The Resilience of Calcareous Grasslands to Climate Change

Stone, Melanie Jane (2020). The Resilience of Calcareous Grasslands to Climate Change. PhD thesis The Open University.



Calcareous grasslands are of high value for a number of ecosystem services, including biodiversity. Soil depth is generally overlooked as an important factor in ecosystem stability, but was found to mediate the effects of change in other environmental variables. A multiscalar approach was used to investigate the interaction of soil moisture, nitrogen availability and form, and soil depth, using a mesocosm experiment, a field-based experiment, and a landscape survey. The field-based experiment also served as verification for a new long-term climate change platform (RainDrop) at Wytham, Oxon.

Soil moisture
• The open-field experiment showed that soil moisture availability significantly influenced both above- and below-ground productivity (Chapter 2).
• An inverse relationship exists between species richness and mean annual rainfall on calcareous grasslands, due to a relative decline in herbaceous forb and legume species, and a corresponding increase in dominance by graminoid species on wetter sites (Chapter 4).

• Nitrogen deposition did not significantly affect species richness on surveyed sites (Chapter 4) or at the RainDrop experiment (Chapter 2).
• Plant productivity at local community scale showed no significant response to nitrogen additions, though total mesocosm biomass increased with both NOx and Nred in shallow soils; responses were dependent on species identity (Chapter 3).

Soil depth
• Species richness increased with increasing heterogeneity in soil depth (range, standard deviation) (Chapter 4)
• Total biomass increased in deeper soil mesocosms (Chapter 3).

Mediation effect of soil depth
• Site-level soil depth variability increased species richness responses to temperature and precipitation; species richness was higher in more variable soils, and also increased with increasing temperature at a faster rate than sites with less variable soil depth (Chapter 4).
• Heterogeneity in soil depth was a positive influence on species richness and productivity, indicating that variation in habitat has potential to support species richness under climate change (Chapters 3 and 4).

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