AbstractChalk heath is an internationally rare plant community characterised by the co-occurrence of calcicole and calcifuge species, growing in shallow soils over a chalk bedrock. Research on chalk heaths has been limited and its vulnerability to scrub encroachment and land use changes over the past century have caused the community to decline to levels whereby only a few small scattered locations remain in the south of England.
The aim of this thesis is to provide empirical evidence of various factors that may influence the structure and biodiversity of the chalk heath community at Lullington Heath NNR, with key emphasis placed on the calcicole and calcifuge species present within the sward. There have been no studies investigating the structure of chalk heath communities in terms of phylogeny, species traits or the pair-wise co-occurrence patterns of the calcicole and calcifuge species. The novel insights provided within this thesis greatly enhances the scientific understanding of this rare community type and consequently provide a baseline evaluation from which future conservation, restoration and management can be quantified and assessed.
Taxonomic clustering is evident within the reserve and soil fertility, species longevity, spread and propagation strategy have been identified as key filters that limit species from the local species pool occurring in the chalk heath community. Calcifuge species have an advantage over calcicole species in terms of establishment, persistence, competitive ability and dispersal; whereas calcicole species have an advantage over calcifuge species in terms of acquiring resources and avoiding and/or tolerating stressful conditions such as grazing; suggesting that biotic factors may be more important in determining the co-occurrence patterns of calcifuge species, whereas abiotic factors may be more important for calcicole species.
Non-random community co-occurrence patterns including non-random species pairs have been identified at spatial and temporal scales as well as related to the effects of restorative management practices. There was a prevalence for the chalk heath community to be structured by segregation at a community scale; however, when non-random pair-wise associations were identified, the number of aggregated species pairs was equal to or higher than the number of segregated species pairs within 80% of trials. This demonstrates that ascertaining non-random pair-wise associations provides a more detailed description of the structure of a plant community and the spatial patterns occurring within it, than at the community level.
Few studies have investigated co-occurrence patterns within plant communities and where it has been studied, non-random patterns of community structure have infrequently been demonstrated. As a result, the spatial, temporal and management co-occurrence patterns detailed in this thesis enhance not only the knowledge of chalk heath communities and calcicole and calcifuge plant species distributions, but also the identification of non-random community structure within plant communities generally.
|Date of Award||May 2018|
|Supervisor||Anja Rott (Supervisor) & Niall Burnside (Supervisor)|