Propagule availability drives post‐wildfire recovery of peatland plant communities

Harry E R Shepherd,Robert T E Mills,Paul D M Hughes,Magda N Steele,Bjorn J M Robroek,Jane A Catford,Marc G Dumont,Josu Alday

doi:10.1111/avsc.12608

Abstract

AbstractQuestionNorthern peatlands are increasingly threatened by wildfire. Severe peatland wildfires can provide opportunities for new non‐peatland species to colonise post fire. Changes in plant colonisation could lead to longer‐term shifts in community composition, compromising recovery of peatland structure and function. Understanding the process of post‐fire recovery can thus inform restoration action and help restore peatland vascular plant communities. In this study, we ask: what drives initial vascular plant recovery following a peatland wildfire?LocationStalybridge moors, England (commonly referred to as the Saddleworth moors).MethodsWe used a series of vegetation surveys and seed germination experiments to identify the composition of vascular plant community one‐year post fire, along with potential propagule sources. We combined this with plant trait data and, using a series of null models, compared observed community trait values against random species assemblages.ResultsOur data suggests that plant species are able to arrive at the burned site through multiple non‐exclusive recolonisation pathways. This includes colonisation through the soil seed bank, along with dispersal from surrounding unburned peatland and non‐peatland vegetation. The composition and structure of the recolonised communities was largely determined by the ability of species to reach the post‐fire site from these donor communities. This resulted in a post‐fire community composed of species possessing lower seed masses relative to the wider pool of potential colonisers.ConclusionsOur results highlight propagule availability as a driver of post‐wildfire vascular plant recovery. This provides opportunities for new non‐peatland species to colonise, potentially driving changes in the direction of vegetation recovery. Ensuring the availability of peatland species following a wildfire could therefore be key to the immediate recovery of these systems.

Highlights

Northern peatlands represent significant terrestrial carbon stores, holding an estimated 265–600 Pg of carbon (Yu, 2012; Hugelius et al, 2020)
The post-fire vegetation composition was distinct from the post-fire seed bank and surrounding peatland vegetation (Figure 4), but shared species with both of these communities (Figure 3)
The initial post-fire vegetation was lower in community-weighted mean (CWM) trait values for seed mass, Specific leaf area (SLA) and Ellenberg moisture value (EMV) than predicted from random assemblages; this varied depending on the species included within the null models (Figure 5)

Summary

Introduction

Northern peatlands represent significant terrestrial carbon stores, holding an estimated 265–600 Pg of carbon (Yu, 2012; Hugelius et al, 2020). Kettridge et al (2015) have, for example, reported the post-fire colonisation of non-peatland species to increase vegetation flammability, inducing positive feedback loops that lead to a further increase in wildfire regularity. If left unrestored, this could eventually shift a peatland from a carbon sink to a carbon source (Kettridge et al, 2015). The restoration of peatland plant community composition could be essential to the post-fire recovery of peatlands, with an overall aim of the preservation of peatland carbon stores

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Conclusion