Free-ranging large grazers, such as cattle and horses,

Summary1. Abandonment and eutrophication are major threats to traditional pastoral landscapes and their wildlife in Europe. Social and economical developments have rendered traditional pastoralism impracticable. More knowledge is needed about the eects of grazing with free-ranging herbivores, which is increasingly used as a substitute for the traditional herding system. 2. We studied the eects of free-ranging cattle on the recovery of Calluna heather, tree encroachment and plant species richness in six habitats in a grass-rich Dutch heathland during a 10-year period. The habitats diered in soil fertility, initial heather±grass ratio and developmental stage of Calluna. 3. Despite preferential grass defoliation, cattle grazing neither reduced grass cover in grass heath nor prevented grass invasion in heather. Grass invasion failed only in a nitrogen-poor turf-stripped Calluna heath. Grazing induced a substantial Calluna recovery in grass heaths on podzolic soils, but its recovery failed in grass heath on a phosphorus-rich medieval arable ®eld. As a consequence, the grass± heather mosaics generated by free-ranging cattle were restricted to habitats of intermediate soil fertility. 4. Grazing did not prevent encroachment by pine and birch. Removal by the site manager prevented conversion of 10±20% of the open heathland to forest. 5. During the ®rst 5 years, grazing induced a signi®cant increase in species richness in all habitats. During the second 5 years, species richness stabilized in grass heath and heather±grass mosaics and it declined in the pioneer Calluna heaths. 6. We found indications of various nutrient-mediated grazing eects on the competitive balance between grass and woody pioneers. These suggest that nutrientmediated feedback might be an important explanatory mechanism for the described vegetation mosaic cycling in heathlands. 7. Free-ranging grazing did not remove the high atmospheric nutrient inputs of the whole area. Substantial amounts of nutrients were redistributed from the grass lawns to the forest. 8. Free-ranging grazing combined with tree cutting appeared to be a suitable management regime for the maintenance of species-rich open heathlands with dynamic grass±heather mosaics. 9. Without tree cutting, free-ranging grazing would have created dynamic tree±grass± heather mosaics in open heathland. Wood±pasture landscapes are fundamentally different from the open heather-dominated heathlands produced by the traditional sedentary farming system. Integrated grazing of heathland, nutrient-rich farmland and forests accelerates this change. Alternative grazing regimes are discussed.

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 (as‐sociational 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.

Most Dutch nature reserves are small, isolated fragments of former semi‐natural landscapes. Cattle and other large domestic herbivores are being increasingly (re)‐introduced in nature reserves as a tool for vegetation management and as an ecological substitute for extinct wild herbivores. The performance of cattle in these single‐landscape areas appears to be seriously limited by a combination of inadequate forage and habitat isolation. Animals cannot move seasonally between different landscape types. We compared the forage quality of three landscape types. Quality parameters included organic matter digestibility and contents of macronutrients: nitrogen (N), phosphorus (P), potassium (K), sodium (K), calcium (Ca), and magnesium (Mg). In landscapes of low fertility, insufficient concentrations were found of P, Na, Ca, and Mg. However, because the assumed maintenance requirements for cattle are possibly overestimated, the prediction of deficiencies for the animals remains uncertain. In landscapes of intermediate fertility, the level of Na is deficient for most of the year. Winter digestibility is inadequate in vegetation remaining ungrazed until winter, whereas in grazed vegetation the quantity of easily‐digestible forage is insufficient to satisfy quantitative intake requirements. In landscapes of high fertility, the mineral supply is adequate, but low digestibility in winter will lead to energy shortage. Insufficient forage quality seems to preclude sustained year‐round grazing in each of the three landscape types. Single‐landscape areas constitute seasonal habitats for cattle, suitable for summer or winter grazing only. Connection of complementary landscapes is essential to create complete year‐round habitats for cattle and other large herbivores. The restoration of linkage of summer and winter range by the creation of corridors is the most natural solution. Seasonal grazing with controlled migration or transportation of the herd between winter and summer range reserves is a second‐best alternative involving less interference than year‐round grazing with supplementation.

Abstract. This paper deals with browsing and grazing as forces driving cyclic succession. Between 1989 and 1994 reciprocal transitions between the dwarf shrub Calluna vulgaris and the grass Deschampsia flexuosa were monitored in permanent plots in a cattle grazed grass‐rich Dutch heathland on podsolic soils in which tree encroachment was prevented. Heather beetles killed Calluna in four of the nine plots during 1991/1992. The monitoring revealed reciprocal transitions and cycles between Calluna and Deschampsia on a subplot scale. Beetles and cattle had additional and complementary effects on the two competing species. Defoliation by beetles and trampling by cattle‐killed Calluna and favoured grass invasion. Grazing and gap creation by cattle in Deschampsia favoured the establishment and recovery of Calluna. Analysis of the causal mechanisms suggests that indirect, resource‐mediated herbivory effects may be as important for the replacement processes as direct effects of defoliation and trampling. Herbivory created differential light and nutrient levels in Calluna and Deschampsia gaps. Grazing and browsing improved the resource‐capturing abilities of Calluna and its resistance to herbivory and abiotic disturbances. The emerged Calluna‐Deschampsia cycle and its driving forces are summarized in a conceptual triangular resource‐mediated successional grazing cycle (RSGC) model, a limit cycle involving herbivore‐plant‐plant resource interactions. It offers a deterministic equilibrium model as alternative for stochastic transitions between the meta‐stable states with dominance of Calluna and Deschampsia respectively. The validity range of the RSGC model and its management implications are briefly discussed.