Analysis of growth trend changes for 51 temperate tree species using Korea national forest inventory data

Individual tree growth rates can be affected by various factors such as species, soil fertility, stand development stage, disturbance, and climate etc. To estimate the effect of changes in tree growth rate on the structure and functionality of forest ecosystem in the future, we analyzed the change of species-specific growth trends using the fifth Korea national forest inventory data, which was collected from 2006 to 2010. The ring samples of average tree were collected from nationwide inventory plots and the total number of individual tree ring series was 69,128 covering 185 tree species. Among those, fifty one species with more than 100 tree ring series were used for our analysis. For growth-trend analysis, standardized regional curves of individual species growth were generated from three forest zone in South Korea; subarctic, cool temperate, warm temperate forest zone. Then individual tree ring series was indexed by dividing the growth of the tree by expected growth from standardized regional curves. Then the ratio of all tree ring series were aligned by year and the Spearman's correlation coefficient of each species was calculated. The results show that most of species had increasing growth rates as forests developed after Korean war. For the last thirty years, 67.3% of species including Quercus spp. and Zelkova serrata had positive growth trends, on the other hand, 11.5% of species including Pinus spp. showed negative growth trends probably due to the changes in successional stages in Korean forests and climate change. These trends also vary with climate zone and species. For examples, Pinus densiflora, which showed negative growth trend overall, had steep negative growth trends in boreal and temperate zone, whereas it showed no specific trend in sub-tropical climate zone. Our trend analysis on 51 temperate tree species growth will be essential to predict the temperate forests species change for the this century.