Soil–vegetation interaction on slopes with bush encroachment in the central Alps – adapting slope stability measurements to shifting process domains

In the European Alps many high mountain grasslands which were traditionally used for summer pasturing and haying have been abandoned during recent decades. Abandonment of mown or grazed grasslands causes a shift in vegetation composition and thus a change in landscape ecology and geomorphology. Alpine areas are very fragile ecosystems and are highly sensitive to changing environmental conditions, which can affect the geomorphic regime of these high energy environments. The effect of land use intensification on erosion rates is well documented, whereas the effect of land abandonment on erosion rates is still discussed controversially, particularly in relation to its short‐term and long‐term consequences. Generally, an established perennial vegetation cover improves the mechanical anchoring of the soil and the regulation of the soil water budget, including run‐off generation and erosion. However, changing vegetation composition affects many other above‐ and below‐ground properties like root density, diversity and geometry, soil structure, pore volume and acidity. Each combination of these properties can lead to a distinct scenario of dominating surface processes. The study of soil properties along a chronosequence of green alder (alnus viridis) encroachment on the Unteralptal in central Switzerland revealed that shrub encroachment changes soil and vegetation properties towards an increase of resistance to run‐off related erosion processes, but a decrease of slope stability against shallow landslides. Copyright © 2014 John Wiley & Sons, Ltd.     

Effectiveness of farmland transfer in alleviating farmland abandonment in mountain regions

Farmland abandonment is a type of land use change in the mountain region, and this change is under rapid development. Whether farmland transfer can prevent this process and promote the effective allocation of land resources or not is a question worth studying and discussion. With the help of the previous research findings, the objective of this paper was to find out the role of farmland transfer on preventing farmland abandonment, by using the methods of multiple view with two factors, and single factor correlation analysis. The results showed that: (1) At village level, a significant negative correlation between farmland transfer and farmland abandonment existed in the study site, with R² = 0.7584. This correlation of farmland with high grade farming conditions presented more outstandingly. The fitted curve for the farmland at Level I had the largest R² at 0.288, while that for the farmland at Level IV had the smallest R² at 0.103. Which indicated that farmland transfer could prevent the abandonment of farmland with high grade farming conditions? (2) At plot level, the abandonment rate of farmland with high grade farming conditions was significantly lower than that of farmland with poor grade farming conditions. It was the lowest at 10.49% for the farmland with Level I farming conditions, whereas the farmland with Level I farming conditions was 26.21%. Abandoned farmland was mainly contributed by farmland with Level IV farming conditions in the study site. (3) At village level, the role of farming conditions on farmland abandonment was insignificant. The univariate correlation analysis revealed that the abandonment ratio was negatively correlated with the proportions of farmland at Levels I and II and their accumulated proportion; however, their R² were small at 0.194, 0.258, and 0.275, respectively. The abandonment of farmland with high farming conditions still existed. The abandonment ratios of farmland at Levels I and II were high at 9.96% and 10.60%, respectively. This presented that farmland transfer on behalf of the land rental market was still not developed. (4) However, the village possessed the high rate of farmland transfer, and its rate of farmland abandonment with high grade farming conditions was all lower. When the transfer ratios of farmland were over 20%, the abandonment ratios of farmland at Levels I and II were 6.47% and 6.92%, respectively. Farmland abandonment was still controlled by the improvement of land rental market. And the functions of land rental market optimizing the utilization of farmland resources have been presented to a certain degree. (5) To further improve the marketing degree of land rental, the probability of farmland abandonment could be reduced. Especially, their function to farmland with high grade farming conditions was very obvious, and could avoid the waste of farmland resources with high grade farming conditions.     

Linking land cover dynamics with driving forces in mountain landscape of the Northwestern Iberian Peninsula

The mountainous areas of the northwestern Iberian Peninsula have undergone intense land abandonment. In this work, we wanted to determine if the abandonment of the rural areas was the main driver of landscape dynamics in Gerês–Xurés Transboundary Biosphere Reserve (NW Iberian Peninsula), or if other factors, such as wildfires and the land management were also directly affecting these spatio-temporal dynamics. For this purpose, we used earth observation data acquired from Landsat TM and ETM + satellite sensors, complemented by ancillary data and prior field knowledge, to evaluate the land use/land cover changes in our study region over a 10-year period (2000–2010). The images were radiometrically calibrated using a digital elevation model to avoid cast- and self-shadows and different illumination effects caused by the intense topographic variations in the study area. We applied a maximum likelihood classifier, as well as other five approaches that provided insights into the comparison of thematic maps. To describe the land cover changes we addressed the analysis from a multilevel approach in three areas with different regimes of environmental protection. The possible impact of wildfires was assessed from statistical and spatially explicit fire data. Our findings suggest that land abandonment and forestry activities are the main factors causing the changes in landscape patterns. Specifically, we found a strong decrease of the ‘meadows and crops’ and ‘sparse vegetation areas’ in favor of woodlands and scrublands. In addition, the huge impact of wildfires on the Portuguese side have generated new ‘rocky areas’, while on the Spanish side its impact does not seem to have been a decisive factor on the landscape dynamics in recent years. We conclude rural exodus of the last century, differences in land management and fire suppression policies between the two countries and the different protection schemes could partly explain the different patterns of changes recorded in these covers.     

Gully-head morphology and implications for gully development on abandoned fields in a semi-arid environment,Sierra de Gata,southeast Spain

In this paper we examine whether gully-head morphology can be used as an indicator for gully development and, hence, for sediment production. A survey was conducted at five hillslopes in the Sierra de Gata where different types of channel heads occur close to each other. The survey included measurements of morphologic and pedologic properties, ground surface, channel and catchment characteristics of every gully head present (n = 59). On the basis of the observed morphologies, the heads were subdivided into four types: gradual, transitional (a short inclined section), abrupt and rilled-abrupt. The analyses showed that it is possible to explain the differences of gully heads and the role of some environmental factors on the basis of their morphologies, at least for the gradual and the abrupt types. The results suggested that steep headcuts (abrupt) were formed from secondary headcuts in the channel, which migrated upstream. The abrupt headcuts were always formed in more than one soil layer of which one was a resistant (stony) layer. However, shear strength measurements (at saturation) showed that the top layer was not always the most resistant one. Width–depth relationships indicated that gradual type headcuts were controlled by fluvial processes and abrupt headcuts by a combination of fluvial and mass-wasting processes. Gradual types occurred more downslope than the abrupt types suggesting that the incisions started by fluvial processes and migrated upwards when knickpoints developed in the channel. The rilled-abrupt types are still actively retreating. Thus, the abrupt types correspond to slower retreat rates. Abrupt gully heads may deteriorate into transitional types when plunge-pool erosion becomes less effective. The conceptual model is supported by data from ephemeral gullies in two other study areas (Sierra de la Torrecilla, Spain, and Alentejo, Portugal). Copyright © 1999 John Wiley & Sons, Ltd.     

1980年以来中国农地利用变化的区域差异

The study of land use change and its driving mechanism has become the focus since the research of land use/land cover change (LUCC) became one of the important areas of Global Environmental Change (GEC) researches in the 1990s (Turner, 1994). Scholars mai…     

The mechanism of farmland marginalization in Chinese mountainous areas: Evidence from cost and return changes

Journal of Geographical Sciences - Farmland marginalization has become the main trend of land-use change in the mountainous areas of China. Using annual survey data of major agricultural production...     

中韩海底光缆(西段)弃置方案可行性研究

中韩海底光缆已于2005年7月宣布废弃.中韩海底光缆是我国宣布废弃的第一条国际海底光缆.通过对中韩海底光缆多种可能的弃置方案进行分析,对比研究了各种弃置方案的利弊及可行性.通过比选,提出了全线打捞回收方案是最佳方案;领海以内打捞回收方案次之,是具有现实性和可操作性的方案;原地弃置方案是最不适合中韩光缆弃置的方案.     

山区耕地撂荒格局及驱动力分析（英文）

耕地撂荒正从发达国家向中国等发展中国家蔓延。由于特定的自然地理条件,我国山区普遍存在耕地撂荒现象。然而,由于缺乏中高分辨率遥感影像监测手段,我国许多山区弃耕地规模尚不明确,耕地撂荒的驱动机制也未厘清。基于此,本文以重庆市忠县为例,利用Landsat 8 OLI＿TIRS遥感影像数据,提出了一种基于土地利用年变化监测的山区弃耕地空间化方法。同时,采用岭回归方法对影响耕地撂荒的因素进行分析。结果表明,重庆市忠县耕地撂荒率为7.86%,耕地撂荒提取的总体精度为90.82%。在影响耕地撂荒的社会经济因素中,农村人口、经济发展和畜牧业发展贡献最大。在地块尺度上,海拔650m以上或坡度大于15°的地方发生了大规模的耕地撂荒。     

Natural revegetation and afforestation in abandoned cropland areas: Hydrological trends and changes in Mediterranean mountains

Water resources availability is one of the main concerns for policy makers around the world in present and future management plans. In the Mediterranean basin, this concern is increased given the extreme variability in climate and the intrinsic aridity conditions. Water resources in the Mediterranean region depend mainly on surface and subsurface supply from mountain areas. Because evapotranspiration comprises a substantial portion of the water budget, recent land cover changes due to cropland abandonment may change transpiration (TRANS) and water supply. Therefore, land management plans must account for these potential hydrologic changes to guarantee water availability in the upcoming decades. Short-term changes to water yield have been shown to follow afforestation or natural revegetation, the main management strategies in abandoned cropland areas. Studies comparing long-term trends of these management practices, however, are scarce due to the lack of long-term hydrological data. In this study, we use the regional hydro-ecological simulation system (RHESSys), to analyse long-term changes and annual and seasonal trends in streamflow (STR) and transpiration following management of abandoned cropland areas. Annual mean values show significant differences between the three management scenarios for both streamflow and transpiration, while differences between climate scenarios are not significant. The Mann Kendall trend analysis shows significant changes to water yield compared to the situation before management. Depending on the total afforested area, afforestation could significantly decrease annual streamflow between 2.3%·decade⁻¹ and 5.9%·decade⁻¹ and increase annual transpiration between 1.1%·decade⁻¹ and 3.5%·decade⁻¹. These trends are attributed to changes during the first 30 years after management, while during the fourth and fifth decade, changes to water yield tend to stabilize or decrease. These results are substantial to optimize land management plans, ensuring sustainable hydrological and ecological ecosystem services.     

湘闽赣山区劳动力转移差异对梯田撂荒决策和规模的影响

丘陵山区梯田撂荒现象频发,成为政府农业部门和学术界关注的热点问题。然而,鲜有研究关注劳动力转移差异对农户梯田撂荒行为的影响。基于此,本文以湘闽赣三省梯田区为研究区域,结合实地调研的1438份农户数据,运用Probit和Tobit模型,从劳动力转移差异的视角,分析劳动力非农转移的数量、距离和质量差异对农户梯田撂荒决策和撂荒规模的影响。结果表明：(1)农户家庭劳动力非农就业的数量、就业距离和就业质量均对农户的梯田撂荒决策和撂荒规模具有显著的促进作用;(2)随着非农转移程度的加深,丘陵山区农户梯田撂荒的规模也会扩大;(3)劳动力转移距离和转移质量能够强化劳动力转移数量对农户撂荒决策的影响。为缓解因劳动力非农转移造成的梯田撂荒现象,要重视农业服务外包和机械化在山区的劳动替代作用,积极推进梯田宜机化改造,完善耕地流转市场,鼓励农户流转梯田。