Analysis of population differences in Betula ermanii Cham. between the northern and western slopes of Changbai Mountain

Based on vegetation surveys of the western and northern slopes of Changbai Mountain, we analyzed and compared density, diameter at breast height (DBH), tree height, age, generation, and population distribution patterns of Betula ermanii Cham., as well as slope differences with altitude, and further explored the disturbance factors of vegetation slope differences. Results showed that:DBH and proportion of second-generation forest on the northern slope were significantly higher than that on the western slope, but the proportion of first-generation forest was lower on the northern slope. The western slope was disturbed by more factors than the northern slope, although it contained better habitat. Similar trends in B. ermanii population characteristics with altitude were found between the northern and western slopes, with population density showing a "single-peak" variation with increasing altitude. The DBH, height, age, and proportion of second-generation forest on the northern slope gradually decreased with increasing altitude, and spatial distribution showed an aggregation-random-aggregation trend, indicating that B. ermanii only occupied part of the habitat at lower and higher altitudes, in accordance with the general mountain vegetation distribution characteristics. The age and height of B. ermanii on the western slope decreased with increasing altitude and the population showed an aggregation distribution. The slope aspect differences in population varied with altitude. DBH, height, and age on the western slope were lower than those on the northern slope at altitudes of 1600-1700 m, but density was higher than that on the northern slope. In contrast, DBH, height, and age on the western slope were higher than those on the northern slope at altitudes of 1800-2100 m, but density was lower than that on the northern slope. These results indicate that disturbance on the western slope shows a random pattern with altitude and is influenced by wind. Therefore, in addition to the known disturbances of volcanic eruption, volcanic ash erosion, and habitat differences, wind disturbance is another important factor causing slope differences in B. ermanii populations.