Despite widespread conservation efforts, global heathland area has substantially decreased in recent decades. Heathland habitats require low nitrogen availability in order to persist. Over the past 150 years, however, nitrogen deposition has increased markedly. Early observational studies and research using artificial N applications have identified N deposition as the primary driver of heathland succession into grassland or woodland, and N enrichment is considered a threat to heathland sustainability. This study investigated soil fertility and vegetation composition at 25 lowland heathland sites in low rainfall regions of mainland Britain within a modelled wet N deposition range of 1.85 to 10.90 kg N ha-1 y-1. A bioassay approach was used to quantify relationships between soil fertility and N deposition, heathland patch size and the management regimes. This study discovered significant positive relationships between N enrichment and C. vulgaris shoot mass, N and P concentrations. No relationship between N enrichment and N : P mass ratio was found suggesting no N induced shift to P limitation. It was determined that soil phosphomonoesterase activity was not up-regulated in response to N enrichment. This suggests that the soil P reserves are sufficient to satisfy demand under current N deposition loads. Heathland patch size was negatively related to C .vulgaris shoot dry-mass which was used as a proxy for soil fertility. Measured atmospheric ammonia concentrations were not related to C. vulgaris growth and shoot chemistry. No relationships were found between any variable tested and heathland vegetation composition suggesting that local factors, such as management intervention, may be substantial determinants of vegetation composition. This study presents relationships between temperature at origin and C. vulgaris growth from populations located along a latitudinal gradient in Western Europe. The findings of this thesis have implications for current heathland management, and for future management under a climate change scenario.