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

Introduction Climate is changing more rapidly than ever: By 2020, global surface temperature has increased by 1˚C relative to the mean of the years 1951–1980 [1]. Global warming is likely to reach 1.5˚C between 2030 and 2052 if it will be continuing to increase at the current rate [2]. Ongoing cli- mate warming is already causing shifts in species phenology, physiological and behavioural traits, geographical ranges, productivity, and disruption of species interactions [3–5]. Among terrestrial biomes, forests are most affected by ongoing global warming, as it not only impacts the survival rate of tree species, but also forces plants to cope with more frequently occurring extreme events such as severe droughts, floods, wildfires, etc. [6]. Since trees are the dominant species of forest ecosystems, any influence on them would cause cascading effects on the envi- ronment in terms of resource availability, local climate stability and ecosystem services [7]. Any impacts on tree species force dependent organisms to alter their life cycles and even cause their extinction in some cases [8]. Thus, understanding the fate of tree species in response to climate change is of crucial importance for conservation and management practices [4,9]. Broadleaf deciduous forests of Asia Minor occur adjacent to two major biodiversity hotspots, the Mediterranean Basin and the Caucasus [10]. The Euxine-Colchic broadleaf forests of Turkey and Georgia, and the Hyrcanian forests of northern Iran are among the most diverse temperate

forest ecosystems in western Eurasia [11]. High landscape diversity in northern Turkey, Trans- caucasia and northern Iran is buffering the effects of climate change and has created refugia for plant species during past glacial periods [12,13]. However, relatively little is known about how future climates will affect the distribution of broadleaf forests in these regions. Beech (genus Fagus) is widely distributed across Eurasia, where it occurs in environments with sufficient rainfall and mild temperatures [14–17]. One of the most common broadleaf species of western Eurasia is the Oriental beech (Fagus orientalis Lipsky), which plays an important role in forming pure or mixed beech-conifer forests. This species occupies a narrow ecological niche being sensitive to late spring frosts and summer drought [18]. Consequently, it has been identified as especially vulnerable to climate change effects [19–21]. Since F. orien- talis acts as a keystone species in its habitat and serves as an important resource to ecosystem services such as plywood, particleboard, furniture, flooring veneer, mining poles, railway tiles, paper, and firewood [22,23], it is of paramount importance to understand the fate of this spe- cies under climate change. The common approach to investigate the impacts of climate change on plant distributions is using species distribution models (SDMs) [24,25]. These models help to identify regions in an area with changing environmental variables that have similar conditions to localities where the

species has been recorded. By using occurrence (presence/absence) and abiotic environmental data, SDMs are frequently used as a tool for estimating the extent of a species’ range in the future or in the past [25,26]. Although a large number of authors have applied SDM to European woody species extensively in order to understand past and future distributions (e.g. [24–30]), there is a paucity of studies focused on Minor Asian tree taxa (e.g. [31,32]). Likewise, a great number of palaeobotanical studies investigated the late Quaternary history of Fagus sylvatica L. in Europe (e.g. [33–36]), and these studies were integrated with phylogeographic investigations (e.g. [37]). In this study, we investigated the potential distribution of the Oriental beech in the past and in the future. To that end, we applied five SDM algorithms provided with the R-package ‘bio- mod2‘to model potential distributions of this species under the present (1960–1990), past [Last Glacial Maximum (LGM), 21 ka, and mid-Holocene (MH), 6 ka], and future (Represen- tative Concentration Pathway (RCP) 2.6, 4.5 and 8.5 for 2050 and 2070) climatic conditions obtained from MIROC-ESM and CCSM4 global climate models. Specifically, we pursue the following objectives: (i) to model the present distribution of F. orientalis, (ii) to reconstruct PLOS ONE Species distribution modeling of Oriental beech (Fagus orientalis) PLOS ONE | https://doi.org/10.1371/journal.pone.0242280 November 17, 2020 2 / 19 (PBX) Website: https://www.ogm.gov.tr/lang/en/ Pages/Contact.aspx Funding: TD acknowledges funding from the

Swedish Research Council (VR grant no. 2015- 03986). Competing interests: The authors have declared that no competing interests exist.