Matrix modelling of prescribed burning in Calluna vulgaris-dominated moorland: short burning rotations minimize carbon loss at increased wildfire frequencies.
Moorlands store large amounts of carbon providing a valuable ecosystem service. In the UK, prescribed burning is often used to manage moorlands, which can produce both positive (biodiversity enhancement and wildfire prevention) and negative impacts (carbon release and reduction in some ecosystem services provision). This issue is pertinent, as wildfire incidence may increase under climate warming, increasing damage to both conservation value and ecosystem services. To better manage these fire-prone ecosystems, an understanding of the effects of prescribed-burning regimes and wildfire on moorland fuel loads is required. As a first approximation of the relative impacts of prescribed burning and wildfire, we have modelled above-ground fuel-load accumulation and carbon release under varying wildfire return intervals at a study site in the Peak District, UK. Above-ground fuel-load accumulation following prescribed burning was assessed using a chronosequence study and combined with carbon loss measurements from prescribed-burning experiments. The stable age structure of vegetation under varying prescribed-burning rotations was then predicted using an age-structured matrix model and moorland above-ground fuel load calculated using a boot-strapping approach. Finally, long-term carbon losses were predicted under varying wildfire return intervals. Delayed vegetation regeneration was also modelled. The model does not consider below-ground carbon or the effect of prescribed fire on wildfire probability. There was a clear interaction between prescribed-burning rotation interval and wildfire return interval. At 50- and 100-year wildfire return intervals, carbon losses were minimized by short prescribed-burning rotations. However, under a 200-year wildfire return interval, carbon loss was minimized by long rotation intervals where delayed regeneration was modelled. Under a 50-year wildfire return interval, 8-year prescribed-burning rotation intervals could reduce carbon loss by 22% or 34% compared with 25- and 50-year rotations, respectively. Synthesis and applications. The modelling approach outlined here provides a first approximation to the above-ground carbon balance between prescribed burning and wildfire frequency at a single site. This may be useful in other dwarf-shrub-dominated ecosystems if prescribed burning is to be used to mitigate the effects of wildfire. At our study site, long prescribed-burning rotations may minimize carbon loss at low wildfire return intervals. However, if wildfire incidence increases, more frequent prescribed burning is likely to minimize overall carbon loss. Well-informed prescribed burning on a short rotation may produce smaller carbon losses than longer rotations under future climate conditions.