Hedgerows are a key semi-natural habitat, providing resources and a refuge for plant and animal species in agricultural landscapes. Agricultural intensification has resulted in the decline and loss of semi-natural habitats, and in the amount of soil organic carbon (SOC) stored in soils. This has contributed to a decrease in farmland biodiversity and a large carbon (C) debt in soils. To mitigate the effects of habitat loss on biodiversity, hedgerows, have been promoted as a tool in conservation policies. In addition, the SOC debt represents an opportunity for hedgerows to sequester C. Therefore, SOC sequestration is seen as a major part of climate mitigation strategies and large-scale ecosystem restoration. Hedgerows are high diversity, linear features that accumulate C in both their woody biomass and soil. Thus, the important role that hedgerows can play in mitigating climate change and restoring biodiversity has been recognised in recent policy reports. For example, the UK Committee on Climate Change (CCC, 2019) proposed that to achieve net zero by 2050 hedgerow length will need to increase by 40%. While, the Natural England Favourable Conservation Status report for hedgerows (Staley et al., 2020) recommended an increase of 60% for biodiversity gain. Hedgerow expansion can occur via a range of ‘actions’, including planting new hedgerows, gapping up to develop a continuous hedgerow, rejuvenating by hedge-laying or coppicing, allowing to grow taller/wider and allowing individual trees to mature.
In the 2007 Countryside Survey, over half of hedgerows in England were of poor quality (in poor structural condition; Carey et al., 2008). Hedgerows in good structural condition may support more species and individuals from a range of plant and animal taxa (Graham et al., 2015). However, we don’t currently know how hedgerow structural composition, the woody species present, hedgerow age and the landscape context may affect the plant species growing in the base of hedges, including woodland specialists. Regarding C storage in hedgerows, there is a lack of studies that have quantified the C stocks in both soil and biomass. Where biomass C stocks have been quantified, it is for a limited number of species and focuses on how stocks change with height and width (Axe et al., 2017). Our recent study showed that SOC stock is controlled by time since planting until it reaches a plateau at ~40 years (Biffi et al., 2022). We also provided the first estimate of how much CO2 could be taken up by hedgerows as a result of increasing total length by 40%. However, there is a need to reduce the uncertainty associated with this estimate by considering the influence of soil type, climate, and management on C sequestration. Improved understanding of how these factors influence the biodiversity and C stocks of hedgerows and whether there are trade-offs or synergies between C sequestration and biodiversity as a result of different hedgerow actions is urgently required. As it will help to ascertain the role hedgerow expansion can make to UK net zero and biodiversity targets, support the ongoing development and rollout of post-Brexit national agri-environment schemes and payment for ecosystem services schemes (e.g. Hedgerow Code).
Aim and Objectives
The major aim of this project is to assess the potential contribution of hedgerow expansion to mitigate biodiversity loss and climate change. This will be achieved via a number of objectives via a combination of (i) analysis of existing national datasets on hedgerow extent and plant communities, (ii) collection of new fieldwork and (iii) upscaling of results using a range of data analysis/modelling approaches:
1) Evaluating how temporal changes to plant communities between 2007 and summer 2023, and regional differences between hedges, are affected by the woody species present, the quality (structural condition), and the age of hedgerows taking into account other landscape factors (such as land management and the amount of semi-natural habitat).
2) Investigating how C stocks and sequestration (in biomass and soil) are influenced by hedgerow condition and woody composition versus soil type, through collection of new data.
3) Estimating the plant diversity and C stocks of the present-day hedgerow network across England (aka ‘natural capital’).
4) Modelling the potential impact of different hedgerow expansion scenarios on climate change mitigation potential and biodiversity gain and identify trade-offs and/or synergies.
The outputs of this research project will be of benefit to academics, conservation organisations and groups, farmers and landowners, policy development, government and society. Via the CASE partnership with Natural England, the research will help inform government policy on agri-environment schemes for hedgerow restoration, management and planting. In addition, the findings will be useful for private and NGO hedgerow planting initiatives, such as those run by the Tree Council under the Close the Gap project and Woodland Trust. The results will also inform the development of payment for ecosystem services schemes & carbon codes.
The student will work under the supervision of Professor Pippa Chapman & Professor Guy Ziv within the School of Geography, University of Leeds and Dr Jo Staley and Dr Lisa Norton from UK Centre for Ecology and Hydrology. The successful candidate will develop a range of research skills, including experimental design, field sampling, statistical analysis and modelling, data interpretation, academic writing skills and giving presentations. Training will be provided in field health and safety procedures and the use of field equipment. In addition, the candidate will develop their understanding of (i) plant identification, (ii) processes related to the cycling and storage of carbon in hedgerow biomass and soils, and (iii) hedgerow management.