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101.
China's Loess Plateau was formed under special conditions. The tectonic movement, topographical characteristics, and monsoon patterns combined to create a favourable environment for the accumulation of thick loessic deposits. The Loess Plateau itself is part of the ‘Monsoon Triangle’ of China, a region very susceptible to climatic changes. Throughout the Upper Pleistocene the palaeoenvironment on the Loess Plateau alternated from steppe, to deciduous forest and coniferous forest, in response to shifts in the atmospheric circulation. Three monsoon patterns appear to be indicated: (1) a full glacial monsoon pattern (18000–15000 yr BP) which induced a cold and dry climate favouring loess accumulation in steppe conditions; (2) an interglacial monsoon pattern (last interglacial and Holocene) in which a warm humid climate prevailed with deciduous forests, leaving palaeosols interbedded within the loess sequence; and (3) a transitional or interstadial monsoon pattern (50 000–23 000 yr BP) in which the climate was cold and humid in the Loess Plateau, encouraging the development of coniferous forest. 相似文献
102.
气候变化对我国红松林的影响 总被引:8,自引:0,他引:8
在对红松适生范围、生态习性等广泛深入调查分析基础上,依据环境因子对树木生长影响的作用规律,首先推出一个能反映红松年生长量与水热因子间关系的W-T模式,进而分析了各种可能的气候变化对红松生长量与分布的影响。结果表明,气温升高,无论降水增减,都将使红松适生范围与生长量大幅度减少。但在可预见的气候变化范围内,红松不会退出我国的东部山地。 相似文献
103.
104.
川江流域防护林区森林地面积仅占全区林地面积的44%,而疏林地、灌木林地、未成林造林地、宜林地等尚需抚育或营造的林地占56%,其中宜林地尚有20%。在分析区内林地利用现状的同时,指出了各类林地的主要土壤类型、主要问题及造林或抚育的难易。着重从森林营造和管理角度,提出了相应的保护林地措施。 相似文献
105.
Jean Servant Georges Kouadio Bernard Cros Robert Delmas 《Journal of Atmospheric Chemistry》1991,12(4):367-380
In the tropical rain forests of the Congo during the dry season, from June to September 1987, carboxylic acid partial pressures (P
gas) in the air above the canopy, at ground level, and at the boundary layer, were estimated from water samples such as fog and rainwater. The concentrations of these acids were also measured in the sap of tree leaves. Tree leaves act as a sink or as a source if the acid P
gas is greater of lower than the acid concentrations in molecular form in sap. For each of these soluble gases, there is a value of P
gas where the exchange is nul. This is called the compensation point. Values of the compensation point for some tree leaves were evaluated according to Henry's law. Henry's law coefficients at ppm levels were redetermined for formic (HCOOH), acetic (CH3COOH), propionic (CH3CH2COOH), and isobutyric (CH3CH(CH3)COOH) acids.By comparison of P
gas and compensation points, it is concluded that the forest was a potential source for these acids. The soil-or the litter-acts as a significant source of a carboxylic acid of C3 or C4 atoms in the aliphatic chain. This carboxylic acid, not yet fully characterized, could play an important role in the rain acidity in forested zones of the equatorial areas.The direct emission of these carboxylic acids by vegetation was the main source in the boundary layer above the forest. The average emissions were 3.1×109, 7.8×109, and 8.4×109 molecules cm-2 s-1 for HCOOH, CH3COOH, and CH3CH2COOH, respectively. The savanna is an exogenous source of HCOOH and CH3CH2COOH during moderately rainy days for 30% of the time. The ozonolysis of isoprene seems to be a small source of HCOOH. 相似文献
106.
107.
S. Pahl P. Winkler T. Schneider B. Arends D. Schell R. Maser W. Wobrock 《Journal of Atmospheric Chemistry》1994,19(1-2):231-252
A resistance model to calculate the deposition of cloud droplets on a coniferous forest and some improved parameterizations of the indispensable input parameters are described. The deposition model is adapted to the coniferous forest at the Kleiner Feldberg site and verified by the data of a drip water monitoring station below the forest canopy. The measurements of liqud water content, wind speed and trace substance compounds in cloud water of the Ground-based Cloud Experiment (GCE) at Kleiner Feldberg in 1990 are used to calculate the cloud water deposition fluxes and the deposition of trace substances via cloud water interception. The calculated deposition of trace substances via cloud water interceptions is three to six times higher than via rain during the experiment. On a long term data basis the yearly amount of cloud water deposition is 180 mm year–1 at Kleiner Feldberg site (840 m a.s.l.) while the precipitation amount is 1030 mm year–1. Due to higher trace substance concentrations in cloud water compared to rain the ionic deposition via cloud water interception and via precipitation were assessed to be of comparable magnitude. 相似文献
108.
Tree stem (>2 m tall) mortality was assessed following a late dry‐season wildfire across a seasonally flooded elevation gradient at Workshop Jungle, near Darwin, in the Northern Territory of Australia. For all species combined, dead stems had significantly smaller diameter at breast height (dbh) than living stems. Assessment of tree‐stem damage following a tropical cyclone at Cobourg Peninsula, NT, revealed that damaged stems had significantly greater dbh than undamaged stems for all tree species sampled across a boundary between monsoon rainforest and savanna. A greater proportion of stems were damaged by the cyclone than by the fire (28 per cent as against 18 per cent), although there were considerable between‐community differences in the proportion of damaged stems at the two sites. The fire caused little impact (<10 per cent) on total basal area of three different forest communities on the elevation gradient at Workshop Jungle. The cyclone was found to cause >50 per cent damage to total basal area of three different communities on Cobourg Peninsula. It is suggested that the combination of a cyclone followed by an intense fire in storm debris could potentially destroy a monsoon rainforest through its impact on all tree‐size classes. This may explain why some monsoon rainforests rapidly contracted following Cyclone Tracy that destroyed the city of Darwin on Christmas Day, 1974. 相似文献
109.
Jean Servant Robert Delmas Jacques Rancher Marcel Rodriguez 《Journal of Atmospheric Chemistry》1984,1(4):391-401
A partial balance of mineral N is given for the basins of two coastal rivers in a forest zone in the Ivory Coast. The dry and wet depositions on the basin surfaces is given for particulate matter (NO3
–, NH4
+). The quantity of mineral N washed away in the rivers is evaluated. The losses from leaching of the soils by rainwater are about 0.33 to 1.0% of the atmospheric depositions for NH4
+–N and 2.2 to 5.8% for NO3
––N. The yearly atmospheric input of N compounds to the ecosystem, about 1.4 g N m–2 y–1, is at least 14% of mineral N formed in the soils and is therefore quite significant. 相似文献
110.
甘肃西部地区高放废物处置库场址预选调查 总被引:1,自引:0,他引:1
本文根据高放废物处置库场址选择的基本要求,对区域地质及深部构造特征、新构造运动及地震分布规律进行了调查,确定北山南带地区为稳定区。在稳定区内根据处置库有利围岩的出露情况,结合岩体工程地质特征分析,初步选出了4个以花岗岩为主体的场址预选区。经综合分析,认为在4个场址预选区中,以I号预选区的条件最优,其次是Ⅱ号预选区,再次是Ⅲ号和Ⅳ号预选区。场址区的最后确定尚待进一步调查和论证。 相似文献