The effect of experimental prescribed fire on the establishment of Scots pine Pinus sylvestris seedlings on heather Calluna vulgaris moorland

A key management objective for native Scots pine (Pinus sylvestris) forests in Scotland is to extend the forest onto treeless moorland, below the natural tree line, dominated by the dwarf shrub, heather (Calluna vulgaris). At Abernethy Forest, Scotland's largest native pinewood remnant, establishment of new tree seedlings on moorland has recently slowed despite the low grazing pressure. To investigate whether fire would be a useful management tool to improve the rate of regeneration of Scots pine, an experiment was carried out in 10 plots, on open moorland, on shallow peat soil, c 300 m from the forest edge. At each plot, 10 small exclosures were established, two for each of four burning treatments, and two controls. Within each exclosure, 100 Scots pine seeds were sown and the numbers of seedlings resulting were counted after 2, 11 and 30 months. Exclosures substantially reduced seed and seedling predation by mammals and invertebrates. The four burning treatments were single and double burns in the year of sowing, and single and double burns 1 year before sowing. Single burns removed largely heather, whilst second burns removed more of the moss. Burnt areas had 3.5 times (95% confidence limits 1.5-8.1) the number of seedlings established as controls, 2 months after sowing. There was no significant additional effect on seedling numbers of either double burning or year of burn. Slower-moving fires and, to some extent, shallower post-fire moss/litter depths, were associated with more seedlings establishing. Seedling numbers declined by 18% between months 2 and 11 and by 27% between months 11 and 30. The pattern of these declines was not significantly affected by treatment, post-fire moss/litter depth, or fire characteristics. The results have wide application at sites where Scots pine regeneration is a management aim, particularly on heather moorland, and where techniques which mimic natural processes are preferred. Managers at such sites should include prescribed burning, in conditions that produce slow-moving fires and shallow post-fire moss/litter depths, as a management option for improved Scots pine seedling establishment.