IAP2-23-052

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

Large herbivores play a significant role in Earth System function and work to date has identified the wide-ranging impacts that the late Quaternary extinction of megaherbivores may have had 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 comparable understanding of their functional role 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 affected 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 but 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 both 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 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 the improved ability of 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 set the observed trends into context with environmental changes. 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 regime change?
– 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 management concerns to develop more accessible evidence about long-term grazing ecology?

Methodology

The research student will receive full training in all of the methods proposed here, through the supervisory team and visits to supervisor’s home institution 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. Dung fungi are more effective sensors at ecologically high grazing intensities (Davies et al. 2022), so both the modern and Holocene objectives of this project focus on changepoints in Scottish vegetation history. 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 (herbivore density, composition) over recent decades to refine the study design, improve replicability and complementarity between proxies (e.g. lakes may provide a more sensitive record of faecal biomarker input within a catchment than peat).

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

Objective 3. Establish effective working relations with National Trust for Scotland (NTS) Archaeology Department, managers at NTS Mar Lodge Estate and in the wider study area to improve the accessibility of palaeo-archives.
Palaeoenvironmental diagrams are challenging for non-specialists to read or interpret, but palaeo-scientists may similarly have limited insight into the priorities of conservation and heritage managers. The student will collaborate with NTS Archaeology Department and Mar Lodge Estate to embed two-way dialogue throughout the project. This will provide opportunities to discuss common interests to inform research design and explore alternative presentation formats that connect past and future woodland dynamics, and potential to contribute to public engagement events and to interpretation and education materials at Mar Lodge Estate. In return, collaboration with NTS staff will ensure that future environmental management is framed by an understanding of long-term cultural and climatic impacts on this landscape.

Project Timeline

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

Training
& Skills

The student will develop the skills necessary to undertake the data collection and analysis outlined here through in-house expertise (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). The project will involve periods of time in the field as well as the lab. Some previous laboratory, ecological and/or palaeoecological experience is strongly preferred. No previous experience of biomarker analysis is required. 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.

References & further reading

Baker, Bhagwat, Willis (2013) Do dung fungal spores make a good proxy for past distribution of large herbivores? Quaternary Science Reviews 62: 21–31.
Brown et al. (2022) New integrated molecular approaches for investigating lake settlements in north-western Europe. Antiquity 96: 1179-1199.
Davies et al. (2022) A multiproxy approach to long-term herbivore grazing dynamics in peatlands based on pollen, coprophilous fungi and faecal biomarkers. Palaeogeography, Palaeoclimatology, Palaeoecology 598: 111032.
Fyfe et al. (2015) From forest to farmland: pollen-inferred land cover change across Europe using the pseudobiomization approach. Global Change Biology 21: 1197-1212.
Hanley et al. 2008. Economic determinants of biodiversity change over a 400 year period in the Scottish uplands. Journal of Applied Ecology 45: 1557–1565.
Jeffers et al. (2018) Plant controls on Late Quaternary whole ecosystem structure and function. Ecology Letters 21: 814-825.
Kuneš, Abraham, Herben (2019) Changing disturbance-diversity relationships in temperate ecosystems over the past 12000 years. Journal of Ecology 107: 1678–1688.
Malhi et al. (2016) Megafauna and ecosystem function from the Pleistocene to the Anthropocene. Proceedings of the National Academy of Sciences 113: 838-846.
McClymont et al. (2023) Biomarker proxies for reconstructing Quaternary climate and environmental change. Journal of Quaternary Science https://doi.org/10.1002/jqs.3559
Tipping et al. (2008) Prehistoric Pinus woodland dynamics in an upland landscape in northern Scotland: the roles of climate change and human impact. Vegetation History and Archaeobotany 17: 251-267.

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