Changes of forest in northeast China over the past 25 years: an analysis based on remote sensing technique

The Northeast China is the largest distribution region of forests in China, thus its changes in forest undoubtedly have great impact on the global carbon cycle. However, no comprehensive analyses of the changes in forest of this region over the past 25 years have been conducted. In this paper, vegetation in Northeast China was first classified with an expert classification method based on different vegetation types with different NDVI time profiles, then the 25-year changes in forest attribution (i.e., area, growing stock and biomass) was examined based on models constructed, and the comprehensive analysis by using the forest identity was also made. The results showed that forest area, growing stock volume and biomass decreased 1.5 Mha (1 Mha = 106 ha), 187 Mm3(1 Mm3 = 106 m3) and 222.75 Mt (1 Mt = 106 ton), respectively, with the relative annual change rates of -0.18%, -0.32% and -0.34% over the past 25 years. The comprehensive analysis showed that the forest carbon storage in Northeast China was estimated 1.21 Pg C (1 Pg = 1015 g) in the period of 2004-2006, and forests of this region released 3.64 Tg C per year (1 Tg = 1012 g), which means that it demonstrated as a carbon source over the past 25 years. However, such changes in forest attribution showed a significant regional variation; for example, the attributes declined in Heilongjiang and Jilin, while increased in Liaoning Province. The declines in forest growing stock volume are mainly due to the decrease in area, which may be further caused by the coupling effects of frequent forest fires and deforestation.