1 引言外部效应的存在是许多林业政策设计的基础,是政府对林业实行干预的主要理由之一。在由计划经济体制向市场经济体制转变之际,深入研究外部性理论显得非常必要。事实表明,凡成功的制度变革,凡行之有效的政策,都是成功地解决了外部性问题的。许多文献在谈到林业的外部性时,首先提及的是林业经济活动中森林公益效能外溢到社会其他行业的问题。无疑环境效益是林业中最具有重要意义的外部性问题之一。但 1 Introduction The existence of externalities is the basis of many forestry policy design and one of the main reasons government intervenes in forestry. In the transition from a planned economy to a market economy, it is necessary to deeply study the theory of externality. Facts show that where successful institutional changes and effective policies are all successful in solving the issue of externalities, When talking about the externality of forestry, many documents first mentioned the issue of forest public welfare spillover to other sectors of society in the economic activities of forestry. Undoubtedly, environmental benefits are one of the most significant externalities in forestry. but