Contributions of competition on Larix kaempferi tree-ring growth were higher than long-term climate in China

Forest tree growth plays an important role in forest ecosystem carbon cycle and carbon sequestration, and tree growth is affected by many factors. However, information on the contribution rate of different factors to tree growth is still limited. Thus, we hypothesized that increased regional competition has a significant negative impact on tree growth in plantations. In order to ascertain this hypothesis, tree-rings width for developing chronologies and competition data of the Larix kaempferi in Chinese plantations were sampled. Using tree-ring climatology method and non-linear models based on maximum likelihood analysis etc., the relationship between the tree-ring growth and competition index and climatic factors and their relative importance were evaluated in different years-interval and climate-zone. The results showed that the competitive effect for trees growth was always much stronger than the climatic or size effect. Competitive effects change over time, with drought effects (vapor pressure deficit (VPD) and standardized precipitation-evapotranspiration index (SPEI)) on tree growth exacerbated. The significant negative effects of neighborhood competition gradually increased over time. Climate moderates competitive effects during stand development, especially the negative effects of drought index on trees. Trees decline in growth due to climate warming with temperature and precipitation changes, and mainly, increased competition. Overall, these results constitute important new information, which not only further deepens our understanding of important theoretical issues related to plantation tree growth, but also helps to formulate new guidelines to make larch plantations adapt to global changes. Therefore, thinning measures are valuable suggestions to change forest density can promote trees growth, it provides highly valuable information for estimating future forest dynamics and changes in carbon storage and carbon neutrality under climate change.