森林在水土資源保育上之功能

The Role of Forests in Soil and Water Conservation

陸象豫(Shiang-Yue Lu)

《台灣林業科學》 11卷3期 (1996/09) Pp. 333-347

https://doi.org/10.7075/TJFS.199609.0333

摘要

本文依據基本學理，並參考國內外研究成果和經驗，分項探討森林在水土資源保育上的功能以及林地變更後對有關水文因子之影響。森林與水資源間並無一致的關係性，所能明確證實地爲改變植物覆蓋面積或組成會影響集水區之出水量；然而集水區出水量受林木變更影響的程度隨降雨量、優勢樹種、砍伐面積或作業方式之不同而不同，本文對各項因子逐一作詳細的說明。森地對集水區水源涵養有間接而正面的功效，森林提供一良好環境使林地土壤層達到最佳之保水蓄水狀況，並藉植物育土、護土的功能維持此最佳狀況。在同一土壤、地形等條件下，森林對減低洪峰流量及延緩洪峰到達時間並無顯著的效用，僅能減輕洪水所造成的災害；洪水之發生主要係受氣候與地形因子所決定，上游集水區土地利用方式對河川流量的影響有限。由於覆蓋良好的林地內非點源沖蝕甚少發生，且根系所及範圍內的崩塌亦較相同深度範圍之裸露地爲少，故森林在防止地表沖蝕與淺層崩塌具有顯著之功效。林木光合作用與蒸發散會消耗一部分輻射能，因而可降低地表溫度，且林木之屏障作用亦會改變能量傳遞，致使森林能影響一地區的微氣候，但區域性之天候狀態仍決定於氣象因素。雨水與樹冠層間之交互反應作用，能吸收及淋洗部分離子，因而森林具中和雨水酸性之功能；而林冠的庇護能降低溪流的水溫，對增加水體含氧量有所助益。森林涵養水源之功效可使大部分的降水進入土壤層，並經由土壤層之過濾與離子交換作用，發揮淨化水質的作用。森林與地下水間關係較不明確，除非是位於地下水水源區，否則林木之有無對地下水位或地下水流量無顯著的相關性。在水土資源保育上，森林之功能雖有其有限性，但毫無疑問地卻是所有土地利用中最佳者。

關鍵字

出水量 ； 水源涵養 ； 洪峰流量

並列摘要

The role of forests in soil and water conservation and the impact of forest removal on related hydrologic factors are discussed by emphasizing basic principles and results of studies throughout the world. It is clear that water yield will change after vegetation conditions of a watershed are altered. However, the relationship of forests to water supply still remains controversial due to the diversity of watershed conditions such as the amount of precipitation, dominant vegetation, cutting area and harvesting operation method. Comparing with other land use patterns, the well-protected forest land with high infiltration capacity provides a better environment for water detention and retention, and makes more water available during drought periods. Forests can not prevent floods caused by heavy rain storms, but they can mitigate their destruction to a certain extent. Floods of major rivers are affected more by meteorological and topographic factors than by land use activities in upland watersheds. Surface and gully erosion are rarely happened in forest land, therefore there is no doubt that forest can prevent erosion to a point. Forests not only lower air temperature inside and above the canopy, because a large portion of input radiant energy is consumed by evapotranspiration and photosynthesis, but also influence the movement of winds which results in the redistribution of heat. Removal of forests can affect microclimates significantly but have little or no impact upon regional climate. Watersheds covered by forests generally promote high quality water by allowing more water to pass through mineral soil layers than other cover conditions. In addition, vegetation cover conditions have less effect on the groundwater system unless they are located in the groundwater recharge areas. Although forests have their limitations, it is clear that forests are the best of all land use patterns as far as soil and water conservation are concerned.

並列關鍵字

water yield ； water conservation and streamflow regulation ； peak flow