Woodlands in England: an appreciation of Hilda Annie Wilcox

In 1933 two maps reconstructing the woodlands of England were published by Hilda A. Wilcox: one of these, woodland 'deduced from early literature', is re-assessed in this paper. The distribution it shows is compared with a recently constructed map of national woodland, created as part of an English Heritage project, and based on the analysis of the Domesday Book by Sir Clifford Darby and his co-workers, together with the results of investigations by numerous place-name scholars. In spite of differences in detail, the two maps are in remarkably close accord. This conclusion is used as the basis for a brief synoptic analysis of the distribution of cleared land and woodland in the centuries preceding 1086, and touching even the Roman period. The recent computer-based reconstruction, drawing upon published, sound and accepted sources, and supported by the earlier and wholly independent work by scholars such as Rackham and Thirsk, provides a national picture of fundamental importance to the historical geography of the English environment.     

知识图谱在构建东北土地环境研究知识谱系中的应用

我国东北地区的自然环境状况一直备受关注,其土地沙化、荒漠化、林地草地退化、森林退化、土地盐碱化等土地环境变化的原因及监测一直是科研的焦点.随着"美丽中国中脊带"的提出,位于该线东北段附近的土地环境相关的研究也不断开展.在涉及该区域土地状况的研究中,常用研究方法有实地考察以及基于遥感卫星影像来进行分析,而本文利用知识图谱...     

基于3S技术的中国东北地区林地时空动态特征及驱动力分析

利用3S技术和中国资源环境数据库中用LandSat TM(ETM)解译获取的东北地区1985,1995,2000年林地空间分布数据,建立林地时空演变模型,定量分析东北地区林地变化时空特征。结果表明:1985~2000年东北地区林地发生较大幅度变化,时空差异明显;1995~2000林地急剧减少趋势得到有效遏止,有林地面积出现一定程度增长,但林地变化的广度和强度仍然超过1985~1995年,突出表现在大兴安岭地区林地动态度增加。从空间格局上看,大小兴安岭、长白山山麓地带林地动态变化最强烈,主要表现为林地与耕地和草地相互转换。     

疏林草原榆树天然更新研究进展

疏林草原是由稀疏乔木以及灌木和草本植物组成的植被类型,其生态系统结构和功能有一定独特性。目前榆树疏林草原面积减少,榆树种群更新不良可能是重要原因。从种群特征、草树关系、微生境、人类活动等4个方面对榆树种群更新进行总结。主要结论是:随年龄增长,榆树种群表现为由集聚到随机的分布趋势;榆树与草本植物通过占据不同生态位实现共生;植被盖度与微生境、人类活动、围封对榆树更新影响很大。还未见报道的问题有:个体成对现象;种子入侵草地空斑;风蚀和沙埋过程对榆树更新的影响;榆树更新的最佳围封年限。最后,指出榆树疏林研究的未来两大方向是榆树疏林与全球环境变化,榆树疏林与沙地植被恢复。     

Patterns of Changes to Woody Vegetation near Resettlement Sites in Semi-arid Northwestern Ethiopia

Communal rangelands provide diverse ecosystem services to millions of pastoralists and agro-pastoralists. Resettling destitute communities into hitherto uninhabited communal rangelands and forests, a common practice throughout Sub-Saharan Africa, is a threat to the sustainable use of range and forest land resources. In order to understand the effect of resettlement on a semi-arid woodland in northwestern Ethiopia, satellite imagery of 23 resettlement villages taken over a period of fourteen years, and woody vegetation floristic data for three old resettlements, three new resettlements, two refugee camps and one protected area were analyzed using ANOVA and canonical correspondence analysis (CCA). The normalized differential vegetation index (NDVI) and canopy cover around all village types decreased with disturbance gradients, while the magnitude of change varied according to the type of settlement. Limited canopy cover was observed in refugee camps and new resettlements, compared to old resettlements and protected areas. Woody vegetation height class showed a J shaped distribution in all sites except refugee camps (RC), indicating a decline in vegetation. CCA showed that variables like site type, altitude and disturbance gradient significantly affected the diversity of woody species at the different sites. Comparison of individual species responses to disturbances indicated that low fodder value invaders like Dichrostachys cinerea, and many Acacia species were increasing in proportion and coverage at the expense of some multipurpose species including Tamarindus indica, Diospyros mespiliformis, and Pterocarpus lucens. In the absence of regulated vegetation use, resettlements result in a decline in overall vegetation cover and a shift in floristic diversity in favor of invasive species.     

基于多源遥感数据的林地信息提取

为准确、快速地进行林地信息提取,实现林地的信息化管理。本文以曹家务乡为例,利用高分一号、资源一号02c和资源三号卫星数据之间的互补性,结合光谱特征、物候特征和植被指数等因子,通过面向对象算法的多尺度分割和阈值分类、模糊分类以及最邻近分类法,对林地信息进行提取,实验结果表明:本文所提出的方法精度较高,能够满足实际生产需求。     

Riparian vegetation and island formation along the gravel‐bed Fiume Tagliamento,Italy

After more than 300 years of river management, scientific knowledge of European river systems has evolved with limited empirical knowledge of truly natural systems. In particular, little is known of the mechanisms supporting the evolution and maintenance of islands and secondary channels. The dynamic, gravel‐bed Fiume Tagliamento, Italy, provides an opportunity to acquire baseline data from a river where the level of direct engineering intervention along the main stem is remarkably small. Against a background of a strong alpine to mediterranean climatic and hydrological gradient, this paper explores relationships between topography, sediment and vegetation at eight sites along the active zone of the Tagliamento. A conceptual model of island development is proposed which integrates the interactions between large woody debris and vegetation, geomorphic features, sediment calibre and hydrological regime. Islands may develop on bare gravel sites or be dissected from the floodplain by channel avulsion. Depositional and erosional processes result in different island types and developmental stages. Differences in the apparent trajectories of island development are identified for each of the eight study sites along the river. The management implications of the model and associated observations of the role of riparian vegetation in island development are considered. In particular, the potential impacts of woody debris removal, riparian tree management, regulation of river flow and sediment regimes, and changes in riparian tree species' distribution are discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

An updated delineation of stand ages of deciduous rubber plantations during 1987-2018 using Landsat-derived bi-temporal thresholds method in an anti-chronological strategy

Timely and accurately monitoring stand ages of deciduous rubber plantations is of great importance for ecological studies and plantations management. The re-establishment of rubber plantations usually experiences a short period (several years) of land clearance and transplantation of rubber seedlings, along with a noticeable landscape change from well-grown forest to bare land and sparse vegetation in situ. With Landsat times series (LTS) data of four commonly-used vegetation indices (VIs), namely the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), Normalized Difference Moisture Index (NDMI), and Normalized Burn Ratio (NBR), and three non-visible spectral bands, i.e. the near-infrared (NIR) and shortwave-infrared (SWIR1/2), in this study, an approach by combining the inter-annual defoliating and foliating features of rubber trees and the intra-annual landscape changes of rubber plantations was presented to detect and map stand ages of deciduous rubber plantations in an anti-chronological manner across Xishuangbanna between 1987 and 2018, one of the most intensive regions of deciduous rubber plantations within the tropics. The approach highlighted the repeated distribution of newly-cleared and replanted plot (NCRP) of rubber seedlings due to rubber management. It applied the bi-temporal VIs thresholds of zero of NBR and NDMI during the defoliation to foliation phases to delineate the stand ages of deciduous rubber plantations at an interval of five years, by combining a Landsat-based rubber map in 2018 and 32-year NCRPs as well as quadri-classified age-groups and seven sub-categories (i.e. ≤5 as infantile rubber plantations (IRP), 6–10 as young rubber plantations (YRP), 11–15 and 16–20 as mature rubber plantations (MRP), 21–25, 26–30, and ≥31 years as old rubber plantations (ORP)). The results showed that the areas of IRP, YRP, MRP, and ORP were 19.1 km², 817.1 km², 1681.7 km², and 573.7 km² in 2018, respectively. Spatially, the YRP are mainly around the outskirts of two county-level administrative centers (Jinghong and Mengla), while ORP primarily distributed along main roads. Nearly 53.9% of ORP, 51.8% of IRP, 47.3% of MRP and 46.3% of YRP were in Jinghong City, and Mengla County had 50.5% of YRP, 48.8% of MRP, 42.4% of IRP and 36.3% of ORP. This study demonstrates that the bi-temporal VIs thresholds method (i.e. NBR_defoliation <0, NDMI_defoliation <0, NBR_foliation <0, and NDMI_foliation <0) have great potential for detecting stand ages of deciduous rubber plantations.     

基于Google Earth和MODIS陆地数据的农林地转换对地表温度的影响——以长江中下游及毗邻地区为例

揭示耕地与林地转换对地表温度的影响对于认识人类活动的气候与环境效应具有重要意义。基于卫星遥感数据的统计分析是揭示土地利用/覆盖变化对地表温度影响的重要手段。但是,在景观破碎度较高地区,混合像元问题成为使用这一技术手段的主要限制性因素,中国南方长江流域尤为典型。为突破这一限制,论文基于Google Earth高清影像,在1 km尺度上辨识了200对耕地与林地纯像元,进而利用MODIS陆地数据产品,对比分析了耕地与林地的地表温度(LST)、叶面积指数(LAI)、地表反照率(Albedo)之差。结果表明：耕地的LST高于林地,白天和夜间温度分别约偏高2.75 ℃和1.15 ℃,并且温差因季节而异,白昼温差呈双峰(分别是5月和10月,温差约3.18 ℃和3.33 ℃),夜间温差为单峰(7月,约2.46 ℃)。同时,温差因地而异,总体表现为西高东低,陕甘交界处的白昼温差最大,年平均约为3.83 ℃;安徽中南部温差最小,约为1.1 ℃。耕地与林地的LST之差主要由蒸散发的差异所致。林地的LAI较大,蒸散发较强,地表向大气的潜热通量较大,用于直接加热地表的感热相对偏少,因而LST相对偏低。上述结果表明近年来长江流域及毗邻地区的耕地转为林地通过增加蒸发产生了一定的致冷效应。