Synchrony of forest responses to climate from the aspect of tree mortality in South Korea

Mortality is a key process in forest-stand dynamics. However, tree mortality is not well understood, particularly in relation to climatic factors. The objectives of this study were to: (i) determine the patterns of maximum stem number (MSN) per ha over dominant tree height from 5-year remeasurements of the permanent sample plots for temperate forests [Red pine (Pinus densiflora), Japanese larch (Larix kaempferi), Korean pine (Pinus koraiensis), Chinese cork oak (Quercus variabilis), and Mongolian oak (Quercus mongolica)] using Sterba's theory and Korean National Forest Inventory (NFI) data, (ii) develop a stand-level mortality (self-thinning) model using the MSN curve, and (iii) assess the impact of temperature on tree mortality in semi-variogram and linear regression models. The MSN curve represents the upper range of observed stem numbers per ha. The mortality model and validation statistic reveal significant differences between the observed data and the model predictions (R2 = 0.55-0.81), and no obvious dependencies or patterns that indicate systematic trends between the residuals and the independent variable. However, spatial autocorrelation was detected from residuals of coniferous species (Red pine, Japanese larch and Korean pine), but not of oak species (Chinese cork oak and Mongolian oak). Based on linear regression from residuals, we found that the mortality of coniferous forests tended to increase when the annual mean temperature increased. Conversely, oak mortality nonsignificantly decreased with increasing temperature. These findings indicate that enhanced tree mortality due to rising temperatures in response to climate change is possible, especially in coniferous forests, and are expected to contribute to policy decisions to support and forest management practices.