肯尼亚和中国农业资源投入与农业单产水平变化

当前，肯尼亚和中国在生产足够粮食以保障粮食安全方面都面临着严峻的挑战。尤其是对于肯尼亚而言，因为其2100年预测的人口将达到2018年的1.4倍，且其粮食生产在过去并没有大幅度的改善。而中国近些年粮食生产能力显著提高。本文系统分析了肯尼亚和中国农业资源投入、种植业和畜牧业单产水平的历史变化，以及农业资源投入与产量之间的关系，为肯尼亚粮食危机和消灭贫困提供更多的理论支撑。研究结果表明，在20世纪60年代，肯尼亚耕地、草地和降水等自然资源人均占有量比中国高2~3倍，且人均食物能量和蛋白质供应显著高于中国。当前，肯尼亚人均资源拥有量仍高出中国约30%，但是其人均食品供应和粮食自给率却远低于中国平均水平。这是由于与肯尼亚相比，中国在种植业和畜牧业长期持续的投入，大幅度地增加了种植业和畜牧业能量或蛋白质单产水平。1961-2017年，中国和肯尼亚作物蛋白的平均单产分别增加282%和44%。中国的数据表明，种植业和畜牧业单产水平与肥料、精饲料、机械和农药的投入具有显著正相关性；农牧业生产结构对单产水平的变化影响也很大，如种植业中蔬菜和水果播种面积占比，畜牧业中单胃动物饲养占比等。总的来说，农业资源投入和农业结构对生产力的提高都有很大的影响，这可能是肯尼亚提高农业生产力的潜在选择。     

Restoration of bottomland hardwood forests across a treatment intensity gradient

Large-scale restoration of bottomland hardwood forests in the Lower Mississippi Alluvial Valley (USA) under federal incentive programs, begun in the 1990s, initially achieved mixed results. We report here on a comparison of four restoration techniques in terms of survival, accretion of vertical structure, and woody species diversity. The range of treatment intensity allowed us to compare native recolonization to direct seeding and planting of Quercus nuttallii Palmer, and to an intensive treatment of interplanting two species that differed in successional status (early successional Populus deltoides Bartram ex Marsh. ssp. deltoides, with the mid-successional Q. nuttallii). Native recolonization varied in effectiveness by block but overall provided few woody plants. All active restoration methods (planting and direct seeding) were successful in terms of stocking. Populus grew larger than Quercus, reaching canopy closure after 2 years and heights after 2 and 5 years of 6 and 12.7 m, respectively. Planted Quercus were significantly larger than direct seeded Quercus in all years, but only averaged 1.4 m in height after 5 years. Interplanting did not seem to facilitate development of the Quercus seedlings. The early success of the interplanting technique demonstrated that environmental benefits can be obtained quickly by more intensive efforts. Native recolonization can augment active interventions if limitations to dispersal distance are recognized. These results should provide landowners and managers with the confidence to use techniques of varying intensity to restore ecosystem functions.