A1: Temperate silvo-arable systems around the world
Chair: Mike Turnbull (International Tree Foundation)
This workshop brings a scientific perspective to temperate silvo-arable systems along with the extensive observations of a Nuffield Scholar who is travelling the world looking at such systems.
Dr Jo Smith: Productivity and economics of a diverse temperate silvo-arable system. Questions remain about whether temperate agroforestry (AF) systems can deliver higher productivity than monoculture systems, but evidence is emerging which indicates that they can. AF systems work through more efficient resource use and ecosystem modification by the trees to the benefit of the crops. In tropical systems an obvious benefit is the shade provided by the trees, but it is harder to see how trees benefit crops in temperate systems where light and water may be limiting. The aim is to maximise the positive interactions and minimise the negative interactions. Positive interactions include increased soil organic matter, nutrient cycling and N fixation, reduced soil erosion, increased pollination and biodiversity, and provision of shelter and a more stable microclimate. Negative interactions are competition for light, water, nutrients, space and labour. These interactions can vary spatially and temporally, introducing another level of complexity. The system design – species selection, spatial and temporal arrangement etc – and management are crucial in manipulating the interactions and therefore in determining productivity. Productivity can be measured using a Land Equivalent Ratio (LER). The is the ratio of the area needed under sole cropping to the area of intercropping at the same management level to obtain a particular yield. Recent results from Wakelyns Agroforestry indicate a LER of 1.31, meaning that 31% more land is needed under monoculture to produce the same yield as that achieved in the AF system.
Stephen Briggs: Temperate silvo-arable systems from around the world. Stephen planted an apple/arable agroforestry (AF) system on his Cambridgeshire fen farm in 2009. Soil erosion is a big issue there and planting trees was a way of countering it. He also wanted to crop ‘the third dimension’ – trees grow higher and deeper – to use more of the available space, thereby increasing productivity. In addition, tree strips would increase habitat diversity on the farm, helping him achieve conservation and habitat protection goals. He designed his system to fit round the large-scale machinery he uses, to retain eligibility for the single farm payment, and within the constraints of a 15 year tenancy and landlord’s requirements. The result was 3m wide apple tree strips and 24m wide cropping alleys between them. Whilst travelling to study other temperate AF systems, Stephen has noted similar spacings; most temperate systems were initially planted on a 12-18m alley width but newer designs are now moving closer to a 24m alley. This allows use of modern machinery and also ensures that the alley width is greater than the final tree height, thereby remaining productive for longer. The combination of trees/crops, and varieties chosen, are important in reducing competition; his cereals use water in the top 1m of soil earlier in the growing season than the trees, which need water later on and from deeper in the soil. Research from abroad also shows that trees grown in AF systems put down deeper roots in order to use resources below the crop rooting level.
- Awareness of AF has increased in the last few years but farmer uptake is hindered by (among other things) a lack of policy support on a national basis.
- We need CAP reform that standardises policy throughout Europe and facilitates the adoption of a variety of agroforestry systems by European farmers.
- There’s an ongoing need for research into temperate AF systems and for current and future findings to be passed on to farmers to help in system design.
- System design and management is crucial to the success of AF systems.
Individual speaker presentations and abstracts
Jo Smith (ORC): Productivity and economics of a diverse temperate silvo-arable system (PDF 969KB)
A key benefit of integrating trees and agriculture in an agroforestry approach is believed to be higher overall productivity due to trees obtaining resources from different parts of the environment to the crops. In temperate climates, however, there is likely to be competition for light, water and nutrients between the crop and tree components, and careful design and management is needed in order to maximise positive interactions and minimise competition between the trees and crops. The presentation uses examples from Wakelyns Agroforestry to illustrate the productivity and economics of silvo-arable systems.
Stephen Briggs (Abacus Organic Associates): Temperate silvo-arable systems from around the world (PDF 6.27MB)
Agroforestry provides multifuntional land use benefits. Improved soil, water and resource protection can be a direct benefit of agroforestry. Whilst systems change over time, net output per unit area is often greater under agroforestry than under monoculture. Agroforestry has the potential to be a more robust form of production in a climate change world. Silvo-arable agroforestry combine tree and arable crops on the same land area. Many combinations of different tree and alley crop are possible. Systems need to ensure that tree and crop components are complementary in terms of resource utilisation (sunlight, water, nutrients). Experiences of different temperate silvo-arable systems from around the world (USA, Canada, Europe, China) will be presented in the context of resource protection, productivity and sustainable intensification.