Deciduous broadleaf forests of the northern hemisphere are one of the most threatened ecosystems on the earth. They occur in three major disjunct regions (western Eurasia, eastern Asia and eastern North America). Globally, the Hyrcanian forest is one of the most important deciduous broadleaf forests, due to its remarkably biodiversity, primeval conditions and large extension.
It stretches in a large arc along the Alborz Mountains in northern Iran and reaches Azerbaijan in its southernmost part. The Hyrcanian forest in Azerbaijan suffers a rapid degradation since 1991 due to intense forestry. Currently, only 17% of the Hyrcanian forest in Azerbaijan is treated as pristine forest, whereas 44% shows heavy degradation.To investigate the impact of forest degradation to the local breeding birds, five forest degradation stages were selected according to an increasing scale of degradation: (1) Natural forest stage, (2) Slightly disturbed forest stage, (3) Intermediate disturbed forest stage, (4) Park-like forest stage and (5) Shrubby woodland stage; and the abundance of territorial bird species for each degradation stages were estimated.
The relative abundance of typical forest species declines with ongoing forest degradation (e.g. Coal Tit, Chaffinch, Eurasian Wren, Eurasian Robin), whereas the relative abundance of open woodland species increased. Most of increasing species were associated with shrubs of open landscapes (e.g. Common Nightingale, Common Whitethroat and Red-backed Shrike).
Fourteen bird species showed a negative response to forest degradation. All of them were forest-dependent species and occurred in the natural forest stage. Higher abundances were visible in natural and slightly disturbed forest stage in comparison to heavier degraded stages. Twelve species showed no response. All of them have been recorded in the natural forest stage. Nineteen bird species that bred in the degradation stages show positive response to degradation, but only six of these species (Hawfinch, European Greenfinch, Common Nightingale, Great Tit, Blue Tit, and Eurasian Jay) are found in the natural forest stage. Black Woodpecker and Eurasian Treecreeper occurred only in the natural forest stage and are therefore highly vulnerable to forest degradation.
In conclusion, the preservation of large-scale forested areas in the Talysh Mountains is crucial to the forest-dependent avifauna. Birds, as a generally well-studied taxonomic group, may stand for the broad variety of further taxonomic groups such as mammals, amphibians, reptiles and insects. The reaction of these groups to forest degradation in that region is completely unknown, but an anticipation of their response can be derived from the observed response of birds. Drawing an analogy from the effect on the birds, I anticipate further local extinctions of individual species among these taxonomic groups with ongoing degradation and fragmentation. This loss of biodiversity can only be avoided or even reduced by sustainable forestry, which is in balance with ecological processes. The slightly or intermediate disturbed forests may serve as models whereby a large amount of the original avifauna can successfully coexist with forest utilization.