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231.
232.
Interannual variability in global CO2 increment (averaged from the Mauna Loa and South Pole Stations) shows certain strong spatial relationships to both tropical and temperate temperatures. There is a fairly strong positive year-round correlation between tropical mean annual temperatures (leading by 4 months) and annual CO2 throughout the time series since 1960, agreeing with the generally held view that the tropics play a major role in determining inter-annual variability in CO2 increment, with a major CO2 pulse following a warm year in the tropics. This ‘almost no lag’ climatic response is very strong during winter and relatively stable in time. However, the correlation with tropical temperature appears to have weakened in the first years of the 1990s in correspondence of the Pinatubo eruption and the positive phase of the AO/NAO. A secondary concurrent temperature signal is linked to summer variations of north temperate belt. Northern summer temperatures in the region 30–60 °N—and especially in the land area corresponding to the central east USA—have become relatively more closely correlated with CO2 increment. This trend has become increasingly stronger in recent years, suggesting an increasing role for growing season processes in the northern midlatitudes in affecting global CO2 increment. Once non-lagged annual tropical temperature variations are accounted for, terrestrial ecosystems, especially the temperate-boreal biomes, also show a coherent large scale lagged response. This involves an inverse response to annual temperature of preceding years centered at around 2 years before. This lagged response is most likely linked to internal biogeochemical cycles, in particular N cycling. During the study period north boreal ecosystems show a strengthening of the lagged correlation with temperature in recent years, while the lagged correlation with areas of tropical ecosystems has weakened. Residuals from a multiple correlations based on these climatic signals are directly correlated with SO, confirming an additional important role of upwelling in interannual variability of CO2 increment. Cooler summers following the Pinatubo eruption and the possible influence of the North Atlantic Oscillation (NAO/AO) are discussed as factors responsible for the shift in the relative importance of different regions over time during the series of data. 相似文献
233.
The overuse of rainforests in the last century and its consequences necessitate a rethinking of logging policies. To this end models have been developed to simulate rainforest dynamics and to allow optional management strategies to be evaluated. Parameterisation of presently existing models for a certain site needs a lot of work, thus the parameterisation effort is too high to apply the models to a wide range of rainforests. Hence, in this paper we introduce the simplified model FORREG using the knowledge we have gained from a more complex model, FORMIX3-Q. 相似文献
234.
Abstract: Numerous exotic earthworm species are colonizing northern hardwood forests of North America, where no native earthworms exist. Upon invasion, earthworms have been shown to alter the surface soil environment and plant populations and communities. We sought to identify land-use factors in the Ottawa National Forest (ONF), Michigan (U.S.A.), that contribute to earthworm invasion in forest dominated by sugar maple ( Acer saccharum Marsh.) so that the susceptibility to additional colonization could be evaluated. We sampled earthworm communities in Sylvania Wilderness Area, a unique old-growth hardwood forest, and nonwilderness sites influenced by recreational fishing, recent timber harvesting, or roads. All the nonwilderness sites contained one to five species of exotic earthworms. In contrast, only 50% of wilderness sites contained exotic earthworms, all of a single species. Nonwilderness sites also had thinner litter and duff layers, higher soil C and N content, and higher nitrogen mineralization potentials than Sylvania sites. Two central differences between Sylvania and nonwilderness sites were that all nonwilderness sites were in close contact with roads and had a history of timber harvest, whereas these factors were not present in Sylvania Wilderness Area. Using average rates of colonization, we constructed two geographic information system models to estimate the percentage of sugar maple on the ONF falling within a theoretical 100-year invasion distance of roads and of second-growth sugar maple as relative indices of susceptibility to invasion. Both models indicated high susceptibility to invasion, with 91.7% and 98.9% of sugar maple habitat falling within a theoretical 100-year invasion distance of roads or historical harvests, respectively. 相似文献
235.
236.
M. Matucha M. Gryndler S. T. Forczek H. Uhlířová K. Fuksová P. Schröder 《Environmental Chemistry Letters》2003,1(2):127-130
The fate of chloroacetic acids (CAA) in forest soils was studied using radio-indicator methods. We showed that chloroacetic acids are both microbially degraded and simultaneously formed by chloroperoxidase-mediated chlorination of acetic and humic acids. The degree of biodegradation of chloroacetic acids in soil depends on their concentration. Dichloroacetic acid (DCA) is degraded faster than trichloroacetic acid (TCA). Chlorination of acetic acid led to a fast formation of dichloroacetic acid, whereas chlorination of humic acids gave rise to trichloroacetic acid. Both processes lead to a steady state in soil, participate in the chlorine cycle and possibly also in decomposition of organic matter in forest ecosystems. 相似文献
237.
238.
新邵县工矿破坏土地的生态重建模式探索 总被引:1,自引:0,他引:1
对新邵县现有的因工程建设、矿产开发而形成的破坏土地进行调查、分类.根据不同的类型采取不同的工程、林学措施,试图重建以木本植物为主的生态群落结构. 相似文献
239.
中国森林资源的过去、现在与未来发展趋势 总被引:1,自引:0,他引:1
中国是少林国家。在20世纪70年代中期进行“四五”清查以前,中国只掌握一些局部性的调查数据。在1978—1981年间又进行了以省为总体的宏观抽样调查,即“五五”清查。两次清查结果很接近,但都表明中国森林太少,远低于世界平均水平和有代表性的国家。 古代中国的林区远比现在为大。森林面积则比现在大若干倍。中国缺林少材的现状是几千年来农业社会发展进程中火烧、滥伐、滥垦、滥牧的结果。其中,置森林于万劫不复的是滥垦和滥牧。这一过程至今尚未停止。 根据中国的自然条件和宜林地资源的状况,有条件大幅度扩大森林面积和增加森林蓄积量。经过努力,森林面积可达到2.53×108ha,蓄积量可达到210×108m3以上。都是现在的2倍多。但对保护生态环境和向国民经济提供木材和林产品来说,仍然不能完全满足需要。 相似文献
240.
论中—下扬子“一盖多底”格局与演化 总被引:1,自引:0,他引:1
本文是“长江中小下游及邻区构造地质图1/100万”(85-901-03)的研究成果。在区内划分出4种变质基底,结合深部资料确定4个构造—地层地体.讨论了各自组成、历史和相互拼接时代,强调了晚元古代普宁运动在地质发展中的重大意义。认为晋宁运动Ⅰ幕(1000-900Ma)是杨子区内各地体向崆岭—董岭古陆拼贴的增生期.扬子地块形成;晋宁运动Ⅱ幕(800-700Ma)是华北—扬子—华夏地块对接时代.形成古中国大陆。古生代以来为盖层发育阶段。提出中下扬子的“一盖多底”的地壳结构。纵览扬子地块地质发展和演化.可分为四个历史时期:基底发育与古中国大陆形成期;盖层发育与加里东运动;欧亚大陆形成与印支运动;陆缘—板内变形与燕山运动。 相似文献