PJB-2010-477
PLANT BIODIVERSITY OF HYRCANIAN RELICT FORESTS, N IRAN: AN OVERVIEW OF THE FLORA, VEGETATION, PALAEOECOLOGY AND CONSERVATION
HOSSEIN AKHANI1*, MORTEZA DJAMALI1,2, ATEFEH GHORBANALIZADEH1, AND ELIAS RAMEZANI3
Abstract
The Hyrcanian forests stretch from Talish in Republic of Azerbaijan and cover the northern slopes of the Alborz Mountains in North Iran, in Gilan, Mazandaran and Golestan provinces. The vegetation is composed mostly of deciduous forests. In the lower altitudes it is represented by a number of relict Arcto-Tertiary thermophilous species such as Parrotia persica, Gleditsia caspica, Zelkova carpinifolia and Pterocarya fraxinifolia. The diversity of tree species increases at higher elevations where the subalpine forests and scrubs of low shrubs of the timber-line are replaced by alpine grasslands in the northern slopes and the Irano-Turanian thorn-cushion steppe at the exposed summits and southern slopes. So far, 3234 species belonging to 856 genera and 148 families of vascular plants have been reported from the northern provinces of Iran and Talish in the Republic of Azerbaijan. Main vegetation types of the Hyrcanian forest zone include: i) sand dune vegetation along the Caspian Sea coasts; ii) C4-dominated grass communities on rocky outcrops; iii) aquatic vegetation on wetlands; iv) riverine and valley forests; v) alluvial and lowland deciduous forests; vi) submontane and montane deciduous forests; vii) subalpine deciduous forests (Quercus macranthera); viii) successional and transitional scrub and woodlands; ix) Cupressus sempervirens and Thuja orientalis woodlands; x) juniper woodlands; xi) subalpine and alpine meadows; xii) montane steppe dominated by xerophytic and thorn-cushion species; xiii) rock cliff communities; xiv) halophytic communities; xv) Artemisia spicigera steppe and desert like dunes; xvi) ruderal habitats and xvii) cultural landscapes and artificial forests. Evidence from studies on loess/palaeosol sequences, long-term Caspian Sea-level fluctuations, and peat/lake deposits in northern Iran give some indication of the climate and vegetation history of the south Caspian region. Based on these investigations, during the early-Pleistocene, at least parts of the area were covered by steppe-like vegetation and the climate was slightly warmer than today. It is also postulated that northern Iran was an extensive area of increased dust accumulation and loess formation during the Pleistocene glaciations, which is contemporaneous with and similar to major climatic changes as in SE Central Europe and Central Asia. These studies further suggest pronounced climate changes for the north of the country in which a dry and cool climate changed to moist and warm conditions during the Pleistocene glaciations. Similarly, a markedly dry period occurred during the early Holocene for the south Caspian area, parallel to the climatic optimum in Europe. Palynological studies have also shown intensified human impact on the lowland forest composition and structure of the area over the last centuries. The forests of the south Caspian area are severely degraded and deforested; in particular, in the alluvial lowlands where only small remnants exist. There are several protected areas in the Alborz Mountains and south Caspian area which suffer from mis-management. Therefore, improving their protection quality and increasing their area or addition of new sites are crucial to guarantee conservation of this very important natural heritage of SW Asia.
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