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Seed dispersal, herbivory and recruitment failure of Persoonia elliptica (Proteaceae) in Western Australian Jarrah (Eucalyptus marginata) forest

Monaco, Sophie (2012) Seed dispersal, herbivory and recruitment failure of Persoonia elliptica (Proteaceae) in Western Australian Jarrah (Eucalyptus marginata) forest. Honours thesis, Murdoch University.

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Persoonia elliptica is a resprouting understorey tree species of the jarrah (Eucalyptus marginata) forests of South-Western Australia. All known populations are lacking in seedlings and saplings, resulting in population structures made up solely of mature trees and exhibiting clear recruitment failure. Little research has been done on this species other than a single study by Abbott and Van Heurck (1988) which described population structures and speculated that increased kangaroo herbivory might be the cause of recruitment failure. This study addresses the issue of recruitment failure, in particular with regards to seed production, viability and dispersal, and herbivory. This work describes the ecology of the species including fruit production, seed viability and population structure. The relationship between P. elliptica and the fauna of the region is examined with regard to seed dispersal vectors and dispersal distances, while the role macropods play in seedling and new growth herbivory and the link with recruitment failure is also examined.

Two study sites were investigated over a period of eight months in the northern jarrah forest region, at Avon Valley National Park and in state forest near Sawyers Valley. Species ecology was examined using fruit counts, tree size measurements and soil seed bank estimation, while seed dispersal and herbivory were examined using seed removal ‘cafeteria’ experiments and infrared motion sensing cameras to detect and record faunal activity.

Fruit production is low in P. elliptica with only 9% of flowers becoming mature fruits. Seed viability is high in new season seeds, but seeds collected from the soil seed bank (assumed aged one year or older) were not viable. Five fauna species act as dispersal vectors of P. elliptica seed; Macropus fuliginosus, Macropus Irma, Strepera versicolour, Mus musculus and Oryctolagus cuniculus. Of these the currawong (S. versicolour) has not previously been observed interacting with P. elliptica seeds. Macropods exhibited a strong browsing preference for P. elliptica when presented with fresh foliage, and are also therefore, likely to consume seedlings. The wallaby, M. Irma, browsed foliage to a height of 0.5 metres while the kangaroo, M. fuliginosus, browsed foliage up to one metre. This level of browsing pressure is a potential cause of recruitment failure.

The key findings of the study highlight that recruitment failure within populations of P. elliptica is likely to be caused by a number of factors potentially relating to the species ecology and relationships with fauna, particularly herbivores. This raises questions on the potential for this species to persist into the future within the jarrah forest and provides vital information concerning possible management approaches to encourage recruitment.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Environmental Science
Supervisor(s): Enright, Neal
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