Sphagnum species, also commonly referred to as peat mosses, are classified as hygrophytes. Consequently, their distribution areas are frequently associated with wetland habitats, such as peatlands (bogs and fens) and mires (Popov, 2016; Glime, 2017). Additionally, they are commonly found in oceanic wet heaths and in swamp forests (Rydin et al., 2013; Campbell et al., 2021). Among the mosses, Sphagnum is the most dominant in the peatlands. The dense carpet-like growth and slow rate of decay of these mosses are the two main reasons for their large volume in bogs. Additionally, the acidic pH and low concentration of dissolved solutes in bogs facilitate the growth of Sphagnum mosses in these habitats. The role of Sphagnum in peatlands is significant, with both dead and living Sphagnum playing an important part in carbon sequestration. Furthermore, the plants have been observed to accumulate more carbon in their bodies than is fixed by all terrestrial vegetation in a single year (Vitt et al., 2008; Gajewski et al., 2001; Zhao et al., 2023).

The number of Sphagnum species is 292 worldwide. The species are distributed across Europe, Asia, Africa, North and Central America, South America, Australia, New Zealand and the Pacific (Michaelis, 2019). A total of 70 Sphagnum taxa have been identified in all European countries (Laine et al., 2018; Hodgetts and Lockhart, 2020). The distribution of Sphagnum in Europe exhibits a south-to-north gradient, with the species occurring in both oceanic and continental regions. Investigations have demonstrated that northern species of Sphagnum are more resilient to cold autumn and winter conditions than those with a southern distribution. Furthermore, there are considerable variations in the growth response to temperature (Breeuwer et al., 2008) and drought tolerance among Sphagnum species (Gerdol and Vicentini, 2011; Genet et al., 2013; van de Koot et al., 2024). While climatic parameters play an important role in their distribution on a global scale (Campbell et al., 2021; Ma et al., 2022), they largely depend on soil moisture (Yoshikawa et al., 2004; Harris et al., 2005) and mineral nutrients on a local scale (Popov, 2016; Hájek and Adamec, 2009). Accordingly, Campbell et al. (2021) proposed that the distribution of Sphagnum species can be effectively explained by a few climatic variables that are linked to their physiological characteristics. The findings indicate that the future of Sphagnum diversity in Europe is most significantly influenced by alterations in water availability and seasonal temperature fluctuations.

The most recent distribution models for Sphagnum species have been developed on a continental scale (Oke and Hager, 2017; Campbell et al., 2021). Oke and Hager (2017) investigated the distribution of Sphagnum taxa in peatland areas across North America. Their findings indicated that the balance between soil moisture deficit and temperature of the driest quarter-year plays a significant role in determining the distribution of Sphagnum peatlands. The authors highlight that all models indicate that Sphagnum peatlands may expand in the future, particularly in coastal areas, under suitable climatic conditions. In a similar vein, Campbell et al. (2021) clarified the current distributions of 45 Sphagnum taxa in Europe, with a focus on biologically relevant climatic variables. It was emphasized that the magnitude of temperature fluctuations throughout the year represents a significant climatic factor that distinguishes current Sphagnum distributions. Popov (2016) correlated the distribution of six Sphagnum taxa from section Sphagnum with local climatic variables in European Russia. The results revealed that strong correlations between these species distribution and temperature and abundance of the Sphagna showed high correlation with maximum relative humidity in the months August and September. In a subsequent study, Popov (2018) employed a modelling approach to examine the distribution of 11 species of Sphagnum from section Acutifolia, with a focus on the gradients of climatic variables across Europea Russia and Eastern Fennoscandia. The findings indicated that high humidity is a crucial factor in promoting the abundance of Sphagnum species. Furthermore, the author dis-covered that the abundance of the majority of Sphagnum taxa is positively correlated with precipitation, humidity, and temperature in the months of August, September, and October.

A number of previous studies on the distribution modelling of Sphagnum species, as previously mentioned, have indicated that Sphagnum and peatland distributions are significantly influenced by climatic variables. To date, no study has been conducted on the distribution modelling of different Sphagnum species in Türkiye (formerly Turkey). The objective of this study is to examine the relationship between relevant climatic factors and Sphagnum distributions in Türkiye, with the aim of identifying potential future distribution areas and populations of the species.

National studies show that Sphagnum species are established in the northern parts of Türkiye, especially near the eastern part of the Black Sea Region. Apart from this, Sphagnum taxa are also present in the western part of the Black Sea Region and Marmara Region (Kürschner and Erdağ, 2021; Kırmacı et al., 2022a). Maps shows a simulation of the future distributions for the Sphagna based on current geographical distribution records and climatic data ( Figures 2 - 6 ).

In the period between 2021 and 2040, the distribution of Sphagnum capillifolium is expected to expand in the region between 40°N and 42°N. There is an increase in the distribution areas of S. capillifolium in the periods 2021-2040 and 2081-2100 according to the future climatic scenarios. Popov (2018) reported a positive correlation between S. capillifolium and high humidity, as well as a negative correlation between the species and both monthly and annual mean temperatures in the Eastern European Plain and Eastern Fennoscandia. Additionally, the species was observed to flourish in regions with an annual precipitation exceeding 450–460 mm and an average annual temperature below +7°C. However, the results of our study indicate that the distribution areas of the species are undergoing a positive development in response to the predicted temperature increase for the coming years, as illustrated in the simulated maps. The selected climate scenarios (SSP1-2.6 and SSP5-8.5) and the applied model indicate that there will be reductions in the current distribution areas for S. auriculatum between 2021 and 2040, with a further decline in the 2081-2100 period. Indeed, the data associated with the SSP5-8.5 scenario points to a more pessimistic outlook with regard to habitat loss but does not disappear at all. In accordance with the projected climate scenarios for the period between 2081 and 2100, it can be stated that S. centrale will experience a notable reduction in its distribution areas as a consequence of rising temperatures, with the potential for even greater habitat loss. Popov (2016) indicates that the abundance of S. centrale exhibits a markedly positive correlation with precipitation and relative humidity during the period from late summer to mid-autumn (August-October), and a negative correlation with temperature during this same period. Furthermore, the author indicates that the presence of this species is inversely correlated with summer temperatures. The fact that the species has lost suitable habitats in its current local distribution in the eastern part of the Black Sea Region with the increase in temperature under different climate scenarios in the coming years supports what was described by Popov (2016).

Sphagnum compactum (shown in the period 2021-2040 and the scenario SSP1-2.6) and S. contortum (shown in the period 2081-2100 and the scenario SSP1-2.6) reaches the highest frequency in the northern distributions of Türkiye with the simulated suitable habitats. Two distinct scenarios for the forthcoming two decades (2021-2040) revealed an eastward expansion in the distribution of S. contortum, accompanied by a southward expansion of the species’ distribution area between the latitudes 38°N and 42°N. In their 2007 study, Hájková and Hájek (2007) reported that S. contortum is a spring-growing species that typically occupies streams. They noted that it is relatively common in Bulgarian mires. However, this species is categorized as VU, EN and LC in the Red List for many different countries (Papp et al., 2010; Ştefănuţ and Goia, 2012; Sérgio et al., 2007; Lazarević et al., 2016; Mišíková et al., 2020). The findings of our study indicate that the species is likely to expand its range in accordance with projected future climate scenarios. The distribution maps simulated for future years indicate a decrease in the distribution of S. divinum, with a particularly notable decline observed in the western and central parts of the Black Sea Region. According to both climate scenarios, the habitat loss in this area is predicted to occur between 40°N and 42°N between the years 2081 and 2100. According to Kırmacı et al. (2022b), S. divinum was evaluated as Near Threatened within the IUCN categories. According to the findings of our study, the fact that the species shows habitat loss under future climate scenarios supports the idea that the species will become threatened in the near future as stated by the authors.

It is projected that the distribution of Sphagnum fallax will expand significantly in comparison to its current range under the selected climate scenarios for the forthcoming years. Furthermore, there are indications of an expansion from the south-eastern part of the Marmara Region to the western part of the Mediterranean Region. The results presented herewith diverge from those observed in the studies conducted by Bragazza et al. (2016); Norby et al. (2019), and Jassey and Signarbieux (2019). Bragazza et al. (2016) presents the findings of a transplantation experiment involving peat mesocosms, which were relocated from high to low altitude in order to simulate a mean annual temperature approximately 5°C higher and a mean annual precipitation approximately 60% lower over a three-year period. The authors posited that the decline in annual productivity observed in the peat moss S. fallax in transplanted mesocosms was attributable to a combination of physical and biological constraints, namely water scarcity and light competition, respectively. Furthermore, it was demonstrated that the productivity of S. fallax declined by 60% in mesocosms that had been relocated to a warmer (+5°C) environment. In a further study, Norby et al. (2019) investigated the impact of experimental warming on the decline of S. fallax in a bog environment. Their hypothesis was based on the observation that S. fallax exhibited a 50% reduction in occurrence when transplanted to a location with a higher temperature (+5°C) and lower humidity. Regarding these contrasting results, Norby et al. (2019) argued that mound-pit microtopography has a greater influence on Sphagnum responses to warming than species-specific traits. Jassey and Signarbieux (2019) demonstrated that the negative effects of summer droughts on S. fallax water content were exacerbated by warming, resulting in an even sharper decrease in water content. The findings of our study suggest that the projected increase in temperature over the coming decades will not have a detrimental impact on the distribution of S. fallax. The estimated distribution maps indicate a slight decrease in the distribution of S. fuscum in the western part of the Black Sea Region and a slight increase in the north-eastern part of Türkiye over the next 20 years. However, the SSP1-2.6 and SSP5-8.5 scenarios predict a significant increase in the current distribution areas of the same species between 2081 and 2100. The distribution of S. fuscum under the SSP1-2.6 and SSP5-8.5 scenarios within the 2081-2100 period is consistent with the findings of different studies. Breeuwer et al. (2008) conducted a greenhouse experiment to investigate the impact of varying temperature treatments. The results demonstrated that the lowest to the highest temperature treatments in monocultures led to an increase in biomass production of S. fuscum. Naumov and Kosykh (2011) observed that the species possesses the capacity to retain moisture for extended periods, which may be regarded as an adaptation to desiccation. Furthermore, Bengtsson et al. (2021) demonstrated that S. fuscum exhibits a diminished reliance on a sustained wet climate, and the moss display enhanced stability and resilience to climatic fluctuations. It is capable of maintaining photosynthetic activity during periods of drought and in the absence of precipitation. The species occurrences in the aforementioned period and scenarios appear to corroborate the hypothesis put forth by the authors in relation to global warming. The most significant habitat loss for S. girgensohnii was observed in the SSP5-8.5 climate scenario between 2081-2100.

The habitat and abundance of Sphagnum inundatum in the Black Sea region during the period 2021-2040, according to both the SSP1-2.6 and SSP5-8.5 scenarios. While there is a notable expansion in the current distribution of S. palustre between 2021 and 2040, it is projected that this species will experience a considerable reduction in its habitat under the SSP5-8.5 climate scenario during the 2081-2100 period. It is likely that S. palustre will persist in a restricted area, particularly in the northeastern regions of the country. According to the results of the regression analysis in the study of Popov (2016), the climatic factors affect the occurrence of S. palustre in the East European Plain. Also, the author explained that the distribution of the species with the increasing of summer temperatures. This idea supports the species distributions in the 2021-2040 and 2081-2100 periods and targeted to the climate scenarios, except the scenario SSP5-8.5 in the year 2081-2100. The future of S. plathyphyllum appears to be rather pessimistic. It is assumed that the species will experience a contraction in its habitat within the next twenty years. Furthermore, it is predicted that it will become extinct in all areas of Anatolia throughout the 2081-2100 period, most notably under the SSP5-8.5 climate scenario. S. plathyphyllum is typically found in wet lo-cations, where it grows submerged or in close proximity to the water surface (Daniels and Eddy, 1990). Similarly, the results of the study conducted by Campbell et al. (2021) indicate that the future of Sphagnum diversity in Europe is most strongly contingent upon alterations in water availability and seasonal temperature fluctuations. The distribution map of S. plathyphyllum, which was created as a result of the model applied by taking into account the 4.4°C temperature increase predicted between 2081-2100, illustrates the impact of habitat loss. This can be explained by the reduction of water availability and the restriction in the potential distribution of the species due to a drier climate, which is a probable consequence of climate change in the eastern part of the Black Sea Region. While the long-term survival of the species S. rubellum is not at risk, it is expected that the species will continue to expand its distribution range towards the northern regions of Anatolia. In a study conducted by Robroek et al. (2007), it was observed that the biomass production of S. rubellum was significantly higher at elevated temperatures than at lower temperatures. According to the authors, this finding aligns with the observation that this species has a more southern distribution. Our findings support the idea of the mentioned study, in connection with global warming. Ma et al. (2022) indicated that the precipitation of the driest month is one of the most significant environmental variables for S. rubellum, with 52.7% of the species currently occurring under such conditions. Similarly, Oke and Hager (2017) found that the temperature of driest quarter as second variable for the occurrence of S. rubellum on peatlands in North America using single-and multi-species models with 26.9%. This finding is consistent with the precipitation of the driest quarter result obtained for the moss, which demonstrated a value of 96%. Therefore, the results indicate that extreme dry periods do not impact the distribution of S. rubellum, as illustrated in the simulated maps.

In the long term and under the SSP5-8.5 climate scenario, the greatest habitat loss and abundance decline will be experienced by Sphagnum subsecundum and S. squarrosum, respectively, in comparison to their current habitats. Daniels and Eddy (1990) reported that the S. subsecundum is most commonly found in habitats adjacent to streams or on wet and peaty slopes. In light of the aforementioned ecological preferences of the species, it is anticipated that there will be a partial reduction in the extent of the species’ habitat as a consequence of rising temperatures in the coming years. The applied model indicates that new distribution areas and an increase in existing habitats for S. teres towards the western part of the Black Sea Region are likely to occur between 2021 and 2040, according to both climate scenarios. However, it suggests that the species may persist only in North-East Anatolia during the 2081-2100-time period and under the SSP5-8.5 climate scenario. Despite the anticipated increase in temperature and aridity over the 2081-2100 period, the most favorable outlook was identified for S. warnstorfii. The most noteworthy observation was made in the 2081-2100-time period and under the SSP1-2.6 climate scenario. The model indicates that the species will experience significant distribution in Thrace, the western and central parts of the Black Sea Region, the north-east of the country and Eastern Anatolia Region during the specified time period and climate scenario. Pakarinen (1979) proposed that this extensive distribution may be attributable to the existence of genetically differentiated ecotypes within S. warnstorfii. Mikulášková et al. (2015) concluded that genetics may explain the relatively broad niche of S. warnstorfii, which consists of numerous cryptic species with broadly overlapping geo-graphical ranges (Hájková and Hájek, 2007). Flatberg et al. (2006) observed the formation of hybrids between the calcium-tolerant S. warnstorfii. Brauer et al. (2023) postulated that natural hybridization may serve to mitigate the vulnerability of species to climate change. The results of our study generally corroborate the aforementioned observations. The projected expansion of this species in response to a temperature increase could be attributed to genetically determined ecotypic differentiation.

Variables that contribute the most to the model applied for the distribution of all Sphagnum species were precipitation seasonality, and mean temperature of the warmest quarter, respectively. The precipitation of the wettest month, the precipitation of the wettest quarter, and the precipitation of the warmest quarter were identified as the other bioclimatic variables that were found to be significant in the creation of species distribution maps, among the remaining variables. The most relative variable can determine the distribution of Sphagnum fuscum was noticed as the precipitation of warmest quarter (Bio18) with 97.7%. Unlike S. fuscum, the precipitation of the driest quarter (Bio17) was identified as the most effective variable for S. rubellum, with a correlation coefficient of 0.96. Seasonality precipitation (Bio15) was the least effective variable in determining the distribution of S. inundatum in Anatolia with a value of 10.5%. Cong et al. (2020) asserts that Sphagnum development is significantly influenced by climatic factors, and that optimal conditions for Sphagnum growth are characterized by specific humidity and temperature levels. Bengtsson et al. (2021) stated that temperature is a significant climatic factor influencing plant production, with increased precipitation expected to enhance growth. Also, Ma et al. (2022) reports that the mean temperature of the coldest quarter and precipitation of the driest month are the primary factors influencing the habitat availability of Sphagnum mosses. Similar to the studies mentioned above, the results of our study confirm these hypotheses.

The objective of this study is to predict the pattern of change in the national-scale distribution of Sphagnum mosses in Türkiye under future climate change scenarios. Given the differing rates at which Sphagnum species respond to future climate scenarios, the ranges of species in Türkiye are subject to constant flux. Climate scenarios for Türkiye predict a drastic reduction in the distributions of S. auriculatum, S. centrale and S. plathyphyllum by the end of the twenty-first century. In light of the potential climatic variables that could negatively impact the distribution of all three species, temperature was identified as the most crucial parameter. The total disappearance of the three Sphagnum species from their native habitats is undoubtedly associated with a consistent decline in precipitation levels, which has led to a notable reduction in the local water balance. The rise in temperature had no adverse impact on the habitats where S. rubellum was present, whereas it had a beneficial effect on S. capillifolium, S. contortum, S. fallax, S. fuscum, and S. warnstorfii. It is predicted that species that will benefit from climate change will be those that are able to survive in habitats that are not at risk of being adversely affected by a changing climate, and which have the capacity to disperse and colonize new areas. It can be reasonably inferred that certain characteristics of Sphagnum may render them less susceptible to fluctuations in temperature. This study is of significant importance for the conservation of Sphagnum species with specialized habitats, as well as for future research on the responses of these species to climate change.

Future research should include an assessment of the potential impacts of climate change on Sphagnum species in Türkiye and conservation strategies to mitigate negative impacts. The aim should be to develop conservation strategies to protect Sphagnum species and associated habitats in Türkiye based on available ecological data and field surveys. Changes in Sphagnum habitats, including changes in hydrology and soil composition, should be analyzed when assessing ecological impacts. In assessing conservation and habitat management strategies, priority conservation areas for Sphagnum species should be identified, ex situ and in situ conservation measures should be developed, including habitat restoration and climate adaptation techniques, and stakeholders (e.g. policy makers, conservation organizations) should be involved to integrate the findings into national conservation plans. The expected outcomes are a detailed projection of the future distribution of Sphagnum species, insights into the wider ecological consequences of possible climate change on Sphagnum habitats in Türkiye, and feasible conservation recommendations to mitigate habitat loss and biodiversity decline.

In summary, this study provides important, data-driven insights to help inform local and regional conservation strategies, support climate adaptation efforts, and guide water and ecosystem management policies. The findings contribute directly to achieving key global goals for climate action, water conservation and biodiversity conservation.