林下養雞生物活動對土壤侵蝕之影響

Effects of biological activities of raising chicken under the forest on soil erosion

現今推廣之林下經濟政策尚未包含林牧活動，但坡地林下飼養雞隻卻是常見的林牧行為，主要因其可充分利用林下閒置空間，然而農民為獲取最大經濟利益而過度的密集飼養，將因雞隻行為特性而對林下環境造成強烈干擾產生加速侵蝕，但目前國內針對林下飼養雞隻對林下水土環境影響之研究甚少。本研究旨在探討林下飼養雞隻（圈養）行為對林地土壤侵蝕程度，由於雞隻於林下活動可能造成土壤侵蝕及改變物理化學特性，影響坡面土壤抗侵蝕能力，針對林下進行圈養雞隻行為採用定性（土壤侵蝕觀察）及定量（沖蝕針觀測法）分析，希冀成果可供未來研擬相關政策時參考之用。研究成果顯示，無論從定性（目測法）或定量（沖蝕針觀測法）方式評估，研究區在飼養雞隻後均有土壤侵蝕情形，試區一到試區四累積土壤侵蝕深度分為-7.5、-9.0、-18及-13.5 mm，主因為雞隻活動特性造成保護地表的植被消失，增加土壤擾動機率而引起後續土壤侵蝕；再將雞隻飼養密度與累積土壤侵蝕深度及土壤硬度進行迴歸分析，均顯示累積土壤侵蝕深度及土壤硬度會隨飼養雞隻密度變大而加深變硬。

Although the under-forest economic policy promoted by the government today has not yet include forest and animal husbandry activities, raising chickens under the forest on the slope has been a common behavior. The main reason is that it can make full use of the idle space in the understory. Intensively raising chickens by farmers to maximize economic benefit may result in accelerated erosion due to strong disturbance to the environment caused by behavioral characteristic of chickens. However, only few studies on the impact of raising chickens under the forest on the soil and water environment were published. The purposed of the study is to investigate the degree of soil erosion on the slope due to raising chickens under the forest. Because activities of the chicken under the forest may cause soil erosion and change physical and chemical properties, qualitative (soil erosion observation) and quantitative (erosion needle measurement) approaches are used to explore the effects of understory chicken captivity on soil erosion. We hoped that the results can serve as a reference for implementing relevant policies in the future. The research results of both qualitative (soil erosion observation) and quantitative (erosion needle measurement) approaches showed that the study area exhibit soil erosion after raising chickens. The cumulative soil erosion depths of the four test plots were -7.5, -9.0, -18 and -13.5 mm, respectively. The main reason of the erosion was that the protective vegetation on the surface disappears due to the movement of chickens, which increased the probability of soil disturbance and resulted in subsequent soil erosion. Regression analysis results showed that the cumulative soil erosion depth and soil hardness would become deeper and harder with the increase of raising chicken density.