臺灣東北部天然闊葉林與柳杉人工林林下光照環境及林下植物多樣性之比較

Abstract

林下植物會影響森林底層微氣候、樹苗建立與營養環循環，無論在天然林或人工林中皆扮演重要角色。本研究調查臺灣東北部低海拔天然闊葉林與柳杉人工林，林下之植物多樣性、生物量、光照環境以及土壤養分，以評估林相差異對林下生物及物理環境的影響。 研究結果顯示天然闊葉林的林下直散光與散射光立地係數及土壤養分含量皆高於柳杉人工林，但是林下植物多樣性顯著低於柳杉人工林；而林下植物生物量在兩種林相之間沒有顯著差異。此外研究亦發現林下植物多樣性與林下直射光立地係數有顯著負相關，且在林下光照較高的天然闊葉林中，冷清草 (Elatostema lineolatum Forse. var. major Thwait.) 有較高的光合作用速率與優勢，在柳杉人工林中則有所縮減，此結果支持在高光照環境中，某些物種擁有高競爭優勢，進而排除其他物種，使得生物多樣性降低，而此現象是否出現在臺灣其他森林中仍待進一步調查。

Understory plants play an important role in both natural forests and plantations through their effects on the microclimate at forest floor, seedling establishment and nutrient cycling. We investigated plants diversity, plants biomass, light environments (using hemispherical photography) and soil nutrient under a low-elevation natural hardwood forest and a Cryptomeria japonica plantation located in northeast Taiwan. The result indicate that natural hardwood forest had higher understory light availabilities, soil nutrient content but lower understory plants diversity than Cryptomeria japonica plantation. There was no significant difference in understory plants biomass between the two forest type. Understory light availabilities had a significant negative correlation with understory plants diversity. Elatostema lineolatum Forse. Var. major Thwait. had higher photosynthesis rate and dominance in natural hardwood forest than in Cryptomeria japonica plantation. The result supports that some species had higher competitive ability and, therefore dominance in high light environments and as such, lead to a decrease in biodiversity. More studies are needed to validate whether the result found in northeastern Taiwan also exists in other forests in Taiwan.