Abstract
Horticulture is a primary source of global weed introductions, especially in urban areas.Approximately, 75% of the world’s naturalized plants are garden escapees, while 66% of invasive plants in Australia are garden plants. Invasive plant species cause significant ecological and economic damage by affecting both managed and natural ecosystems. The most efficient way to alleviate such damage is to prevent the introduction of potentially invasive non-native species and to identify and eradicate any naturalized species before they can spread widely or become invasive. While pre-border weed risk assessment can screen for species with weedy potential, this does not address the issue of a large number of non-native plant species already present in gardens that could become invasive in the future. The primary objective of
this thesis was to determine the key factors that influence the naturalization and invasion of woody, non-native, horticultural plants in an urban landscape. Factors that potentially influence naturalization and invasion success include propagule pressure, or planting effort, residence time, certain species traits, and climatic tolerances. I examined the importance of these variables on the naturalization of 1439 horticultural, woody, non-native species introduced to Canberra, Australia over 150 years. Canberra is a unique city for this purpose because it was a planned city with extensive horticultural plantings originating primarily from government nurseries, meaning there are records documenting planting effort from the time the city was
established.
I showed that the introduction and naturalization of introduced species increased with the rising urbanization and population growth, and species with greater planting effort, longer residence time, smaller seeds, and with obvious dispersal mechanisms were more likely to naturalize. Cold hardy and tall plants were also more likely to naturalize, but cold hardiness and height mostly affected naturalization success indirectly via planting effort. Introduced species tended to have a long lag-phase between introduction and naturalization (20-170 years). Species planted in consistently higher numbers per year had a shorter lag-phase, while taller
species had a more extended lag phase. In addition, there was a marked increase in
naturalizations associated with increased plantings due to population growth and urban development in Canberra peaking in the 1970s. Hence, the long lag-phase of many species may reflect early introduction and low planting rates early on, with naturalization rates increasing as the planting effort increased as the population expanded. I used a model for naturalization developed using the Canberra data, along with other weed risk assessment approaches to try and predict naturalization outcomes at a specific location (Bendora Arboretum in the Australian Capital Territory), which was planted in the 1940s. The Canberra model failed to predict
outcomes at Bendora Arboretum, perhaps because the model was applied to a very restricted set of species, which required a longer lag-phase to naturalize. Overall, the findings of this study will be useful in developing a predictive model to quantify the potential invasion risk of exotic woody horticultural species.
| Date of Award | 2020 |
|---|---|
| Original language | English |
| Supervisor | Richard DUNCAN (Supervisor) & Paul Downey (Supervisor) |