Past, present and future distributions of Oriental beech (Fagus orientalis) under climate change projections

The situation is similar in the Iranian Alborz Mountains, where Quercus macranthera replaces Fagus at higher elevations [89]. The Amanos Mountains are distinctive, because Ori- ental beech is confined to higher elevations under a distinct microclimate, thus, it is remark- able that the model could identify this relict population here [90]. Past reconstructions and palynological data comparison Probability estimates for occurrences of Oriental beech during the LGM by ‘biomod2’ (Fig 2A) are to some extent congruent with known pollen records. Unambiguous occurrences of beech pollen from LGM deposits are known from the Sea of Marmara, off the central northern Turk- ish Black Sea coast, and from Sukhumi. These occurrences coincide with highly probable model estimates (red in Fig 2A). While estimates on presence in Transcaucasia and southwest of the Caspian Sea are sensible although not supported by palynological data, a refuge area in Turkmenistan at 60˚E east of the Caspian Sea is highly unrealistic in view of the present arid climate in this region. During the LGM, a cold continental climate would not have provided suitable conditions for the growth of beech. ‘biomod2’ reconstructed a further refugium in the Alborz Mountains south of 35˚N. Although no pollen record is available for this region, the Amanos Mountains with a high relief, deep valleys, and slopes facing the sea likely provided a refuge for beech populations during the LGM. The core region of F. orientalis estimated for the MH (Fig 2B) includes the Turkish Black

Sea Coast and the Caucasus. This is also suggested by unambiguous pollen records known from this area (Fig 2B and Table 4). In contrast, ‘biomod2’ with RF predicted a rather limited distribution south of the Caspian Sea, from where abundant pollen records of beech are known as well. Palynological data and paleoclimate modelling [91, 92] suggest that temperate regions during the MH might have been warmer than today during summer and colder during winter because of astronomical forcing. Today, fully humid, warm temperate Cf climates are much less common along the southern Caspian Sea coast than south of the Black Sea and along the northern and southern foothills of the Caucasus ([16]; http://koeppen-geiger.vu- wien.ac.at/kmz/Global_1986–2010_KG_5m.kmz.zip provided by Veterinary University of Vienna, http://koeppen-geiger.vu-wien.ac.at/present.htm). In northern Iran, a stronger Medi- terranean influence is expressed by lower summer precipitation and higher summer tempera- tures (http://koeppen-geiger.vu-wien.ac.at/kmz/Global_1986–2010_KG_5m.kmz.zip). Hence, warmer summers during the Mid Holocene would have increased this Mediterranean influ- ence and resulted in a much-reduced distribution of Oriental beech in the models. As today, these unfavourable conditions might have been compensated by high air moisture and a sky covered with fog for most of the year and particularly during the growing season [89]. How- ever, the predicted presence of beech in the western corner of the Caspian coast makes sense,

as this area–constrained by wind directions and high mountains to the south and a large water body to the north, very likely could have supported growth of beech during the MH (Fig 2B). Future projections Future projections show that F. orientalis will face a dramatic range contraction in the future (Figs 3B–3D and S1–S10). The projections suggest that the species will mainly thrive in the Fig 3. Distribution maps of present and future projections of F. orientalis are shown from the random forests outputs of a) present, b) optimistic future scenario RCP 2.6, c) moderate future scenario RCP 4.5, and d) pessimistic future scenario RCP 8.5. Red areas show the contraction of species occurrence based on observed data and future projections, brown areas show the contraction of species occurrence based on present and future projections, blue areas represent overlap of species occurrence based on observed data and present projection, green areas show the expansion of species occurrence based on observed data and projections. We quantified the cell numbers for each category in Table 5. Spatial resolution: 2.5’. https://doi.org/10.1371/journal.pone.0242280.g003 PLOS ONE Species distribution modeling of Oriental beech (Fagus orientalis) PLOS ONE | https://doi.org/10.1371/journal.pone.0242280 November 17, 2020 11 / 19