© 2004 by Institute of Chartered Foresters
A model of a natural wooded landscape in Britain as influenced by large herbivore activity
1 English Nature, Northminster House, Peterborough PE1 1UA, England
The generally accepted view of the natural forests that once covered much of Britain has been of largely closed-canopy woodland with regeneration in gaps created by the death or destruction of small groups of trees, or occasional catastrophic blow-downs. An alternative view has recently been promoted in which large herbivores grazed open areas that eventually went through scrub and woodland phases. Regeneration within the woodland phase was prevented by grazing so that, when the trees died, open areas formed again. For regions where the herbivore-driven process predominated a model of possible landscape structures was developed for an area of 5 5 km (2500 ha) over a 500-year cycle. Different combinations of open and closed landscapes resulted, depending on the assumptions made about how long, for example, the closed woodland or open park phases lasted and whether patches of a particular phase were clumped or scattered. Possible implications for different species groups are illustrated. The balance between open and closed areas depends on assumptions made about the duration of the different phases. However, a predominantly wooded landscape (50 per cent in the woodland phase, 25 per cent in the park phase, with the balance as scrub (15 per cent) or break-up (10 per cent) stands) is compatible with a herbivoredriven dynamic process. Continuity of both open conditions and old trees over time and space can be achieved in this wooded landscape with an intimate mix of habitats at the scale of a few hundred metres. Modern conservation priorities in Britain are set against a background of 3000 years (at least) of a cultural landscape and controlled agricultural-type grazing is part of the management used to maintain some priority habitats and species. Under modern conditions free-range grazing regimes may not produce the same effect and so cannot, a priori, be assumed to be better in biodiversity terms than controlled grazing in all circumstances. However, the model results suggest that over large spatial scales and a long time period varied habitat mosaics may be generated by naturalistic grazing regimes. Naturalistic grazing regimes should be trialled therefore to determine what range of habitats and species they can now support and as a way of improving our understanding of how the former natural landscape might have functioned. There are practical issues including animal welfare and public liability that need to be resolved if such trials are to be taken forward.