Change in propagule banks during prescribed burning: a tale of two contrasting moorlands.

摘要

Moorlands on blanket bog are high-priority ecosystems from a conservation viewpoint in the British Isles; they are often managed through using prescribed burning to increase their productivity for sheep and Red grouse. However, there is an increasing demand to conserve these moorlands for other environmental services, e.g. carbon sequestration and water supplies. There is, therefore, a need for experimental evidence on the role that fire and fire-rotation intervals have on these moorlands ecosystems for the development of ecologically-sound management plans. Here, the impact of prescribed burning on the propagule banks was evaluated at two contrasting geographical moorland locations differing in productivity, climate and past pollution history. Two different approaches were used; chronosequences of elapsed time since burning and a long-term replicated grazing and burning experiment (1954-2010) where different burning rotations were applied. The propagule banks in both moorlands were very species-poor and the species present were mainly common ones. The chronosequences showed that few species had significant effects with elapsed time since burning; the dominant Calluna vulgaris increased in the above-ground litter fraction which acted as a barrier to seed transfer to the underlying peat. Within the experiment, the seed bank of C. vulgaris and the frequency of occurrence of Sphagnum species increased as rotation-interval increased. It is suggested that prescribed burning rotations simultaneously at two temporal scales within a moorland landscape may be needed to conserve Sphagnum species, short-rotation burns (every 10-years) to enhance its abundance in the vegetation and long-rotations (>55 years) to maintain Sphagnum propagules in the surface peat.