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891.
Population growth and loss of arable land 总被引:1,自引:0,他引:1
Bo R. Ds 《Global Environmental Change》2002,12(4)
I discuss the loss of cropland in developing countries in connection with the ongoing land conversion caused by the growing population and socio-economic development, resulting in an increased demand for housing, industry, infrastructure, etc.Based on assumptions about the required space per capita for other purposes than agriculture, the portion of this area that is removed from presently used cropland, and the quality of the available land reserves, the required demand for land reserves has been calculated.The main conclusions are that during the next three decades (i) the loss of cropland is likely to be within the range 30–60 Mha, (ii) the reserve land utilized will be about 100–200 Mha, and (iii) the reserve land still in use after 30 years, about 50–100 Mha. 相似文献
892.
近50年河南降水变化对水资源的影响 总被引:4,自引:0,他引:4
利用河南32个代表站1951~2002年降水量资料,分析了20世纪50年代以来全省年降水资源和水资源的变化趋势以及对旱涝灾害的影响。结果表明,自20世纪80年代中期以来,河南已进入一个降水量偏少时期,干旱化程度加重,水资源短缺已成为影响工农业生产和国民经济发展的主要因素。 相似文献
893.
894.
895.
城市土地利用对植被特征影响的研究 总被引:17,自引:0,他引:17
城市土地利用对植被的影响是城市生态学中研究的重要问题。简单综述了国内外在该领域中的研究现状。通过在北京市进行的研究,对城市植被的特点及其与土地利用的关系进行了分析,结论为:①藜科(Chenpodiac eae)和蓼科(Polygonac eae)植物种类数量相对增加,归化植物占的比例大是城市植物区系的特征;②与非城市区域相比,生活型谱中一二年生植物比例增高,属的区系地理成分构成中世界分布属所占比例也明显提高;③城市土地利用类型对生境和植物群落特征的影响明显;④生境多样化对维持城市植物物种多样性而言,比面积大小具有更为显著的作用。 相似文献
896.
897.
The scientific evaluation of tourism resources is not only an important prerequisite for the development of agri-cultural heritage tourism (AHT), but it can also promote the conservation and management of Important Agricultural Heritage Systems (IAHS). With the goal of providing scientific support for the sustainable management of tourism resources, this review systematically analyzes the overall situation, research regions, developmental timeline trends, key fields and hot topics of resource evaluation research related to AHT over 2005-2020. With a comprehensive perspective that incorporates both traditional literature review and quantitative literature review, the study revealed four important aspects of AHT research. (1) Relevant articles could be divided into two phases, a development-oriented period (2005-2012) and a conservation-oriented period (2013-2020). (2) GIAHS accounts for the absolute majority (about 66.7%) of relevant studies. In particular, Longji Terraces System, Hani terraces system and Dong’s Rice-Fish-Duck System were the research hotspots IAHS, and Yunnan, Zhejiang and Guangxi were the research hotspot provinces. (3) Terraced landscapes and tea culture were the most popular themes in tourism resource evaluation, while sports tourism, tea culture tourism and study tours are becoming the new trends in IAHS sites. (4) Research methods have undergone a shift from qualitative to quantitative approaches, and a combination of these two in an interdisciplinary manner is becoming a new research trend. By reviewing and prospecting the relevant literature, this study not only makes a unique contribution to the tourism resource evaluation of IAHS, but also helps to enrich the relevant evaluation theories and further promote the sustainable development of heritage tourism from theoretical and methodological perspectives. 相似文献
898.
Multistage deformation events have occurred in the northeastern Jiangshao Fault (Suture) Belt. The earliest two are ductile deformation events. The first is the ca. 820 Ma top-to-the-northwest ductile thrusting, which directly resulted from the collision between the Cathaysia Old Land and the Chencai Arc (?) during the Late Neoproterozoic, and the Jiangnan Orogenic Belt that formed as the ocean closed between the Yangtze Plate and the jointed Cathaysia Old Land and the Chencai Arc due to continuous compression. The second is the ductile left-lateral strike-slipping that occurred in the latest Early Paleozoic. Since the Jinning period, all deformation events represent the reactivation or inversion of intraplate structures due to the collisions between the North China and Yangtze plates during the Triassic and between the Philippine Sea and Eurasian plates during the Cenozoic. In the Triassic, brittle right-lateral strike-slipping and subsequent top-to-the south thrusting occurred along the whole northeastern Jiangshao Fault Zone because of the collision between the North China and Yangtze plates. In the Late Mesozoic, regional extension took place across southeastern China. In the Cenozoic, the collision between the Philippine Sea and Eurasian plates resulted in brittle thrusts along the whole Jiangnan Old land in the Miocene. The Jiangshao Fault Belt is a weak zone in the crust with long history, and its reactivation is one of important characteristics of the deformation in South China; however, late-stage deformation events did not occur beyond the Jiangnan Old Land and most of them are parallel to the strike of the Old Land, which is similar to the Cenozoic deformation in Central Asia. In addition, the Jiangnan old Land is not a collisional boundary between the Yangtze Plate and Cathaysia Old Land in the Triassic. 相似文献
899.
基于Laio土壤水分动态随机模型(Laio模型),利用2006-2010年5~9月土壤水分连续监测数据及日降水资料,分析科尔沁沙地固定沙丘和沙质草地生长季根系层土壤水分动态及其与降水格局的关系,研究点尺度土壤水分概率密度函数,并对Laio模型涉及的13个参数进行了敏感性分析。结果表明:① 研究区年降水的季节分配极不均匀,主要集中在4~10月的生长季,占全年降水量的93%;0~5 mm降水事件占全年降水事件的73%,但其降水量只占全年降水量的25%;降水间隔期以0~10 d为主,占全年无降水期的38%,其频数最高,占全年间隔期频数的87%。② 固定沙丘和沙质草地根系层厚度分别为0~100 cm和0~70 cm,沙质草地根系层土壤水分显著高于固定沙丘;两类沙地7月份的土壤水分都显著高于生长季其他月份。③ 两类沙地生长季根系层土壤水分均服从正态分布;通过Laio模型得到了两类沙地生长季根系层土壤水分概率密度函数p(s),其峰值及峰值出现的位置和峰的阔度均与观测结果很接近,说明Laio模型能对科尔沁沙地土壤水分概率密度函数进行较好的模拟。④ Laio模型涉及的13个参数中,对p(s)最为敏感的参数是降水频率λ、平均降水量α、最大蒸散量Emax、水分胁迫点s*和凋萎系数sw,主要影响p(s)曲线的峰值。 相似文献
900.
着重阐述了近10年来,为推动陆地表层研究深入发展,国家自然科学基金在重点发展领域、重大研究计划、重大项目、申请代码及学科分类体系细化等层面对资助方向的引导作用。 相似文献