Recent rise to dominance of Molinia caerulea in environmentally sensitive areas: new perspectives from palaeoecological data

Abstract

1. A characteristic of some heath and moorland areas in maritime north-west Europe is the widespread dominance of Molinia caerulea (purple moor grass). The overwhelming local supremacy of this species concerns farmers, owing to its relatively low palatability for grazing stock, and conservationists, owing to the monotonous, species-poor landscapes that often result under Molinietum. 2. In some environmentally sensitive areas (ESAs) in England and Wales, Molinietum is believed to have ousted Callunetum in recent decades; experiments sponsored to control the species have predicated its infiltration and replacement of heather-dominated stands. 3. Experimental control of Molinia in ESAs on Exmoor, England, was paralleled by palaeoecological studies to verify its recent rise, assess its status in moorland, and test the utility of the techniques for such research. 4. Peat profiles from two localities on Exmoor were sampled and subjected to recently developed techniques of plant macrofossil counting and to conventional pollen analysis. One locality was ‘white moor’, clearly dominated by Molinia; the other was ‘grey moor’ (an admixture of ericaceous shrubs) that had become invaded (allegedly recently) by Molinia. 5. Dating of profiles employed a range of methods, including conventional radiocarbon dating, Accelerator Mass Spectrometry (AMS) dating and the counting of spheroidal carbonaceous particles, to attempt to delimit horizons of recent peat growth. 6. The pollen and macrofossil data confirmed the recent ousting of Calluna and rise to dominance of Molinia in the grey moor, but also provided evidence of an earlier unsuspected (pre-Callunetum) presence of Molinia. The overwhelming dominance of Molinia in the white moor was also a recent phenomenon, but was only partly at the expense of Calluna. The palaeoecological data indicated a greater antiquity and former abundance of Molinia than is often appreciated and suggested that, over the past millennium, vegetation dominance has alternated between Callunetum and grass moor containing at least some Molinia, while the former Calluna-dominated grey moor itself developed originally from grass moor. 7. These findings have implications for conservation management and for restoration targets in ‘degraded’ moorland. Similar palaeoecological studies have since been adopted in Wales, directly to inform conservation and management policy