CR2025_16 Does wilder grazing enhance ecosystem processes?

Lead Supervisor: James Bullock, UK Centre for Ecology and Hydrology

Email: jmbul@ceh.ac.uk

Co-supervisors: Luca Borger, Department of Biosciences and Biomathematics, Swansea University; David Brown, National Trust; Anita Diaz, Department of Ecology, Bournemouth University

Rewilding is “a captivating, controversial, 21^st century concept to address ecological degradation”¹. It aims at the reorganisation of biota and ecosystem processes to set an ecological system on a trajectory towards becoming self-sustaining and governed by natural processes. It can involve a variety of actions, including: introducing large herbivores and/or predators, allowing natural regeneration of trees, or reinstating a more natural hydrology. There is some evidence of rewilding benefits to biodiversity and ecosystem functioning, but the concept is controversial, with issues around the varying definitions of rewilding, concerns about societal acceptability, and, critically, insufficient knowledge about its potential outcomes². Understanding rewilding trajectories is problematic because of the large scale at which it works, meaning rewilding is not amenable to the plot-based field experiments that dominate ecology, and the lack of a solid quantitative and predictive foundation.  Rewilding science, and ecology more generally, requires a new research paradigm of large-scale process studies to facilitate predictive understanding. This PhD will develop and realise just such a paradigm.

Transitioning to wild grazing is a major rewilding strategy. One extreme is to develop completely wild grazing (e.g. in the Swiss National Park³). Alternatively, ‘naturalistic grazing’ uses domestic livestock, deploying a variety of functionally different species and allowing free-range behaviour, but does not aim for the full range of wild processes, e.g. natural mortality or large predators. Questions concern the forms of rewilding that can take place in highly populated landscapes, especially with conservation priorities that include semi-natural ecosystems such as heathland. To inform this issue, we require robust data on how ecological processes are affected by wilder grazing. We can hypothesise that a wider variety of free-ranging grazers, having a diversity of diets and feeding behaviours, will create a variety of disturbances, provide a range of ecological functions, and facilitate dispersal of a range of species. The resulting complex, heterogeneous and dynamic vegetation is likely to diversify species assemblages.

This PhD will focus on the Purbeck Heaths ‘Super National Nature Reserve’ that encompasses multiple landowners, with the National Trust playing a key role. The driving principle for this super-NNR is to shift from a traditional conservation approach of managing small reserves to a target state, towards the restoration of natural processes to create a more dynamic, complex landscape. In roughly half of the super-NNR, wilder grazing has been initiated using ancient breed cattle, equines and mangalitsa pigs alongside wild deer, allowing larger foraging ranges, a wide range of grazing guilds, and herds behaving as naturally as possible.

A major aspect in assessing how wilder grazing impacts ecosystems is to understand where grazers go and what they do. This is made possible by Global Positioning System (GPS)-enabled multi-sensor tags, developed at Swansea University⁴, which we have deployed on domestic and wild ungulates as well as wild boar. These tags collect high frequency location, accelerometer, magnetometer and temperature data. The student will be able to deploy these units on the grazers and make use of the ‘DDMT’ software we have developed at Swansea to handle the large biologging datasets generated and identify high-resolution behaviours, as well as methods to derive high resolution movement tracks, resource selection, and predict emerging large-scale spatial patterns⁵. This high-resolution information on movement tracks and behaviours can be linked to satellite mapping of the reserve, and fieldwork on the impacts of the different grazer activities on plants and other animals, via processes including disturbance and dispersal. This can involve camera trapping of larger animals (e.g., deer), vacuum sampling of invertebrates, and quadrats for plant species, depending on the focus decided upon.

Overall, we expect the PhD will address the following aims:

1. Quantify and map high-resolution movements and behaviour of grazers under wilder grazing schemes in a complex rewilding site
2. Assess effects of functionally different grazers on local habitat heterogeneity, multi-species connectivity for plants and invertebrates, and the potential for increasing biological complexity
3. Predict and scale-up wild grazing-driven modification of ecological processes and assess the efficacy to meet rewilding objectives

Training opportunities:

A major aspect of this PhD will be the extended time spent with the National Trust staff and volunteers. This will provide first-hand experience of wilder grazing conservation practice and facilitate research practicalities such as access to livestock.

The UKCEH provides opportunities for the student as a bridgehead between academic research and its application in conservation bodies as well as industry. Bournemouth provides expertise and data on habitat and grazing monitoring within the reserve. Swansea provides bespoke state-of-the-art training in tracking animals, analysis and creating models using these data, which will be a key element of this PhD. 

Student profile:

This project will be suitable for students with a degree in ecology or zoology, or a closely related environmental or physical science. An interest in conservation is ideal alongside an ability to learn quantitative approaches. This will suit someone who desires a career in academia, but the training will also be useful for a student interested in working in conservation or policy.

Please note: For international candidates, this project will be hosted at Swansea University under lead supervision of Luca Borger.

Co-Sponsorship details:

The project will receive co-sponsorship from the National Trust.

References:

1. Pettorelli, N. et al. Making rewilding fit for policy. Journal of Applied Ecology 55, 1114–1125 (2018).
2. Pettorelli, N. & Bullock, J. M. Restore or rewild? Implementing complementary approaches to bend the curve on biodiversity loss. Ecological Solutions and Evidence 4, e12244 (2023).
3. Perino, A. et al. Rewilding complex ecosystems. Science 364, 5570 (2019).
4. Painter, M. S., Silovský, V., Blanco, J., Holton, M., Faltusová, M., Wilson, R., Börger, et al. Development of a multisensor biologging collar and analytical techniques to describe high-resolution spatial behavior in free-ranging terrestrial mammals Ecology and Evolution 14: e7026 (2024).
5. Potts, J. R., Börger, L., Strickland, B. K. & Street, G. M. Assessing the predictive power of step selection functions: How social and environmental interactions affect animal space use. Methods in Ecology and Evolution 13, 1805–1818 (2022).