Climate Change Impacts on the Distribution and Diversity of Major Tree Species in the Temperate Forests of Northern Iran

Regional Environmental Change (2019) 19:2711–2728 https://doi.org/10.1007/s10113-019-01578-5

ORIGINAL ARTICLE

Climate change impacts on the distribution and diversity of major tree species in the temperate forests of Northern Iran

Hamid Taleshi1 & Seyed Gholamali Jalali1 & Seyed Jalil Alavi1 & Seyed Mohsen Hosseini1 & Babak Naimi2,3 & Niklaus E Zimmermann4

Received: 22 May 2019 /Accepted: 18 October 2019 /Published online: 27 November 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract This study aimed to assess the impacts of climate change on the distribution of major tree species in the temperate forests of Northern Iran (also known as Hyrcanian forests). We analyzed the current distributions of the eleven major tree species using an ensemble approach involving five different species distribution models (generalized linear model, generalized additive model, generalized boosting model, classification tree analysis, and random forests) and generated the ensemble maps of the current and future distribution of each species. For the future, we used five general circulation models and two representative concentration pathways (RCPs). Finally, we mapped beta-diversity and changes in alpha-diversity of the tree species under climate change. Our analyses showed that generally, the climatically suitable habitats for most of the species tend to shift and shrink in the future. A shift in major trees boundaries will be expected both along an east-west gradient and along an altitudinal gradient under climate change scenarios. The results demonstrated that climate change is likely to exert a strong influence on beta-diversity and richness of the major tree species in northern forests of Iran. In total, beta-diversity of tree species will be higher in the central and eastern parts compared with the western areas under the climate change scenarios and the mid-elevations of the western Hyrcanian forests will likely experience the lowest beta-diversity through time, meaning that the impacts of climate change on these regions are minimal. The impacts of climate change on the distribution of major tree species in the Hyrcanian forests can be considered very severe and pose a high risk of loss in forest functions and services. Forest managers will encounter several uncertainties in the wood productions, plantation, restoration, and conservation plans due to climate change in the Hyrcanian forests.

Keywords Beta-diversity . Ensemble models . Hyrcanian forests . Species distribution models . True turnover . Uncertainty

Introduction

Living organisms are the relevant components of eco- Communicated by Wolfgang Cramer systems, and their survival and functioning heavily de- Electronic supplementary material The online version of this article pend on climatic conditions (Woodward 1987). Keeping (https://doi.org/10.1007/s10113-019-01578-5) contains supplementary their balance with climate is necessary for the sustain- material, which is available to authorized users. ability and stability of global ecosystems (Khaine and Woo 2015). It is a focal premise of biogeography that * Seyed Jalil Alavi climate is one of the principal factors controlling the [email protected] natural distribution of plant species over large areas such as an ecoprovince or forest region (Guisan and 1 Department of Forestry, Faculty of Natural Resources and Marine Zimmermann 2000; Pearson and Dawson 2003;Rose Sciences, Tarbiat Modares University, Noor, Iran and Burton 2009). Understanding the mechanisms and 2 Ecosystem Management, Department of Environmental Systems impacts of climate on tree species is essential for suc- Science, ETH Zurich, 8092 Zurich, Switzerland cessful management and conservation of forest resources 3 Department for Migration and Immuno-ecology, Max Planck (Rose and Burton 2009). Institute for Ornithology, 78315 Radolfzell, Germany Climate change is one of the major challenges of our time. 4 Swiss Federal Research Institute WSL, Birmensdorf, Switzerland Warming of the climate system has been accelerated since 2712 H. Taleshi et al.

1950s, and many of the observed changes such as warming Forest managers need to adopt long-term management de- atmosphere and oceans, decreasing snow and ice, rising sea cisions while uncertainty about the impacts of climate change water levels, and increasing greenhouse gas concentrations is still large (Keenan 2012; Lindner et al. 2014). There are occur at unprecedented pace (IPCC 2014). In each of the last many sources of uncertainty including (a) climatic uncer- three decades, the surface temperature of earth has been con- tainties, arising from the different general circulation models sistently warmed compared with preceding decades since the (GCMs) and greenhouse gas emission scenarios, b uncertainty 1850s. The global mean of the combined land and ocean sur- arising from the sensitivity and response of forests, c algorith- face temperature reveals a warming of 0.85 °C over the period mic uncertainties, arising from the differences in simulation of 1880 to 2012 (IPCC 2014). Moreover, the data shows that models, and the inputs and parameters of models, and d biotic the last 30 years have been the warmest period in the last uncertainties, arising from the inappropriate assumptions of 1400 years in the Northern Hemisphere (IPCC 2014). the biology of a species (Lindner et al. 2014; Pacifici et al. The impacts of climate change on tree species can affect the 2015). Due to the inherent variability of the natural systems in sensitive balance within ecosystems (Vessella et al. 2017). space and time, models of natural systems, including SDMs, Future climate change can lead to shifts in the distribution inevitably include some degrees of uncertainty (Gould et al. and abundance of species (Ehrlén and Morris 2015; Thomas 2014). One of the main challenges of SDMs is the appropriate et al. 2004;Wangetal.2018), extinction of species popula- model selection among the wide variety of available models tions (Bestion et al. 2015; Keith et al. 2008;Thomasetal. (Buisson et al. 2010). Ensemble forecasting is an appropriate 2004), range shifts (Bellard et al. 2012; Chen et al. 2011; solution to quantify the variation originating from a range of Iverson and McKenzie 2013; Nenzén and Araújo 2011), phe- choices made during the modeling process (Araújo and New nological changes (Anenkhonov 2009; Merilä and Hendry 2007). An ensemble forecasting which ultimately combines 2014; Wolkovich et al. 2012), and physiological trait changes the predictions of different SDMs and GCMs can thus be used (Bozinovic and Pӧrtner 2015;Dillonetal.2010). In addition, to quantify uncertainties associated with model projections climate change can affect the distribution and composition of under climate change (Vieilledent et al. 2013). forests (Dunckel et al. 2017; Joshi et al. 2012;Wangetal. Global climate change has started to exert unavoidable 2013). Shifts in plant species, geographical distributions, and consequences in Iran. Analyses of the recent climate change range contractions with extinctions at the lower elevational show an increasing temperature trend in many synoptic and latitudinal limits can be the consequence of changes in weather stations of Iran (Azizi and Roshani 2008; Molavi- the normal patterns of temperature and humidity. These pat- Arabshahi et al. 2016). Given that Iranian forests already have terns of changes are among the prime expected impacts of been strongly affected by droughts, it can be clearly concluded projected future climate change (Koralewski et al. 2015; that the climate has been warming in the temperate forest Ladányi et al. 2015; Schwart 1993; Thuiller 2007; Zomer ecosystems of Northern Iran, the Hyrcanian forests (Attarod et al. 2015). et al. 2017; Jafari 2008; Molavi-Arabshahi et al. 2016). Species distribution models (SDMs) have been used wide- Despite many concerns about the impacts of climate change ly in biogeography to characterize the ecological niche of on biodiversity, its effects on plant and animal species in Iran plants and animals and to predict the geographical distribu- are unknown to date. Although in the recent years, many stud- tions of their habitats. Species distribution modeling is usually ies have investigated the impacts of climate change on the based on characterizing the statistical relationship between future distributions of trees species in different regions of the environmental variables and the occurrence or abundance of world (Benito Garzón et al. 2008; Chala et al. 2016;Iverson species (Guillera-Arroita et al. 2015; Guisan and and Prasad 2002;Koralewskietal.2015;Lengetal.2008; Zimmermann 2000; Hasui et al. 2017;Miller2010). SDMs Remya et al. 2015; Trisurat et al. 2011;Xuetal.2009; Zhang generate a probabilistic projection of the realized ecological et al. 2018), a very few studies addressed these issues in the niche for a species in a geographic space for a given period of forests of Iran. In a study by Haidarian Aghakhani et al. time (Guisan et al. 2017). They are widely used to project the (2017a) that investigated the redistribution of Amygdalus future distributions of organisms under climatic and land-use scoparia species under climate change using GLM, CTA, change scenarios (Bruneel et al. 2018; Chala et al. 2016; ANN, GBM, and RF in Chaharmahal and Bakhtiari province Enquist 2002;Khanumetal.2013;McKenneyetal.2007; in Iran, the results indicated that suitable habitats of Santos et al. 2015), assess invasion risk of exotic species A. scoparia will be decreased about 43% and 59%, respective- (González-Muñoz et al. 2014; Jones 2012; Lemke et al. ly, under RCP 4.5 and RCP 8.5 by 2050. Further, Haidarian 2011; Liang et al. 2014; Vardien et al. 2012), prioritize con- Aghakhani et al. (2017b) analyzed the future distribution of servation managements (Liu et al. 2013; Porfirio et al. 2014; Quercus brantii species using GLM, GAM, CTA, ANN, and Watling et al. 2015), and map the distribution of rare and RF in Chaharmahal and Bakhtiari province. The results sug- endangered species (Engler et al. 2004;Marceretal.2013; gested that the percentage of suitable habitats loss and gain Williams et al. 2009; Wilson et al. 2011). will be 35.7% and 61.4%, respectively, under RCP 4.5 by Climate change impacts on the distribution and diversity of major tree species in the temperate forests of... 2713

2070. Alavi et al. (2019) studied the current and future distri- considerable relicts of Arcto-Tertiary forests in the western bution of Taxus baccata using ensemble model including four Eurasia (Scharnweber et al. 2007). They are one of the last species distribution models in the Hyrcanian forests of Iran. remnants of natural deciduous forests in the world that contain The results of the range size analyses showed that no stable a number of relict Arcto-Tertiary thermophilous species, such suitable habitats will be left under RCP 8.5 by 2070. as ironwood (Parrotia persica C.A. Meyer), Caspian honey This study aimed to assess the impacts of climate change locust (Gleditschia caspica Desf.), Caucasian elm (Zelkova on the distribution of major tree species in northern forests of carpinifolia (Pallas) K. Koch), and false walnut (Pterocarya Iran, also known as the Hyrcanian forests. The Hyrcanian fraxinifolia (Poir) Spach) (Sagheb-Talebi et al. 2014). The forests has recently been added to the UNESCO’sWorld most important reason for the protection of Hyrcanian flora Heritage List in July 2019 (UNESCO World Heritage Centre during the Ice Age is related to the tempering effects of the 2019).We analyzed the current distributions of the eleven ma- proximity to the Caspian Sea and even the Black Sea (Leroy jor tree species using an ensemble approach involving five and Arpe 2007). Native and endangered tree species of different SDM algorithms and generated the ensemble maps Hyrcanian forests include Caspian honey locust, false walnut, of the current and projected future distribution of each species. ironwood, Siberian elm, box tree, Caspian poplar, and a few For the future projections, we used five GCMs and two rep- conifer species such as yew and oriental arborvitae (Sagheb- resentative concentration pathways (RCPs), namely, RCP 4.5 Talebi et al. 2014). and 8.5. We prepared the ensemble maps of future distribution of each species under each of the two RCPs using five GCMs Tree species for 2070. Finally, we mapped beta-diversity and changes in alpha-diversity (richness) of the studied tree species under The presence and absence data of eleven major tree species climate change conditions. (Table 1) were obtained from the Hyrcanian Forest Inventory of the Iranian Forests and Rangelands Organization. The records have been collected from the sample plots across the Materials and methods Hyrcanian forests on a 5 × 1-km network. We also selected additional inferred absences for tree species in the areas with Study area no forest trees according to the GlobeCover map 2009 (Arino et al. 2012) using the ecospat package (Di Cola et al. 2017), in The study area is the temperate forests of Northern Iran which order to allow for better assessing the climatic limits of the tree are located between the northern slopes of Alborz mountain species distributions. Such information is not available when ranges and the southern coasts of the Caspian Sea. They sampling trees only within a forest; therefore, we added 1000 stretch across three Northern provinces of Iran, namely, inferred absences selected randomly in non-forest classes in Gilan, Mazandaran, and Golestan. These forests also are the GlobeCover map. called Hyrcanian or Caspian forests. Their spatial extent covers the latitudes 35° 48′ N and 37° 55′ N to longitudes Environmental variables 48° 31′ E and 56° 10′ E. This zone is approximately 800 km long and 110 km wide with a total area of 1.85 million ha. The We obtained 19 bioclimatic variables as the predictors with a Hyrcanian forests stretch out from the sea level up to an alti- spatial resolution of 1 km for both the current and projected tude of 2800 m (Sagheb-Talebi et al. 2014). In the Hyrcanian future climate from the global climate dataset of Worldclim region, the mean annual rainfall ranges from 530 mm in the (Hijmans et al. 2005). Here, we used the downscaled data east to 1350 mm in the west. Their mean annual temperature from five general circulation models (GCMs) from the varies from 15 °C in the west to 17.5 °C in the east over the CMIP5 archive (IPCC 2014), namely, BCC-CSM1-1, past decade. Inceptisols (Brown soils) are the most abundant CCSM4, HadGEM2-ES, MIROC-ESM, and MRI-CGCM3, soils in the Northern forests and comprise approximately 90% simulated for two representative concentration pathways of the Hyrcanian region (Mohadjer 2012; Sagheb-Talebi et al. (RCPs), RCP 4.5 and RCP 8.5. These scenarios were used 2014). The area has a subtropical climate with mild winters to represent the different future climate conditions by 2070 and hosts a vast biodiversity, including many broadleaved tree (average for 2061–2080). In addition, a digital elevation mod- species (Oladi et al. 2011). It differs climatically from other el (DEM), obtained from the U.S. Geological Survey (USGS) areas in Iran because of its high annual precipitation (600– at 30 m spatial resolution, was used to generate the variables 2000 mm) and encompasses a gradient of floristic changes, of slope angle, slope aspect, and topographic exposure using both altitudinally and longitudinally (Moradi et al. 2016). the raster package (Hijmans et al. 2017). The aspect values These forests contain about 80 tree and 50 shrub species were transformed to a range between − 1 to + 1, which repre- (Mohadjer 2012), and include various forest types (Rouhi- sent the slope aspects from south to north, respectively. Moghaddam et al. 2008). The Hyrcanian forests are the most Further, the map of soil resources and land suitability, 2714 H. Taleshi et al.

Table 1 Scientific and common names and number of presences No. Scientific name Common name Number of Number of and absences of the tree species presences absences included in the study 1 Acer cappaducicum Gled. Cappadocian maple 472 3131 2 Acer velutinum Boiss. Velvet maple 622 2981 3 Alnus subcordata C.A.Mey. Caucasian alder 717 2886 4 Carpinus betulus L. Common hornbeam 1975 1628 5 Diospyros lotus L. Date-plum 735 2868 6 Fagus orientalis Lipsky Oriental beech 1092 2511 7 Gleditsia caspica Desf. Caspian honey locust 158 3445 8 Parrotia persica C.A.Mey. Ironwood 681 2922 9 Quercus castaneifolia C.A.Mey. Chestnut-leaved oak 677 2926 10 Tilia platyphyllos Scop. Large-leaved lime tree 259 3344 11 Zelkova carpinifolia (Pall.) K. Koch Siberian elm 130 3473 obtained from the Iranian Soil and Water Research Institute at optimizations. For GAM, we used a moderate flexibility of the scale of 1:1,000,000, was used to extract the soil categor- the response shape, by setting the k parameter to a value of − ical values at the sample locations and to use them as the soil 1. For CTA, we used a five-fold cross-validations (the mini- variable. We used a stepwise procedure implemented in the R mum number of observations in any terminal node = 5, the usdm package (Naimi et al. 2014) to test the issue of minimum number of observations that must exist in a node multicollinearity among the environmental variables by esti- in order for a split to be attempted = 5 and complexity param- mating the variance inflation factor (VIF) and retained only eter = 0.001). The GBM models were constructed by fitting the variables with VIF < 10 (Graham 2003). Finally, we kept 9 2500 trees and a three-fold cross-validations (depth of each environmental variables for the modeling step, including tree = 3, minimum number of observations in the trees termi- isothermality (BIO3), mean temperature of wettest quarter nal nodes = 5 and shrinkage = 0.001). For RF, we grew a for- (BIO8), mean temperature of warmest quarter (BIO10), pre- est of 500 classification trees with minimum size of terminal cipitation seasonality (BIO15), precipitation of coldest quarter nodes equal to 5. (BIO19), slope, aspect value, topographic exposure, and soil To assess the predictive capacity of the models, five ran- categories. dom partitions were used in the five SDMs. Each partition was generated by randomly choosing 70% of the presence records Statistical analyses of species distributions as calibration data, and the remaining 30% as evaluation data for each tree species. We measured the accuracy of the models We used five species distribution modeling methods included using the area under the (ROC) curve (AUC) statistic. Models generalized linear models (GLM; McCullagh and Nelder with the values of AUC ≥ 0.7 were retained for the ensemble 1989), generalized additive models (GAM; Hastie and building and for projecting the tree species distributions under Tibshirani 1990), generalized boosting model (GBM; different climate conditions (Shirley et al. 2013). Friedman 2001), classification tree analyses (CTA; Breiman For each tree species, the probabilistic predictions of the et al. 1984), and random forests (RF; Breiman 2001). These distributions were produced under different climate conditions methods were used to link the current environmental condi- (Current, RCP 4.5/2070, and RCP 8.5/2070). To classify the tions to the species presence and absence data, and subse- probabilistic predictions from the statistical SDMs into quently, to predict and map the spatial distribution of the spe- presence/absence maps, we used two different thresholds: cies for the current and projected future climates. The models one based on maximizing the true skill statistic (TSS; were fitted by assigning the equal weight to each presence and Allouche et al. 2006) and another one based on maximizing absence record in a way that the sum of the weights for the Kappa (Cohen 1960). Further, the binary presence/absence presence records was equal to the sum of the weights for the maps were ensembled by simple mean values for each tree absence records (Barbet-Massin et al. 2012). SDMs were con- species under different climate conditions. Finally, the ensem- structed using the Biomod2 package (Thuiller et al. 2014), an ble of individual classified binary maps were reclassified into ensemble platform for species distribution modeling in R. For three habitat ensemble suitability classes based on the propor- GLM, we used linear and quadratic terms with no interactions, tion of the predicted values as species presence among the and optimized the model based on a stepwise variable selec- statistical and climatic models at each pixel for each species tion procedure, starting from a full model with all variables (Chala et al. 2016): (i) < 30% of the models predict the pres- included, and using both backwards and forward search ence (=habitat is unsuitable with certainty), (ii) 30–60% of the Climate change impacts on the distribution and diversity of major tree species in the temperate forests of... 2715 models predict the presence (=habitat suitability is uncertain), the habitats that is considered uncertain regarding its suitabil- and (iii) > 60% of models predict the presence (=habitat is ity (30–60% of model combinations agree on suitability). In suitable with certainty). three species, including G. caspica, Tilia platyphyllos, and For assessing the change in the rage size, we reclassified Z. carpinifolia, the area simulated as uncertain regarding hab- the ensemble maps for each species into two classes; (i) < 60% itat suitability was larger than the area of suitable habitat (> of the models predict the presence (=habitat is unsuitable) and 60% of model combinations agree on suitability) under cur- (ii) > 60% of the models predict the presence (=habitat is rent climate conditions. suitable). Finally, we overlaid the current and projected future According to the species distribution projections under cli- range size maps and derived the following four categories: (i) mate change (Table 3; Supplementary Fig. A12-A22), the stable presence; pixel is currently occupied by a given species highest decrease of suitable habitat was projected for and is predicted to remain occupied in the future, (ii) loss; A. subcordata (− 87.33%) under RCP 4.5. P. persica was pixel is currently suitable but predicted to become unsuitable projected to undergo the lowest decrease of suitable habitat by 2070 for a given species, (iii) gain; pixel is currently un- (− 10.90%), while Q. castaneifolia and Z. carpinifolia were suitable for a given species but predicted to become suitable in projected to increase their suitable habitat under RCP 4.5 by the future, (iv) stable absence; pixel is not currently occupied 2070. The suitable habitat for all the eleven tree species will by the given species and will remain so. decrease under RCP 8.5. The highest decrease of suitable habitat was projected for A. subcordata (− 96.49%).Z. Quantifying biodiversity responses to climate change carpinifolia showed the lowest decrease of certain suitable habitat (− 8.22%) under RCP 8.5 by 2070. At each pixel, we quantified the values of beta-diversity and its components, including nestedness and true turnover Range size trends under climate change (Baselga 2010) under different climate change models and scenarios between the current and projected future climates The results of the range size analyses under RCP 4.5 (Table 4; using the “betapart” package (Baselga and Orme 2012). The Figs. 1 and 2; Supplementary Fig. A23-A31)revealedthatthe ensemble binary maps used in this analysis were the same as range size of 9 species, including A. cappaducicum, those used in the analysis of the changes in the range size. We A. velutinum, A. subcordata, C. betulus, D. lotus, then generated the maps of richness changes of tree species F. orientalis, G. caspica, P. persica,andT. platyphyllos, will under different climate change conditions in the Hyrcanian likely see shrinking ranges, while the range of two species forests by combining the binary maps of tree species. including Q. castaneifolia and Z. carpinifolia will be increasing in size by 2070. The maximum range size loss was related to A. subcordata (− 87.33%) while the range size for Results Q. castaneifolia and Z. carpinifolia was found to increase by + 16.80% and + 20.30%, respectively. The highest and lowest Climate change impacts on species distributions loss were related to G. caspica (− 95.71%) and Z. carpinifolia (+ 16.84%), respectively, under RCP 4.5 by 2070. The highest The predictive accuracies of the models were relatively high and lowest gained suitable area was found for Q. castaneifolia across all the eleven tree species with a mean AUC value of (+ 62.68%) and F. orientalis (+ 3.14%), respectively by 2070. 0.77 (St. dev = ± 0.01) (Table 2; Supplementary Table A1). A Under RCP 8.5 (Table 4; Figs. 1 and 2; Supplementary Fig. model with an AUC value of 0.70 is considered as a model A23-A31), all the eleven trees will likely see shrinking ranges, with an acceptable discriminatory power (Shirley et al. 2013). indicating a severe loss of these commercially important trees Fagus orientalis with a mean AUC value of 0.86 (St. dev = ± in the region. The highest decrease in the range size was found 0.02) had the highest predictive power while Gleditsia caspica for A. subcordata (− 96.49%). Regarding loss of currently and Zelkova carpinifolia with a mean AUC value of 0.71 (St. suitable area, A. subcordata had the highest (− 99.71%) and dev = ± 0.01) had the lowest prediction success. Z. carpinifolia had the lowest (− 38.01%) loss in suitable hab- The results of the habitat suitability modeling for all tree itat by 2070. The highest and lowest gains in suitable area species (Table 3; Supplementary Fig. A1-A11)showedthat compared with current climate were obtained for Carpinus betulus had the largest area of suitable habitat Q. castaneifolia (+ 46.36%) and F. o rie nt al is (+ 3.02%), re- (26,685 km2)whileG. caspica had the lowest area of suitable spectively, by 2070. habitat (10,993 km2) under the current climate condition in the Hyrcanian forests. The area of suitable habitats for eight spe- Biodiversity trends under climate change cies, including Acer cappaducicum, Acer velutinum, Alnus subcordata, C. betulus, Diospyros lotus, F. orientalis, The nestedness map of the tree species (indicating richness Parrotia persica,andQuercus castaneifolia were larger than change through time) under RCP 4.5 by 2070 (Fig. 3a) 2716 H. Taleshi et al.

Table 2 Model accuracies given by mean AUC values against the Modeling algorithms independent dataset GLM GAM CTA GBM RF Avg. St. dev

Acer cappaducicum 0.736 0.732 0.700 0.742 0.728 0.73 ± 0.01 Acer velutinum 0.738 0.740 0.700 0.744 0.740 0.73 ± 0.02 Alnus subcordata 0.734 0.772 0.713 0.776 0.776 0.75 ± 0.03 Carpinus betulus 0.806 0.826 0.786 0.834 0.844 0.82 ± 0.02 Diospyros lotus 0.796 0.810 0.782 0.816 0.814 0.80 ± 0.01 Fagus orientalis 0.864 0.868 0.824 0.876 0.884 0.86 ± 0.02 Gleditsia caspica 0.714 0.710 - 0.723 0.710 0.71 ± 0.01 Parrotia persica 0.806 0.840 0.796 0.850 0.850 0.83 ± 0.02 Quercus castaneifolia 0.676 0.702 0.693 0.742 0.762 0.72 ± 0.03 Tilia platyphyllos 0.796 0.782 0.723 0.796 0.766 0.77 ± 0.03 Zelkova carpinifolia 0.704 0.700 0.710 0.730 - 0.71 ± 0.01 Averages 0.76 0.77 0.74 0.78 0.79 0.77 ± 0.02

Models with AUC < 0.70 values excluded and therefore did not contribute to the statistic showed that the nestedness change will likely be higher in the with the only difference that the rate of decrease in the richness eastern Hyrcanian forests than in the western parts (mostly values is higher for all the species. because of species loss). The species are projected to lose in all the elevational ranges in the central and eastern Hyrcanian forests while the major loss of tree species is expected to occur Discussion in the lowlands and highlands of the western Hyrcanian forests. The true turnover map (corrected for richness change) of General discussion the species (Fig. 3b) revealed that species replacements are high in the highlands of the eastern parts as well as mid- The ratability of projected impacts of climate change can be elevations of the western Hyrcanian forests. The beta- improved by using an ensemble forecasting framework com- diversity (nestedness plus true turnover) showed the highest bining the outputs of several sources of uncertainty (Buisson values in the lowlands and highlands of the Hyrcanian forests et al. 2010). Our analysis considered different sources of un- (Fig. 3c). Also, eastern and central parts are expected to ex- certainty in the distribution of major tree species under climate hibit higher beta-diversity than the other parts. change in the Hyrcanian forests of Iran. We used an ensemble The nestedness map of tree species under RCP 8.5 in 2070 approach involving five different SDMs, five random parti- (Fig. 4a) showed that the nestedness change will likely be high in tions in the five SDMs, two threshold criteria, five GCMs, and all the elevational zones of the central Hyrcanian forests with two RCPs. major changes in the lowlands and highlands of the western Our analyses provide evidence that the climatically suitable parts. The true turnover through time of tree species (Fig. 4b) habitats for most of the species in this study tend to shift and showed high rates of species replacements in the highlands of shrink generally in the Hyrcanian forests in the future (i.e., the eastern and mid-elevations of western Hyrcanian forests. Overall, year 2070). These changes can be considered very severe and beta-diversity will be high in all parts of the Hyrcanian forests pose a high risk of loss in forest functions and services except mid-elevation parts of the western parts (Fig. 4c). (Ozolinčius et al. 2014). The predicted species habitat suitabil- Richness trends in tree species under RCP 4.5 by 2070 ity under different climate conditions showed that suitable (Fig. 5a) showed that the species loss will be higher in the habitats of all the species (all modeled species except for central and eastern Hyrcanian forests than in the western parts. Quercus castaneifolia and Zelkova carpinifolia) will likely In the central and eastern regions, tree species richness will see shrinking ranges in the Hyracanian forests under RCP decrease in all the elevational zones (lowlands, mid- 4.5 by 2070. Four of the species, including Acer velutinum, elevations, and highlands) while it will decrease only in the Alnus subcordata, Fagus orientalis, and Gleditsia caspica lowlands of the western part. In some parts of the central and will lose at least 70% of their suitable habitats under the mod- eastern Hyrcanian forests, 10 tree species are likely lost, while erate future climate change scenario (i.e., RCP 4.5), while the richness will increase by up to 5 species in the highlands of under RCP 8.5, the same species plus Carpinus betulus will the western parts. The pattern of the richness change is almost lose at least 83% of their suitable habitats by 2070. Among the the same under RCP 8.5 compared with RCP 4.5 (Fig. 5b), world’s ecosystems, mountain forests and their unique lmt hneipcso h itiuinaddvriyo ao reseisi h eprt oet of... forests temperate the in species tree major of diversity and distribution the on impacts change Climate

Table 3 Predicted habitat suitability for tree species under different climate conditions

Tree species Climate conditions Unsuitable Changes in unsuitable habitat* Uncertain Changes in uncertain habitat * Suitable habitat Changes in suitable habitat* habitat (km2) habitat (km2) (km2) km2 %km2 %km2 %

Acer cappaducicum Current 86,001 - - 9709 - - 11,149 - - 2070 RCP 4.5 88,424 + 2423 + 2.82 11,876 + 2167 + 22.32 6559 − 4590 − 41.17 RCP 8.5 94,337 + 8336 + 9.69 9547 − 162 − 1.67 2975 − 8174 − 73.32 Acer velutinum Current 84,355 - - 9035 - - 13,469 - - 2070 RCP 4.5 97,835 + 13,480 + 15.98 5610 − 3425 − 37.91 3414 − 10,055 − 74.65 RCP 8.5 102,703 + 18,348 + 21.75 2734 − 6301 − 69.74 1422 − 12,047 − 89.44 Alnus subcordata Current 79,946 - - 10,866 - - 16,047 - - 2070 RCP 4.5 97,697 + 17,751 + 22.20 7129 − 3737 − 34.39 2033 − 14,014 − 87.33 RCP 8.5 103,557 + 23,611 + 29.53 2739 − 8127 − 74.79 563 − 15,484 − 96.49 Carpinus betulus Current 76,227 - - 3947 - - 26,685 - - 2070 RCP 4.5 82,864 + 6637 + 8.71 13,580 + 9633 + 244.06 10,415 − 16,270 − 60.97 RCP 8.5 91,957 + 15,730 + 20.64 10,452 + 6505 + 164.81 4450 − 22,235 − 83.32 Diospyros lotus Current 86,541 - - 5597 - - 14,721 - - 2070 RCP 4.5 85,193 − 1348 − 1.56 9027 + 3430 + 61.28 12,639 − 2082 − 14.14 RCP 8.5 85,714 − 827 − 0.96 15,139 + 9542 + 170.48 6006 − 8715 − 59.20 Fagus orientalis Current 85,370 - - 4114 - - 17,375 - - 2070 RCP 4.5 96,454 + 11,084 + 12.98 6918 + 2804 + 68.16 3487 − 13,888 − 79.93 RCP 8.5 103,083 + 17,713 + 20.75 2013 − 2101 − 51.07 1763 − 15,612 − 89.85 Gleditsia caspica Current 80,121 - - 15,745 - - 10,993 - - 2070 RCP 4.5 91,207 + 11,086 + 13.84 13,233 − 2512 − 15.95 2419 − 8574 − 78.00 RCP 8.5 101,880 + 21,759 + 27.16 4353 − 11,392 − 72.35 626 − 10,367 − 94.31 Parrotia persica Current 76,084 - - 14,647 - - 16,128 - - 2070 RCP 4.5 72,865 − 3219 − 4.23 19,624 + 4977 + 33.98 14,370 − 1758 − 10.90 RCP 8.5 74,160 − 1924 − 2.53 24,708 + 10,061 + 68.69 7991 − 8137 − 50.45 Quercus castaneifolia Current 76,506 - - 12,929 - - 17,424 - - 2070 RCP 4.5 66,799 − 9707 − 12.69 19,708 + 6779 + 52.43 20,352 + 2928 + 16.80 RCP 8.5 67,999 − 8507 − 11.12 26,628 + 13,699 + 105.96 12,232 − 5192 − 29.80 Tilia platyphyllos Current 95,769 - - 7379 - - 3711 - - 2070 RCP 4.5 93,679 − 2090 − 2.18 10,785 + 3406 + 46.16 2395 − 1316 − 35.46 RCP 8.5 93,814 − 1955 − 2.04 11,433 + 4054 + 54.94 1612 − 2099 − 56.56 Zelkova carpinifolia Current 79,377 - - 14,742 - - 12,740 - - 2070 RCP 4.5 79,627 + 250 + 0.31 11,907 − 2835 − 19.23 15,325 + 2585 + 20.29 RCP 8.5 82,889 + 3512 + 4.42 12,277 − 2465 − 16.72 11,693 − 1047 − 8.22

*The minus sign (−) indicates decrease and the plus sign (+) indicates increase 2717 2718 H. Taleshi et al.

Table 4 Range size changes of tree species under different climate conditions

Tree species Climate conditions Range size (km2) Stable Loss Gain Species range changes *

km2 %km2 %km2 %km2 %

Acer cappaducicum Current 11,149 ------2070 RCP 4.5 6559 2388 21.42 8761 78.58 4171 37.41 − 4590 − 41.17 RCP 8.5 2975 619 5.55 10,530 94.45 2356 21.13 − 8174 − 73.32 Acer velutinum Current13,469------2070 RCP 4.5 3414 1842 13.68 11,627 86.32 1572 11.67 − 10,055 − 74.65 RCP 8.5 1422 366 2.72 13,103 97.28 1056 7.84 − 12,047 − 89.44 Alnus subcordata Current16,047------2070 RCP 4.5 2033 1081 6.74 14,966 93.26 952 5.93 − 14,014 − 87.33 RCP 8.5 563 46 0.29 16,001 99.71 952 3.22 − 15,049 − 96.49 Carpinus betulus Current26,685------2070 RCP 4.5 10,415 6898 25.85 19,787 74.15 3517 13.18 − 16,270 − 60.97 RCP 8.5 4450 1699 6.37 24,986 93.63 2751 10.31 − 22,235 − 83.32 Diospyros lotus Current14,721------2070 RCP 4.5 12,639 10,170 69.08 4551 30.92 2469 16.77 − 2082 − 14.14 RCP 8.5 6006 4172 28.34 10,549 71.66 1834 12.46 − 8715 − 59.20 Fagus orientalis Current17,375------2070 RCP 4.5 3487 2942 16.93 14,433 83.07 545 3.14 − 13,888 − 79.93 RCP 8.5 1763 1238 7.13 16,137 92.88 525 3.02 − 15,612 − 89.85 Gleditsia caspica Current10,993------2070 RCP 4.5 2419 472 4.29 10,521 95.71 1947 17.71 − 8574 − 78.00 RCP 8.5 626 44 0.40 10,949 99.6 582 5.29 − 10,367 − 94.31 Parrotia persica Current16,128------2070 RCP 4.5 14,370 8285 51.37 7843 48.63 6085 37.73 − 1758 − 10.90 RCP 8.5 7991 3438 21.32 12,690 78.68 4553 28.23 − 8137 − 50.45 Quercus castaneifolia Current17,424------2070 RCP 4.5 20,352 9430 54.12 7994 45.88 10,922 62.68 2928 + 16.80 RCP 8.5 12,232 4155 23.85 13,269 76.15 8077 46.36 − 5192 − 29.80 Tilia platyphyllos Current3711------2070 RCP 4.5 2395 1158 31.20 2553 68.80 1237 33.33 − 1316 − 35.46 RCP 8.5 1612 404 10.89 3307 89.11 1208 32.55 − 2099 − 56.56 Zelkova carpinifolia Current12,740------2070 RCP 4.5 15,325 10,595 83.16 2145 16.84 4730 37.13 2585 + 20.29 RCP 8.5 11,693 7898 61.99 4842 38.01 3795 29.79 − 1047 − 8.22

*The minus sign (−) indicates decrease and the plus sign (+) indicates increase habitats are clearly exposed to climate change (Nogués-Bravo climate conditions likely provide more suitable habitats for et al. 2007). A sharp decrease in the range of species distribu- this species compared with the current climate that is probably tion due to the climate change is common property of moun- the reason for the increase in the projected range size. tain systems, which have only decreasing land area left for the A similar pattern was also provided in the study by Iverson upward shifts of plant species (Engler et al. 2011). The et al. (2008) that showed the expanding ranges for two species Hyrcanian forests are extended from the west to the east as a (Quercus stellate and Q. marilandica) under the climate narrow strip, which is a predisposition for a big loss of suitable change. In another study, Dale et al. (2010) suggested that habitats under climate change. the increase in the range size of the white oaks (Quercus alba) Our study showed that the range size of Q. castaneifolia is likely due to drought conditions favoring that species. will expand due to climate change (especially under RCP4.5). Similarly, Zolkos et al. (Zolkos et al. 2015) found that the area This species is a drought-adapted species that colonizes low to of suitable habitats for Quercus stellate and Quercus falcate mid-elevations (Bahri et al. 2014). Therefore, the future will increase under climate charge. Our simulated range Climate change impacts on the distribution and diversity of major tree species in the temperate forests of... 2719

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(b) Fig. 1 Range size changes of Alnus subcordata in the different climate conditions. a Range size changes under RCP 4.5 in 2070; b range size changes under RCP 8.5 in 2070 expansion is thus in line with a general view that oaks tend to the east (Sagheb-Talebi et al. 2014). These differing climate be one of the few species groups that can benefit from climate conditions are likely responsible for the generally higher loss change. in suitable habitats in the eastern and central regions compared Further, our results suggest that the impacts of climate with the western regions of the Hyrcanian forests. change are more severe on the eastern parts of the Hyrcanian The range size analyses in our study revealed an upward forests compared with the western parts. The two regions differ shift of all the tree species due to climate change. In the moun- remarkably in precipitation regimes (Akhani et al. 2010)and tainous regions, tree species are generally expected to shift to the mean annual temperature increases from the west to the east higher elevations in response to climate change (Lin et al. while the mean annual precipitation decreases from the west to 2014), and many other studies have confirmed such 2720 H. Taleshi et al.

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(b) Fig. 2 Range size changes of Quercus castaneifolia in the different climate conditions. a Range size changes under RCP 4.5 in 2070; b range size changes under RCP 8.5 in 207 elevational shifts due to climate change (Beckage et al. 2008; beta-diversity and its components, nestedness, and true turn- Cheaib et al. 2012; Haidarian Aghakhani et al. 2017b; Lenoir over are projected to be higher under RCP 8.5 than under RCP et al. 2008;Nogués-Bravoetal.2007). 4.5 by 2070. In total, beta-diversity of tree species will be higher in the central and eastern parts compared to the western Turnover in tree species under climate change areas under the climate change scenarios. and implications for conservation In addition, the mid-elevations of the western Hyrcanian forests will likely experience the lowest beta-diversity through In summary, our analyses demonstrated that climate change is time, meaning that the impacts of climate change on these likely to exert a strong influence on beta-diversity and richness regions are minimal. Increasing beta-diversity under climate of the major tree species in the Hyrcanian forests. The rate of change can be due to decreasing the local richness, without Climate change impacts on the distribution and diversity of major tree species in the temperate forests of... 2721

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(c) Fig. 3 Beta-diversity of tree species and its component maps under RCP 4.5 by 2070. a Nestedness; b true turnover; c beta-diversity 2722 H. Taleshi et al. driving regional extinctions (Socolar et al. 2016), which rep- volume and 2.7% of the stem numbers), Acer cappaducicum resents the nestedness component of beta. Such patterns in the (accounting for 1.2% of the standing volume and 1.5% of the beta-diversity and its components (turnover and nestedness) stem numbers), and Alnus subcordata (accounting for 9.1% of express the change in species compositions of analyzed re- the standing volume and almost 5% of the stem numbers) are gions, and severe turnover has clear implications for biogeo- other economically important species with high proportional graphic, ecological, conservation (Baselga 2010), and man- volume in the Hyrcanian forests of Iran (Sagheb-Talebi et al. agement issues. In landscapes with high beta-diversity, the 2014). Our results demonstrated that suitable habitats of these network of protected areas faces the challenges of successfully four species will likely be reduced by more than 60% and 73% managing the loss and replacement of species and to compen- under RCP 4.5 and RCP 8.5, respectively. Since the sate the loss in protection functions. Thus, turnover can have Hyrcanian forests are the only source of Iranian industrial strong implications for conservation decisions. Conservation timber, climate change is expected to have severe negative management in areas of high turnover will have to carefully impacts on the timber production in Iran which subsequently support the low number of richest habitats while, in the areas influences the Iranian timber industry. with high nestedness, a larger number of different habitats, not necessarily the richest ones, will have to be maintained (Baselga 2010; Wiersma and Urban 2005). Implications for forest management According to the available floristic data and our findings, it seems that the Western Hyrcanian region has the highest bio- Climate change is one of the major challenges in forest man- diversity and the least affected part of the forest by future agement due to direct impacts on forest functions and services, climate change. This does not mean that the conservation as well as the long-standing gap between management deci- measures there should be less strict than the eastern section sions and their consequences (Yousefpour et al. 2017). The of the Hyrcanian forests. By contrast, it is necessary to protect general assumption has been that the site conditions, especial- this part as a “sanctuary” and genetic reservoir for the ly climatic parameters, are more or less constant. This assump- Hyrcanian species. Thus, imagine that after a long-term miti- tion is no longer valid due to climate change which can affect gation, the upward-shifted thermo-mesophilous species need species habitat suitability (Brang et al. 2014). to descend to their lowland and plain habitats. This means that Acer velutinum is one of the most popular trees for planta- the lowland habitats should also strictly be protected. tions and restoration of different forest stands in the Hyrcanian forests (Sagheb-Talebi et al. 2014). Our results projected a Climate change impacts on the Iranian timber decrease in its range size by 74.65% and 89.44% under RCP production 4.5 and RCP 8.5, respectively. Under such changes, only a small portion of suitable habitats for velvet maple will remain Our analyses revealed massive changes and loss in suitable in high-elevations of eastern Hyrcanian forests. It can thus be habitats for the economically important tree species of the concluded that A. velutinum is no longer a proper suitable Hyrcanian forests due to climate change; a loss as such can species for plantation and restoration of the Hyrcanian forests have severe economic consequences (Hanewinkel et al. under climate change. 2013). Suitable habitats of the economically important species Alnus subcordata is widely used for plantations and resto- Fagus orientalis, Carpinus betulus, Acer velutinum,and ration of degraded stands in the Hyrcanian forests (Sagheb- Alnus subcordata are projected to be reduced by more than Talebi et al. 2014). Due to the projected decline in suitable 60% and 83% under RCP 4.5 and RCP 8.5, respectively. habitats of this species by 87.33% and 96.49% under RCP 4.5 Slightly increasing suitable habitats are only projected for and RCP 8.5 respectively, the species can no longer be rec- the economically important species Quercus castaneifolia ommended as suitable for restorations. Therefore, only small (+ 16.80%) under RCP 4.5, while under RCP 8.5, the same patchesofsuitablehabitatsforAlnus subcordata are likely to species will also see shrinking habitats (− 29.80%). Fagus remain in the high-elevations of eastern Hyrcanian forest. orientalis forests are the most productive and economically Quercus castaneifolia is another important species for res- important forest stands that currently cover approximately toration and plantation in the Hyrcanian forests (Sagheb- 17.6% of the total forest area, 30% of the standing volume, Talebi et al. 2014). Climate change projections showed that and 23.6% of the stem numbers in the Hyrcanian forests the range of suitable habitats for this species will either in- (Sagheb-Talebi et al. 2014). Our results revealed that the suit- crease (+ 16.80% under RCP 4.5) or slightly but not dramat- able habitat area of Fagus orientalis will reduce by at least ically decrease (− 29.8% under RCP 8.5) by 2070. 79.93% under moderate climate change scenario (RCP 4.5) Q. castaneifolia can thus be considered a suitable species for and even more under RCP 8.5. Carpinus betulus (accounting plantations and restoration of the Hyrcanian forests under cli- for 30.5% of the standing volume and 30% of the stem num- mate change, especially under moderate climate change bers), Acer velutinum (accounting for 5.8% of the standing scenario). Climate change impacts on the distribution and diversity of major tree species in the temperate forests of... 2723

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(c) Fig. 4 Beta-diversity of tree species and its component maps under RCP 8.5 by 2070. a Nestedness; b true turnover; c beta-diversity 2724 H. Taleshi et al.

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(b) Fig. 5 Richness change maps of tree species under climate changes by 2070. a Richness changes under RCP 4.5; b richness changes under RCP 8.5

Conclusions changes pose a high risk of loss in forest functions and services. A shift in major trees boundaries will be expected both Hyrcanian forests are now a UNESCO’s World Heritage due along an east-west gradient (with moist tree species expanding to their “remarkable” biodiversity. Aside from resourcing further west) and along an altitudinal gradient (with species wood, these forests exhibit a range of supporting services to adapted to the warmer, lower elevations migrating to higher the environment and to the local population. They play a vital altitudes). Considerable efforts should be undertaken to eval- role in the maintenance of soils and the purification of water. uate more different tree species for its response to climate Climate change will likely severely affect these functions of change, notably species for which no sufficient data is avail- the Hyrcanian forests. Overall, we found significant loss in able to date; some species as such might offer management suitable habitats for almost all of the studied species under alternatives under climate change that are currently RCP 4.5 and virtually for all species under RCP 8.5. Such overlooked. Also, it is strongly suggested to model the Climate change impacts on the distribution and diversity of major tree species in the temperate forests of... 2725 impacts of climate change on the distribution of relict boreal Bestion E, Teyssier A, Richard M, Clobert J, Cote J (2015) Live fast, die species (i.e., Betula spp.) in the Hyrcanian Forests. young: experimental evidence of population extinction risk due to climate change. 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