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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	German forests and their avian communities in the context of changes in society and environment.
Auteurs :	Wulf Gatter, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (125(3-4) 2004)
Article en page(s) :	151-176
Résumé :	The traditional forms of woodland husbandry until about 200 years ago was accompanied by soil degeneration through permanent over-exploitation of timber, foliage, leaf fodder, fruits, pollarding, and humus. The steady change over the last 200 years to a high-forest management type, with its older stands, has been accompanied by humus enrichment which, along with nutrient input from the atmosphere, has resulted in an increase in growth and a lengthening of the growing season (especially through nitrogen). This forest transformation and the increase in forest area has gone hand in hand with the change from deciduous to predominantly coniferous forest cover. The present-day spatial differentiation of agriculture and forestry has led to a historically unprecedented sharp division between agricultural land and managed forest. This, along with the high-forest system, has supported a limited spectrum of woodland bird species which today occur in densities that they probably never had before. The transition to high forest, with its considerably greater timber stock and vegetation volume, as well as higher forest mean age, combined with the mostly Mosaic-like integration between deciduous and coniferous woodland, creates internal habitat edges, raises the number of structural elements in the vegetation, and increases both tree and arthropod numbers per unit area. Outside extensive monocultures, the expansion of coniferous forests into the lowlands unites within small areas vegetation forms which originally would have been separated by 1000 m of altitude, or in a N-S direction by 1000 km. This conditions support boreal and mountainous faunal elements, but at the same time are detrimental to light- and warmth-loving species. Particularly affected are those species that originally profited from overgrazing and vicarious events, as well as from the forest, field, and fire practices in agriculture.In the near-natural forestry concept, which is actually favoured, the optimal and decay phases as well as the youngest age classes (gap and initialisation phase) are widely missing and replaced by natural regeneration under the sheltering canopy of mature stands. One result is higher tree seed crop which, for the first time, remain completely at the disposal of wild animals. However, all the phenomena described support almost exclusively populations of resident birds and partial migrants, leading to increased competition for long-distance migrants. These enormous changes in the forest ecosystem had affected not only birds. The population increases of Red Fox and both marten species, the huge rise in the numbers of Wild Boar and Edible Dormouse and their influence on bird populations show that a one-sided concentration on the avifauna is not helpful. Woodland covers one-third of the German land area but supports more than 50% of our landbirds. Species that breed in woodland but forage on farmland are today taking over some of the niches deserted by the ground-breeders of open habitats. It has been too readily assumed that forest as a rapidly changing ecosystem is in itself stable and this has led to many misinterpretations of the population changes in our avifauna. The reality is that through forestry, external impacts, and autogenic developments, the most revolutionary transformation of our floristic environment has occurred, meriting close attention as one of the most interesting areas in current synecological studies.

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