Agroforestry: a profitable land use. An overview of the 12th North American Agroforestry Conference

This special issue features papers contributed by presenters at the 12th North American Agroforestry Conference held June 4–9, 2011 in Athens, Georgia, USA. The conference brought together agroforestry researchers, educators, practitioners, and students to highlight agroforestry research, implementation, policy, education, and entrepreneurial opportunities across North America. Eight papers cover topics ranging from adoption of silvopastoral systems across eco-regions and countries; economics of pine straw production; and timber and alley crop production in the Southeastern U.S.; reduction of sublimation of snow with shelterbelts in Canada, carbon offset incentives for agroforestry practices; consumer and market dynamics for chestnut and elderberry specialty crops; and web-based graduate degree and certificate programs in agroforestry.     

Agroforestry systems in North America

Agroforestry systems in North America vary widely in terms of components (tree, forb, graminoid, and shrub species) and outputs. Most of the agroforestry systems used in North America have emphasized wood and livestock production. The objective of each system has been to produce annual and long term economic returns and sustainable yields. Inputs such as fossil fuels, fertilizers, herbicides and pesticides are relatively low compared to those used in conventional agriculture.Major agroforestry system types in each of eight North American regions are described. The major species used as vegetational components in each system are enumerated by region. The numerous variations in how these components are mixed have created an almost endless number of actual systems. Management problems and solutions, economic concerns, and system comparisons have also been addressed for each region.     

Agroforestry strategies to sequester carbon in temperate North America

Information on carbon (C) sequestration potential of agroforestry practices (AP) is needed to develop economically beneficial and ecologically and environmentally sustainable agriculture management plans. The synthesis will provide a review of C sequestration opportunities for AP in temperate North America and the estimated C sequestration potential in the US. We estimated carbon sequestration potential for silvopasture, alley cropping, and windbreaks in the US as 464, 52.4, and 8.6?Tg?C?yr^?1, respectively. Riparian buffers could sequester an additional 4.7?Tg?C?yr^?1 while protecting water quality. Thus, we estimate the potential for C sequestration under various AP in the US to be 530?Tg?yr^?1. The C sequestered by AP could help offset current US emission rate of 1,600?Tg?C?yr^?1 from burning fossil fuel (coal, oil, and gas) by 33?%. Several assumptions about the area under different AP in the US were used to estimate C sequestration potential: 76?million?ha under silvopasture (25?million?ha or 10?% of pasture land and 51?million?ha of grazed forests), 15.4?million?ha (10?% of total cropland) under alley cropping, and 1.69?million?ha under riparian buffers. Despite data limitation and uncertainty of land area, these estimates indicate the important role agroforestry could play as a promising CO₂ mitigation strategy in the US and temperate North America. The analysis also emphasizes the need for long-term regional C sequestration research for all AP, standardized protocols for C quantification and monitoring, inventory of AP, models to understand long-term C sequestration, and site-specific agroforestry design criteria to optimize C sequestration.     

Agroforestry education

Development of agroforestry education is following the pattern of evolution of some other areas of study such as plant pathology, genetics, and statistics. At universities these three areas began within another department or departments, and after being moved into their own departments began to flourish and develop their own identity. However, the main question is what can or should be done to further the process? The increasing number of agroforestry projects in the world, the lack of trained agroforesters, and the estimated increased need for agricultural scientists are all indicators for the future demand for trained agroforesters. Career opportunities for professional agroforesters lie in three areas: as research scientists, as extension agents, or as development agroforesters. Two broad educational approaches to setting educational objectives are to (1) set objectives on the basis of the perceived problems likely to be encountered in agroforestry and (2) set objectives according to roles which agroforesters are likely to assume. The design of both undergraduate and postgraduate curricula are discussed. The unique core is the agroforestry system per se and the development of a systems analysis methodology. The institutional structure and clear goal definition can facilitate the development of an agroforestry program, but in the final analysis it is the dedication and enthusiasm of the individual staff that will count for success.     

Windbreaks in North American agricultural systems

Agroforestry Systems - Windbreaks are a major component of successful agricultural systems throughout the world. The focus of this chapter is on temperate-zone, commercial, agricultural systems in...     

北美制材厂：生产削减

经过先前几个季度的努力,到9月份,北美的制材工业毫无疑问已经减少了针叶锯材的生产,并且,2007年10月,北美制材工业的公司宣布第四季度的生产再次进行削减,并且其中已有一些公司在实施这项计划。生产将会暂时缩减,除了单班生产取消,有些工厂无限期停产。在此期间,有的工厂宣布暂时停工1到2周,将按周进行检查，根据市场的发展变化停产可能进一步扩大。对于再次削减生产理由，这些公司提到了北美地区对针叶锯材需求的持续紧缩和供应过剩。在过去的几周里，这样的情况引起了价格的暴跌。     

北美洲和世界的定向刨花板工业

现在，定向刨花板（OSB）是木材产品工业的“宠儿”，在全世界特别是在北美洲应用越来越广泛。其每1000ft^2（厚度7／16．in）价格在2003年4月突破200美元，此后保持在此价格之上，最高价格曾高达520美元／1000ft^2，一般在400美元／1000ft^2上下摆动。上世纪70年代后期北美洲建设了第一座OSB厂，OSB厂的规模从仞期平均年产1亿ft^2提高到现在的8亿ft^2。2003年北美洲OSB产量为237亿ft^2（3／8in厚度），占世界份额的86％。下表列出了2003年世界顶级20家OSB公司的产量，     

北美定向刨花板（OSB）行业的创新

在国际人造板杂志（WBPI）的独家文章中,不列颠哥伦比亚大学（University of British Columbia）的教授Philip D Evans介绍了北美定向刨花板（OSB）生产商开发的创新,解决了边缘膨胀的问题。 创新是我们经常使用的与高科技和生物医药产业相关联的词,也许与木材制造业不相关。然而,对于北美定向刨花板（OSB）产业而言,是存在创新的。     

由公司经营之原料策略谈起

有位美国朋友,由江浙一带进口木地板,到美国来销售。由于其所接触的地板生产工厂接到美国Home Depot一个200柜的订单,为了帮助该厂确保地板原材料供应,他联想到是否自己也出口些美国板材给工厂来赚些大钱。另外今年六月,美国硬木出口协会（AHEC）在杭州举办了一场由设计师为主要讲者的说明会,     

北美栎树引种试验研究

系统引种了北美栎属10个树种在江苏育苗、造林。观察记录栎树苗期生长及在不同地点造林成活率、保存率、树高、地径、冠幅生长，秋季物候及叶色等性状变异，并与江苏乡土栎树麻栎、小叶栎、栓皮树和青冈栎等进行比较。综合生长、适应性及观赏性状指标，初步选择水栎和柳叶栎为优良速生用材观赏树种，南方红栎、红栎和北方红栎为优良秋叶观赏树种。认为江苏地区引种北美栎树应以分布于气候较相似的美国东南部亚热带的水栎、柳叶栎和南方红栎等树种为主。     

The periderms of three North American conifers

Summary The anatomy of periderms in three North American conifers are described and compared. The phellems of balsam fir and eastern hemlock consist of tangential bands of thin-walled phellem (TnP) separated by one, or sometimes more, cell layers of thick-walled phellem (TkP). The phellem of white spruce contains tangential bands of TnP and TkP, as well as one to several cell layers of crystalliferous phellem (CP) abaxially adjacent to every TkP zone. The TkP, and to a lesser extent the TnP, are distinctive for each of the three conifers.The terminations of phellem growth cycles in fir and hemlock are delineated by thickened adaxial suberinic walls in the last-formed layer of TnP cells. In spruce, the adaxial suberinic walls of the last-formed layer of CP cells are thickened. TkP marks the geginning of phellem growth cycles in all three conifers.TkP cells are true suberized phellem cells, not phelloids.     

农林复合经营系统及其实践

在阐述农林复合经营系统概念的基础上，将该系统划分为６个类型即农林复合型，林农复合型，林牧复合型，农林渔复合型，林特复合型，地域性农林复合型，并作概要描述，对国内外农要复合经营系统的实践也作了典型介绍，这些典型的共同特点是根据生态学和经济学原理，利用物种在时空上合理布局，保持组合的动态平衡，提高经济效益。     

华北低丘山区核桃-决明子复合模式的根系分布

采用分层挖掘法,对株行距为3 m×8 m的核桃-决明子复合模式中的根生物量、总根长密度、吸收根的根长密度和根系直径等进行了调查。结果表明：核桃单作的总根长密度比核桃间作的高7%左右,且在各个土层中吸收根的根长密度都高于核桃间作,而二者的总根生物量和根系直径则差异较小。决明子单作的根系直径比间作决明子的大27.73%,但二者的根长密度和根生物量则差异不大。在核桃-决明子复合模式中,核桃总根生物量和吸收根长均占复合模式总根量的一半以上,其中,在水平方向上,决明子在树行南侧2.5、4.0 m位置根系分布最多,而树行南北1.5 m范围内则较少;核桃根系则主要分布在树行两侧1.5 m范围内。垂直方向上,核桃在30~80 cm土层中的根生物量和吸收根长分别占其总量的64.79%和61.17%,而59.54%的决明子根系分布在0~20 cm土壤中。     

云南山区林农结合模式的探讨

针对云南山区农村的综合治理和开发的现实,面向山区农业的两个转变及体制改革,遵照生态经济原则,从农业生态系统的生态经济协调出发,遵循林农结合系统的“整体、协调、循环、再生”的原则,把云南山区区划为冷温性湿润型、温凉性湿润型、暖温性湿润型、暖温性半湿润型、暖热性湿润型、热性湿润型、热性半干旱型7种林农结合系统,分系统论述该区域的行政范围、自然条件、资源状况、农林生产特点、林农结合的经营模式.经比较分析,归纳与发掘出80种以上的云南山区林农经营模式.每个系统中都有10种以上模式.既反映山区自然的特点,又具有地方、民族特色.     

Agroforestry practices in Nigeria

The problems of too much pressure on land for the production of food and wood for the increasing population have made it mandatory to look into the various ways of maximising the uses of agricultural land in different parts of the world. Under this high demand for land, the system of shifting cultivation which has been practised from time immemorial can no longer support the needs of farmers in Nigeria. As a result of this, the different agroforestry practices have received increased attention. The experiences obtained with shifting cultivation, homestead gardens, taungya, alley-farming and scattered farm tree methods including shelterbelt planting in the country are reviewed in this paper and some research findings on these practices are highlighted.     

Agroforestry and portfolio theory

Portfolio theory is used to analyse the risk of hypothetical agroforestry systems. It is shown that the relationship of the returns of the components of an agroforestry system, expressed in terms of the covariance or correlation of returns, is of vital importance in correctly defining risk. Agroforestry systems can be classified as efficient or inefficient. Inefficient systems are such that an alternative system exists which has a greater return for the same level of risk. Thus, inefficient systems do not represent rational choices for agroforestry systems. Finally, the conclusion is reached that it is impossible to design a best system, but rather a set of efficient systems of differing risk and return can be defined. This set of efficient systems is referred to as the efficient frontier.     

Agroforestry and organic agriculture

Current conventional agriculture is considered unsustainable and inadequate to address great societal challenges such as climate change, environmental pollution, food security, dependence on fossil energy as well as the decline of natural resources and biodiversity. Many of these problems are related to agricultural specialization (i.e. monoculture) and the consequent simplification of the agroecosystem. In this respect, efforts aimed at improving individual agronomic techniques and at increasing the use-efficiency of external inputs (e.g. synthetic inputs, fossil fuels), without modifying the structure and functions of the whole system, appear to be insufficient to achieve sustainability in most conventional and intensive farming systems. Current organic farming systems adopting the so-called input substitution approach remain intensive and highly specialized and not necessarily able to significantly improve their sustainability. This would require system diversification and redesign of the agroecosystem to increase the spatial and temporal diversification of all its components and promote positive ecological relationships between them. Agroforestry is an agricultural approach based on the diversification of the agroecosystem production components (woody perennials, such as trees or shrubs, plus crops and/or livestock) and on the intensification of the agroecological relationships between these components. As such, it has transformative potential, providing an opportunity for increasing the sustainability of organic farming. In this article we review how the adoption of agroforestry practices could contribute to increasing sustainability in organic farming, and discuss the challenges and opportunities of this adoption.