Date of Award


Degree Type


Degree Name

Bachelor of Science Honours


School of Natural Sciences


Faculty of Computing, Health and Science

First Advisor

Ray Froend

Second Advisor

Will Stock


The distribution of obligate and facultative phreatophytic vegetation reflects the gradient of ecohydrological habitats in a landscape. Preliminary investigations of Banksia vulnerability to xylem embolism have reported that obligate phreatophytes are more susceptible to water stress than facultative phreatophytes (Froend & Drake 2006). A quantitative measure of plant susceptibility to water stress is vital when establishing environmental water requirements. This study investigated interspecific differences in vulnerability to water stress for two facultative phreatophytes (B. attenuata and B. menziesii) and two obligate pln·eatophytes (B. ilicifolia and B. littoralis) at the same position along an ecohydrological gradient on the Gnangara Groundwater Mound, Westem Australia. In addition, intraspecific differences to water stress between populations that occupy contrasting ecohydrological habitats were also determined. Plant susceptibility to water stress was established using vulnerability curves, which demonstrate the xylem potentials at which vessels become embolised. Stem-specific and leaf-specific hydraulic conductivity, as well as Huber values (ratio of stem to leaf area), were also determined to support these findings. It was found that ecohydrological habitats are a primary detennining factor of plant hydraulic architecture, particularly vulnerability to xylem embolism. At the same ecohydrological habitat, where water is readily accessible there were no interspecific differences in vulnerability to water stress. In contrast, the facultative phreatophytes, B. attenuata and B. menziesii, appeared to be plastic in vulnerability to embolism in response to developing in a more xeric environment. Both facultative phreatophyte species were found to be more resistant to xylem embolism at the more xeric dune crest site in contrast to the bottom slope site. B. ilicifolia did not differ in vulnerability to embolism, supporting its classification as an obligate phreatophyte. This study highlights the importance of understanding site hydrological attributes when determining environmental water allocation for obligate and facultative phreatophytes.

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