Abstract
Peat mosses (genus Sphagnum) dominate most Northern mires and show distinct distributional limits in Europe despite having efficient dispersal and few dispersal barriers. This pattern indicates that Sphagnum species distributions are strongly linked to climate. Sphagnum-dominated mires have been the largest terrestrial carbon sinks in Europe over the last few millennia. Understanding the climatic drivers of Sphagnum species distributions is important for predicting the future functionality of peatlands. We used MaxEnt, with biologically relevant climatic variables, to model and clarify the current distributions of 45 Sphagnum species in Europe. We used a dataset of 238 316 records from across Europe (30° to 90° N, -30° to 63° E; Sahara to the Arctic, Azores to Ural mountains). We used annual degree-days, annual water balance and their monthly standard deviations (i.e. seasonality) as climatic predictors over a range of spatial resolutions (from 10 to 200 km pixel size). With these climatic predictors, we produced reasonably accurate projections of the distribution of 45 species (overall AUC >0.8). Large pixels (100 and 200 km) resulted in loss of detail, but smaller pixels (10-50 km) performed well across fit measurements. Projected distributions at the 50 × 50 km resolution showed the largest resemblance to published distribution maps. Suitable climate for many Sphagnum species was associated with the northern, western and mountainous parts of Europe. We found that annual water balance was an important indicator of Sphagnum presence. Limits in relation to annual water balance were the same as reported by bioclimatic peatland models from North America. Most Sphagnum species were limited to annual degree-days between -5000 °C y-1 and 5000 °C y-1. Seasonality in both climate variables separated species, with degree-day seasonality having a stronger influence than water balance seasonality. High degree-day seasonality as a consequence of cold temperature sets a northern distribution limit to some species. The results suggest that the future of Sphagnum diversity in Europe is most strongly dependent on changes in water availability and in seasonal temperature variation.
Highlights
Understanding the distribution of peat mosses (Sphagnum species) is important as they are the main drivers behind the carbon accumulation in northern peatlands over millennia (Clymo and Hayward 1982)
area under the curve (AUC) did decrease with increased pixel size and the lowest AUCs were found at the 200 × 200 km resolution
As for temperature, our models suggest that suitable climate for Sphagnum falls within a range between -5000 and 5000 °C y-1, but with rather narrow peaks around 0 °C y-1
Summary
Understanding the distribution of peat mosses (Sphagnum species) is important as they are the main drivers behind the carbon accumulation in northern peatlands over millennia (Clymo and Hayward 1982). In Europe there is a wide diversity of mire types circumscribed by climatic zones. Shallowpeated tundra mires occur in northern arctic and alpine areas. Fens and huge aapa mire complexes cover large parts of the landscape from Fennoscandia eastwards. Further south in Europe, mires become small and scattered and quite variable. In the Mediterranean and semi-arid areas with summer drought, peatlands are confined to depressions with standing water all year. Even though Sphagnum species have effective long-distance dispersal (Sundberg 2010, 2013), they vary in their distribution in Europe from south to north and from oceanic to continental areas. We expect that the biogeography of Sphagnum can be predicted by physiologically relevant aspects of the climate (cf. Woodward and Williams 1987)
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