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

Abstract

and {The Heather Trust, The Cross, Kippen, Stirlingshire FK8 3DS, UK Summary 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 in®ltration 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 pro®les 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 pro®les 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 con®rmed 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 ®ndings 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.

Restoration of Rivers Used for Timber Floating: Effects on Riparian Plant Diversity

“…Similarly, the fact that channelized and restored sites tended to be dominated by the same species, even if the degree of dominance varied, suggests that increased flood frequency affects competition and dominance within existing species pools to a greater extent than it alters habitat conditions or introduces new species. (2) The species that accounted for the greatest proportion of the dissimilarity in species composition between channelized and restored sites (M. caerulea) is a competitive dominant that grows in clumps and tends to exclude other species in the absence of frequent disturbance (Chambers et al 1999, El-Kahloun et al 2000, Marrs et al 2004. That it was more abundant at channelized sites suggests an increase in competitive advantage due to less frequent flooding.…”

Mid- to late-Holocene vegetation history of Greater Exmoor, UK: estimating the spatial extent of human-induced vegetation change

“…Palaeoecological studies have demonstrated a possible strong causal link between charcoal and Molinia from macrofossil work (e.g. Chambers et al 1999), and the deciduous nature of Molinia may lead to positive feedback in the frequency of fire on grass-heath. The upland vegetation of Dartmoor shows a strong relationship between charcoal (taken to be a proxy for fire frequency) and grass-heath (Caseldine and Hatton 1993).…”

Carbon balance of UK peatlands: current state of knowledge and future research challenges

“…Although there are many other sites with SCP data available in the literature, most of these only used SCPs to provide dates for palaeoenvironmental reconstructions (e.g. Chambers et al 1999), and relatively few sites have bulk density and/or C content data available, which are needed to transform depths and dated layers to net C accumulation rates. There are sufficient data to provide some insights into C accumulation rates over the last 150 yr on peatlands in the UK.…”