Metaforen voor de wildernis : eik, hazelaar, rund en paard

This thesis is a literature study. It focuses on the theory that a climax vegetation of closed forest systems covered the lowlands of Central and Western Europe in prehistoric times before man intervened and that it would still be there had this intervention not taken place. The theory also states that man's intervention, notably the introduction of livestock, has led to the disappearence of this climax vegetation in a process known as retrogressive succession. By the grazing of livestock the forest was degraded to thorny scrub and ultimately to grassland. According to the theory, it will revert to its natural vegetation of closed forest systems once the grazing of livestock is stopped.The problem central to this study is that literature shows that pedunculate oak ( Quercus robur ) , sessile oak ( Q. petraea ) and hazel ( Coryllus avellana ) do not regenerate and cannot survive in closed forest systems while pollen analyses show that these species were present continuously in Central and Western Europe for 10,000 years since the end of the ice age. On the other hand these species do regenerate in park-like landscapes in the presence of grazing by cattle and horses, domesticated descendants of wild progenitors, and deer in so called wood-pastures.The null hypothesis formulated in this thesis is that pedunculate oak, sessile oak and hazel have survived in the closed forest systems in the lowlands of Central and Western Europe and that the grazing of the indigenous large herbivores, such as aurochs ( Bos primigenius ), tarpan or European wild horse ( Equus przewalski gmelini ), European bison ( Bison bonasus ), Elk ( Alces alces ), red deer ( Cervus elaphus ), and roe deer ( Capreolus capreolus ), that inhabited these regions did not affect the composition of species or the succession of the forest in prehistoric times. The alternative hypothesis is that, in prehistoric times, the natural vegetation in the lowlands of Central and Western Europe was a park-like landscape, consisting of a mosaic of grasslands, scrub and solitary trees and groves surrounded by margins of scrub and forb fringe communities. The structure, composition of species and succession of this vegetation was largely determined by the large herbivores that inhabited the landscape.The null hypothesis has been tested against succession theories, pollen investigations, historical texts, research into spontaneous succession in forest reserves and the ecology of the tree species that formed the climax vegetation in prehistoric times according to the theory being in force. A synthesis of the findings led to the conclusion that the primeval vegetation in the lowlands of Central and Western Europe was not a closed forest but a park-like landscape. In this landscape the vegetation followed a cyclical process, in which large herbivores played an essential role. The process was that in grazed grassland stands of thorny scrub evolved in which trees grew up being protected from damage by grazing. Eventually the trees developed into a forest which again slowly degenerated to grassland under the influence of large herbivores and "catastrophes" such as drought and storms, after which the cycle began anew. The result was that various biotopes varying from grassland, scrub to forest were permanently present but not always in the same place. This is called the theory of cyclical vegetation turnover. On the basis of the conclusion and this theory, the null hypothesis is rejected in favour of the alternative hypothesis. The importance of these findings for nature conservation in Central and Western Europe, with respect to the reference frames used by nature conservationists, is explained in an epilogue.</p

Grazing Ecology and Forest History

It is a widely held belief that a climax vegetation of closed forest systems covered the lowlands of Central and Western Europe before man intervened in prehistoric times to develop agriculture. If this intervention had not taken place, the forest would still be there, and if left the grassland vegetation and fields now present would revert to a natural closed forest state, although with a reduced number of wild species. This book, which an updated and expanded version of the author's 1997 thesis (presented to the Wageningen University, Netherlands), challenges the traditional view, using examples from history, pollen analyses and studies on the ecology of tree and shrub species such as oak and hazel. It tests the hypothesis that the climax vegetation is a closed canopy forest, against the alternative hypothesis that species composition and vegetational succession were governed by large herbivores, and that the Central and Western European lowlands were covered by a park-like landscape consisting of grasslands, scrub, solitary trees and groves bordered by a mantle and fringe vegetation. Comparative information from the eastern USA is also included throughout the book (this was not present in the thesis), because the forests there are commonly regarded as being analogous to the primeval vegetation in Europe. The book is arranged in 7 chapters: (1) General introduction and formulation of the problem; (2) Succession, the climax forest and the role of large herbivores; (3) Palynology, the forest as climax in prehistoric times and the effects of humans; (4) The use of the wilderness from the Middle Ages up to 1900; (5) Spontaneous succession in forest reserves in the lowlands of Western and Central Europe - including examples from France, Germany, Austria, Slovenia, Sweden, Poland; (6) Establishment of trees and shrubs in relation to light and grazing; and (7) Final synthesis and conclusions. Twelve appendices are included giving further information, and there are 67 pages of references and a subject index.<br/

Shifting Mosaics in Grazed Woodlands Driven by the Alternation of Plant Facilitation and Competition

Free-ranging large grazers, such as cattle and horses, are increasingly reintroduced to former agricultural areas in Western Europe in order to restore natural and diverse habitats. In this review we outline mechanisms by which large grazers induce and maintain structural diversity in the vegetation (mosaics of grasslands, shrub thickets and trees). This variation in vegetation structure is considered to be important for the conservation of biodiversity of various plant and animal groups. The process of spatial association with unpalatable plants (associational resistance) enables palatable plants to establish in grasslands maintained by large grazers. In this way, short unattractive (thorny, low quality or toxic) species facilitate taller unattractive shrubs, which facilitate palatable trees, which in turn outshade the species that facilitated their recruitment. Established trees can, therefore, not regenerate under their own canopy, leading to cyclic patch dynamics. Since this cyclic dynamic occurs on a local scale, this contributes to shifting mosaics. The mechanisms involved in creating and maintaining the resulting shifting mosaics are described for temperate flood-plain and heathland ecosystems, including the effects on nutrient transport within grazed landscapes. How grazing leads to shifting mosaics is described in terms of plant functional types, allowing potential generalisation to other ecosystems. The resulting interaction web of grasses, unpalatable forbs and shrubs, palatable light-demanding trees and shade-tolerant trees is discussed, and was found to contain various interesting direct and indirect effects. The key process contributing to spatial diversity in vegetation structure is the alternation of positive (facilitation) interactions between plant species at one life cycle stage, and competitive displacement at another stage. Grazing thus causes directional successional sequences to change to shifting mosaics. The implications of this theory for nature conservation are discussed, including the relevant management problems, possible choices and practical solutions. We conclude that the theoretical framework outlined in this review provides helpful insights when coping with nature conservation issues in temperate woodland habitats.

Ecological anachronisms in the recruitment of temperate light-demanding tree species in wooded pastures

1. Light-demanding trees and thorny shrubs in temperate plant communities may reflect adaptations to now-extinct large grazers, such as aurochs and tarpans, rendering these adaptations ecological anachronisms. 2. We explored the ecological functions of plant traits of Quercus robur and Prunus spinosa in areas grazed by cattle and horses, the domesticated descendants of aurochs and tarpans. Specifically, we tested the hypothesis that grazing induces a shifting mosaic of grassland, shrub thickets and woodlands through the key process of associational resistance: the protection of palatable young trees by thorny shrubs. 3. An exclosure experiment with transplanted Q. robur seedlings revealed that Q. robur grew best in grassland exclosures and on the edge of thorny shrub thickets, which may be viewed as an optimal balance between sufficient protection from large herbivores and sufficient light availability. 4. A cross-site comparison of four floodplain woodlands in north-western Europe showed that Q. robur can regenerate in the presence of large herbivores through spatial association with P. spinosa. However, we found that expansion of P. spinosa shrubs and Q. robur coincided with periods of low rabbit abundance and not with livestock density. From this, it appears that the process of associational resistance does not work with rabbits. 5. Synthesis and applications. With extensive grazing by large (domesticated) grazers in temperate floodplains, a shifting mosaic of grassland, shrubs and trees may develop that has high conservation value. Palatable, light-demanding Q. robur seedlings can successfully regenerate in spiny P. spinosa shrubs through associational resistance. This process does not offer protection from abundant small herbivores, such as rabbits, that can inhibit the recruitment of shrubs and trees in this mosaic vegetation. In floodplain meadows frequent flooding may be an efficient way to reduce rabbit populations, with dry conditions in summer and wet in winter. When floodplain meadows are combined with adjacent higher grounds, large herbivores can escape the floods through migration.