The subnival-nival vascular plant species of Iran: a unique high-mountain flora and its threat from climate warming

This study provides a first country-wide overview of the vertical distribution patterns and the chorology of vascular plant species that occur in the uppermost elevation zones in Iran. The current distribution patterns are discussed with respect to potential warming-induced species losses. Iran's subnival and nival vegetation zones are found at elevations above 3600-3900 m in a highly fragmented distribution across Alborz, Zagros, and NW-Iran. Based on literature research and on field observations, all vascular plant species living in the subnival-nival zone of Iranian mountains were identified (151 species) and classified into three altitudinal groups: Group A comprises species that occur mainly in subnival-nival habitats (51 species). Group B are species being common in subnival-nival areas but are equally present in the alpine zone (56 species). Group C are species that can reach to subnival areas but also grow in alpine, subalpine and sometimes lower altitudes (44 species). The chorological patterns differ among the three groups. The percentage of species being endemic to Iran decreases from group A, to B and C, with 68, 53 and 20%, respectively. A narrow altitudinal distribution at high elevations is clearly related to a small-scaled geographical distribution range. The outstanding rate of high-altitude endemism appears to result mainly from orographic isolation of the country's highly scattered cold areas and by the absence of extensive Pleistocene glaciations. The narrow distribution of most of Iran's cold-adapted mountain flora and the low potential of alternative cold habitats render it highly vulnerable to climate change.