The Effect Of Climate Change On Radial Growth Of Masson Pine In China

Much attention had been paid to climate change which was mainly caused by the emission of greenhouse gases. As the largest terrestrial ecosystem forests play a key role in the global carbon balance. And masson pine (Pinus massoniana) as one of the main conifer species in south China was widely distributed in 14 provinces of the Subtropical Region, with the largest plantation area and wood volume. Therefore, to study the relationship between maason pine growth and climate variations can help us understand its growth response to the changing climate in the future and prove reference to forestry management.According to the natural distribution range of masson pine, nine study sites were set in the northern, central and southern subtropical regions, which situated in Hanzhong of Shaanxi Province, Xinyang of Henan Province, Chunan of Zhejiang Province, Guixi and Fenyi of Jiangxi Province, Jingzhou of Hunan Province, Longli of Guizhou Province, Pingxiang in Guangxi and Heyuan in Guangdong. Old masson pine plantations with little human disturbance were chosen, stem cores was extracted at the breast height from the predominant trees, then dendrochronological method were used to get the ring width indices chronologies of different study sites, relationship between the chronologies with the historical climate were analysed. At the same time, net productivity of the masson pine plantation in Jigongshan of Xinyan was caculated with the tree ring and the stand'conditions, relationship was analysis with the productivity and climate; Hanzhong is located in Northwestern edge of the geographical distribution, temperature was the key factor due to the adequate water supply, on the basis of daily mean temperature we attempted to explore the critical temperature to the radial growth of masson pine.The result showed that mean ring width was significantly correlated with annual mean temperature, but the inter-annul growth was more correlated significantly with the soil water conditions. Among the nine sites, sensitive climate factors varied from each other. In the North subtropical region, the total precipitation in the growing season was the limiting factor, while in the South with rich precipitation high temperature may become the limiting factor. It suggested that thermal condition was the basis of the annul growth, whereas water supply conditions led to the inter-annual variations, the variations of the limited factors among the geographic range indicated that masson pine growth was sensitively to climate, but they depended on the local special climate conditions. In the future most of the masson pine growth may increase by the wormer temperature and abundant water supply.In Jigongshan the results indicated that biomass of the plantation increased more than three times in the past 30 years, from 59.00 t·hm^-2 in 1980 to 254.75 t·hm^-2 in 2009, and mean net productivity of the stand was 6.64 t?hm^-2·a-1. Net productivity was closely correlated with climatic factors. The effects of temperature, sunshine, precipitation and humidity on net productivity were different. There were positive correlations between productivity and precipitation in last August, temperature in February, precipitation in March, humidity in May, and temperature and sunshine in October. There were negative correlations between productivity and sunshine in May, precipitation and humidity in October. Productivity was correlative positively with PDSI from February to September. Seventy one percent of the changes of productivity could be interpreted by climatic factors. Generally, biomass of masson pine plantation in North Subtropical Region could accumulate as high as that in low-latitude area but net productivity in the region was much less than that in low-latitude area. Annual changes of net productivity were mainly caused by climatic factors, especially the length of growing season and soil water availability during the growing season. It is implied that both biomass and mean net productivity of the plantations could increase in the future due to possible increase of temperature and precipitation in the North Subtropical Region.The results showed that the onset day with 6.0℃-7.5℃had significantly negative correction with the width indices chronology, with 6.0℃was the most significant. The ring growth was positively correlated with the ending day of 10.5℃. The growing season of 10.0℃and 10.5℃was significantly positively related to the growth. The accumulative temperature of growing season was also significantly positively correlated with the growth. These sensitive-temperatures of the first day and last day of the growing season were respectively related to the onset of photosynthesis and the needle emergence in spring, and shutting down of the cambium activity in autumn. This study suggested the rising temperature led to change phenophases and increase the radial growth of Masson pine in Hanzhong.All the results suggested that the changing climate would lead to the growth change of masson pine. In the future masson pine in China will growth faster in the wormer condition, but the changes of precipitation may lead to the uncertainty.