更新。 Three different stands of Chamaecyparis formosensis Type in the Juiyen Nature Reserve were studied. We surveyed the composition of woody plants of which DBHs were greater than or equal to 1 cm. Stand僅consisted of 13 connected plots, each being 20m單20m. The canopies of this stand were not connected well, so that the forest floor was overgrowth with weeds which inhibited the regeneration of woody plants and caused the low density of only 517 trees/ha. This stand had 6 huge Taiwan red cypress trees, of which DBHs were all greater than 2.5m but no seedling or sapling. Machilus thunbergii had the highest relative density and regenerated quite well but others trees didn_t have a good regeneration. We could describe this stand as an old mature forest. Stand 優 consisted of 10 connected plots each being 20m單 20m. The density of this stand was 3,281 trees/ha and had 36 tree species. The DBH class distribution of most dominant species in this stand showed an inverse J-shape which indicated the good regeneration. These species were Chamaecyparis formosensis, Castanopsis carlesii,Machilus thunbergii,Rhododendron ellipticum,Elaeocarpus japonicus,Neolitsea acuminatissima, Cleyera japonica var. morii, etc. Many of the seedlings of Taiwan cypress were found on or around the fallen logs. According to the analysis of growth rings, small Taiwan red cypress had compressed rings and grown very slowly. This stand could be described as an mature forest. Stand 取 consisted of 13 plots each being 2m單50m. These plots were set along the roadside and apart from each others by 50m. The road was constructed in 1971 and crossed the virgin forest with 3m width. There were many seedlings and saplings of Taiwan red cypress and other hardwood species in this stand. However, the composition was quite different from former two stands. The hardwood species were mostly pioneer species, including Alnus formosana, Acer morrisonense, Trochodendron aralioides, etc. Analysis of growth rings of small Taiwan red cypress showed that they grew faster than those under the forest. From this study we might deduce that Taiwan red cypress in the Juiyen Nature Reserve have both the characteristics of gap species and pioneer species.