租地造林乃緣於日本領台期間林木過度採伐，台灣光復後政府財力及物力不足，林務管理欠周，林地遭濫墾、占用隨處可見，故期能透過引進民間人力、物力以及財力，加速完成造林工作。1990年代，政府為防止天然林的快速消逝對國土保育及環境造成負面影響，而全面禁止砍伐天然林，加上我國加入WTO後，開放進口大陸廉價木材，致國產木材逐漸失去競爭力，林農經營林業入不敷出，而拓展種植果樹之面積，改種高經濟價值作物，如茶葉、咖啡、葡萄、柳丁及檳榔等。然而，在林地上同時存有林業與農業使用，並不能直接類比為永續的「混農林業」經營模式，其特殊條件值得進一步探討。 起源自游耕活動的混農林業具有多功能性且符合土地倫理的概念，包括社會經濟上增加林農收入外，亦可分散經營風險，提升地方生活水準與競爭力，並可使當地文化習俗得以傳承；而在生態環境方面，樹木可供應作物生長所需氮素，增加養分獲取與留存，並可增加碳吸存力，以及維持生物多樣性等，因而在國際間頗受推崇，然在我國則面臨政策以及法規的考驗。 本研究修正Walck & Strong所提出的土地倫理分析架構為永續性混農林業影響模式，並以臺大實驗林契約林地為案例，透過文獻評析、參與觀察、問卷調查以及深度訪談，目的為探求國有放租林地發展混農林業之正當性，以及研擬混農林業之發展對策，獲得以下結論：1.過去混農林業政策多採有條件限制施作；2.林地管理政策與法規範難以戢止林農違規使用行為；3.放租林地改作永續混農林業具有正當性。而本研究之建議包括：1.調整政府租地造林管理制度；2.有條件允許混農林業；3.重視林農土地倫理價值觀；4.以永續農業維持林地健康。 / The government owned forest in Taiwan were overexploited during the Japanese Colonial Period and the poor forestry management after Second War World resulted in deforestation for illegal cultivation, occupying. In order to remedy the negative effects, government speeds up afforestation on national forestlands, and rent them to local tenant. Since 1990s, logging natural forest was prohibited and the cheap timber was imported from Mainland China after 2002 while Taiwan joined WTO, the forest tenants deforested part of the leased forestland and grew fruits, tea, coffee, etc., to fight against low price of forestry products to gain more income. However, growing crops on forestry land is no analogy to agroforestry, some specific conditions have to be investigated. Agroforestry is multifunctional and manipulated based on land ethics. On economic and social aspects, it is not only increase local tenants income, but also disperse the risks of operation, improve local living standard and forestry competitiveness and inherit local culture and customs to the next generation. On ecological aspect, trees provide nitrogen and nutrient, raise carbon sequestration, and sustain biological diversity. Hence, it is highly valued in other countries, but is taken as illegal activity in Taiwan. This study revises the framework of land ethics, power relationships and land use, land health raised by Walck & Strong for sustainable agroforestry analysis, and take the Experimental Forest of National Taiwan University as a case study. Through methods of literature review, participation observations, questionnaire survey, in-depth interviews, the research findings are as follows: 1) the cultivation of agroforestry was confined conditionally; 2) the current forestry policy and laws cannot prevent tenants from illegal land uses; 3) agroforestry in leased forestland is legitimate if it is operated sustainably. Hence, the policy implications are: 1) adjusting the management institution of leased forestland; 2) conditionally permitting agroforestry; 3) respecting tenants’ value of land ethics; 4) maintaining forestland health by sustainable agroforestry.