The impact of woodland planting on hydrogeological variables at different proximities to woodland

Abstract:

One of the impacts of a changing climate in the UK is that flooding is likely to become more frequent. Consequently, the application of Natural Flood Management (NFM) methods are prudent, wherever possible, to achieve a more sustainable and naturally-based approach to flood risk management. Despite this, there are few evidence-based studies assessing the benefits of NFM methods in reducing flood risk, but one method that is assumed valuable, although under-investigated, is woodland planting. Tree roots enhance soil macro-porosity, infiltration and capacity while also reducing overland flow. However, to date, few long-term studies have been conducted to investigate the effect of woodland planting on hydrogeological variables and overland flow reduction.

The Heart of England (HofE) Forest charity has planted 1,883,928 trees across 2832 hectares of Warwickshire, England. At the study site, Spernal Farm, tree planting began in 2006 and continued annually until 2012, at which point the woodland was left to grow with very little human interference. This study aims to determine to what extent woodland planting by HofE Forest has influenced soil hydrogeological variables, and how these change depending on proximity to tree and tree maturity. To achieve this, a Mini Disk Infiltrometer (MDI) was used to measure infiltration rate and infiltration capacity at 10 and 200cm away from trees planted in 2006, 2008, 2010, 2012, 2014 and 2020. Additionally, historic woodland planted pre-1900 was sampled on the site, along with a grassland control.

Results confirm that average total infiltration is higher 10cm away from the tree compared to 200cm away. Furthermore, infiltration rates near more mature woodland (e.g. pre-1900) are higher than the grassland control.

The information to be collected throughout the remainder of this study will contribute to the current lack of empirical studies regarding the use of woodland planting as a method of NFM. Additionally, findings will aid in justifying the use of woodland as an effective, amenable and sustainable method of flood defence in light of a changing climate.