The location and mechanisms responsible for the carbon sink in northern mid-latitude lands are uncertain. Here, we used an improved estimation method of forest biomass and a 50-year national forest resource inventory in China to estimate changes in the storage of living biomass between 1949 and 1998. Our results suggest that Chinese forests released about 0.68 petagram of carbon between 1949 and 1980, for an annual emission rate of 0.022 petagram of carbon. Carbon storage increased significantly after the late 1970s from 4.38 to 4.75 petagram of carbon by 1998, for a mean accumulation rate of 0.021 petagram of carbon per year, mainly due to forest expansion and regrowth. Since the mid-1970s, planted forests (afforestation and reforestation) have sequestered 0.45 petagram of carbon, and their average carbon density increased from 15.3 to 31.1 megagrams per hectare, while natural forests have lost an additional 0.14 petagram of carbon, suggesting that carbon sequestration through forest management practices addressed in the Kyoto Protocol could help offset industrial carbon dioxide emissions.

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Urbanization, a dominant global demographic trend, leads to various changes in environments (e.g., atmospheric CO 2 increase, urban heat island). Cities experience global change decades ahead of other systems so that they are natural laboratories for studying responses of other nonurban biological ecosystems to future global change. However, the impacts of urbanization on vegetation growth are not well understood. Here, we developed a general conceptual framework for quantifying the impacts of urbanization on vegetation growth and applied it in 32 Chinese cities. Results indicated that vegetation growth, as surrogated by satellite-observed vegetation index, decreased along urban intensity across all cities. At the same time, vegetation growth was enhanced at 85% of the places along the intensity gradient, and the relative enhancement increased with urban intensity. This growth enhancement offset about 40% of direct loss of vegetation productivity caused by replacing productive vegetated surfaces with nonproductive impervious surfaces. In light of current and previous field studies, we conclude that vegetation growth enhancement is prevalent in urban settings. Urban environments do provide ideal natural laboratories to observe biological responses to environmental changes that are difficult to mimic in manipulative experiments. However, one should be careful in extrapolating the finding to nonurban environments because urban vegetation is usually intensively managed, and attribution of the responses to diverse driving forces will be challenging but must be pursued.rbanization, one of the most dramatic forms of land conversion, leads to various changes in atmospheric and climatic conditions (e.g., atmospheric CO 2 increase, urban heat island), vegetation community structure, species abundance and diversity, and biogeochemical cycles (1-4). Cities experiencing elevated temperature (i.e., urban "heat island" warming), CO 2 , and nitrogen deposition decades ahead of the projected average global change are regarded as the "harbingers" of the future global change (5, 6). It is for this reason that cities have been regarded as ideal natural laboratories for global change studies and particularly valuable to elucidate the potential responses of other nonurban ecosystems to future climate and environmental changes (2, 6, 7).It has long and widely been believed, particularly in the horticultural and landscaping communities, that trees grow slower in cities than in rural settings because of the heightened environmental stresses experienced by urban trees (e.g., higher temperature, lower air humidity, lower soil moisture content) (e.g., 8, 9). Field observations seem to challenge this belief. For example, Gregg et al. (10), using manipulative paired experiments, found that tree seedlings in New York City grew twofold faster than their rural counterparts. Recently, Briber et al. (11) found that the growth rates of trees in remnant forests were mostly accelerated after urbanization in Boston. Imhoff et al. (12) compared the v...

Since China's economic reform in the late 1970s, Shanghai, the country's largest and most modern city, has experienced rapid expansion and urbanization. Here, we explore its land‐use and land‐cover changes, focusing on the impacts of the urbanization process on air and water quality, local climate, and biodiversity. Over the past 30 years, Shanghai's urban area and green land (eg urban parks, street trees, lawns) have increased dramatically, at the expense of cropland. Concentrations of major air pollutants (eg SO2, NOx, and total suspended particles) were higher in urban areas than in suburban and rural areas. Overall, however, concentrations have decreased (with the exception of NOx), due primarily to a decline in coal consumption by industry and in private households. Increased NOx pollution was mainly attributed to the huge increase in the number of vehicles on the roads. Water quality changes showed a pattern similar to that of air quality, with the most severe pollution occurring in urban areas. Differences in mean air temperatures between urban and rural areas also increased, in line with the rapid pace of urban expansion, indicating an accelerating “urban heat island” effect. Urban expansion also led to a decrease in native plant species. Despite its severe environmental problems, Shanghai has also seen major economic development. Managing the tradeoffs between urbanization and environmental protection will be a major challenge for Chinese policy makers.

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