Modelling the persistence of post-management disturbance in Calluna vulgaris communities

Abstract

O_LICalluna vulgaris is often managed in the UK by rotational burning, but this practice has recently been banned on peat with depth greater than 30-40 cm. It is unclear how then to manage the large areas of Calluna on blanket bogs used for sport shooting because without managed burning, fuel loads and wildfire risk will increase as the Calluna ages within the artificially narrow age distributions created by burn management. C_LIO_LIWe developed a model of Calluna mortality and management to understand duration and persistence of post-management effects. This allows us to assess how long it will take to reach a more natural age structure which would allow increased diversity if management ceases. C_LIO_LIOur results show that management effects persist for around 50 years depending on site-specific mortality rates. Active management may therefore be needed either to mitigate the elevated risk of severe wildfire or to speed up this transition. C_LIO_LISome studies have employed, as unmanaged analogues, Calluna stands that were last managed <50 years ago, but such studies may have unintentionally biased their results by observing Calluna still in post-management recovery leading to an over-estimation of wildfire risk associated with more natural blanket bogs. C_LIO_LISynthesis and applications: with the banning of burning as a management tool for Calluna on deep peat, alternative management is now likely needed as our model shows it could take around 50 years for the Calluna to reach a more natural age distribution. Mowing can replicate some of the effects of managed burning but requires repeated intervention and may compress the peat surface from repeated machine tracking. Rewetting and Sphagnum reintroduction may offer a more sustainable management approach to lowering Calluna fuel loads and reducing severe wildfire risk by creating wetter sub-optimal conditions for Calluna growth and thereby altering the competitive balance between Sphagnum and Calluna. Further work is needed to assess the efficacy of rewetting in controlling fuel loads and how this varies with climate and local pressures. More broadly, this work highlights the need to quantify the persistence of past management regimes to understand ecological trajectories. C_LI