Calluna vulgaris-dominated habitats are valued for ecosystem services such as carbon storage and for their conservation importance. Climate and environmental change are altering their fire regimes. In particular, more frequent summer droughts will result in higher severity wildfires. This could alter the plant community composition of Calluna habitats and thereby influence ecosystem function. To study the effect of fire severity on community composition we used rain-out shelters to simulate drought prior to experimental burns at two Callunadominated sites, a raised bog and a heathland. We analysed species abundance in plots surveyed ca. 16 months after fire in relation to burn severity (indicated by fire-induced soil heating). We found that fire severity was an important control on community composition at both sites. Higher fire severity increased the abundance of ericoids, graminoids and acrocarpous mosses, and decreased the abundance of pleurocarpous mosses compared to lower severity fires. At the raised bog, the keystone species Sphagnum capillifolium and Eriophorum vaginatum showed no difference in regeneration with fire severity. Species and plant functional type beta-diversity increased following fire, and was similar in higher compared to lower severity burns. Our results further our understanding of the response of Calluna-dominated habitats to projected changes in fire regimes, and can assist land managers using prescribed fires in selecting burning conditions to achieve management objectives. CAVU = Calluna vulgaris, CECO = Cephalozia connivens, CL.sp = Cladonia spp., DEFL = Deschampsia flexuosa, DISC = Dicranum scoparium, Duff = Duff, ERCI = Erica cinerea, ERVA = Eriophorum vaginatum, HYJU = Hypnum jutlandicum, HYSP = Hylocomium splendens, Litter = Litter, LOBI = Lophocolea bidentata, ODSP = Odontoschisma sphagni, PLSH = Pleurozium schreberi, PLUN = Plagiothecium undulatum, POER = Potentilla erecta, POJU = Polytrichum juniperinum, RHSQ = Rhytidiadelphus squarrosus, SPCA = Sphagnum capillifolium, VAVI = Vaccinium vitis-idaea.

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Burning increases post-fire carbon emissions in a heathland and a raised bog, but experimental manipulation of fire severity has no effect.

Background: Prescribed burning in peatlands is controversial due to concerns over damage to their ecological functioning, particularly regarding their key genus Sphagnum. However, empirical evidence is scarce. Aims: The aim of the article is to quantify Sphagnum recovery following prescribed burns. Methods: We completed nine fires at a raised bog in Scotland, achieving a range of fire severities by simulating drought in some plots. We measured Sphagnum cover and chlorophyll fluorescence F v /F m ratio (an estimate of photosynthetic capacity) up to 36 months post-fire. Results: Cover of dominant Sphagnum capillifolium was similar in unburnt and burnt plots, likely due to its high moisture content which prevented combustion. Burning decreased S. capillifolium F v /F m 5 months after fire from 0.67 in unburnt plots to 0.44 in low fire severity plots and 0.24 in higher fire severity (drought) plots. After 22 months, F v /F m in burnt plots showed a healthy photosynthetic capacity of 0.76 and no differences between severity treatments. Other Sphagnum species showed similar post-fire recovery though their low overall abundance precluded formal statistical analysis. Conclusions: S. capillifolium is resilient to low-moderate fire severities and the same may be true for a number of other species. This suggests that carefully applied managed burning can be compatible with the conservation of peatland ecosystem function.

In arctic and boreal ecosystems, ground bryophytes play an important role in regulating carbon (C) exchange between vast belowground C stores and the atmosphere. Climate is changing particularly fast in these high‐latitude regions, but it is unclear how altered precipitation regimes will affect C dynamics in the bryosphere (i.e. the ground moss layer including senesced moss, litter and associated biota) and the closely associated upper humus layer, and how these effects will vary across contrasting environmental conditions. Here, we set up a greenhouse experiment in which mesocosms were assembled containing samples of the bryosphere, dominated by the feather moss Hylocomium splendens, and the upper humus layer, that were collected from across a boreal forest chronosequence in northern Sweden which varies strongly in nutrient availability, productivity and soil biota. We tested the effect of variation in precipitation volume and frequency on CO2 exchange and dissolved organic carbon (DOC) export, and on moss growth. As expected, reduced precipitation volume and frequency lowered net CO2 efflux, DOC export and moss growth. However, by regulating moisture, the lower bryosphere and humus layers often mediated how precipitation volume and frequency interacted to drive C dynamics. For example, less frequent precipitation reduced moss growth only when precipitation volume was low. When volume was high, high moisture content of the humus layer helped avoid moss desiccation. Variation in precipitation regime affected C cycling consistently in samples collected across the chronosequence, despite large environmental variation along the sequence. This suggests that the bryosphere exerts a strong buffering effect on environmental variation at the forest floor, which leads to similar responses of C cycling to external perturbations across highly contrasting ecosystems. As such, our study indicates that projected increases in droughts and ground evapotranspiration in high‐latitude regions resulting from climate change will consistently reduce C losses from moss‐dominated ecosystems.