Does the restoration of shallow marginal peatlands alter the distribution or abundance of bog asphodel (Narthecium ossifragum)?

Abstract

Bog asphodel, Narthecium ossifragum, is a flowering plant, commonly found in many wet acidic habitats, including upland blanket bogs where sheep and cattle grazing has been considered as the most feasible economic activity. It can be fatally toxic, especially to lambs, so there is concern that re-establishing blanket bog habitat will increase the distribution and abundance of bog asphodel and thus further threaten the marginal livelihoods of upland livestock farmers. Analysis of vegetation survey data collected pre- and post-restoration from 43 restored shallow peatland sites on Exmoor, an upland area on the northern coast of the UK’s southwestern peninsula, showed only a small (4 %) increase in spatial distribution following restoration (rewetting). No increase in bog asphodel abundance was seen at six sites for which pre- and post-restoration percentage cover data were available. Moreover, bog asphodel did not appear post-restoration at any of the 21 sites (48 %) where it had not been recorded pre-restoration. A separate detailed study at one site demonstrated typical bog asphodel phenology and a life history strategy of growing and reproducing very slowly but persisting despite cold, wet and acidic conditions. Therefore, bog asphodel is ecologically unlikely to respond within a decade to any major change in its environment, such as rewetting of the peat. However, bog asphodel on Exmoor does show significant variability in size and in the proportion of plants that flower year on year. While the mechanisms by which bog asphodel exerts its toxic effect when ingested by ruminants have yet to be fully elucidated, the inconsistent pattern of toxicity seen in other parts of the UK and in northern Europe, where bog asphodel poisoning is reported to be a serious economic problem, may be driven by the influence of environmental factors on bog asphodel growth.

Keywords

• blanket bog
• ditch blocking
• exmoor
• life history strategy
• phenology
• toxicity