Tree-ring growth patterns of Masson pine (Pinus massoniana L.) during the recent decades in the acidification Pearl River Delta of China

Long-term changes of the ring-widths of Masson pine (Pinus massoniana L.) growing at polluted and unpolluted sites in the Pearl River Delta of south China were compared to evaluate the growth patterns in response to the atmospheric pollution since the late 1970s. Trees at the currently polluted sites had statistically lower ring-widths than those at the unpolluted site since the early 1980s. Standard chronologies at the polluted sites showed consistent decrease in growth since the 1990s. Climate-growth model developed by the multi-stepwise regression at the unpolluted site explained 91.1% of the tree growth variation from year to year and thus it was suggested to be a control chronology index to predict the growth patterns of the pine trees in the study. Growth patterns at the polluted sites estimated by the model revealed negative departure from the control chronology index since the 1980s. The actual and estimated tree-ring indices even at the polluted sites showed synchronousness and statistical correlation in growth patterns prior to the 1980s. The significant increase of the mean differences between the actual and estimated indices and the statistical decrease of the correlation between the control index and the polluted ones after 1980 (especially after 1990) also demonstrated that the growth of pine trees deceased during the most recent years and the atmospheric pollution might be the main factor contributing to the growth decrease. The method of tree-ring analysis demonstrated high suitability and urgent necessity to assess the pine forest health and to improve the forest management in south China where potential forest decline (in particular, current die back) of Masson pine was on process.