To graze or not to graze?

Woodland ecologists have a difficult relationship with large herbivores whether these are domestic livestock such as sheep and cattle, or wild ones like deer.

In Wytham, for example, there are tensions.  We have a scatter of large old oak and ash on former common land that became part of the woods in the 19th century.  Without the grazing that used to keep regeneration in check these are now being overgrown by young growth and we have to actively ‘halo’ some of them to help their survival. Meanwhile in parts of the ancient woodland the woodland flora and shrub layers were eaten-out by an expansion in the deer populations during the 1980s and 1990s.

Wytham – (a) a haloed oak and (b) grass-dominated plot following a decade of grazing.

There is also ambiguity in trying to determine the role that large herbivores might have played in the development and functioning of the tree cover that developed after the last glaciation. It had been assumed that, while the wildwood did contain deer, wild ox, moose and on the continent also wild horse and bison, these had only limited effects on the composition and structure of the landscape. Then, in 2000, Frans Vera’s book  ‘Grazing ecology and forest history’ set the cat amongst the pigeons by arguing that in fact the herbivores had been the dominant shapers and drivers of the landscape.  It would not have been a solid blanket of trees, but more like a crocheted bedspread, with open grassland, patches of scrub, areas with open grown isolated trees and some areas of closed woodland. The New Forest, though clearly a cultural landscape, has been suggested as a possible analogue.

(a) The aurochs skeleton from the Danish National Museum, Copenhagen; (b) New Forest oak grove.

The ensuing debates (often heated) have not resolved matters one way or the other. Part of the problem is that it is not a question of whether various elements (openness, scrub, trees, closed woodland, grazing animals etc) were present – that is not disputed – but their extent and significance. Would grazing animals have been the dominant driver of change just in some areas, or almost everywhere?  Did open grassland occupy 10%, 50% or 80% of the ground? Models suggest a variety of landscape outcomes are possible (depending on assumptions) from the grazing theory. Vera himself acknowledges that the wooded (grove) stage of his mosaic might extend to tens or hundreds of hectares, so actually finding evidence that is conclusive for one side or the other is very difficult. My feeling is that the balance was more towards a wooded landscape with about 20-30% openness.

(a) the Chillingham Park cattle in Northumberland; (b) New Forest largely closed oak-beech stand

An added complication has been that we have become more aware that humans were changing the nature of the ‘natural’ landscapes (whatever they were!), certainly from the Neolithic period onward. However, our influence goes back much further, particularly if you include contributions to the extinction of megaherbivores such as mammoth and woolly rhinoceros.

One reason why the debate about the role of large herbivores has attracted such attention is that it coincided with a revival in interest in the conservation of wood-pastures and their veteran trees. This was a particular interest of a recent conference in Poland http://www.woodscapes.ur.edu.pl/ .It has also fed into thinking about ‘rewilding’, for example at Oostvaardersplassen in the Netherlands and in a tamer way on the Knepp Estate in Sussex, the subject of another recent meeting https://knepp.co.uk/vera-conference-1/ . Lessons from these should contribute to future development of the debate.

(a) Heck cattle in the Oostvaardersplassen Reserve; (b) Longhorns on the Knepp Estate

In the mean-time, we remain stuck in the situation where there is either too much or too little grazing in woods, never the Goldilocks level!

HARTEL, T. & PLEININGER, T. 2014. European wood-pastures in transition: a socio-ecological approach, Abingdon, UK, Earthscan/Routledge.

HODDER, K. H., BUCKLAND, P. C., KIRBY, K. J. & BULLOCK, J. M. 2009. Can the pre-Neolithic provide suitable models for re-wilding the landscape in Britain? . British Wildlife (supplement), 20, 4-15.

KIRBY, K. J. 2004. A model of a natural wooded landscape in Britain as influenced by large herbivore activity. Forestry, 77, 405-420.

KIRBY, K. J., THOMAS, R. C., KEY, R. S., MCLEAN, I. F. G. & HODGETTS, N. 1995. Pasture woodland and its conservation in Britain. Biological Journal of the Linnean Society, 56, 135-153.

NOBLE, G. 2017. Woodland in the Neolithic of Northern Europe, Cambridge, Cambridge University Press.

VERA, F. W. M. 2000. Grazing ecology and forest history, Wallingford, CABI.

 

 

 

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