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Title: The environmental impact of Crassula helmsii
Author: Smith, Tim
ISNI:       0000 0004 5915 1081
Awarding Body: Canterbury Christ Church University
Current Institution: Canterbury Christ Church University
Date of Award: 2015
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The aquatic macrophyte Crassula helmsii is a non-native species and classed as 'invasive' in the UK. This study was carried out in an attempt to provide empirical evidence as to whether the establishment and growth of Crassula helmsii has a measurable impact on the ecology of invaded sites. Dispersal and distribution patterns across England were explored using databases and GIS interpretation. Ecological impact was measured by comparing invaded sites with uninvaded control sites on a range of habitats and waterbody types across Kent and East Sussex. The analysis of spread patterns provided evidence that the plant is likely to have been dispersed due to the horticultural trade, as well as natural vectors into neighbouring habitats. Macrophyte analysis showed that species losses did not occur when C. helmsii was present. Changes to species composition did occur, with rarer plant species being associated with the presence of C. helmsii. Freshwater macroinvertebrates showed no change in either species number or species rarity. The seed banks of invaded and control sites showed no difference, but active management was shown to reduce the total number of seeds in the soil significantly. The water chemistry of invaded and uninvaded sites showed a relationship between the presence of C. helmsii and reduced total organic nitrogen. The results of this study show that the expected species loss associated with non-native species may not be occurring with C. helmsii. Active management may be impacting the ability of native species to recolonise. Further work on other habitats and waterbodies across a wider geographic range are required to explore whether this is a localised effect.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QK Botany ; QK0900 Plant ecology ; SB Plant culture