Browsing by Author "van der Werf, Wopke"
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Item Open Access Development and application of bio-economic modelling to compare silvoarable, arable, and forestry systems in three European countries.(Elsevier Science B.V., Amsterdam., 2007-04-01T00:00:00Z) Graves, Anil R.; Burgess, Paul J.; Palma, João H. N.; Herzog, F.; Moreno, G.; Bertomeu, M.; Dupraz, Christian; Liagre, F.; Keesman, Karel; van der Werf, Wopke; Koeffeman, de Nooy A.; van den Briel, J. P.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 grantItem Open Access Implementation and calibration of the parameter-sparse Yield-SAFE model to predict production and land equivalent ratio in mixed tree and crop systems under two contrasting production situations in Europe(Elsevier Science B.V., Amsterdam., 2010-07-10T00:00:00Z) Graves, Anil R.; Burgess, Paul J.; Palma, João H. N.; Keesman, K. J.; van der Werf, Wopke; Dupraz, Christian; van Keulen, Herman; Herzog, F.; Mayus, MartinaSilvoarable agroforestry, the integration of trees and arable crops on the same area, has the potential to offer production, ecological, and societal benefits. However, the uptake of such systems in Europe has been limited by a combination of unsupportive policies and uncertainty concerning their productivity, profitability, and environmental impact. Faced with a lack of experimental data, the parameter-sparse Yield-SAFE model offers one method for generating plausible yield data and improving understanding of production in mixed tree–crop systems under European conditions. The applicability of the model was examined by: (i) selecting two contrasting sites in France and the UK with measured agricultural, silvoarable and/or forestry data, (ii) implementing the model in a software package, and (iii) inputting data and parameters on the climate, soils, management regime, and tree and crop types. Following calibration, Yield-SAFE provided credible descriptions of measured arable and tree (Populus spp.) yields in the monoculture and silvoarable systems at the two sites. An examination of the response of the model to changes in model parameters and environmental and management data showed that silvoarable crop yields were most sensitive to variations in tree parameters. Increased soil depths increased timber yields, and increasing stand density increased stand volume whilst decreasing individual tree volume. In all the simulations, the model predicted greater efficiency in use of land, i.e. greater land equivalent ratios, when trees and crops were combined rather than grown as sole crops. These results, supported by the sparse experimental data available, indicate that agroforestry provides a method of increasing food, timber and biomass production from limited land resources in EuropItem Open Access Silvoarable agroforestry in Europe - systems for meeting food and industry crop requirements with improved resource-use efficiency(2009-05-12T00:00:00Z) Palma, João H. N.; Graves, Anil R.; Burgess, Paul J.; van der Werf, Wopke; Herzog, F.Item Open Access System identification in production ecology: from theory to agroforestry practice(2009-07-08T00:00:00Z) Keesman, K. J.; Graves, Anil R.; van der Werf, Wopke; Burgess, Paul J.This paper introduces a system identification approach to agricultural ecosystems. In particular, the identification of an agroforestry system, combining trees with crops, is subject of study. Typically, for these systems N < p, where N is the number of data points and p the number of parameters in a (process-based) model. In this paper, we follow a constrained optimization approach, in which the constraints are found from literature or are given by experts. Given the limited a priori systems knowledge and very limited data sets, after decomposition of the parameter estimation problem and after model adaptation, we were able to produce an acceptable fit to validation data from a real-world agroforestry experiment.Item Open Access Yield-SAFE: A parameter-sparse, process-based dynamic model for predicting resource capture, growth, and production in agroforestry systems.(Elsevier Science B.V., Amsterdam., 2007-04-01T00:00:00Z) van der Werf, Wopke; Keesman, Karel; Burgess, Paul J.; Graves, Anil R.; Pilbeam, David; Incoll, L. D.; Metselaar, Klaas; Mayus, Martina; Stappers, Roel; van Keulen, Herman; Palma, João H. N.1. Silvoarable agroforestry (SAF) is the cultivation of trees and arable crops on the same parcel of land. SAF may contribute to modern diversified land use objectives in Europe, such as enhanced biodiversity and productivity, reduced leaching of nitrogen, protection against flooding and erosion, and attractiveness of the landscape. Long-term yield predictions are needed to assess long-term economic profitability of SAF. 2. A model for growth, resource sharing and productivity in agroforestry systems was developed to act as a tool in forecasts of yield, economic optimization of farming enterprises and exploration of policy options for land use in Europe. The model is called Yield- SAFE; from “YIeld Estimator for Long term Design of Silvoarable AgroForestry in Europe”. The model was developed with as few equations and parameters as possible to allow model parameterization under constrained availability of data from long-term experiments. 3. The model consists of seven state equations expressing the temporal dynamics of: (1) tree biomass; (2) tree leaf area; (3) number of shoots per tree; (4) crop biomass; (5) crop leaf area index; (6) heat sum; and (7) soil water content. The main outputs of the model are the growth dynamics and final yields of trees and crops. Daily inputs are temperature, radiation and precipitation. Planting densities, initial biomasses of tree and crop species, and soil parameters must be specified. 4. A parameterization of Yield-SAFE is generated, using published yield tables for tree growth and output from the comprehensive crop simulation model STICS. Analysis of tree and crop growth data from two poplar agroforestry stands in the United Kingdom demonstrates the validity of the modelling concept and calibration philosophy of Yield-SAFE. A sensitivity analysis is presented to elucidate which biological parameters most influence short and long-term productivity and land equivalent ratio. 5. The conceptual model, elaborated in Yield-SAFE, in combination with the outlined procedure for model calibration, offers a valid tool for exploratory land use stud