Dynamic Change Of The Biomass And Net Primary Production For China Based On National Forest Inventory

In this study, Chinese forest distribution area is chosen as study area, based on eight continuous National Forest Inventory data from 1973 to 2013, Chinese forest biomass in recent 40 years is estimated with the variable Biomass Expansion Factor Function?variable BEEF? method, then net primary production is calculated according to the relationship between the biomass and net primary productivity, furthermore, the dynamic change of forest biomass and net primary production is analyzed for 16 different forest types, different age classes and different climatic zones, finally, the spatial distribution pattern of Chinese forest biomass and biomass density is explored. This study will provide some fundamental data for a comprehensive and correct assessment of biomass and net primary production of Chinese forest vegetation, better management of forest resources, and the studies exploring global carbon cycle and carbon sequestration capabilities. The results showed that:?1? From 1973 to 2013, China's total forest biomass increased from 7049.79×10⁶t to 14059.01×10⁶t, meanwhile, the corresponding total net primary production increased from 901.67×10⁶t·a^-1 to 2124.92×10⁶t·a^-1, Among them, biomass and net primary production of bamboo and economic forest was continuing to increase with the spread of distribution area.?2? China Biomass increased from 6635.41×10⁶t in 1973-1976 to 13125.09×10⁶t in 2009-2013, meanwhile, corresponding biomass density increased from 61.55 t·hm^-2 to 79.74 t·hm^-2; Net primary production increased from 787.88×10⁶t·a^-1 to 1249.41×10⁶t·a^-1, meanwhile, net primary productivity increased from 7.31 t·hm^-2·a^-1 to 11.31t·hm^-2·a^-1.?3? Subtropical mixed evergreen-deciduous broadleaved forest has the largest average annual biomass in 16 forest types with 1964.05×10⁶t, followed by Picea, Abies, and Tsuga forest?1185.62×10⁶t?, temperate typical deciduous broadleaved forest?1171.82×10⁶t?, Betula and Populus forest?1106.56×10⁶t?. These four forest types stand against Chinese Biomass contribution rates were 22.34 %, 13.31 %, 13.02 %, and 12.59 %. The biomass density range in different forest types changed from 16.29- 158.73 t·hm^-2 in 1973- 1976 to 40.74- 164.67 t·hm^-2 in 2009-2013.According to the variation trend of biomass density, 16 forest types can be divided into three categories: increasing type, stable type and reducing type.?4? From the perspective of biomass and biomass density in different forest age classes, in the same period, Biomass and biomass in order always were: old-growth forest > middle-aged forest > young forest. Nearly 40 years, the three's biomass and biomass density all showed an increasing trend, in which, old-growth forests has the biggest increment in biomass, while young forest has the biggest increment in biomass density. In addition, the old-growth forest's biomass density was 3.41 times as much as middle-aged forest's, and 1.66 times as much as young forest's.?5? Nearly 40 years, the rank of biomass in different climatic zones was: subtropical zone?4739.24×10⁶t? > cold temperate and temperate zone?3358.91×10⁶t? > warm temperate zone?724.24×10⁶t? > tropical zone?79.95×10⁶t?, while the rank of biomass density in different climatic zones was:tropical zone(102.67 t·hm^-2)> cold temperate and temperate zone(78.52 t·hm^-2) > subtropical zone(68.48 t·hm^-2) > warm temperate zone(54.74 t·hm^-2).?6? From the perspective of biomass in the spatial distribution, Tibet, Sichuan, Yunnan, Heilongjiang, Inner Mongolia and Jilin were the main distribution provinces of China biomass resources. The biomass density increased from 0.00?Shanghai?- 167.49 t·hm^-2?Tibet? in 1973-1976 to 36.11?Beijing?- 184.36 t·hm^-2?Tibet? in 2009-2013.In biomass density, In addition to sichuan, qinghai and gansu biomass density declined slightly, other various provinces and regions of forest biomass density increased. In biomass density, in addition to Sichuan, Qinghai and Gansu decreased slightly, each of the other provinces have increased.?7? Nearly 40 years, Subtropical mixed evergreen-deciduous broadleaved forest was 265.14×10⁶t·a^-1, with the largest in average net primary production, followed by Betula and Populus forest(205.30×10⁶t·a^-1), temperate typical deciduous broadleaved forest(154.16×10⁶t·a^-1) and subtropical evergreen broadleaved forest(120.13×10⁶t·a^-1), the four accounted for 59.60% of China's net primary production in total. With the average annual net primary productivity in the most of 16 forest types increased in fluctuations, ranged from 4.17 t·hm^-2·a^-1 to18.95 t·hm^-2·a^-1.?8?As the young forest, middle-aged forest and old-growth forest increased, the ratio of this three changed from 1:1.40:1.85 in 1973-1976 to 1:1.02:1.14 in 2009- 2013, it follows that the highest growth rate of net primary production was young forest, and that old-growth forest were main contributor. For the net primary productivity, the sequence of three forest age classes was: middle-aged forest(10.59 t·hm^-2·a^-1) > old-growth forest(9.86 t·hm^-2·a^-1) > young forest(8.08 t·hm^-2·a^-1). With the three have different rate of increase, the young forest has the biggest was 156.81 %.?9? Nearly 40 years, the sequence of net primary production in four climatic zones was: subtropical zone(639.43×10⁶t·a^-1) > cold temperate and temperate zone(419.83×10⁶t·a^-1) > warm temperate zone(115.61×10⁶t·a^-1) > tropical zone(14.51×10⁶t·a^-1), while for the net primary productivity, the sequence was: tropical zone(18.64 t·hm^-2·a^-1) > boreal temperate(9.81 t·hm^-2·a^-1) > subtropics(9.24 t·hm^-2·a^-1) > warm temperate(8.74 t·hm^-2·a^-1).