Agroforestry, soil health and delivery of public goods

农林业是在同一块土地上故意种植树木与可耕地作物和/或牧场的做法（图1）。农林业被视为一种可持续的土地管理做法，树木和农业共存，提供多种效益。因此，农林业的增长和创新有可能提高农田生产力，恢复力和多样性，同时保持和/或改善其他生态系统服务的提供，通过改善土壤健康（Dollinger & Jose，2018;），固碳（De Stefano & Jacobson，2018; Lorenz & Lal，2014）和减缓径流（马歇尔等人，2009年）。虽然长期以来在亚热带和热带气候中建立，但在温带农业系统中采用农林业的速度缓慢，特别是在英国（林地信托，2018年）。为了实现这一潜力，迫切需要更好地了解在温带农业系统中种植树木如何影响土壤健康指标，从而有助于减少洪水和缓解气候变化。虽然文献综述表明，农林复合经营可以增加土壤中储存的碳量（De Stefano & Jacobson，2018; Lorenz & Lal，2014），从而有助于减缓气候变化，但大多数研究（约80%）位于热带和亚热带气候，温带气候不到20%。Oelbermann等人（2014年）发现，在温带地区，由于周转率低于热带地区，农林业必须建立10年以上才能增加土壤碳。此外，目前还不清楚在牧场种树是否与在耕地种树对土壤有机碳含量有相同的好处（Upson等人，2016）。英国最近的研究表明，在农田上种植树木可以增加土壤渗透率（例如，马歇尔等人，2009年）。然而，这些研究是在一个研究中心进行的。此外，尚不清楚在低地农业系统中是否会观察到类似的影响;这突出表明需要进一步研究。鉴于研究农林业的发展以及作物、动物和树木之间复杂的相互作用需要很长时间，经过校准和验证的模拟模型可大大有助于理解和量化环境效益，并预测系统对预测气候变化的适应能力（Cardinael等人，2018).因此，该项目的主要目的是确定农林业对土壤健康的影响，特别是对土壤碳储存、土壤结构和水文特性的影响。您将与利兹大学的科学家合作，并得到林地信托基金的支持，以量化不同农林复合系统对温带气候中关键土壤健康指标（如碳，容重，渗透性，蓄水量）的影响，以了解农林复合系统如何影响更广泛的生态系统服务，如减缓气候变化和防洪。这将通过在约克谷一个新建立的造林地、20世纪80年代在利兹大学农场建立的一个较老的造林地以及英国、法国、西班牙、意大利和德国的其他农林地进行实地考察来实现。特别是，根据您的特定研究兴趣，学生奖学金可以解决以下目标的组合：1。确定农林业对土壤健康指标的短期和长期影响。2.评估不同的农林复合类型（造林，造林，防护林和树篱）对土壤健康指标的影响。研究了不同林龄农林复合生态系统土壤健康指标的距离和深度效应.通过基于过程的土壤过程建模，量化气候变化对农林系统碳循环的影响。

Agroforestry is the practice of deliberately growing trees in combination with arable crops and/or pasture on the same piece of land (Figure 1). Agroforestry is seen as a sustainable land management practice, where trees and agriculture co-exist to provide multiple benefits. Therefore growth and innovation in agroforestry has the potential to improve farmland productivity, resilience and diversity while maintaining and/or improving the provision of other ecosystem services, via improving soil health (Dollinger & Jose, 2018;), sequestering carbon (De Stefano & Jacobson, 2018; Lorenz & Lal, 2014) and slowing water runoff (Marshall et al., 2009). While long-established in sub-tropical and tropical climates, uptake of agroforestry in temperate agricultural systems has been slow, particularly in the UK (Woodlands Trust, 2018). In order to realize this potential, there is urgent need for greater understanding of how planting trees in temperate agricultural systems impacts upon soil health indicators and thus helps to reduce flooding and mitigate climate change. While literature reviews have shown that agroforestry can increase the amount of carbon stored in the soil (De Stefano & Jacobson, 2018; Lorenz & Lal, 2014) and thus help to mitigate climate change, the majority of studies (~80%) were located in tropical and sub-tropical climates, with less than 20% in temperate climates. Oelbermann et al. (2014) found that in temperate zones agroforestry had to be established for greater than 10 years in order to see an increase in soil carbon due to lower turnover rates than in the tropics. In addition, it is unclear whether planting trees in pastures has the same benefit for soil organic carbon content as planting trees in arable fields (Upson et al., 2016). Recent studies in the UK have shown that planting trees on farmland can increase soil infiltration rates (e.g. Marshall et al., 2009). However, these studies were carried out at one site. In addition, it is not clear if similar impacts would be observed in lowland agricultural systems; highlighting the need for further research. Given the long time required to study the development of agroforestry and the complex interactions between crops, animals and trees, calibrated and validated simulation models can significantly contribute to the understanding and quantification of environmental benefits and to forecast the resilience of the systems to the predicted climate change (Cardinael et al., 2018).The major aim of this project is therefore to determine the impact of agroforestry on soil health, in particular its impact on soil carbon storage, soil structure and hydrological properties. You will work with scientists at the University of Leeds and supported by the Woodlands Trust to quantify the impact of different agroforestry systems on key soil health indicators (e.g. carbon, bulk density, permeability, water storage) in temperate climates to understand how agroforestry impacts upon wider ecosystem services such as climate change mitigation and flood control. This will be achieved through fieldwork at a newly established silvopastural site in the Vale of York, an older silvoarable site established at the University of Leeds farm in the 1980s, and other agroforestry sites across the UK, France, Spain, Italy and Germany. In particular, according to your particular research interests, the studentship could address a combination of the following objectives: 1. Determine short-term and longer-term impacts of agroforestry on soil health indicators. 2. Evaluate the impact of different agroforestry types (silvoarable, silvopasture, shelter belts, and hedges) on soil health indicators.3. Investigate the effects of distance and depth on soil health indicators in a range of different aged agroforestry plots soil types .4. Quantify the impact of climate change on carbon cycling in agroforestry systems via process-based modelling of soil processes.