Impacts of climate, management and nitrogen deposition on the dynamics of lowland heathland

The design of a cell-based spatial simulation model of heathland vegetation dynamics including the impacts of rainfall, nitrogen deposition and management is described. The model includes aspects of life history, colonization and seed dispersal for Calluna vulgaris and Deschampsia flexuosa, a common heathland grass. The interactive effects of rainfall, nitrogen deposition and management by cutting or rotovating on vegetation dynamics, and particularly relative cover of Calluna and Deschampsia are investigated. Management by cutting or rotovating resulted in more stable vegetation dynamics, with pure Calluna stands being persistent in the longer term and Deschampsia expanding more slowly when management was imposed. Cutting and rotovating management interacted differently with rainfall and nitrogen deposition. A smaller management interval was required to maintain high Calluna cover by cutting when rainfall was low. More frequent cutting was also required under conditions of high nitrogen deposition. This effect was greatest in simulations with moderate to high rainfall. The outcome of management by rotovating was little affected by rainfall or nitrogen deposition. It is concluded that heathlands that experience varying climates may show different responses to nitrogen deposition and management. This variation should be taken into account when defining critical loads or designing management prescriptions.