Date of Award

2000

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Ray Froend

Abstract

The hydrology of 19 Swan Coastal Plain wetlands was described in relation to its influence on the composition and stn1cturc of wetland vegetation. Sixty species were identified as ‘wetland’ plants. The water depth ranges, or hydrological envelopes, of these species were determined and species grouped together based on the water regimes they experienced. Descriptions of wetland hydrology suggested that the surface and groundwater levels of the majority of study wetlands had declined in both the short (3-5 years) and long-term (20-50 years). Wetlands belonging to the Bibra Suite did not follow this trend as surface water levels either increased or remained relatively constant in the long term. Ordinations and TWINSPAN analysis illustrated that wetlands with similar physical characteristics generally shared similar species composition. Species richness and the number of exotics, wetland species and perennial shrubs were also important in determining similarities and differences between wetlands. The hydrological envelopes established in the study were compared to the literature. Water depth ranges for all study trees and the majority of perennial shrubs and emergent macrophytes were generally supported by previous studies. Seven perennial and two annual hydrotype groups were established. Species from four of the perennial groups experienced a similar depth of inundation, but the depth to groundwater at the dry end of their range varied. Species from the other three hydrotypes did not tolerate inundation and also experienced differences at the dry end of their ranges. Of the two annual hydrotypes, one group tolerated inundation while the other did not. Comparisons with the literature and the low occurrence rate of some species resulted in modifications to the hydrotype groupings. Twenty-three perennials and five annual species representing the nine hydrotypes remained in the final hydrotype scheme. A test case was presented as an example of how hydrotypes could be used to predict the impact of altered hydrology on wetland vegetation composition and structure. The results from this study indicated that the hydrology of Swan Coastal Plain wetlands was changing and that, by grouping wetland species into hydrotypes based on water depth ranges they experience, the effects of these changes on vegetation structure and composition could be predicted.

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