基于森林详查与遥感数据降尺度技术估算中国林龄的空间分布

Spatial pattern of forest ages in China retrieved from national-level inventory and remote sensing imageries

森林的林龄结构及空间分布是评估区域尺度森林生态系统碳汇潜力的重要参数。以第五次全国森林详查获取的省级优势树种的平均林龄及分布面积为基础，以同期生长季节的NOAA／AVHRRNDVI遥感数据为辅助，在空间降尺度统计技术的支持下，得出了全国8km分辨率下的森林林龄的定量分布。结果表明：中国林龄在空间分布具有很大异质性。东南地区的林龄较低，省平均林龄主要介于20～30年。林龄大于120年的森林主要分布在四川中部及新疆西北部地区。西藏东南部、黑龙江西北部、内蒙古东北部以及云南南部地区的林龄介于两者之间，其值大多介于70～120年。从全国范围看，森林的林龄主要介于10～80年，其面积占森林总面积的85．4％，其中林龄在20～40年之间的森林面积占35．3％。全国总的平均林龄为40．6年，标准差为26．6年，在概率分布上呈现单峰非正态分布。

The structure and spatial distribution of forest age are important parameters for assessing carbon sequestration potential of forest ecosystems at regional scale. In this study, we tried to estimate those parameters based on survey data of the average forest age and area of dominant tree species retrieved from detailed investigation of the fifth national forest at provincial level, along with the growing season NDVI data derived from NOAA AVHRR sensors in the same period. We then analyzed the spatial patterns of forest ages in China with remote sensing downscaling techniques. The results indicate that the spatial distribution of forest ages showed significant heterogeneity. The forest age of southeast China was lower than that of rest of the country, with average values ranging from 20 to 30 years. The forests aged over 120 years are mainly distributed in central Sichuan and northwestern Xinjiang. And the forest ages of the southeastern Tibet, northwestern Heilongjiang, northeastern Inner Mongolia and southern Yunnan are mostly between 70--120 years. From the national-level perspective, the main forest age is ranged from 10 to 80 years, with their area accounting for 85.4% of the total forest area. The area of forest aged 20--40 years accounted for 35.3% of the total forest area. The average forest age was 40. 6 years in China, whose standard deviation is 26.6 years. As for the probability, Chinese forest ages showed a single peak of abnormal distribution.