IAP-25-037

Transforming landscapes: the role of large herbivores in Holocene ecosystem dynamics

Large herbivores play a significant role in Earth System function and late Quaternary extinction of megaherbivores has had wide-ranging impacts on ecosystem function (Mahli et al. 2016). By contrast, in long-settled regions like NW Europe, large herbivores – wild and domesticated – are often implicated in Holocene landscape transformation (Fyfe et al. 2015), but we lack a clear understanding of their role in ecosystem function and how this has altered over the long timescales involved in vegetation development or climate change.

This gap matters for ecology and conservation (e.g. setting baselines for a ‘wilder’ landscape), as well as archaeology and history (e.g. how transitions between wild and domesticated grazing regimes affect biodiversity). These issues are particularly relevant to the Scottish Highlands, the focus for this project, because this is a landscape in flux: animals have been an influential component since prehistory, were instrumental to socio-economic and ecological transitions in the historic past (Hanley et al. 2008) and remain a source of tension in contemporary management. The extent to which climate has constrained or facilitated tree growth alongside dynamic grazing regimes also remains unclear and is highly relevant to future woodland resilience.

Palynology (pollen analysis) has been the most widely used proxy for studying herbivory over long timescales but is an imperfect tool: using pollen to identify grazing disturbance and its effects on plant communities adds potential circularity to causal arguments, and pollen cannot be used to infer which animals were present. Innovations in palaeoenvironmental and archaeological science mean that additional proxies can help are available alongside pollen data to address these gaps, notably using dung fungi to identify major shifts in herbivore abundance (Baker et al. 2013) and faecal biomarkers to discriminate between animal species (McClymont et al. 2023). Independent records of climate change can also be extracted from the biomarker signal. To date only a few studies have combined these proxies (Davies et al. 2022, Brown et al. 2022). Integrating these methods can address Scotland-specific and broader long-term ecological questions. For example, using dung fungi and pollen, Jeffers et al. (2018) found little evidence that herbivore disturbance regulated plant communities during the early-mid Holocene, while Kunes et al. (2019) used pollen data to suggest that the relationship between disturbance and plant diversity changed during the later Holocene due to intensified disturbance, but they did not explicitly examine the role of herbivores. As a result, much remains to be understood about the extent to which large herbivores acted as ‘ecosystem engineers’ and how this altered through the Holocene.

The project aims to address these gaps by combining dung fungi, biomarkers and pollen into a palaeo-grazing toolkit to evaluate the role of large herbivores in Holocene vegetation transitions, with emphasis on woodlands. It will examine the following research questions:
– Sensitivity testing: How does the sensitivity of the grazing signal vary between proxies and site type (peat, lake) when applied to recent grazing regimes?
– Temporal interactions: How does the grazing signature and its palynological vegetation impact vary between sites and over time (e.g. between periods with contrasting large herbivore assemblages)?
– Impact agenda: How can palaeoecological data combined with contemporary concerns about environmental management to develop more accessible evidence about long-term grazing ecology?

The research student will receive full training in the methods proposed through the supervisory team and visits to their laboratories.

Objective 1. Assess how the sensitivity of each grazing proxy varies with sedimentary environment using ecological experiments.
Sensitivity testing is essential for robust science, particularly when applying new combinations of methods. The modern and Holocene objectives of this project focus on changepoints in Scottish vegetation history because dung fungi are more effective sensors at ecologically high grazing intensities (Davies et al. 2022). This first stage will characterise the pollen, dung fungal and faecal biomarker signatures in surface samples and short sediment cores from paired peat and lake sites and compare these with known changes in grazing regime over recent decades to refine the study design, improve replicability and complementarity between proxies (e.g. are faecal biomarkers in lakes more sensitive to catchment grazing than localised peat signatures?).

Objective 2. Apply the toolkit to investigate the role of grazing as a driver of change during periods of Holocene woodland transition.
The toolkit will be applied to selected time periods at two-three sites to create a spatio-temporal network of records. These periods could include the establishment of upland farming in the Neolithic (transition from wild to domesticated regime), woodland fragmentation during the mid-Holocene (climatic and grazing impacts are hypothesised), and the transformation of rural land-use in the late eighteenth and nineteenth centuries (dispersed farming communities were removed to make way for extensive sheep farms and sporting estates). The results will be analysed to compare vegetation impacts and herbivore proxies (e.g. dissimilarity indices, biodiversity metrics).

Objective 3. Establish effective working relations with natural and cultural heritage organisations and managers in the study region to improve the accessibility of palaeo-archives.
Palaeoenvironmental diagrams are challenging for non-specialists to read and interpret, but palaeo-scientists may similarly have limited insight into the priorities of conservation and heritage managers. Several organisations and landowners in the Cairngorms study area (NE Scotland) have previously engaged with palaeoecology, but the influence of exposure to long-term evidence remains unclear. The student will introduce the project to key stakeholders in the area to identify common interests and explore alternative presentation formats that connect past and future woodland dynamics, and the potential to contribute to public engagement events.

Year 1

Literature review and research design. Begin work on Objective 1 including full training in laboratory methods with supervisory team. Establish when Objective 3 meetings and events are most appropriate for student and wider actors.

Year 2

Complete Objective 1 and write up findings as chapter and/or paper for submission, commence Objective 2 and continue Objective 3.

Year 3

Complete Objectives 2 and 3.

Year 3.5

Write up thesis.

The student will develop the skills necessary to undertake the data collection and analyses through in-house training (pollen, dung fungi) and by spending time in Durham (biomarkers), with opportunities to attend external training courses (e.g. data analysis and visualisation, science communication), although some previous laboratory, ecological and/or palaeoecological experience is strongly preferred. The project will involve periods of time in the field as well as the lab. Further training in transferable skills, including project management, oral and written presentation and media and outreach engagement is available through the Centre for Educational Enhancement and Development (CEED) at the University of St Andrews. The student will be expected to present their work at appropriate national and international conferences throughout their PhD. They will join the Environmental Change Research Group and terrestrial environments reading group, including multiple PhD students, at St Andrews.