Abstract: The Altai Mountains forest is the only southern Taiga forest in China, and it is an important water conservation forest area for regional social and economic development. The Irtysh River it conserves is the only river in China that flows into the Arctic Ocean. Forests have ecological benefits such as water conservation, water and soil maintainance, snow line rise control, and climate regulation. The Altai Mountains forest plays a decisive role in the Altai region’s social and economic development, such as industry, agriculture, animal husbandry, and territorial ecological security. The forest also contributes to the social and economic development of the lower reaches of the Irtysh River in China and influences the relevant watersheds of Kazakhstan and Russia. The Altai Mountains forests are mainly distributed in the mid-mountain zone at 1400-2000 m, which is a cold temperate Taiga forest type, and the forest coverage rate is 45.73%. To quantify the value of the ecological services of various types of vegetation and forest farms, this study follows“Specifications for assessment of forest ecosystem services in China”(LY/T 1721- 2008). Based on second- level survey data of forest resources, this paper analyzes forest types and the service functions of different forest farms. The results are as follows. The value of forest ecological services in the Altai Mountains forest is 47,957.79 × 106 yuan · a ^{? 1}. The value of ecosystem services consists of water conservation, carbon fixation and oxygen release, biodiversity protection, atmospheric purification, soil conservation, and nutrient accumulation. Most of the value of ecological services for different forest ages comes mainly from mature and overmature forests. The value of ecosystem services, from highest to lowest is as follows: mature forest, overmature forest, near-mature forest, middle-age forest, and young forest. To achieve improve the proportion of forest age it is recommended to reasonably thin trees of higher forest age and reduce human disturbances to lower age forests. Forest ecosystems are divided according to forest farms, and the values of ecosystem services from the Altai Mountains forest from highest to lowest, are from the following farms: Fuyun Forest Farm, Altai Forest Farm, Xinjiang Altay Mountains Two River Source Nature Reserve, Burqin Forest Farm, Qinghe Forest Farm, Habahe Forest Farm, and Fuhai Forest Farm. Mountain forests are a natural barrier for protecting oases, making them an important guarantee for maintaining ecological security in Xinjiang and the foundation of sustainable social and economic development. Evaluating the service function value of the forest ecosystem in the Altai Mountains provides guidance for the scientific management of forest resources. It also has important theoretical and practical significance for establishing an ecological compensation system.

Key words: forest ecosystem, service function, forest farms, Altai Mountains