Predicting effects of the Common Agricultural Policy on farmland birds

Background

Despite the commendable intention of EU’s subsidy system (the Agri-Environmental Schemes, AES and the Cross compliance regulations) under the Common Agricultural Policy (CAP) to halt biodiversity decline in farmland, little evidence to date suggests this has been successful (Kleijn et al., 2011).

However, the CAP is regularly reformed with the intention to increase the ability for CAP to meet biodiversity targets. For example, a reform of the CAP is planned to take effect after 2013 (CAP framework 2014–2020), with the aim of enhancing incentives for farmers to manage land for preserving long-term productivity while adopting and maintaining farming systems/practices favourable to EU’s environmental, biodiversity and climate objectives.

To evaluate consequences of such policy changes aimed at preserving biodiversity, typically, statistical models applied to historical data are used to inform about the future. However, the ability to forecast the consequences on biodiversity of changes in policies is constrained by a lack of evaluated models able to predict the full chain policy – agricultural land-use – biodiversity.

In order for decision makers to choose between policy alternatives based on their ability to meet intended effects, there is need for a versatile predictive tool that as accurately as possible can forecast their effects, using good quality background data on land-use and biodiversity. In other words, the tool should be able to make extrapolated predictions in time and space, with narrow precision (prediction intervals) and should be reasonably realistic facilitating inference of mechanistic relationships.

Aim

The aim of this project is to develop such a predictive tool for forecasting the ability of proposed policy changes to meet stated policy objectives and to evaluate the efficacy of this tool in terms of predictive accuracy and precision. While the framework will have components of more general applicability, the focus is on the Common Agricultural Policy (CAP) and its objective to promote sustainable land management, in particular in terms of maintaining farmland biodiversity.

Description

The tool is comprised of a model describing the relationships between policy, land-use and biodiversity. Input to this model would be proposed measures from the CAP (for example subsidies for maintaining semi-natural grasslands or cross compliance) framed in expected changes in agricultural markets and the output would be predictions of species abundances and farmland biodiversity. The relationship between land-use and populations is modelled by fitting a statistical model (habitat association model, HAM) to training data from specifically designed surveys, whereas the relationship between policy and land-use is modelled using an agent-based simulation model. The results from these two modelling efforts will be combined into predictions for farmland biodiversity. The approach will yield predictions for both land-use and biodiversity and these will be evaluated on historical data.

The project focuses on birds as a measure of biodiversity. Although they constitute only a small part of all biodiversity in farmland, there are good reasons to use them as indicators. They are at the top of the food chain and hence, changes in the abundance of birds likely reflect changes occurring at lower levels if the chain. There also exist a well-developed monitoring program with associated indicators of population dynamics at both national and supranational scales (Gregory and others, 2005) and the association between populations trends of farmland birds and changes in agricultural environments are well established in the literature (Donald and others, 2006; Wretenberg and others, 2010). They are also highly relevant for this project since an indicator of population trends among 36 farmland bird species (the European Farmland Bird Index, EFBI) has been adopted as a Structural and Sustainable Development Indicator by the EU (Butler et al., 2010).

We work in close collaboration with the Swedish Board of Agriculture from which spatially explicit data on landuse in farmland is available in the form of an Integrated Administration and Control System (IACS) database. Apart from own bird surveys we also utilise bird monitoring data from the Swedish Bird Survey. Agent-based modelling of the step from policy measures within CAP via farmers’ production decisions to changes in landuse is performed using the Agricultural Policy Simulator (AgriPoliS) in which the behaviours of farmer character types (agents) are predicted through algorithms of simulated interactions with a number of other entities including spatial (landscapes), technological (machinery and farming practices), and politic and economic environments (markets, policies) under the objective to maximize farmer income. Predictions from AgriPoliS are coupled to the IACS to make spatially explicit predictions for future landuse.

One of the key requirements for the models produced is to explicitly incorporate the uncertainty of parameters estimates since they will be used in predictions at later stages. Therefore we use Bayesian modelling techniques in which the output consists of samples from the posterior distributions of model parameters. The Bayesian modelling approach provides a natural framework when the focus of the statistical modelling is to estimate parameters. In this way, uncertainty in model estimates can be easily incorporated into predictive models without the need for complex or intractable algebraic calculations of prediction errors. A further advantage is that the Bayesian approach allows incorporation of prior knowledge into the models.

References

• Butler, S.J., Boccaccio, L., Gregory, R.D., Vorisek, P., Norris, K., 2010. Quantifying the impact of land-use change to European farmland bird populations. Agriculture, Ecosystems & Environment 137, 348–357.
• Donald, P.F., Sanderson, F.J., Burfield, I.J., van Bommel, F.P.J., 2006. Further evidence of continent-wide impacts of agricultural intensification on European farmland birds, 1990–2000. Agriculture, Ecosystems & Environment 116, 189–196.
• Gregory, R.D., van Strien, A., Vorisek, P., Meyling, A.W.G., Noble, D.G., Foppen, R.P.B., Gibbons, D.W., 2005. Developing indicators for European birds. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences 360, 269–288.
• Kleijn, D., Rundlof, M., Scheper, J., Smith, H.G., Tscharntke, T., 2011. Does conservation on farmland contribute to halting the biodiversity decline? Trends Ecol Evol 26, 474–481.
• Wretenberg, J., Pärt, T., Berg, Å., 2010. Changes in local species richness of farmland birds in relation to land-use changes and landscape structure. Biol.Conserv. 143, 375–381.