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Conservation biology

Openness in management

Should conservation strategy concentrate on intensive management involving practices such as mowing, or should the aim be to protect wilderness? Studies of past ecological conditions can inform that debate.

There is a striking difference between conservation strategies in western Europe and North America, and one that is rarely made explicit. In western Europe, the emphasis is on intensive reserve management, compared with North America and much of the rest of the world where the main aim is to protect wilderness, especially dense woodland. These approaches are based upon an impression of the past — in particular, that closed forest was often the natural state. Writing in Biological Conservation, J.-C. Svenning1 has re-evaluated these impressions in the European context. He has looked at the literature on the pollen record, and records of vertebrate and invertebrate occurrences, to show that the pre-agricultural European landscape consisted of a combination of extensive open areas combined with closed forest. When the past is taken as the template for conservation strategies, research such as this is invaluable.

A guiding principle for conservation in North America is that much of the eastern side of the continent was once forest, but that European settlers cleared large tracts of it. The aim of conservationists, then, is to protect and recreate woodlands to restore the original state. By contrast, in western Europe the main principle stems from the long history of human modification of the landscape, starting with Neolithic farmers who either managed woods intensively by repeated cutting and felling, or cleared them altogether. The species now present in the cleared areas are those that survive or flourish in open habitats, and their well-being depends on the continuation of farming practices such as mowing, stock grazing or scrub clearance. For example, all of the threatened grassland plant species in the Lorraine region in France require some management to prevent the encroachment of scrub, although the optimal degree of cutting or grazing varies between species2.

But how has the landscape of Europe changed? In pre-agricultural times, was it largely dense forest as is often assumed? Vera3 has provided an alternative interpretation, in which there was a shifting mosaic of grassland, scrub and woodland maintained by herbivores such as deer, moose, wild boar, bison and the wild antecedents of domesticated cattle and horses. His arguments include the following points: hazel is abundant in the pollen record yet does not flower within dense woods; oak rarely regenerates in dense woods but does so within open habitats; and many other plants and animal species that are currently present depend on open habitats.

To examine the generality of Vera's ideas, Svenning1 reviews the evidence from pollen data to assess vegetation structure in western Europe during previous interglacials and since the last Ice Age but before the advent of agriculture. He concludes that there was a complex pattern and that the extent of open habitat varied with physical conditions. The evidence suggests that there was frequent open habitat as a result of herbivore grazing or fire on flood plains, infertile soils and chalk. Open areas were abundant in dry and warm areas. On fertile uplands there was predominantly closed forest with some, more open, patches maintained by herbivores.

Pollen analysis has a range of associated biases — not least, grazed plants do not produce pollen. So Svenning also looked at the literature on vertebrate remains. Thus, the existence of lynx and woodmouse implies the presence of forest, whereas spotted hyena and field voles are indicative of much more open habitat. Similarly for birds: the presence of capercaillie indicates woodland; red kite, magpie and golden eagle suggest open habitat. Although some of the animal communities characteristic of open habitats were found in coastal regions, flood plains or arid regions, many others were not. So the message to emerge from this analysis is the same as that from the pollen data: during previous interglacials, and in the pre-agricultural present interglacial, there were clearly large areas of open or semi-open habitat as well as more closed forest. This message is also supported by the analysis of invertebrate remains.

For North America, it is commonly thought that before the arrival of European settlers there was almost continuous forest between the Atlantic and the Great Plains, with grassland habitat and grassland species arriving later. However, there are several lines of evidence suggesting that there have always been considerable areas of more open habitat. For instance, three species of bird that favour grassland each have separate eastern subspecies, implying that they have long occurred in isolation, and there are several endemic species of grassland plant4. Moreover, the observations of early Europeans in North America, and the pollen, bird and mammal records, indicate that open-habitat communities existed4. In both Europe and North America, then, 'wilderness' does not necessarily mean continuous forest.

How might a change in historical perspective within Europe change conservation practices? Insight comes from the Oostvaardersplassen in the Netherlands (Fig. 1), a 5,600-hectare reserve created in 1974–78 in the lowest section of a recently created polder. The philosophy has been to allow water levels to fluctuate within wide limits, to encourage natural processes and to reinstate the historical herbivore community. As well as the roe deer already present, 150 more red deer and some beavers were introduced. To replace extinct species the introductions included 200 Polish ponies — descendants of wild tarpan, the original European wild horse — and 300 heck, a cow bred to resemble the extinct auroch. Unexpectedly, 60,000 greylag geese have appeared in this site each autumn and their grazing has been a major factor in maintaining open habitat over much of the wetland. This experiment is still in its early stages and has its critics, but it has had many ecological successes, including some remarkable populations of scarce birds. The herbivorous mammals and birds have created a mosaic of habitats, including many open areas. Overall, with the lack of obvious human intervention, the impression is one of wilderness.

Figure 1
figure1

EDDY MARISSEN/FOTO NATURA

The Oostvaardersplassen — an experiment in maintaining a mosaic of habitats by natural means.

The main message is that natural habitats included open areas, upon which many species are dependent. The options are to allow such open habitats to disappear (as is often happening in North America), to restore natural processes (the Oostvaardersplassen model) or to manage with the use of farming techniques (the western European approach). Each option has its own strengths when applied in the appropriate location, but it is likely that everyone could learn from the approaches of others. Conservationists in North America could think more seriously about the importance of biodiversity within open habitats, such as farmland5, and ways of managing them4. Those in western Europe could look more towards a North American model of nature conservation in which there is a greater distinction between farmed and unfarmed landscapes. The lessons from restoring natural grazing regimes are probably of wide applicability. Detailed accounts of the ecological history, as described by Svenning1, can greatly inform thinking on these issues.

References

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    Svenning, J.-C Biol. Conserv. 104, 133–148 (2002).

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    Muller, S. Biodiversity Conserv. 11, 1173–1184 (2002).

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    Vera, F. W. M. Grazing Ecology and Forest History (CABI, Wallingford, 2000).

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    Askins, R. Restoring North American Birds: Lessons from Landscape Ecology (Yale Univ. Press, New Haven, 2002).

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    Freemark, K. E., Boutin, C. & Keddy, C. J. Conserv. Biol. 16, 399–412 (2002).

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Correspondence to William J. Sutherland.

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Sutherland, W. Openness in management. Nature 418, 834–835 (2002). https://doi.org/10.1038/418834a

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