Mixed systems of agriculture incorporating combinations of trees and crops have formed key elements of the landscape of Europe throughout historical times, and many such systems continue to function in the present day. In many cases they represent formerly widespread traditional systems in decline and a number have already become extinct or exist only in a threatened state. The causes are both practical and economic. The agricultural subsidy regime within the European Union is presently unfavourable towards silvoarable practices, which has been a major factor in their recent decline. The silvoarable systems of Europe can be split into two classes according to location -northern Europe and the Mediterranean. The latter contains not only a greater area of silvoarable cultivation, but also a greater diversity of systems due to the broader range of commercial tree and crop species grown. In general, the systems of northern Europe are limited by light, whilst those of the Mediterranean are limited by the availability of water. Mixed systems of agriculture present an opportunity for future European rural development and have the potential to contribute towards the increased sustainability of agriculture and enhancement of biodiversity, whilst preserving landscapes that are both culturally important and aesthetically pleasing. A better understanding of the legacy of traditional silvoarable systems, combined with the formulation of a consistent definition and specific European policy towards them will be invaluable in ensuring that the benefits of mixed agriculture are fully exploited in the future.

Silvoarable agroforestry could promote use of trees on farms in Europe, but its likely effect on production, farm profitability, and environmental services is poorly understood. Hence, from 2001 to 2005, the Silvoarable Agroforestry for Europe project developed a systematic process to evaluate the biophysical and economic performance of arable, forestry, and silvoarable systems in Spain, France, and The Netherlands. A biophysical model called "Yield-SAFE" was developed to predict long-term yields for the different systems and local statistics and expert opinion were used to derive their revenue, costs, and pre-and post-2005 grant regimes. These data were then used in an economic model called "Farm-SAFE" to predict plot-and farm-scale profitability. Land equivalent ratios were greater than one, showing Yield-SAFE predicted that growing trees and crops in silvoarable systems was more productive than growing them separately. Pre-2005 grants in Spain and The Netherlands penalised silvoarable systems, but post-2005 grants were more equitable. In France, walnut and poplar silvoarable systems were consistently the most profitable system under both grant regimes. In Spain, holm oak and stone pine silvoarable systems were the least profitable system under pre-2005 grants, but only marginally less profitable than arable systems under post-2005 grants. In The Netherlands, low timber values and the opportunity cost of losing arable land for slurry manure application made silvoarable and forestry systems uncompetitive with arable systems under both grant regimes.

Increased adoption of silvoarable agroforestry (SAF) systems in Europe, by integrating trees and arable crops on the same land, could offer a range of environmental benefits compared with conventional agricultural systems. Soil erosion, nitrogen leaching, carbon sequestration and landscape biodiversity were chosen as indicators to assess a stratified random sample of 19 landscape test sites in the Mediterranean and Atlantic regions of Europe. At each site, the effect of introducing agroforestry was examined at plot-scale by simulating the growth of one of five tree species (hybrid walnut Juglans spp., wild cherry Prunus avium L., poplar Populus spp., holm oak Quercus ilex L. subsp. ilex and stone pine Pinus pinea L.) at two tree densities (50 and 113 trees ha-1) in combination with up to five crops (wheat Triticum spp., sunflower Helianthus annuus L., oilseed rape Brassica napus L., grain maize and silage maize Zea mays L.). At landscape-scale, the effect of introducing agroforestry on 10 or 50% of the agricultural area, on either the best or worst quality land, was examined. Across the 19 landscape test sites, SAF had a positive impact on the four indicators with the strongest effects when introduced on the best quality land. The computer simulations showed that SAF could significantly reduce erosion by up to 65% when combined with contouring practices at medium (> 0.5 and < 3 t ha-1 a-1) and high (> 3 t ha-1 a-1) erosion sites. Nitrogen leaching could be reduced by up to 28% in areas where leaching is currently estimated high (>100 kg N ha-1 a-1), but this was dependent on tree density. With agroforestry, predicted mean carbon sequestration through immobilization in trees, over a 60year period, ranged from 0.1 to 3.0 t C ha-1 a-1 (5 to 179 t C ha-1) depending on tree species and location. Landscape biodiversity was increased by introducing SAF by an average factor of 2.6. The implications of this potential for environmental benefits at European scale are discussed.

No abstract

No abstract