The Pistacietea verae: a new class of open, deciduous woodlands in Middle and Southwestern Asia

Aims: To analyse the syntaxonomy of open, deciduous woodlands at the southern margin of the steppe zone in the colline and montane belts of the Pamir-Alai, western Tian Shan and Iranian Mountains (Irano-Turanian region). Study area: Tajikistan (Middle Asia) and Iran (Southwestern Asia). Methods: We prepared two datasets: the first dataset contained 110 relevés from Tajikistan and Iran representing pistachio groves, the second one was a comparative dataset of 1,276 relevés of pistachio groves and floristically related woody and grassland phytocoenoses from the Irano-Turanian and Mediterranean regions. These two datasets were classified separately with the modified TWINSPAN algorithm with pseudospecies cut levels 0%, 2%, 10% and 25%, and total inertia as a measure of cluster heterogeneity. Diagnostic species were identified using the phi coefficient as a fidelity measure. A NMDS ordination was used to explore the relationships between the distinguished groups. Results: We found that Pistacia open woodlands are very distinctive in terms of species composition, including numerous endemics. Our observations in Pamir-Alai, Kopet-Dagh, Zagros, Alborz and other Central and southern mountains of Iran proved that pistachio open woodlands form distinct zonal vegetation of the colline-montane belt. We thus propose a new class Pistacietea verae, with the order Pistacietalia verae and appropriate type alliance Pistacion verae, including two associations: Pistacietum verae and Pistacietum khinjuk. Conclusions: Our research has shown that the Pistacia open woodlands are a distinct vegetation typical of the Irano-Turanian region and due to its specific ecology, phytogeography and unique species composition, should be regarded as a vegetation class Pistacietea verae. It needs further examination and comparison with similar vegetation in the western Irano-Turanian and Hindu Kush regions. Recognizing the unique pistachio open woodlands as a distinct vegetation class in the Irano-Turanian region is crucial for establishing effective conservation strategies in these understudied yet ecologically significant ecosystems, spanning potentially from the Zagros, Alborz and other Central and southern Mountains of Iran to Tajikistan, Afghanistan, Uzbekistan, and Pakistan. Taxonomic reference: Plants of the World Online (POWO 2023), with World Flora Online (WFO 2023) for some problematic cases and Nobis et al. (2020) for Stipa spp. Syntaxonomic references: Mucina et al. (2016) for SE European syntaxa, Nowak et al. (2022a, 2022b) for all other syntaxa. Abbreviations: NMDS = Non-metric multidimensional scaling.