15 November 2010

Not so different

This blog post was written by postgraduate student Rohith C. Yalamanchali as part of the course, Research Methods in Ecology (Ecol608).

Australia and New Zealand: different environments, similar weeds.
Sourced from Google Earth.

Invasion biologists use the term “naturalisation” to describe when introduced species form self-sustaining wild populations. A subset of naturalised species become so widespread and have such large impacts that they are regarded as pests and weeds. An important step in predicting new pests and weeds is predicting which introduced species will naturalise.

The success of naturalisation of the introduced species depends on factors such as the geological, climatic, and biological conditions of the habitats it is introduced into. The native species present in the habitat also play role in this success (competition for resources).

Australia and New Zealand are closely neighbouring countries separated by 1600 km of sea. The significant differences between two countries include Australia having 29 times more land area, 5 times greater population and very different types of wildlife than New Zealand. Also, the indigenous people of Australia are Melanesian in orgin while New Zealand Maori are Polynesian (see Yahoo! Answers for a wide ranging discussion about the many differences between New Zealand and Australia).

Along with these differences there are similarities which will aid the understanding of this article. Similarities, include the recent European colonisation history and the presence of temperate climate zones (although much of Australia is warmer and drier than any of New Zealand). Surprisingly, naturalisation of introduced plant species turns out to be another similarity between these two countries, despite their many environmental differences.


Jeff Diez, Phil Hulme, Richard Duncan and Jon Sullivan from Lincoln University, and colleagues, have analysed the naturalisation patterns of introduced plants in New Zealand and Australia (Diez et al (2009)).

The results of the study showed that out of the 12927 species that were introduced in both countries the number of them naturalised in both countries are surprisingly similar (Australia 1713 species (13%) and New Zealand 1617 species (13%)). Similar patterns are seen in genera naturalised; out of 2663 genera introduced to both countries, 807 (30%) naturalised in Australia compared 746 (28%) in New Zealand. Of the 155 families introduced to both countries, 152 (98%) naturalised in Australia compared to 155 (100%) in New Zealand.

The analysis of the plant families successfully naturalised in both countries showed that the top four families are the same in both countries: Juncaceae (76% of introduced species in this family naturalised in NZ and 61% in Australia), Poaceae (46%-NZ and 30% Australia), Cyperaceae (42% NZ and 39% Australia), and Amaranthaceae (36% NZ and 43% Australia).

Note that ranking of these families within the top four differs between the countries. Juncaceae and Cyperaceae are the two families which hold the same positions (first and third respectively) in both countries. The other two families Poaceae (second in NZ, fourth in Australia) and Amaranthaceae (fourth in NZ, second in Australia) switch between second and fourth positions depending on the country they are in. A similar pattern is shown with the other families in two countries with some exceptions.

We can conclude that naturalisation patterns of introduced species in both the countries are not so different, most likely due to similarities in colonization history and overlapping temperate climate zones. The study by Diez and colleagues can be used as a guideline for future studies with regards to naturalisation patterns of introduced plant species in these two countries. It also suggests that environmental differences between invaded countries are less important for predicting new naturalisations than differences in the country’s cultures of plant introduction and cultivation.

Diez, J. M., Williams, P. A., Randall, R. P., Sullivan, J. J., Hulme, P. E., and Duncan, R. P. 2009. Learning from failures: testing broad taxonomic hypotheses about plant naturalization. Ecology Letters, 12:1174–1183.

08 November 2010

Urban Realities: the contribution of residential gardens to the conservation of urban forest remnants

This blog post was written by postgraduate student Elisabeth Christensen as part of the course, Research Methods in Ecology (Ecol608).

Urbanization has destroyed and fragmented natural areas, resulting in decreasing native biodiversity. Fragmented natural areas can only sustain small populations of plants and animals, and these are often vulnerable to extinction. Minor fluctuations in climate or resources, which would be unremarkable in large populations, can be catastrophic in small, isolated populations. Furthermore small populations have higher risks of inbreeding and a decrease in genetic diversity.

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In Christchurch City, the urban remnant Riccarton Bush is an example of such an isolated fragment of natural habitat. In Riccarton Bush, the number of native vascular plant species has declined by a third, from 106 to 67, over the last 125 years. In order to achieve sustainable wild plant populations, the management of urban remnants needs to find a way to expand the plant populations into the surrounding urban areas and thereby increasing their effective population size and genetic diversity. A recent study shows that residential gardens have the potential to play an important role in the conservation of native plant species.


Brendan Doody, Jon Sullivan, Glenn Stewart, Harvey C. Perkins, all from Lincoln University, together with Colin Meurk from Landcare Research, recently published the first results from an ecological and sociological study in the journal Biodiversity and Conservation where they answered the three following questions:

  1. Are native woody species naturally dispersing from the urban forest remnant and establishing in surrounding urban residential gardens?

  2. How are garden management practices influencing the establishment of native woody species in urban residential gardens?

  3. What is the awareness of and support for the use of native plants among local residents?

Kahikatea tree
Photo by Alan Liefting
As an example of an urban remnant they specifically looked at Riccarton Bush, which is the only remnant in Christchurch dominated by the native tree species kahikatea (Dacrycarous dacrydioides, shown in picture and also known as white pine). Jon Sullivan says about the significance and rarity of Riccarton Bush: "It is the only old growth lowland forest in Christchurch to have survived the creation of the city. It is also one of only two lowland old-growth forest fragments left in mid-Canterbury that are not associated with the Southern Alps or Banks Peninsula." Nationwide, only 2% of pre-settlement kahikatea forest remain.

The study revealed that some of the native woody species, especially kahikatea, are dispersed by birds into the surrounding gardens, mostly within a radius of 250 meters. However it also showed that the juvenile trees never reach maturity as most gardeners tend to remove all non-planted woody species.

These results suggest that there exists a natural potential for regeneration but that it is insufficient without human intervention. This is where the last part of the study becomes interesting. What is the attitude towards native plants among garden-owners?
A carefully designed questionnaire was developed to answer this.

The results from their questionnaire revealed that attitudes towards New Zealand's native flora were overall positive. 84% agreed or strongly agreed that ‘species unique to New Zealand are important to our identity’ and 81% that ‘native plants are attractive’. When it came to having native plants in their own gardens the answers were a bit more reluctant yet still positive - 54% agreed or strongly agreed ‘they would be prepared to plant Riccarton Bush species in their garden’.

Kahikatea seedlings.
Photo by Mollivan Jon

The study also found that people in general lack knowledge of native species, for example only 2% were able to correctly identify a seedling of the kahikatea tree. This suggests that information and education is an important step towards engaging people in conserving native plants. Another important factor is for the garden-owners to have control over the location of plantings as many are concerned about too much shade in the garden.

If this article has encouraged you to get out there and help preserve New Zealand's native plants, you can get in contact with an organization such as Trees for Canterbury which does community projects and environmental education and has a native plant nursery. The majority of their trees in the nursery are grown from seed collected in the Canterbury Plains and Banks Peninsula in order to ensure genetic integrity of the native plant populations. This is an important fact to remember, as the genes of native plant populations in the urban remnants are adapted to make them fit for the local environment. However this may be threatened by gene flow from non-local or modified plants in the surrounding gardens.

Doody, B. J., Sullivan, J. J., Meurk, C. D., Stewart, G. H., and Perkins, H. C. 2010. Urban realities: the contribution of residential gardens to the conservation of urban forest remnants. Biodiversity and Conservation, 19:1385–1400.