磺港溪口植物及土壤對四斑細蟌的影響

Abstract

屬於近危物種的豆娘 ― 四斑細蟌 (Mortonagrion hirosei) 於台灣僅於淡水河系下游三處濕地被發現，台北市磺港溪口為其中之一。然而，此處以往已歷經橋樑建設等大型工程開發，因此，環境破壞與四斑細蟌生存的關係成為需要被關注的課題。本研究由水質、土壤、植物及微氣候因子之分析，探討四斑細蟌與環境的關係，以利未來保育及棲地維護工作之落實。成蟲調查結果顯示，在此人為開發導致44.8 % 植被面積減少的樣區中，四斑細蟌的分布較為侷限。分析整體樣區風速分布，發現橋梁構造對棲地風速造成影響、植被具有降低風速的效果，此兩項地景對四斑細蟌之分布具影響力。水質調查中，發現此樣區有強酸性水質之磺港溪流經，其pH < 3，可能對四斑細蟌造成威脅。在環境因子偏好的研究中， 發現四斑細蟌在具蘆葦(Phragmites australis)密度差異的棲地中呈叢聚分布 (aggregated)，偏好蘆葦密度介於200 枝/m2–500 枝/m2，而蘆葦密度對溫度及照度造成差異，可能為影響其挑選蘆葦密度的原因。最後討論棲地維護的方向，由重要的環境因子 ― 蘆葦密度為目標，分析其與土壤的關係，結果顯示本樣區中土壤變異主要來自土壤有機質，且有機質與蘆葦密度呈顯著正相關。整體而言，本研究建議工程建設應將蘆葦破壞導致的棲地縮減及碎裂化納入考量，維護適當密度的蘆葦，並由土壤有機質的保存，進行四斑細蟌棲地的經營與維護。

Mortonagrion hirosei is a damselfly species which has been categorized as “near threatened” in IUCN red list. In Taiwan, it has only been found in three wetlands along the downstream of Tamsui River, and Huang Gang Creek estuary is one of them. However, recently this habitat has experienced large-scale bridge construction; the living condition of M.hirosei under human disturbance, therefore, requires special concerns. This study analyzes the correlation between M.hirosei’s density and environmental factors including water, soil, plants, and microclimate. A decrease of 44.8% vegetation coverage is found, restricting the distribution of M.hirosei. A major factor is the increase of wind speed, which used to be lowered by plantation, these two landscape elements turned out to be crucial for maintaining its habitat. An extremely acid water quality (pH < 3) is found as an asset of this estuary. Particularly, reeds with a density of 200 to 500 branches/m2 are found most favorable. Temperature and light intensity are observed as important environment factor of reed density. Soil organic matters dominate the soil heterogeneity, which also presents a significantly positive correlation with reed density. Finally, this study suggests that human should consider the cause of habitat loss and fragmentation by reed destroyed in estuary development, and emphasis on preserve soil organic matters to maintain proper reed density.