應用地形與降水資訊探討台灣櫻花鉤吻鮭潛勢物理棲地分布

Abstract

大尺度的環境物理特性調查可得到較細微之資料，但耗費的人力物力成本亦隨著研究範圍的大小遞增。因此，若能在執行現地細微資料收集之前，對於整體狀況有效的了解，便能將資源投入較關鍵之目標。 本研究從數值高程模型(DEM)的分析以及降雨模式推估出發，粹取潛在水系分布並估算各項水文因子。接著，模擬在設定前人研究中所提出之各項水文限制條件下，櫻花鉤吻鮭族群潛勢分布的範圍為何，並與歷史分布範圍相比較。進一步地，找出限制族群分布可能的物理因子，以作為未來改善棲地、復育族群的參考指標。 分析結果指出，本研究中以程式Netrace估算而得之數項水系特性與實際的調查值相當一致。若將依前人研究所提出之潛在限制標準：0.03(m m-1)≦平均坡度≦0.06 (m m-1)；1,500(m)≦地形高程≦2,000(m)以及0.06(cms)≦年均流量≦21(cms)，則研究範圍內僅七家灣溪、雪山溪(武陵溪)和司界蘭溪的棲地環境具有較連續的潛勢分布溪段。然而若要得到一個與歷史棲地接近的分布範圍，其限制標準應為：0.00(m m-1)≦平均坡度≦0.06 (m m-1)；1,390(m)≦地形高程≦2,000(m)以及0.06(cms)≦年均流量≦21(cms)。此外，平均坡度為本研究區內主要決定潛勢棲地分布範圍的限制因子。而在歷史分布範圍內之各溪段中，其Valley constraint特性介於medium ~ high之間。上述各項研究結果，可作為未來棲地復育改善之參考指標。

To realize the relationship between physical environmental factors and the potential habitats of the Formosan landlocked salmon, a widespread field survey needs to be conducted. Through an extensive field investigation, fine quality environmental data can be obtained. However, the broader a research area is, the higher the costs involved would be. Therefore, it would be more effective in utilizing resources if we could assess the basic environmental conditions before conducting a field survey. The main goal of this study is to formulate a framework for integrating topographic and precipitation information and then to build a model on how potential habitats of the Formosan landlocked salmon would change under different physical criteria. The study proceeds from estimating the precipitation models and then delineates and characterizes the stream system within the study area. Based on potential habitat limiting criteria extracted from literature and the stream characteristics generated by a digital elevation model (DEM) analysis program, the intrinsic potential habitats of the Formosan landlocked salmon are then determined. The result indicated that the modeled stream characteristics coincided with the filed surveyed ones. The results also suggested that in order to obtain a distributional range resembling the historical one, the potential habitats for the species should be within 1,390 ~ 2,000 m in elevation, with a mean gradient less than 0.06 m m-1, and an annual discharge rate between 0.06 and 21 cms. These ranges are broader than the ones given in the current literature. In addition, the degrees of valley constraint (VWI) for the potential habitats should be between medium and high. This study suggested that the mean gradient is the main habitat-limiting factor for the Formosan landlocked salmon within the study area.