Abstract
AbstractQuestionsDo burn severity and soil chemistry drive species and trait composition on recently burned clear‐cuttings? Does the spatial distribution of common, easily dispersed colonizers vary with distance to fire perimeter?LocationA 13,000 ha production forest landscape in boreal southern Sweden burned in a wildfire in 2014.MethodsVascular plants and bryophytes were recorded in permanent plots on clear‐cuts two and five years following fire, covering a burn severity gradient. Soil carbon content (reflecting burn severity), pH and nutrients were measured at plot level. Trait data were retrieved from the BIEN and LEDA databases and analyzed using community‐weighted mean (CWM) trait values. Statistical analyses included generalized linear mixed models (GLMMs), non‐metric multidimensional scaling (NMDS) and multivariate ANOVA.ResultsLow burn severity resulted in higher frequency of legacy species (e.g.Vaccinium myrtillus), while high burn severity facilitated colonizing species (e.g.Senecio sylvaticus). Vegetation varied with soil chemistry, expressed through pH. Species composition changed between years and deviated from unburned clear‐cuts. After five years the most common taxa on burned plots were the vascular plantsChamaenerion angustifolium,Betulaspp. andPopulus tremulaand the bryophytesCeratodon purpureusandPolytrichum juniperinum. CWM specific leaf area (SLA) decreased markedly with time and root buds increased with total carbon content in the soil (i.e., toward less severely burned plots), while soil pH was not associated with any studied trait.Chamaenerion angustifoliumdecreased with distance to the fire perimeter, whileCeratodon purpureusincreased.ConclusionsBurn severity and soil pH weakly drive vegetation dynamics in the early phase following fire on clear‐cuts, indicating a large influence of stochastic processes. Deciduous trees are common already after five years and their further expansion will affect light and nutrient availability. To understand future vegetation trajectories on burned clear‐cuts, studies need to incorporate the light factor and links between tree species’ identity and soil nutrient availability.
Highlights
Fire is a main disturbance agent in boreal forests, giving rise to large variations in disturbance extent and severity, depending on site conditions and the landscape context (Kuuluvainen, 2009; Shorohova et al, 2011)
We report on vegetation dynamics the first five years after a large and intense fire, focusing on links to burn severity and soil chemistry
Indicator species analysis revealed that Chamaenerion angustifolium and Senecio sylvaticus were associated with burned clear-cuts while Betula spp., Deschampsia flexuosa, Picea abies, Vaccinium myrtillus and Vaccinium vitis-idaea were associated with unburned clear-cuts (Appendix S1)
Summary
Fire is a main disturbance agent in boreal forests, giving rise to large variations in disturbance extent and severity, depending on site conditions and the landscape context (Kuuluvainen, 2009; Shorohova et al, 2011). We present a post-fire vegetation time series from Sweden across a boreal production forest landscape to investigate the early succession phase after fire. Life-form response to burn severity was evident in a Finnish restoration experiment in which evergreen dwarf shrubs and forest mosses decreased, and pioneer mosses increased with burn severity while intermediate severity promoted herbs and grasses (Hekkala et al, 2014) These studies suggest that examination of species’ traits related to dispersal (e.g. seed weight) and regeneration (root buds, seed bank) may assist our understanding of post-fire recolonization patterns under variable fire severity. About half of the affected area has been set aside as a nature reserve, offering an unusual opportunity in boreal Europe to study natural vegetation succession over a large area that covers the gradient in burn severity (Figure 1). Our predictions are: (i) that in this early phase, burn severity and soil chemistry are the most important drivers of vegetation dynamics; (ii) that on severely burned soils, species with traits associated with rapid
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