The interactions between land use and climate change are complex. Agriculture and changes in land use are an important source of greenhouse gases, and changes in climate and carbon dioxide concentrations have implications for crop, grass, and tree growth. Globally about 22% of greenhouse gas emissions are associated with agriculture, and land use and land-use change including deforestation (IPCC 2023). In the EU, for period 2016–2018, land use, land use change and forestry (LULUCF) and agriculture were associated with an annual average net source of about 118 Mt CO2e, derived from annual average agricultural emissions of about 386 Mt CO2e (European Environment Agency 2023) and an annual average sink from LULUCF of 268 Mt CO2e (European Commission 2018). In the United Kingdom (UK) in 2019, agriculture emitted 46 Mt CO2e and LULUCF was associated with another 6 Mt CO2e being down from a total of 18 Mt CO2e in 1990 (BEIS 2021).
Agroforestry or “farming with trees” is one method that farmers can use to mitigate against and adapt to the impact of climate change. The European Commission (2013) define agroforestry as a land use system in which trees are grown in combination with agriculture on the same land. Silvopasture, the combination of trees with grazing animals, is the main agroforestry system in Europe, whilst silvoarable, the integration of trees with arable crops, is present on much smaller areas (den Herder et al., 2017; Rubio-Delgado et al., 2023).
A large and growing body of literature has investigated the benefits of integrating trees in agricultural land. These include agricultural outputs such as cereals and livestock, and outputs derived directly from the tree component such as fruit, nuts, timber and wood fuel (Reed et al., 2017; Wiebe et al., 2022). There can also be enhanced ecosystem services from integrating trees into agricultural systems such as carbon sequestration, regulation of runoff, and biodiversity enhancement (Giannitsopoulos et al., 2020; Torralba et al., 2016; Medinski et al., 2015).
Agroforestry systems can offer production benefits per unit area of land compared to growing trees on separate areas of land from pasture or crop production. This is because the trees and the crops or pasture can be complementary in terms of the capture of solar radiation and water (Cannell et al., 1996). For example, when establishing widely spaced trees, an interrow arable crop can make effective use of the solar radiation and water not intercepted by the trees (Burgess et al., 2005; Ivezic et al., 2021). Hence the combined yields of timber and arable crops within an agroforestry system are typically greater than when trees and crops are grown separately. Trees can also moderate microclimatic extremes, providing more stable environmental conditions for understory species such as avoiding heat stress (Arenas-Corraliza et al., 2018).
Since the pre-industrial period, land surface air temperature has risen nearly twice as much as the global average temperature (land and ocean) (IPCC, 2023). Additionally, increases in frequency and intensity of weather extremes are adversely impacting terrestrial ecosystems and the services they provide (Seneviratne et al., 2021). A system which can absorb perturbations, bounce back, or adapt whilst still retaining the same functions can be defined as “resilient” (Viñals et al., 2023). Combinations of trees and annual crops have been reported to enhance agro-ecosystem resilience to extreme weather, contribute to soil and water conservation and improve the carbon stock and sequestration potential (Kay et al., 2019; Kumar et al., 2020).
Although they are simplified simulations of reality, models can be used to investigate the interactions of crops, trees and the environment (Burgess et al., 2019). They can guide decision-making and help land managers and policy makers to identify potential challenges related to, for instance, climate change and climate variability, and possible ways to address the effects. Even though there are agroforestry biophysical simulation models of varying complexity, the application of these models to climate adaptation is lacking (Farrell et al., 2023). Hence this study aims to examine the effects of current and future climates on crop yields, timber volumes, and soil organic carbon under grassland, arable, woodland, and agroforestry systems by carrying out simulations using a biophysical agroforestry model based on Yield-SAFE (van der Werf et al., 2007; Burgess et al., 2023). The modelled predictions of tree and crop growth under current weather conditions were validated by using data from two long term experimental sites in Northern Ireland. The model was then used to run virtual experiments to explore the effect of climate change, and the effect of different tree densities.