Understanding farmland abandonment in the Polish Carpathians     

《Applied geography (Sevenoaks, England)》2017

For more than 100 years, forest cover in Europe has increased substantially due to afforestation and natural forest expansion. The latter, resulting typically from farmland abandonment and subsequent secondary forest succession, has played a major role in marginal mountain areas and possesses various highly important environmental and economic consequences. In the Polish Carpathians, farmland abandonment is a spatially dispersed, locally specific process because of small farm and land parcel sizes, and its extent in the entire region is not well known. This study aims therefore to map current farmland abandonment in the Polish Carpathians and to identify its spatial determinants. To map farmland abandonment we detected secondary forest succession on abandoned fields using Airborne Laser Scanning (ALS) point clouds and topographic data in 230 sample areas (tiles) distributed throughout the Carpathian communes. To reveal the spatial determinants of current farmland abandonment, we investigated variables describing the accessibility and environmental, land cover, and socioeconomic conditions of communes, using best subset regression modelling. The results showed that 13.9% of agricultural land was abandoned and underwent secondary forest succession in recent decades. Topography (mainly slope gradients) and employment outside of agriculture were the two most important spatial determinants of farmland abandonment. Consequently, a substantial forest expansion may be observed in the coming decades throughout the Polish Carpathians if no counteractions are taken.  相似文献   

天然林资源保护一期工程生态成效评估——以甘肃小陇山地区为例   总被引：1，自引：0，他引：1  

孙传谆  甄霖  王超  胡洁  杜秉贞 《地理科学进展》2017,36(6):732-740

天然林资源保护工程是在中国广泛开展的一项重要生态建设工程。本文在构建生态多元评估指标体系的基础上,评估工程实施的生态成效,对于其进一步决策与管理具有重要的科学意义。通过遥感、生态系统质量等多源数据融合,采用生态系统宏观格局、生态系统质量、生态系统服务等方面指标的现状和时空变化特征,评估小陇山地区天然林保护一期工程(2000-2010年)实施成效。结果表明：①工程实施后,小陇山地区落叶阔叶林、落叶阔叶灌木林、草地等生态系统类型的面积大幅度增加,生态系统宏观状况转好,其中黄河流域生态系统宏观状况转好趋势明显好于长江流域。②研究区叶面积指数(LAI)和最大植被覆盖度(FC)在2000-2010年期间的多年变化斜率分别为0.022和0.510,生态系统质量上升趋势明显。其中黄河流域改善程度高于长江流域。③2010年研究区固碳量为700.20 t/hm²,相比工程初期的2000年增加了4.69%;工程实施之后的10年间,研究区水源涵养量呈增长趋势,土壤保持量亦呈增长趋势;就流域而言,黄河流域的生态系统服务的提升程度均更为明显。  相似文献   

Microcoring and dendrometer-detected intra-annual wood formation of Populus euphratica in the Ejina Oasis,northwestern China     

XiaoMei Peng  ShengChun Xiao  GuoDong Cheng  QuanYan Tian  HongLang Xiao 《寒旱区科学》2017,9(1):54-66

Seasonal stem radial growth and wood formation of trees have become research hotspots because of their significance for dendroclimatological and dendroecological studies. However, until recently, these studies concentrated on coniferous tree species in high-altitude and high-latitude regions, while detailed information on arid-zone riparian forests is scarce. The main focus of this study is to monitor the intra-annual dynamics of radial growth and tree ring formation in a deciduous species, Populus euphratica. In 2013, we combined the dendrometer and microcoring methods to study this species in the riparian forest of the Ejina Oasis, in arid northwestern China. Vessel enlargement began in early May, and the maximum rate of cell production occurred in early June. The cell division then ceased from early to mid-July. The dendrometer method failed to reliably detect the date of growth initiation and cessation, but succeeded to detect the time of maximum growth rate just like the microcoring method did. We found that weekly stem radial increment data described xylem growth more accurately than daily datasets. Based on correlation analysis among climatic and hydrologic variables, and weekly stem radial increment, weekly ring width increase dataset, the depth to groundwater was the main factor that limited tree ring growth. From a practical perspective, such studies of intra-annual wood formation can provide empirical guidance for seasonal water allocations within a river basin.  相似文献   

Mapping fine-scale population distributions at the building level by integrating multisource geospatial big data     

Yao Yao  Xia Li  Jinbao Zhang  Zhaotang Liang  Ke Mai 《International journal of geographical information science》2017,31(6):1220-1244

Fine-scale population distribution data at the building level play an essential role in numerous fields, for example urban planning and disaster prevention. The rapid technological development of remote sensing (RS) and geographical information system (GIS) in recent decades has benefited numerous population distribution mapping studies. However, most of these studies focused on global population and environmental changes; few considered fine-scale population mapping at the local scale, largely because of a lack of reliable data and models. As geospatial big data booms, Internet-collected volunteered geographic information (VGI) can now be used to solve this problem. This article establishes a novel framework to map urban population distributions at the building scale by integrating multisource geospatial big data, which is essential for the fine-scale mapping of population distributions. First, Baidu points-of-interest (POIs) and real-time Tencent user densities (RTUD) are analyzed by using a random forest algorithm to down-scale the street-level population distribution to the grid level. Then, we design an effective iterative building-population gravity model to map population distributions at the building level. Meanwhile, we introduce a densely inhabited index (DII), generated by the proposed gravity model, which can be used to estimate the degree of residential crowding. According to a comparison with official community-level census data and the results of previous population mapping methods, our method exhibits the best accuracy (Pearson R = .8615, RMSE = 663.3250, p < .0001). The produced fine-scale population map can offer a more thorough understanding of inner city population distributions, which can thus help policy makers optimize the allocation of resources.  相似文献   

On the profiles of wind velocity in the roughness sublayer above a coniferous forest     

A. Wenzel  N. Kalthoff  V. Horlacher 《Boundary-Layer Meteorology》1997,84(2):219-230

Wind velocity and temperature measurements from a 200 m tower, locatedin a forest near Karlsruhe were used to investigatethe modified profile function of the wind velocity in theroughness sublayer.To avoid determination of the friction velocity we introduced analternative analysis with the expression instead of From the observed Fm* profiles we evaluated the profile function m*. The wind profiles observed under neutral conditions were well representedby a modified non-dimensional profile function with physically based boundary values at the top and at the bottom of theroughness sublayer.The results of our analysis can be used to take into consideration themomentum exchange between the atmosphere and a forest in mesoscaleatmospheric models in a refined way.  相似文献   

Early Eocene sea floor spreading and continent-ocean boundary between Jan Mayen and Senja fracture zones in the Norwegian-Greenland Sea     

Tsikalas  Filippos  Eldholm  Olav  Faleide  Jan Inge 《Marine Geophysical Researches》2002,23(3):247-270

Sea floor spreading anomalies in the Lofoten-Greenland basins reveal an unstable plate boundary characterized by several small-offset transforms for a period of 4 m.y. after opening. North of the Jan Mayen Fracture Zone, integrated analysis of magnetic and seismic data also document a distinct, persistent magnetic anomaly associated with the continent-ocean boundary and a locally, robust anomaly along the inner boundary of the break-up lavas. These results provide improved constraints on early opening plate reconstructions, which include a new anomaly 23-to-opening pole of rotation yielding more northerly relative motion vectors than previously recognized; and a solution of the enigmatic, azimuthal difference between the conjugate Eocene parts of the Greenland-Senja Fracture Zone if the Greenland Ridge is considered a continental sliver. The results confirm high, 2.36–2.40 cm yr^–1, early opening spreading rates, and are consistent with the start of sea floor spreading during Chron 24r. The potential field data along the landward prolongations of the Bivrost Fracture Zone suggest that its location is determined by a Mesozoic transfer system which has acted as a first-order, across-margin tectono-magmatic boundary between the regional Jan Mayen and Greenland-Senja Fracture Zone systems, greatly influencing the pre-, syn- and post-breakup margin development.  相似文献   

南海北部地壳的深地震地质结构探测   总被引：13，自引：1，他引：13  

阎贫  刘昭蜀 《海洋地质与第四纪地质》1997,17(2):21-27

１９９３年５月，中国科学院南海海洋研究与日本东京大学地震研究所等单位合作南海北部共同开展了综合地球物理测量实验，本文介绍了其中的海底地震仪海上资料采用，室内资料处理，根据资料的初步处理解释结果，文中分析了测区的地壳地质结构。  相似文献   

东海海底末次冰期埋藏风尘黄土地层初步研究   总被引：7，自引：3，他引：7  

郑祥民  郑玉龙 《海洋地质与第四纪地质》1993,13(3):49-56

大量海底调查及钻孔岩芯资料揭示,东海海底全新世疏松沉积物之下,往往埋藏着一层厚度不大的黄褐色、暗绿色硬质粘土层。类似的硬土层在长江三角洲东部平原地层中普遍存在。作者曾对苏北、苏南平原地层中该硬土层与下蜀黄土地层进行对比研究工作,并在野外地层剖面上发现两者为连续延伸地层,认为该硬土层为末次冰期风尘黄土沉积物经埋藏后的次生成土作用演变而成。 本文通过对东海海底硬土层岩芯地层综合分析研究,以及与长江三角洲东部平原区硬土层和下蜀黄土地层沉积物特征对比,认为东海海底硬土层为末次冰期低海面期间,干、冷气候条件下的风尘黄土堆积物,后经埋藏后的次生变化而形成。而在绝大部分海底,由于受到全新世海进作用的强烈冲蚀而缺失,只在局部地区仍有保留。  相似文献   

基于土壤水分和气象要素的林火预报研究——以广东省为例     

蔡霁初  邱建秀  王大刚  林凯荣  阳坤  曾庆峰 《地理科学》2021,41(9):1676-1686

基于国内现行的森林火险气象指数和单因子火险贡献度模型,以及逻辑回归模型和随机森林模型,在林火预报中引入微波遥感土壤水分信息,使用MCD14DL火点数据集和地面气象观测资料对广东省不同时间尺度的林火发生概率进行预测。结果表明：逻辑回归模型和随机森林模型构建的林火预测模型显著优于现行的森林火险气象指数和单因子火险贡献度模型,预测精度提升约20%。其中,随机森林模型对林火频数的解释程度最高（两者相关系数为0.476）。此外,加入微波土壤水分信息后,相较原有的基于气象要素的林火预测模型,2种机器学习模型的预测精度均略有提升,体现了表层土壤水分信息在林火预报中的重要性。研究可为高效提取对地观测信息,以改进华南地区不同时间尺度的林火预报工作提供参考。  相似文献   

树轮稳定氮同位素记录的进展与展望     

王可逸  刘晓宏  曾小敏  徐国保  张凌楠  李春越 《地理学报》2021,76(5):1193-1205

树轮稳定同位素比率是研究气候变化与环境演变的有效代用资料,耦合分析树轮稳定同位素记录的信息可揭示森林生态系统碳—水—氮时空变化特征及相互作用,反映环境变化对植物特定化合物的生理影响。树轮稳定氮同位素比率（δ¹⁵N）与树木生长的环境条件密切相关,其变化可以反映长时间尺度森林生态系统氮循环的动态特征,弥补监测资料的不足。本文综述了树轮稳定氮同位素的分馏机理与测定方法,解析了树轮δ¹⁵N在样品预处理和测试中需要关注的问题,系统梳理与归纳了基于树轮δ¹⁵N进行气候变化、环境演变和人类活动氮排放研究的进展。指明中国树轮稳定氮同位素研究潜力及其在未来亟需着重发展的方向,旨在推动森林生态系统氮循环时空特征深入研究。  相似文献