Relations between growth of Picea crassifolia forest and environmental factors on different altitudinal gradients in mid-mountain belt of Pailugou Basin of Qilian Mountains, Gansu Province

By selecting Picea crassifolia forests on altitude of 2 900 ~ 3 300 meters in mid-mountain zone of Pailugou watershed in Qilian Mountains as research object, the relations between the growth of P. crassifolia forests in different altitudinal gradients and environmental factors(climate and soil) were investigated and studied. The results are as follows:(1)In the range from closed forest in 2 900 meters above sea level to alpine timberline in 3 300 meters, the growth of DBH and tree height of P. crassifolia were obviously affected by environmental stress effects, this was confirmed by the changing laws of regeneration seedlings and nonregeneration seedlings on different altitudinal gradients.(2)With the increase of altitude per 100 meters, the average annual precipitation growth rate in P. crassifolia forests was 19.94 mm, the average annual temperature lapse rate was-0.67 ℃; P. crassifoliagrowth minimum tempe rature was-1.72 ℃; To a certain extent, the heat conditions inhibited the growth of P. crassifolia which grew at the altitude of 3200 meters.(3) In different soil profiles, the average temperature of soil continuously decreased with increasing altitude, while soil moisture constantly increased with increasing altitude; The contents of organic matter, total N and available N in soil increased with the increasing altitude; The contents of total P, available P, total K and available K in soil had no obvious change with the increasing altitude; The p H of soil in different altitude was alkaline; The contents of organic matter and total nitrogen were rich in P. crassifolia forests, but the soil temperature in the forests decreases with the increase of altitude, which affected the effective of nutrient supply.(4) The variance analysis indicated that the order of effects of environmental factors under the influences of altitude gradients on the growth of Picea crassifolia in different altitude ranked from big to small as follows: soil chemical properties(10.261) meteorological factors(7.900) soil physical properties(2.535), this proved that soil chemical properties of forest land was the key factor to influence tree growth. The findings of the study can provide theory reference and data support for forest cultivation and protection in Qilian Mountains, and also present theory basis for responses of sub alpine mountain region vegetations in arid and semi-arid areas to environmental change mechanism.