Competition between heather and grasses on Scottish moorlands: Interacting effects of nutrient enrichment and grazing regime
Article first published online: 24 FEB 2009
2001 IAVS - the International Association of Vegetation Science
Journal of Vegetation Science
Volume 12, Issue 2, pages 249–260, April 2001
How to Cite
Alonso, I., Hartley, S.E. and Thurlow, M. (2001), Competition between heather and grasses on Scottish moorlands: Interacting effects of nutrient enrichment and grazing regime. Journal of Vegetation Science, 12: 249–260. doi: 10.2307/3236609
- Issue published online: 24 FEB 2009
- Article first published online: 24 FEB 2009
- Received 10 January 2000; Revision received 25 October 2000; Accepted 17 November 2000.
- Calluna vulgaris;
- Canopy height;
- Deschampsia cespitosa;
- Deschampsia flexuosa;
- Nardus stricta;
- Stace (1991)
Abstract. Considerable losses and degradation of heathlands (in moorlands and lowlands) have been reported across Europe, with Calluna vulgaris (heather) being replaced by other species, often grasses. Increasing atmospheric nitrogen deposition and overgrazing have been suggested as the driving factors behind this change. This possibility was investigated in a study of the interacting effects of nutrient inputs and grazing on heather and three grass species (Nardus stricta, Deschampsia cespitosa and D. flexuosa) in the field, on a moorland in northeastern Scotland. In addition, the interacting effects of increasing nutrients and Calluna canopy height on N. stricta and D. cespitosa were studied using turves in an outdoor experimental area. In the field, fencing had a larger effect than fertilizer on the growth of all species, except for N. stricta, the species most unpalatable to herbivores. Fencing led to an increase in the height of the Calluna canopy, which may reduce light availability for the grasses. In the turf experiment, the height of the Calluna canopy affected the diameter of the grass tussocks and percentage of green matter (i.e. live leaf material), with plants under the more closed Calluna canopies being smaller.
This study suggests that the slow-growing, evergreen Calluna is a more effective competitor than the faster growing grasses when it has a tall, intact canopy, even at increased levels of nutrient supply. However, overgrazing promotes gap formation in the Calluna canopy, providing an opportunity for grasses to take advantage of increased nutrients. Thus the conservation of heather moorlands requires an understanding of the grazing level which allows Calluna to maintain sufficient canopy structure to outcompete grasses for light.