Tree Suitability Modelling.
The UK Government has set a target to achieve net zero emissions by 2050. The target requires all sectors of the UK economy, including agriculture and forestry, to make contributions. In 2019, the Committee for Climate Change (CCC) commissioned a study to investigate the application of spatial modelling to tree species and site selection in Wales to see if its ambition of planting 152,000 ha in Wales was feasible.
The project focused on one coniferous (Sitka Spruce) and one broadleaved (Sessile Oak) tree species. The project built on draft modelling outputs from the Welsh Government Capability, Suitability and Climate Programme, where Environment Systems worked in collaboration with Cranfield University and ADAS to spatially model differences in land suitability for growing 118 crops.
The afforestation case study evaluated land suitability for Sessile Oak and Sitka Spruce based on biophysical properties alone, and in combination with legal and policy constraints to tree planting. Spatial modelling and statistical analysis were undertaken for the present day, and for four future climate change scenarios; 2050 and 2080, under medium and high greenhouse gas emissions.
This project utilised Agricultural Land Classification data, which considers different aspects of climate and soil properties, and assigns grades for each environmental factor. This ranks the quality of the land in terms of soil wetness, droughtiness, stoniness and rockiness, in addition to steepness of slope and overall climate of a location. This dataset was supplemented by additional modelling carried out by Environment Systems to include frost risk, wind exposure and salt spray effects. Natural Resources Wales flood risk data were also incorporated into the models.
Biophysical factors are clearly vital for understanding where it is possible to grow crops. However, legal and policy decisions also exert a very real effect on the land available for growing crops. The project considered significant constraints to tree planting, such as areas of deep peat and priority habitats where tree planting is not currently possible (or desirable). It also considered ‘sensitivities’ such as historic and open access land, where tree planting may be possible, however, additional planning and consultation may be required.
The modelling revealed that the CCC tree-planting ambition for Wales is achievable however, it is likely to require the use of land that is less than biophysically ideal, and which is likely to be under pressure from competing land uses such as agriculture and energy generation. Significantly, it questions whether the target is sufficient to achieve the level of climate mitigation required, given the likely slower growth rates of trees on limited suitability land.
The full report can be accessed here.