North-east （NE） China covers considerable climatic gradients and all major forests types of NE Asia. in the present study, 10 major forest types across the forest region of NE China were sampled to Investigate forest distribution in relation to climate. Canonical correspondence analysis （CCA） revealed that growing season precipitation and energy availability were primary climatic factors for the overall forest pattern of NE China, accounting for 66% of the explanatory power of CCA. Conversely, annual precipitation and winter coldness had minor effects. Generalized additive models revealed that tree species responded to climatic gradients differently and showed three types of response curve： （i） monotonous decline; （ii） monotonous Increase; and （iii） a unimodai pattern. Furthermore, tree species showed remarkable differences in limiting climatic factors for their distribution. The power of climate in explaining species distribution declined significantly with decreasing species dominance, suggesting that the distribution of dominant species was primarily controlled by climate, whereas that of subordinate species was more affected by competition from other species.
This study measured stable carbon and nitro- gen isotope ratios in phytoplankton, zooplankton, five inver- tebrates species, eight fishes species and three seabirds spe- cies collected in Bohai Bay. δ 13C ranged from ?25.38‰ to ?11.08‰ showing a relative low enrichment in the food web from Bohai Bay. The mean δ 13C of mullet is higher than that of other organisms, and this might be due to that mullet is migration fish and feeds mainly on inshore sources. δ 15N ranged from 4.08‰ to 13.98‰, and showed a step-wise en- richment with trophic level of 3.8‰. The δ 15N enrichment factor was used to construct an isotopic food web model to establish trophic relationships within this marine food web. According to this model, exact trophic levels of all organisms were estimated as 1.46?2.10, 1.91?3.32, 2.55?4.23 and 2.98?4.28 for plankton, invertebrates, fishes, and seabirds.
Using China's ground observations,e.g.,forest inventory,grassland resource,agricultural statistics,climate,and satellite data,we estimate terrestrial vegetation carbon sinks for China's major biomes between 1981 and 2000.The main results are in the following:(1)Forest area and forest biomass car-bon(C)stock increased from 116.5×10^(6) ha and 4.3 Pg C(1 Pg C=10^(15) g C)in the early 1980s to 142.8×10^(6) ha and 5.9 Pg C in the early 2000s,respectively.Forest biomass carbon density increased form 36.9 Mg C/ha(1 Mg C=10^(6) g C)to 41.0 Mg C/ha,with an annual carbon sequestration rate of 0.075 Pg C/a.Grassland,shrub,and crop biomass sequestrate carbon at annual rates of 0.007 Pg C/a,0.014―0.024 Pg C/a,and 0.0125―0.0143 Pg C/a,respectively.(2)The total terrestrial vegetation C sink in China is in a range of 0.096―0.106 Pg C/a between 1981 and 2000,accounting for 14.6%―16.1%of carbon dioxide(CO_(2))emitted by China's industry in the same period.In addition,soil carbon sink is estimated at 0.04―0.07 Pg C/a.Accordingly,carbon sequestration by China's terrestrial ecosystems(vegetation and soil)offsets 20.8%―26.8%of its industrial CO_(2) emission for the study period.(3)Considerable uncertainties exist in the present study,especially in the estimation of soil carbon sinks,and need further intensive investigation in the future.
There is a general agreement that forest ecosystems in the NorthernHemisphere function as significant sinks for atmospheric CO_2; however, their magnitude anddistribution remain large uncertainties. In this paper, we report the carbon (C) stock and itschange of vegetation, forest floor detritus, and mineral soil, annual net biomass increment andlitterfall production, and respiration of vegetation and soils between 1992 to 1994, for threetemperate forest ecosystems, birch (Betula platyphylla) forest, oak (Ouercus liaotungensis) forestand pine (Pinus tabulaeformis) plantation in Mt. Dongling, Beijing, China. We then evaluate the Cbudgets of these forest ecosystems. Our results indicated that total C density (organic C perhectare) of these forests ranged from 250 to 300 t C ha^(-1), of which 35—54 t C ha^(-1) fromvegetation biomass C and 209-244 t C ha^(-1) from soil organic C (1 m depth, including forest floordetritus). Biomass C of all three forests showed a net increase, with 1.33—3.55 t C ha^(-1) a^(-1)during the study period. Litterfall production, vegetation autotrophic respiration, and soilheterotrophic respiration were estimated at 1.63—2.34,2.19—6.93, and 1.81 —3.49 t C ha^(-1)a^(-1), respectively. Ecosystem gross primary production fluctuated between 5.39 and 12.82 t Cha^(-1) a^(-1), about half of which (46%-59%, 3.20-5.89 t C ha^(-1) a^(-1)) was converted to netprimary production. Our results suggested that pine forest fixed C of 4.08 t ha^(-1) a^(-1), whereassecondary forests (birch and oak forest) were nearly in balance in CO_2 exchange between theatmosphere and ecosystems.
FANG JingYun LIU GuoHua ZHU Biao WANG XiaoKe LIU ShaoHui
