Reversibility of Interannual Tree Growth Variability in Southern Boreal Forest

The southern boreal forest has experienced a profound shift in growth pattern because of climate change. However, it remains underexplored whether climate variation has increased interannual tree growth variability and if this trend is reversible under climate warming. On the basis of a field investigation and dendrochronological analysis, we evaluated the temporal changes in interannual tree growth variability across a temperate-boreal forest ecotone in northeastern China. Our results indicate that the interannual growth variability of Dahurian larch (Larix gmelinii), the dominant boreal tree species, increased significantly (0.005 year^-1) during a rapid warming period (1980-2006), whereas the annual growth rate, measured by standardized basal area increment, declined significantly. This increase in growth variability was mainly explained by an increase in the interannual variability of moisture during both mid-growing season and the non-growing season, and interannual variability of temperature during the growing season. During the subsequent period (2007-2018), the interannual growth variability decreased rapidly (-0.04 year^-1) to the level in the early 1980s, whereas the annual growth rate exhibited no significant trend. The decrease in growth variability was largely attributable to a reduced interannual variability in growing season temperature and increased mean temperature during the non-growing season. Moreover, the rate of decline in growth variability was higher near the boreal forest, and the spatial variation was primarily regulated by tree height and the rate of change in the mean temperature of the growing season's starting month. Our findings suggest that the trend and level of interannual tree growth variability in the southern boreal forest remain reversible under near-term climate warming. This result provides a more nuanced perspective compared to the assumption of irreversible shifts in tree growth stability in southern boreal forest because of climate warming.