Badlands,Seed Banks,and Community Disassembly

Soil seed banks are a key component of ecological resilience as they provide a temporal reserve for plant species richness and diversity. Soil seed banks depend on on-site reproduction, seed longevity, and seed immigration for maintenance. When immigration of seeds is lost due to a change in land use or a disturbance, such as fragmentation, seed banks rely on on-site reproduction and longevity for maintenance. Within a fragment without seed immigration, seed banks become vulnerable to extinction debt leading to community disassembly over a long time scale. Therefore, we investigated how long-term fragmentation impacts community disassembly in seed banks. Seed bank samples were taken from grassland fragments (sod tables, n = 28) and from the surrounding area (matrix, n = 28). Seed banks were germinated, and emerging plants were identified. We found that community disassembly was not predictable in regard to species identity, and specialist (P < 0.001) and perennial (P < 0.001) species were lost from fragments. However, seed banks in fragments maintained a similar grass-to-forb ratio compared with the surrounding vegetation. Therefore, the ability of seed banks to provide ecological resilience may be limited after long-term fragmentation and land managers may need to reseed specialist species and perennials into grassland fragments.     

路基回弹模量衰减对公路沥青路面厚度设计的影响

针对使用中存在的路基回弹模量衰减问题,应用《公路沥青路面设计规范》（JTG D50-2006）和弹性多层体系理论研究了设计年限内路基回弹模量衰减对公路沥青路面厚度设计的影响.实例计算结果表明：当路基回弹模量衰减超过20%时,所设计的沥青路面厚度已小于使用要求的限度.研究成果可供考虑路基回弹模量衰减的公路沥青路面厚度设计时参考.     

An appraisal of soil organic C content in Mediterranean agricultural soils

Low soil organic carbon (SOC) levels in dry areas can affect soil functions and may thus indicate soil degradation. This study assesses the significance of SOC content in Mediterranean arable soils based on the analysis of a broad data set of 2613 soils sampled from Mediterranean grasslands and agricultural land. The distribution in values of SOC, pH, clay and carbonates was analysed according to different climatic areas (semi‐arid, Mediterranean temperate, Mediterranean continental and Atlantic) and with respect to six different land uses (grassland, cereal crops, olives and nuts, vineyards, fruit trees and vegetable gardens). The general trend was for low SOC in arable land and decreased with aridity. In wet areas (Atlantic and Mediterranean continental), acidic soils had a higher SOC content than did calcareous soils, whereas in the Mediterranean temperate area SOC had little relationship to soil pH. In low SOC arable soils, the SOC content was related to clay content. In calcareous arable soils of the Mediterranean temperate zone, SOC content was more closely related to carbonates than to clay. In contrast to the Atlantic area, Mediterranean grassland soils had much lower amounts of SOC than forest soils. Mediterranean calcareous and temperate acidic soils under grassland had SOC‐to‐clay ratios similar to or only slightly greater than that under a crop regime. In contrast, Mediterranean continental acidic soils under grassland had a much higher SOC‐to‐clay ratio than arable soils. This suggests a low resilience of the Mediterranean temperate and calcareous arable soils in terms of SOC recovery after the secession of ploughing, which may be a result of intensive use of these soils over many centuries. Consequently, we hypothesize that the Mediterranean calcareous soils have undergone significant changes that are not readily reversed after ploughing ceases. Such changes may be related to alterations in soil aggregation and porosity which, in turn, are associated with soil carbonate dynamics. Decarbonation processes (the depletion of active carbonates) may therefore be relevant to the reclamation of highly calcareous arable soils through fostering soil re‐aggregation. The article concludes by discussing the suitability of zero tillage, manuring or the introduction of woody species to increase SOC in calcareous arable soils that are highly depleted of organic matter.     

粮食主产区典型镇域的农业系统变化与农户生计韧性评价——以河南省高杨店镇为例

为探寻粮食主产区农业系统韧性和农户生计韧性提升的路径,以传统农区河南省高杨店镇为例,分析不同阶段农业系统的适应性循环过程及变化特征,采用CRITIC-TOPSIS法定量评价不同类型农户生计韧性,并揭示农业系统韧性与农户生计韧性的关联机制。结果表明： 20世纪50年代以来,高杨店镇农业系统经历了两个完整的适应性循环,从自给自足的小农经营逐步过渡到规模化经营和新型农业经营主体培育阶段,农户生计逐步多样化。气候变化、制度变革、政策响应、工业化和城镇化以及技术革新是农业系统适应性循环演进的主要驱动力。根据农户收入来源及其占比,研究区农户生计类型可划分为种养殖型、工资保障型、自主创业型、社保依赖型、兼业均衡型5种,且不同类型农户的生计韧性存在显著差异。农户生计分化受到农户自主发展能力与国家政策、市场力量、社会关系等内外部力量共同驱动。农业系统韧性和农户生计韧性存在尺度嵌套和相互影响,当农户生计韧性累积到一定程度即表现为农业系统整体的韧性。     

给水管网优化设计的多目标遗传算法

为兼顾给水管网优化设计中的经济性和可靠性问题,以管网年费用和管网系统可靠性为目标函数建立给水管网优化设计的多目标遗传算法数学模型;并将系统可靠性定义为"节点富余水头加权平均值"和"管网恢复力",进而对多目标遗传算法模型求解过程进行分析。最后以一个典型的工程案例加以验证,结果表明,多目标遗传算法所得到的目标函数值和管网水力性能明显优于传统设计方法,充分说明了多目标遗传算法用于管网优化设计的实用性和有效性。     

生物土壤结皮发育及其影响因素研究进展

生物土壤结皮在干旱、半干旱地区分布较为广泛,约占陆地总面积的40%,生物土壤结皮是支撑该区生态系统主要的生物表面特征,在改善生态环境和草地土壤养分调控方面起着重要作用。自1960年以来,国内外许多学者对其生态功能进行了大量研究,但对生物土壤结皮演替机制及其微生境土壤养分变异特征的研究尚不明确。为此,本文就国内外该领域近50年来的研究进展和成果进行了详细阐述,以期了解生物土壤结皮发育对土壤肥力的作用过程;同时,也为研究干旱半干旱区退化草地生态系统的恢复与重建提供一定的科学思路。     

城市社区洪灾抗逆力影响因素及其评价——以河南省新乡市红旗区为例

[目的]对城市社区洪灾抗逆力影响因素进行分析和评价,为城市社区洪水防灾减灾规划和风险管理提供决策依据。[方法]以河南省新乡市红旗区所辖社区为研究对象,通过问卷调查的方式,在文献调研和专家咨询的基础上,初步选取影响社区洪灾抗逆力的64个因子建立预选指标集,利用相关分析和主成分分析对64个初选指标进行降维处理,并在此基础上对研究区的9个城市社区的抗逆力进行综合评价。[结果](1)物理因素、制度因素、经济因素和人口因素是影响城市社区洪灾抗逆力水平的关键因素;(2)红旗区城市社区洪灾抗逆力整体水平不高,近80%的社区洪灾抗逆力处于中等偏下水平;(3)物理因素是影响红旗区城市社区洪灾抗逆力的主要因素,其次为经济和人口因素,制度因素影响最低。[结论]在分析城市社区洪灾抗逆力影响因素及其评价的基础上,提出具体的、有针对性的提升策略和措施,是一个可行的途径。     

Use of Landsat multi-temporal imagery to assess secondary growth Miombo woodlands in Luanshya,Zambia

Miombo woodlands are the most extensive natural forest type in subtropical Africa, supporting the livelihood of over 100 million urban and rural settlers. These forests continue to experience extensive deforestation and land degradation due to land use land cover (LULC) changes. The aim of this study is to use remotely sensed images from the Landsat archive to provide the baseline for the spatial extent of Miombo woodlands in Luanshya district of the Copperbelt Province, Zambia. It also assesses the implications of spatial-temporal changes for the conservation of these woodlands. A hybrid classification method involving ISODATA and Support Vector Machine classifiers was used to generate LULC maps for 1986, 1998, 2001, 2004, 2011 and 2016, with an overall accuracy of 82.0%–99.6% and kappa coefficient of 0.80–0.99. Unlike previous studies that have mainly focused on comparison between two or three time periods, a longitudinal analysis over the 20-year periods of this study shows that there are complex net and gross changes in different LULC types over different scales. Landscape change metrics indicate that woodlands have been declining in extent, but are partly offset by regeneration. Rates of deforestation (regeneration) for the periods 1986–1998, 1998–2001, 2001–2004, 2004–2011 and 2011–2016 are 10% (1%), 38% (30%), 15% (7%), 11% (8%) and 9% (2%) per annum, respectively. These results suggest that over 68% of Miombo woodlands present in 2016 are second-growth forests. Restoration strategies such as assisted natural regeneration are necessary in order to accelerate the recovery of natural forests. Targeting under-used and degraded land for assisted natural regeneration and empowering local communities in sustainable environmental stewardship are crucial in remediating against continued forest degradation.