Subalpine larch (Larix chinensis) is an endemic coniferous tree distributed above 3,100 m above sea level and forms treeline ecotone at the elevation of 3,450 m above sea level in the Qinling Mountains of north-central China. However, two prevailing but competing hypotheses (i.e., the carbon limitation hypothesis and the growth limitation hypothesis) based on carbon supply/demand balance cannot yet provide a broad explanation for the formation of alpine treeline.