I recently attended the Native Woodland Discussion Group’s conference with this title at Perth (http://www.nwdg.org.uk). It was a fascinating day, kicked-off by Frans Vera, talking about the role that large herbivores might have played in shaping such forests. My reflections on the day are set out below.
A challenge to conservation thinking
I first read Frans Vera’s book Grazing and Forest History on a train in late 2000, travelling to a previous meeting of this group to speak on wood-pasture. The train was so delayed I had time to change my talk in the light of his ideas. There is no doubt that we had overlooked, perhaps not totally but significantly, the impact that grazing animals had on the pre-Neolithic landscape.
Vera’s work challenged us to revisit assumptions, we were not aware that we were making. He argues that the evidence has been misinterpreted by foresters and the early ecologists such as Clements and Tansley. Large herds of bison, wild horse, aurochs and deer drove the vegetation cycle across at least the lowlands of north-western Europe, allowing light-demanding species such as oak and hazel to flourish. Tree regeneration occurred as single trees or groups of trees (groves) in the protection of thorny shrubs, part of a shifting mosaic, a half-open landscape, not the dense primeval forest of traditional ecological thought.
Not so much a blanket of trees as a crotched quilt.
The book appeared at a time when ideas on grazing in woodland were changing: Oliver Rackham had presented a paper to forest history conference in Nottingham in 1996 on Savanna in Europe (Rackham 1998); the Veteran Tree Initiative had raised the profile of wood-pasture systems (Kirby 1995); work led by Fraser Mitchell and Alison Hester (Mitchell & Kirby 1990; Kirby et al. 1994; Hester et al. 1996) explored some positive aspects of grazing in woodland for conservation.
Upland wood-pasture with veteran trees and Naddle Wood, the site for grazing experiments.
Conservation was moving out into the wider countryside through various types of agri-enivronment schemes and large-scale Heritage Lottery Fund support, rather than solely focussing on protected sites. This encouraged people to look at different ways of managing land for conservation and on a bigger scale. Some of the ideas inspired by what was happening in Oostvaardersplassen seemed, in 2000, rather way-out. There was talk of re-introducing large predators, allowing free-range grazing of cattle over large areas, letting nature, rather than nature conservationists decide what should happen. These were badged under the name of rewilding, then a term that was hardly known in the UK. The best-documented projects to emerge from this movement are probably the Knepp Estate in Sussex (Tree 2018) and Carrifran in the Borders (Ashmole and Ashmole 2009).
Views of the Knepp Estate and Carrifran
Frans’s advocacy for the role of large herbivores in both the pre-Neolithic forest and for modern conservation practice has been, and continues to be, one of the most significant influences on woodland conservation thinking in the last couple of decades.
Re-visiting the paleo-ecological evidence
Not everyone accepts that grazing animals would have been the most significant driving factor, or that the early Holocene landscape was a half-open mosaic of grassland and trees (at various densities). Fraser Mitchell emphasised that the pollen record, when corrected for various biases in terms of differential pollen production, still pointed to a predominantly tree-covered landscape (Mitchell 2005). Moreover, where the pollen record could be tested against independent, written evidence of past high tree cover, as in the Eastern United States, the two strands were well-matched. Small-hollow pollen records, that reflect just the immediate surrounding vegetation, do not show the sort of change over time from tree to grassland dominance and back again, that might be expected from a shifting mosaic landscape. There could be reasons why the absence of grass-type pollen might not reflect an absence of grassland in the landscape, if the grass was so heavily grazed it never flowered for example. However it seems to be me, that there must be independent evidence that the grassland did exist before it is reasonable to invoke this explanation.
A lowland fen pollen sample site
Ralph Fyfe expanded on the approaches developed in the last decade to improve the relationship between what is shown in the pollen record and the vegetation that produced it (Fyfe et al. 2013). Modern pollen records can now be modeled to produce a good match to modern vegetation patterns at a regional scale. When these models are applied with early Holocene pollen data they do show higher openness than inferred from the raw pollen record, but the pattern suggests a climatic driver – more open woodland in the less continental climates of Ireland, Britain and western France; higher tree cover in central Europe. New pollen records from development-funded archaeological surveys across London may offer the potential to look at past variations in landscape composition at a local scale. At any given time-slice in the record what proportion of the samples are predominantly tree-ed or open?
Pollen records remain the most widespread indicators of the past landscape composition, but increasing use is being made of other proxies: charcoal, sub-fossil beetle remains, snail shells. Each will have its own strengths and weaknesses with regard to what interpretation can be put on them. These need to be tested as strongly as the palynologists are now doing with the pollen record.
Sub-fossil snail remains in the soil suggest the area around Stonehenge and Avebury has always been rather open in contrast to the chalk landscapes of the south-east.
One of the most recent proxies to be investigated are the spores of fungi that live on animal dung (Innes and Blackford 2003). These might be able to show where large concentrations of grazing animals were occurring, and perhaps eventually provide an indication of herbivore density. Althea Davies outlined her work to see whether it was possible to distinguish grazed, from un-grazed, moorland vegetation through sampling in long-established exclosures, across sites where the grazing animals and densities differ in a known way, and sites where grazing pressures are known to have changed over time. This work shows promise, although one uncertainty is whether the records may be confused by spores from fungi on the dung of small herbivores such as grouse.
Will fungal spores eventually allow us to detect herds such as these at Oostvaardersplassen?
The human factor
We have also had to rethink the role of humans in shaping our landscape, with a greater appreciation of our role in wiping out much of the mega-fauna, not just in Europe but globally; this trend unfortunately continues. Loss of the mega-fauna seems to have allowed a more tree-ed landscape to develop since the last ice-age than in previous inter-glacials (Sandom et al. 2014) and will also have affected large-scale movement of nutrients and seed dispersal across the landscape (Doughty et al. 2013).
Do we need to bring back elephants?
Human impacts become much more obvious with the arrival of Neolithic cultures. Gordon Noble illustrated how trees and wood played an important role in their societies (Noble 2017). Many massive wooden structures are being identified involving posts from trees up to 1.5 m diameter in some cases. Patterns of root-pits from fallen trees found under or around such structures might be used in future to explore tree form and densities.
The landscape continued to change through later cultures to the point that human interventions, past and present, predominate over natural processes in shaping the vegetation structure and composition. The temptation is then to assume that everything we see is the product of just the last couple of centuries of farming and forestry practice. Ian Rotherham countered this view, with examples of what might be survivals of unenclosed wood-pastures, perhaps dating back to pre-Medieval period, identified through studies of old maps and woodland indicator plants (Rotherham 2017).
Where to now?
Frans Vera’s challenge to accepted thinking has stimulated much more cross-disciplinary dialogue and working. The different strands of paleo–ecology have had to try to reconcile their different interpretations of the past; landscape ecologists and archaeologists have been brought in to try to factor out the human influence; mammal ecologists and grazing specialists have added their comments as to whether the large herbivores could have had the postulated impacts. I know that I have ended up reading papers from disciplines that I would not otherwise have explored.
There is a consensus building that there was more openness in the landscape and that large mammals had a critical part to play in helping to maintain that openness in some places and at some times. The challenge is now to make this more quantitative and landscape-specific.
In any 10 x 10 km square (not quite twice the size of Oostvaardersplassen, seven times the size of the Knepp Estate, fifteen times the size of Carrifran) what proportion of the landscape would have been open, how much in continuous canopy groves, how much as scattered open grown trees? Would the next 10 x 10 km square have been similar or would different soils and topographies have led to a different disturbance regime predominating (flood, wind, landslide)? How would the pattern in a 10 km square in the wet, windy conditions around Beinn Eighe with a limited range of trees and shrubs, differ from a square in the sandy desert of Breckland, or one in the Weald of Sussex?
Frans has brought the role of large herbivores in past and future landscapes to the fore, but are there other factors that need to be brought in? The role of the predators is still subject to much debate; climatic factors and the impact of extreme events (droughts, storms, floods) would probably benefit from revisiting in the light of the new insights of the last two decades.
So, thank you, Frans, for opening-up Pandora’s box and making woodland ecology a much more exciting, if more uncertain topic of debate.
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TREE, I. 2018. Wilding: The Return of Nature to a British Farm, Pan Macmillan.
VERA, F. W. M. 2000. Grazing ecology and forest history, Wallingford, CABI.