INTRODUCTION

Τhe Interpretation Manual for the Natura 2000 network and forests (European Commission 2003), also includes anthropogenic/transitional habitats (i.e. habitats evolving towards a potentially more mature vegetation state), such as heathlands, wooded peatlands, open/grazed forests, natural grasslands, or pastures. There are assigned to one of the three functional groups of the Annex I habitat types of Community importance (Directive 92/43/EEC).

Agro-forest habitat types occupy a spatial level between an ecosystem and a landscape, meaning they are in fact a complex of varying habitat types. These habitat/ecosystem complexes may be continuous because they refer to a series of plant communities/ecosystems along a successional gradient, or to a connected series of spatially adjacent plant communities. Agro-forest habitat types comprise elements of both ecosystem complexes, which can only be understood when the ecology and dynamics of the plants and their communities are known. This objective has not yet been achieved at European level.

In places where grassland and woodland are kept apart, their margins are welldefined and the ecotone is narrow, in contrast to the margins of wood-pasture which are wide, indistinct, and not always identifiable.

In patchy wood-pastures, the wood-pasture ecotone forms a major part of the entire wood-pasture area. A high ecotone proportion is the key factor for high species and niche densities of pastoral woodlands (Bergmeier 2010). Wood-pastures provide a wide range of local climate conditions, vegetation and soil types, thus creating a variety of microhabitats.

Threats And Problems

Threats to wood-pasture habitats result primarily from changes in traditional landuse practices caused by overall social and economic changes in rural activities. Such changes may follow two different paths:

(a) intensification of livestock farming that leads to overgrazing and hence to an increase in herds or grazing intensity, or

(b) abandonment of livestock farming followed by loss of small-scale habitat diversity.

As for other non-intensively used habitats, agricultural expansion and intensification, urbanization and road construction and other infrastructure lead to an increased fragmentation of wood-pasture habitats. More specific problems include:

Reduction in old-growth tree density

Much of the diversity of grazed forests and wood-pastures depends on the presence and abundance of old-growth, tall and broad-canopy trees, such as oaks, beeches, chestnuts, or other species. If the natural loss of old trees is not compensated by rejuvenation, the results are either open pastures or stone/rocky slopes, when overgrazing is practiced, or a more or less dense forest, through dynamic vegetation succession processes, when woodlands are not grazed.

Overgrazing

A main problem of existing wood-pastures in Greece and Spain is the lack of regeneration and woodland ageing (Dimopoulos and Bergmeier 2004; Plieninger et al. 2003). It is not yet known whether this is a problem associated with permanent, century-old wood-pastures, or a problem that has only arisen during the last decades of overgrazing. The lack of seedlings and juvenile trees is mainly observed in grazed forests, with sheep and goat grazing. Due to the high number of animals, the surface soil layer is affected by trampling, and young trees and shrubs are affected by selective browsing. Overgrazing also reduces the area of herbaceous vegetation under bushes. Otherwise, shrubby plants would serve as a shelter for the shade-demanding tree seedlings. In recent years an (ecologically) unacceptable replacement of sheep and goats by large beef cattle has been observed in Greece, which in many cases (especially in areas with friable soils and steep slopes) cause overgrazing and soil erosion.

Abandonment of livestock farming

While lowland wood-pastures in Western and Central Europe were primarily abandoned in the 19th century, rural abandonment and agricultural abandonment in the European Mediterranean mainly took place in the second half of the 20th century and is continuing to this day. The abandonment of livestock farming and the consequent absence of grazing in woodlands led to scrub penetration and expansion and to denser woodlands (Figure 1), with a corresponding increase in fire risks and loss of the patchiness that is characteristic of many types of wood-pastures.

Removal of old olive groves

Groves with old olive trees are a characteristic feature of the Mediterranean cultural landscape, often used in many ways, including grazing. The vegetation underneath the ancient olive trees is often very rich in species, especially orchids and other bulbous plants. In the last two decades, large areas of old olive groves have been cut down and replaced by olive-plantations of high yielding varieties. In addition, when grazing is abandoned, these plantations are ploughed to prevent the establishment of shrubs and competing herbaceous vegetation, irrigated, and sometimes sprayed with pesticides, resulting in a reduction of plant diversity. Such plantations have been established in former fields and wood-pastures, especially in southern mainland and insular Greece, in Italy, and in Spain.