An upshift of the treeline, dominated by erman’s birch (Betula ermanii), in Changbai Mountain in the northeast of China has been attributed to climate change. The process and the mechanism, however, are far from being clear. For a better understanding of the mechanisms of the population dynamics of Betula ermanii in response to climate change over the past 55 years (1953-2008), 310 quadrats were sampled in 7 plots located in the upper treeline region along the north-facing slopes of Changbai Mountain, China. IKONOS images were used to identify the spatial distribution of Betula ermanii with the aid of a digital elevation model (DEM). Meteorological data were corrected in the field throughout the study area and downloaded from a nearby long-term weather station as well to reconstruct the temperature and precipitation changes. We collected tree-ring samples from a total of 1197 Betula ermanii shrubs and trees. Via statistical analysis facilitated by GIS technology, we calculated the correlation coefficients between each of 14 climate parameters and an aggregated annual index of population dynamics for each of the 310 quadrats over the corresponding years.
Results/Conclusions
The results show that population dynamics of Betula ermanii was more sensitive to changes in air temperature than to changes in precipitation. During the period when air temperature increased at a slower pace, its population steadily expanded with asexual reproduction. Betula ermanii adapts to such a graduate warming in the form of vegetative propagation to overcome a still harsh and occasional extreme low winter temperature. During the period when air temperature increased rapidly, its population responded through rapid sexual reproduction and produced many progenies with a higher survival rate. Betula ermanii’s capability of adjusting reproductive strategies in response to climate change clearly is responsible for a wide spread population expansion that pushes the treeline further upward to a higher elevation in Changbai Mountain, especially along the valleys (For more detail, see Wang et al. 2018, Current Science, 115(9):1751-1760.