Position of Betula ermanii population ecotone in Changbai Mountains Boundary form effects of timberline ecotone on colonization of woody plants and timberline dynamics in Changbai Mountain Carbon Supply Status in the Betula ermanii in Changbai Mountain Response of leaf functional traits of Betula ermanii saplings to the altitudinal Variation Physiological response of Betula ermanii at different altitudes in Changbai Mountain Geostatistical analysis of the pattern of Betula ermanii population in Changbai Mountain The effect of climate warming on the structure characteristic of the timberline in Laotudingzi Mountain Spatial patterns of a treeline Betula ermanii Cham. population on the north slope of Changbai Mountain