Integrated assessment of silvoarable agroforestry at landscape scale

InEurope, agroforestry systems have been used mainly in traditional agriculture toprovide a variety of agricultural and tree products. However, during the last three centuries, the agricultural landscape inEuropehas seen a steady reduction of agroforestry. The reduction has been greatest since 1950, as the introduction of land consolidation programmes and agricultural mechanisation encouraged the removal of hedges and isolated trees from agricultural land. However, as the environmental costs of intensive agriculture have become apparent, there has been an increasing interest in the promotion of ecologically sound practices. Novel silvoarable techniquescould potentially offer a range of environmental and economic benefits in comparison with conventional arable cropping.The EU project "Silvoarable Agroforestry forEurope" investigated the European context of modern silvoarable agroforestry. It aimed to reduce uncertainties concerning the productivity and profitability of silvoarable systems, and to suggest European policy guidelines for agroforestry implementation.Within this broad framework, an integrated assessment of the environmental and economic performance of SAF was undertaken with the objective of assisting decision-makers implement ecologically sound land management practices. This was done in four steps: (i) developing an environmental assessment platform, (ii) applying the platform to test sites across Europe, (iii) co-ordinating economic assessments to the same test sites, and(iv) joiningboth environmental and economic results into an integrated interpretation.Chapter 2 describes the environmental assessment methodology to evaluate SAF systems based on the adaptation of existing models and the development of specific algorithms to predict the environmental effects of SAF at a farm- and landscape-scale. Modeling is needed when experiments are costly or too time consuming as in the case of agroforestry, where we assumed an average rotation to last 60 years.The framework comprised the assessment of soil erosion, nitrogen leaching, carbon sequestration and landscape diversity and allowed the comparison of the environmental performance of SAF with arable monocropping using these four indicators.The method opted for a broad view of the four environmental indicators, is applicable over a large geographic range (fromMediterraneanto Temperate Europe) and is based on spatial data that are generally available.The method was tested in three landscape test sites inSpain, inFranceand in The Netherlands.A total of five tree species were modelled: wild cherry (Prunus aviumL.), black walnut (Juglanshybr.), poplar ( Populus spp), holm oak (Quercus ilexL. subsp. ilex) and stone pine (Pinus pineaL.). 

Chapter 3 systematically assesses the environmental effects of SAFfor a stratified random sample of 19 landscape test sites (LTS) in Mediterranean and Atlantic regions ofEurope.For each LTS, existing geographical and statistical data were compiled, harmonized and complemented by field surveys. LTS were subdivided into a maximum of four land units (LU) using cluster analysis. The LUs were considered to be homogenous with respect to soil properties and climatic conditions and were used to represent farm management units. The LUs were ranked according to their potential productivity from "best land" to "worst land".The impact of SAF was explored by introducing SAF over 10% or 50% of the farm/landscape to simulate "pessimistic" and "optimistic" adoption by the farmer. Two tree densities (50 and 113 trees ha ^-1 ) were compared and SAF could be implemented in the best or worst quality land of the LTS to simulate different management priorities.

Across the 19 landscape test sites, SAF had a positive impact on the four environmental 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. Nitrogen leaching could be reduced by up to 28% in areas where leaching currently is high (>100 kg N ha ^-1 a ^-1 ), but this was dependent on tree density. With agroforestry, predicted mean carbon sequestration, over a 60-year 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.  

From the beginning of the research, Chapters 3 and 4 were co-ordinated and carried out in the same test sites. While Chapter 3 assessed the environmental effects of silvoarable agroforestry, Chapter 4 evaluated the profitability of the same scenarios as Chapter 3.

Time-series of annual production data and economic data for crops and trees (grants, revenue and costs) for each LTS were combined in the farm-scale bio-economic spreadsheet model FarmSAFE. The economic performance of the arable and silvoarable systems was compared using the infinite net present value( iNPV ) for a time-frame of 60 years (discount rate = 4%).

The Common Agricultural Policy (CAP) payments were modelled for arable and silvoarable systems assuming: 1) No CAP payments; 2) Pre-2005 CAP payments; and 3) Post-2005CAPpayments, assuming in the case of silvoarable systems that a Single Farm Payments would be made to the whole cropped area (whilst cropping occurred) and that 50% of tree costs would be covered for the initial 4 years of the tree rotation.

The analysis inFrancesuggests that walnut and poplar silvoarable systems could provide a profitable alternative to arable and forestry systems, while inSpaina modest restructuring of the amount and delivery of agricultural payments would increase the attractiveness of silvoarable systems of holm oak and stone pine. In the Netherlands, low timber value and the opportunity cost of losing arable land for slurry manure application made both silvoarable and forestry systems uncompetitive with arable systems.  

Chapter 5 is the integration of results obtained in Chapters 3 and 4 into a multi-criteria decision analysis (MCDA). ThePROMETHEE outranking approach was used to evaluate the integrated performance of silvoarable agroforestry relative to a status quo, on hypothetical farms in the nineteen LTS inSpain,France, and theNetherlands. The criteria used in the evaluation were soil erosion, nitrogen leaching, carbon sequestration, landscape biodiversity, and infinite net presentvalue,the latter assessed under six levels of government support. The MCDA was not configured to reflect the position of a specific stakeholder (e.g. an NGO might rate environmental criteria higher than profitability, whereas farmers might rate profitability higher than environmental criteria) but a neutral weight distribution was adopted.

InFrance, the analysis showed, assuming equal weighting between environmental and economic performance, that silvoarable agroforestry was preferable to conventional arable farming. The best results were observed when agroforestry was implemented on 50% of the highest quality land on the farm; the effect of tree density (50-113 trees ha ^-1 ) was small. By contrast, inSpainand theNetherlands, the consistently greater profitability of conventional arable agriculture relative to the agroforestry alternatives made overall performance of agroforestry systems dependent on the proportion of the farm planted, and the tree density and land quality used.

The environmental and economic performance of SAF in Europe is highly variable since each country/region has its specific biophysical and economic conditions. However, inEurope, ecological integrity is increasingly seen as fundamental to economic and social well-being. This work provided an initial approach for an integrated environmental and economic analysis of SAF systems. The findings could be refined to support policy development for silvoarable agroforestry as a new land-use alternative for farmers. At the same time, the framework could be adapted to the investigation of environmental and economic consequences of other land-use alternatives (e.g. new crops, forestation) at the landscape / farm scale.