北亚热带马尾松年轮宽度与NDVI的关系

北亚热带地处暖温带向亚热带的过渡地区,对环境变化较为敏感。因此,研究北亚热带马尾松年轮宽度与森林NDVI的关系对于揭示陆地生态系统对全球气候变化的响应具有重要意义。以马尾松自然分布北界的南郑县和河南省鸡公山自然保护区为研究地点,利用北亚热带马尾松年轮宽度指数和1982-2006年逐月NOAA/AVHRR的归一化植被指数(NDVI)数据及气候数据,在分析年轮宽度及NDVI与气候因子关系的基础上,重点讨论了北亚热带马尾松径向生长与NDVI之间的关系。结果表明:北亚热带NDVI受水热条件的共同控制,其中与月均温相关性较强,且以正相关为主,与月降水量和干旱度指数多负相关;马尾松的径向生长与上一生长季的温度呈正相关,降水和干旱度指数为负相关,当年生长季内的温度和降水以促进作用为主,而与干旱度指数的关系在两地区内相反;南郑县和鸡公山地区年轮宽度与NDVI年值之间关系均不显著(P>0.05)。单月来讲,南郑县3、4、12月NDVI值与年表显著相关,鸡公山地区9月份的NDVI值与差值年表RES相关性最大;南郑县树木生长受温度影响最大,而鸡公山地区受温度和降水的综合作用。因此,在北亚热带地区,长时间序列的年轮宽度数据并不能很好反应NDVI的长期变化,利用树轮宽度指数来重建北亚热带地区NDVI需要进一步研究。

Relationship between masson pine tree-ring width and NDVI in North Subtropical Region

North Subtropical Area of China, located in the transition from warm temperate zone to the subtropical, is more sensitive to environmental changes. Therefore, study on the relationship between masson pine (Pinus Massoniana) tree-ring width data and NDVI in north subtropical region where masson pine growth is more sensitive to changes of climatic factors, is of much importance to reveal how the terrestrial ecosystems respond to global climate change. As the northern boundary of masson pine natural distribution, Nanzheng county of Shanxi Province and Jigongshan National Nature Reserve of Henan Province were selected. Using masson pine tree-ring width indices, monthly normalized difference vegetation index (NDVI) and climatic data from 1982 to 2006, the relationships between tree-ring width indices, NDVI, and climatic data, including monthly mean temperature, precipitation and the Palmer Drought Severity Index (PDSI) were analyzed firstly. Then, the relationship between tree-ring width indices and NDVI of forest was explored. The results showed that North Subtropical vegetation index NDVI was influenced by the hydrothermal conditions, and monthly NDVI was mainly positive to monthly mean temperature, negatively related to monthly mean precipitation and PDSI. In addition, the correlation coefficient between NDVI and temperature was larger than other factors. Masson pine radial growth was positive to temperature of last growing season, while negative to precipitation and PDSI. Temperature and precipitation during the growing season of the same year promoted the pine radial growth, the influences of PDSI on Nanzheng county and Jigognshan were opposite. In northern subtropical region, the relationship between masson pine tree-ring width and forest NDVI was not significant (P>0.05). However, NDVI of Nanzheng County in March, August and December were significantly associated with two chronologies, NDVI of Jigongshan region in September associated with the RES chronology with the biggest correlation coefficient. Through analyzing synthetically, we figure out that the tree growth of Nanzheng county was mainly affected by temperature, that of Jigongshan was influenced by the interaction of temperature and precipitation. In conclusion, we imply that long time series of ring width data does not reflect well the long-term vegetation changes in the northern subtropical region, and it is unreasonable to model and reconstruct the long-term vegetation changes and productivity using tree radial growth. Therefore, the further study is still required to reconstruct regional NDVI using tree-ring width chronologies in the North Subtropical Region.