Control of Molinia caerulea on upland moors.
Abstract
Molinia encroachment has been viewed as a major threat to moorland conservation in the UK and elsewhere in Europe. In England and Wales agri-environment schemes are in place that aim to reduce Molinia caerulea and encourage the development of dwarf shrub vegetation. We tested a range of management treatments to achieve these objectives in two regions (the North Peaks and Yorkshire Dales) in England. Within each region, the same experiment was carried out on two types of moorland vegetation, Molinia-dominated 'white' moorland and a mixture of Molinia and Calluna vulgaris 'grey' moorland. Burning, grazing and herbicide (glyphosate) treatments were applied in factorial combination at each of the four sites (two regions × two moor types). The responses of both vegetation and individual species were assessed. In addition, on the white moors two techniques for Calluna re-establishment were investigated, (i) removal of Molinia litter by raking and (ii) application of Calluna seed. The data were analysed using a combination of univariate and multivariate analysis of variance to identify trends in this complex data set. The only treatment that had consistent effects in the univariate analysis of variance was glyphosate application, which had similar effects on Molinia at all study sites. There was little difference between the use of low and high application rates (0.27 and 0.54 kg ai ha-1). There was little impact of herbicide use on other moorland species. Some species were affected on some sites in some years, but there were no consistent effects. Tentative identification of species that responded positively, negatively and erratically to glyphosate application was made. Greater Calluna seedling densities were found in the plots where herbicide was applied, the Molinia litter was removed and seed was added. However, after initial colonization, there was a reduction in Calluna seedling densities as the Molinia recovered. This indicated that disturbance, seed addition and follow-up management are required for successful Calluna establishment. There were significant differences in community response between both the regions and moorland types. The Dales had a relatively greater contribution of grassland species than the Peaks, where the grey site had a relatively greater dwarf shrub component. Burning had little effect on community composition but both grazing and herbicide application had important effects. Grazing of the grey sites, even at the very low levels used in this study, tended to push the communities towards bog-moorland vegetation, but little effect was found at the white sites. Glyphosate treatment tended to push communities towards acidic grassland at the Dales grey site but not at the Peaks. Successional change was also noted, with marked change between the third and fourth year and again between the fifth and six year. Grey sites showed the greatest temporal change. Synthesis and applications. In terms of Molinia control and subsequent restoration of dwarf shrubs, there was marked variability of response between 'apparently similar' vegetation types in different regions. There were abrupt temporal changes taking place some years after treatment application and a significant length of time was required for change to be detected. Managers need to obtain a greater knowledge of initial floristic composition before starting the restoration process, be prepared to accept multiple outcomes of response (acid grassland vs. dwarf shrubs), be prepared for a long-term monitoring process and perhaps the inclusion of additional treatments for continued Molinia control (application of selective graminicides) and dwarf shrub restoration (disturbance and seed addition treatments).