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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Biomass, population density and species number in avian communities of upland and submontane broad-leaved and coniferous forests in Southwest-Germany.
Auteurs :	Wulf Gatter, Auteur ; Rainer Schuett, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (125(3-4) 2004)
Article en page(s) :	251-258
Résumé :	This study examines the relationship between population density, species number and biomass of birds and forest type (broad-leaved, mixed, or coniferous) as well as forest age. The study material is based on territory mappings between 1967 and 1995. The abundance of birds in forests with pre-dominating Beech Fagus sylvatica and Northern Spruce Picea abies increases from deciduous through mixed to coniferous forests. The avian biomass, however, remains roughly the same in all three forest types because the average weight of the birds decreases from deciduous (26.8 g) through mixed (26 g) to coniferous (19.4 g) forests: in coniferous forests there are smaller birds occurring at greater densities. In coniferous forests, the dense evergreen foliage restricts the movement of birds, and the thick arboreal structure supports an avifauna of small 'flitters'.In young stands there is a decline in population density after the thicket stage. After the pole stage, population density and bird biomass increases again with stand age, especially in broad-leaved woodland. No clear dependence on: a particular stand age is discernible in coniferous forests, at least when younger than 1,00 years. Other factors, such as presence of clearings and proportion of dead wood, are probably more significant. Extremely high population densities in small, old, protected forests with up to 275 territories/10 ha cannot be extrapolated to corresponding extensive forests. In coniferous and deciduous woodland there are on average 23 +/- 5 species/10 ha, in mixed woodland over 26 +/- 5. There are indications that the number of species rises with stand age in mixed and coniferous woodlands, but probably less in deciduous woodland. Before leaves appear on deciduous trees, coniferous forests and even single evergreen trees provide early breeders with protection from predators. They also give shelter against the cold and buffer climatic extremes, thereby supporting early breeding. The expansion of coniferous plantations at the end of the 19(th) century has allowed several bird species (e.g. Coal Tit Parus ater, Crested Tit P. cristatus, Firecrest Regulus ignicapillus) to considerably increase their range and numbers in Central Europe.

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