The westernmost site of birch (Betula litwinowii Doluch.) in Hyrcanian forests, Iran: Darya Sar in Tonekabon county

Background and objectives: Birch trees are ancient remnants of the evolutionary and transformational history of the Hyrcanian forests. Evidence suggests that these trees were once widely and continuously distributed. Prior to recent systematic-ecological studies in the Alborz range, these trees were introduced as the species Betula pendula Roth. However, investigations into Iran’s flora revealed that Alborz birch trees belong to B. litwinowii Doluch. Currently, these trees are isolated in some rocky habitats and at altitudes above 2500 m in the Hyrcanian zone and some southern slopes. The aim of this study is to identify unknown and discrete habitats of this valuable species in Iran’s northern forests.
Methodology: This survey was conducted in the high elevations of the Daryasar plain of the Dohezar region of Tonekabon city. The existence of birch stands, based on evidence and structural similarities of the stands located in the rocky mountains of the region, as well as ecological conditions almost similar to other birch sites in other Hyrcanian high forests, guided extensive investigations in the vegetation of the region. According to the geological structure and the shape of the mountains of the Daryasar plain, as well as the presence of vegetation with different physiognomic forms on the cliffs and rocks, surveys were conducted using the method of floristic study, ground observations, and investigation of stands and vegetation. The presence of birch in this area was confirmed and documented. By carrying out a survey on the sites, the area of the site was determined, which was confirmed by taking measurements in different geographical directions and checking with Google Earth maps. All companion plant species in the stand were collected and noted, and for additional identification and confirmation of the species that had rich and valuable plant biodiversity, they were transferred to the herbarium of Nowshahr Botanical Garden and identified based on sources and valid identification keys. The prepared list of species will be used for additional and comparative studies with other birch sites in the Hyrcanian region.
Results: Previous studies showed that the easternmost birch habitat belongs to the Siahmarzkooh in the Fazel Abad valley of Golestan province. According to a number of habitats in the middle Alborz areas, the central sites in the Chalus Valley were the westernmost range of these trees in the Hyrcanian forests until the current reviews. The recent survey in the Daryasar site showed the presence of a small stand of these trees. Birch trees in this forest are mixed with the sub-nival trees and shrubs, such as the Sorbus graeca (Spach) Lodd. ex S.Schauer, Quercus macranthera Fisch. & C.A.Mey., Carpinus orientalis Mill. and two coniferous species, including Juniperus communis L. and J. sabina L., on the steep slopes and the walls of high rocks. The re-recognition of this site not only underscores the importance of the presence of these trees in the Hyrcanian forests and the necessity of their protection, but it also records the westernmost range of their distribution in the Hyrcanian forests. The vegetation of the eastern parts of this habitat is severely destroyed by livestock. Erosion and soil collapse indicate deteriorating conditions. Cutting the branches of the birch trees for grazing goats and sheep is a common problem in this habitat, and ranchers damage these trees in various ways.
Conclusion: In light of the conservation status of B. litwinowii and its significant biodiversity values, particularly in the Daryasar habitat, it is evident that the current conditions are not conducive to the growth and regeneration of these trees. Therefore, it is of utmost importance to raise awareness and provide training to local ranchers about conservation practices. Implementing protective measures is crucial to safeguard the remaining trees and ensure their survival.