Field Survey Based Models for Exploring Nitrogen and Acidity Effects on Plant Species Diversity and Assessing Long-Term Critical Loads

Empirical critical loadsare based on current evidence for relationships between the rate of pollutant deposition and changes to ecosystems observed in experiments and surveys. When considering longer-term change and effects of changes in deposition rate after periods of deposition in excess of the critical load, dynamic modelling approaches are useful. This chapter describes two soil-vegetation-floristics model chains, similar in concept, that are being applied in the Netherlands and the UK to explore pollution scenarios and calculate long-term critical loadsfor acidity and nutrient-N. These model chains consist of dynamic models of soil and vegetation biogeochemistry, combined with environmental suitability modelsthat define the realised niche for the species or assemblage. The environmental suitability modelsdescribed in this chapter are based on empirical relationshipsbetween species (MOVE, PROPS, MultiMOVE) or assemblage (NTM3) occurrence and environmental conditions, defined on multiple axes. They are driven by different biogeochemical models, forming the model chains SMART2-( SUMO2)-PROPS/NTM3 and MADOC-MultiMOVE. In this chapter these model chains are described in detail, and applications to scenario exploration and setting critical loadsare demonstrated.