Study on Relationship between Height and DBH of Mountain Coniferous Forests in Xinjiang

Growth of trees includes two dimensions,i.e. diameter and height. The height-diameter relationship is affected by climatic and topographic conditions as well as species properties. In this paper,the relationship between stem diameter at breast height (DBH) and stem height (H) of coniferous forests is analyzed based on 120 sample plots investigated from 11 locations in the Altay Mountains (Altay),Kunlun Mountains (KL in abbreviation,the same below),and northern and southern slopes of the Tianshan Mountains (NT and ST respectively) in Xinjiang. The potential heights (H*) of trees in each plot were estimated. The results show that the taper of coniferous forests in KL,calculated with DBH/H,is higher than that in other regions,and the potential height in KL is lower than that in Altay and NT. For different forests,the taper of Pinus sibirica,Abies sibirica and Picea obovata forests is lower than that of Larix sibirica and Juniperus forests. The taper of Picea schrenkiana forests is lower than that of Juniperus forests but higher than that of Picea obovata forests. The H* of Juniperus forests is lower than that of other forests. Taper increases with the increase of altitude but decreases with the increase of AP in whole Xinjiang. For different regions,taper increases but H* decreases with the increase of altitude in Altay and NT,but there is no notable change of taper and H* with the increase of altitude in ST and KL. For different forests,the taper and H* of L. sibirica and Picea schrenkiana forests increase and decrease significantly with the increase of altitude separately. The taper of Pinus sibirica and A. sibirica forests increases significantly with the increase of altitude. According to the GLM (General Linear Model) analysis,change of the height-diameter relationship with environmental factors is different from different regions and scales. Annual precipitation (AP),aspect of sample plots (ASP) and forest type are the most important variables to taper and H* in whole Xinjiang. ASP,slope position (POS) and mean annual temperature (MAT) are important in north Xinjiang,and ASP,AP and MAT are important in south Xinjiang.