Maximizing crop yield in alley crops

A simple graphical model is presented illustrating the balance between facilitation and competition necessary for maximizing crop yield in alley cropping systems. Three functions are composed into the decision function: (1) the percent increase in crop yield from facilitation resulting from prunings, (2) the amount of prunings resulting from different tree densities, and (3) the percent reduction in crop yield from competition from trees. The resulting function illustrates how the balance between facilitation and competition may provide a window of opportunity for the beneficial use of alley crops. This revised version was published online in August 2006 with corrections to the Cover Date.     

Grazing and heat stress protection of native grass by a sand-fixing shrub in the arid lands of northern China

Shrub species are used in restoration projects on dryland for their facilitation effects, which include environmental improvements and protection from herbivore feeding. Facilitation effects on forage grasses are potentially important in improving grazing capacity on rangelands. However, the morphology-dependent performance of benefactor plants in facilitating forage species growth and supplementation under moderate grazing intensity remains unclear. Here, our main purpose was to measure facilitation performance in terms of the survival of a native forage grass, Agropyron cristatum (L.) Gaertn. (Gramineae)., in accordance with the growth conditions of a sand-fixing benefactor shrub, Caragana microphylla Lam., in the Hulun Buir Grassland, northern China. Six study sites with patches of A. cristatum and C. microphylla were established at the foot of fixed sand dunes. At each site, five quadrats were set in places where C. microphylla coverage was 100% and A. cristatum grew among the shrubs (shrub quadrats), and another five were set where A. cristatum grew alone without C. microphylla (grass quadrats). We measured the morphological traits of C. microphylla and A. cristatum in all 60 quadrats, along with the soil water content and soil temperature. The data were compared between the shrub and grass quadrats by generalized linear mixed-effect models to assess the shrub's facilitation effects. We also used such models to elucidate the relationship between the average height of C. microphylla and the morphological traits of A. cristatum in the shrub quadrats. The maximum height, average grazed height, and the number of seed heads of A. cristatum were greater in the shrub quadrats than in the grass quadrats. The soil surface temperature was lower in the shrub quadrats. The maximum height and seed head number of A. cristatum were positively associated with the average height of C. microphylla. These results suggest that the grazing impact and heat stress were smaller in shrub quadrats than in grass quadrats, and that the degree of this protective effect depended on the shrub height. The shrub canopy seemed to reduce the increase in soil temperature and keep the grass vigorous. Livestock likely avoided grazing grasses in the C. microphylla patches because of the shrub's spiny leaves; only the upper parts of the grass stems (including the seed heads) protruding from the shrub canopy were grazed. The sand-fixing shrub thus moderates the grazing impact and soil temperature, and contributes to vegetation restoration and grazing system sustainability.     

White spruce recruitment distances relative to lodgepole pine in southern Yukon,Canada

Eleven seral, postfire forest stands in southern Yukon (Canada) were sampled to determine where western white spruce (Picea albertiana ssp. albertiana) seedlings occurred with respect to distance to the nearest lodgepole pine (Pinus contorta var. latifolia) tree. Seedling-to-nearest tree distances were assessed at 10-cm increments up to 220?cm. On average, seedlings occurred 54?cm from the nearest pine (n?=?490), but peak frequencies were 20–50?cm away, compared to a potential separation distance of 103?cm. Greatest average seedling density occurred 10–20?cm from pine (0.81?m^?2), with values between 10 and 120?cm decreasing logarithmatically with increasing distance from pine (r?=?0.994, p?n?=?11). Spruce seedling densities were <0.02?m^?2 beyond 120?cm. The differences in frequency, which represented moderately strong aggregation (Clark-Evans Index 0.34–0.52), and density suggest greater spruce recruitment near lodgepole pine was facilitated by more favorable ecological conditions than further away, for example, greater nutrient availability. The bias in seedling-to-nearest tree distances occurred regardless of stand age (57–165 years), pine density (1599–5935 stems?ha^?1), or understory vegetation type, although the bias may be weakened by the abundant presence of feathermosses (Hylocomium splendens) on the forest floor.     

Interactions between Fusarium verticillioides and Fusarium graminearum in maize ears and consequences for fungal development and mycotoxin accumulation

Fungal interactions of Fusarium verticillioides and F. graminearum in maize ears and the impact on fungal development and toxin accumulation were investigated in a 2‐year field study at two locations in France. Maize ears were inoculated either with a spore mixture of F. graminearum and F. verticillioides or using a sequential inoculation procedure consisting of a first inoculation with F. graminearum followed by a second with F. verticillioides 1 week later. Toxin and fungal biomass were assessed on mature kernels, using HPLC and quantitative PCR. Correlation between the levels of DNA and toxin was high concerning F. graminearum DNA and deoxynivalenol (R² = 0·73) and moderate for F. verticillioides DNA and fumonisin (R² = 0·44). Fusarium graminearum DNA either decreased in mixed inoculations or was not influenced by subsequent inoculations with F. verticillioides, compared to single inoculations. In contrast, F. verticillioides DNA either significantly increased or was not affected in mixed and sequential inoculations. In two of the replicates, it can be assumed that natural contamination by F. verticillioides was favoured by previous contamination with F. graminearum. Overall, the results suggest that F. verticillioides has competitive advantages over the F. graminearum strains. Additionally, the data provide, for the first time, key evidence that previous contamination by F. graminearum in maize ears can facilitate subsequent infections by F. verticillioides.     

种间互作的生态效应 Ⅱ.与蚕豆间作对作物生长的影响

在2种不同土壤条件下,测定3种间作系统(蚕豆/小麦、蚕豆/油菜和蚕豆/大蒜)和4种单作系统(蚕豆、小麦、油菜和大蒜)生物量、株高、荚数、经济产量的变化。结果表明,在胶泥土和砂壤土中与大蒜间作均能促进蚕豆生物量增加;而与小麦和油菜间作时,只有在砂壤土中才对蚕豆生长具有促进作用。在2种土壤条件下,3种作物均不同程度抑制蚕豆的株高,尤以大蒜抑制作用最强。在胶泥土中,大蒜促进蚕豆结荚作用最强,小麦促进蚕豆结荚作用最弱;大蒜对蚕豆经济产量促进作用最弱,小麦对蚕豆经济产量促进作用最强。在砂壤土中,大蒜对蚕豆生物和经济产量的促进作用均为最强。在2种土壤条件下,小麦间作蚕豆以后,小麦除生物产量稍有降低外,经济产量、株高和分蘖数均有少量提高;油菜间作蚕豆后,油菜经济产量和株高均得到提高;大蒜间作蚕豆后,蒜薹与蒜瓣产量下降,而株高增加。以上结果表明,在农田生态系统中,种间相互作用或强化作物间的竞争或强化物种间的化感效应,影响间作系统中不同植被类型的生长潜力。     

天然格氏栲林乔木层种群种间关联性研究

格氏栲 (ＣａｓｔａｎｏｐｓｉｓｋａｗａｋａｍｉｉＨａｙａｔａ) ,也称青钩栲 ,属国家二级保护植物 ,是壳斗科常绿阔叶大乔木 ,是亚热带珍贵稀有树种之一 ,其自然分布范围狭窄 ,在我国主要分布于福建、台湾、广东、广西、江西等地区 ,多零星生长在海拔 2 0 0～ 1 0 0 0ｍ的丘陵地的常绿阔叶林中。但在福建三明小湖地区有近 70 0ｈｍ2以珍稀濒危植物格氏栲占优势的林分 ,多由百年以上的大树组成 ,是中国目前较为罕见稀有的天然群落。其原生植被受人干扰 ,现为天然次生植被。格氏栲林以其整齐林相、丰富的物种等独特的森林景观 ,自 1 958年…     

Participatory modelling to enhance social learning,collective action and mobilization among users of the mafungautsi forest,Zimbabwe

Participatory modelling can be a useful process to encourage critical examination of livelihood options and foster sustainable natural resource use through enhanced social learning, collective action and mobilization. The broom-grass group in the Mafungautsi Forest Reserve serves as a case study of the process and outcomes of such participatory modelling. Innovative group facilitation methods enhanced participation in the modelling process. The modelling process complements broader efforts to achieve higher levels of adaptive collaborative management. This work was conducted as part of the Adaptive Co-Management project of CIFOR, the Center for International Forestry Research. We are grateful to the UK’s Department for International Development (DFID) and the European Community for financial support of this project.     

封山育林模式与发展对策研究

封山育林能快速、经济地恢复和增加林草植被, 形成的植被群落稳定, 是深远山区生态建设的重要途径.河北省在生态环境建设中, 实施封山育林, 在充分利用自然环境自我修复能力的同时, 采取必要的人工促进措施, 加快封山育林成林速度, 提高封山育林质量, 促进山区生态产业发展.本文总结提出了河北省封山育林中应用的自然封育、飞封结合、封造结合、封改结合、封保结合等主要山区生态建设模式, 并分析了封山育林效益和存在的主要问题, 提出了增加投入、落实政策等加快封山育林的对策措施.     

贸易便利化水平对中国农产品出口影响——基于东盟10个进口国的实证分析

在全球贸易自由化背景下,从贸易便利化角度探讨其对中国农产品出口的影响对于提升中国农产品出口竞争力有重要意义.研究选取20102019年中国与东盟10国农产品出口的面板数据,以基础设施、海关环境、规制环境以及电子商务4个一级指标以及航空基础设施、海关手续、政策透明度等17个二级指标构建贸易便利化评价指标体系并采用扩展的引...