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Plantation escapees form subject of trans-continental research

Matthew Larcombe
PhD student, University of Tasmania

Professor Silva records fine scale data in the Green Triangle.

Genetic introgression from Eucalyptus globulus plantations to neighbouring native eucalypts requires multiple generations of hybridisation (Potts et al., 2003). Logically, most gene flow research to date has focused on identifying, predicting and understanding the fitness of hybrids arising directly from plantations (Barbour et al., 2003; Potts et al., 2003; Barbour et al., 2008a; Barbour et al., 2008b). In previous articles I have explained that I am investigating the frequency at which E. globulus x native eucalypt hybrids are establishing in the wild (see related article in Biobuzz 13) and whether or not these hybrids are of equal or reduced fitness in comparison to their pure native species siblings (see related article in BioBuzz 14). Two of our findings from these studies have given us cause to shift our focus from hybrids to pure E. globulus wildlings as a potential source of future gene flow. Firstly, we found that hybrid establishment was rare in the wild, particularly in comparison to wilding establishment; and secondly, we found that fitness of hybrids was significantly lower than fitness of pure native species seedlings in the wild, although there were occasional exceptions. If the wildlings do establish in and around native forest and reach reproductive maturity then they could pose a weed risk and also provide a potential secondary long term source for pollen-mediated gene flow.

Given that E. globulus is one of the most widely planted trees in the world, and there are reports of it becoming naturalised as an exotic (e.g. California – Kirkpatrick, 1977; Ritter and Yost, 2009), there is surprisingly little published information quantifying the extent of wildling establishment or the factors influencing the likelihood of escape of E. globulus from cultivation. The impact of E. globulus naturalisation is currently being assessed in Portugal (Silva et al., 2011), and UTAS recently hosted Professor Joaquim Sande Silva from the Centre of Applied Ecology at the University of Lisbon. Professor Silva is a fire ecologist interested in recruitment of E. globulus following wild fire in Portugal. He visited UTAS under the TRANZFOR research exchange program that operates between European countries and Australia and New Zealand for research in the forestry sector.  We developed a project that would enable us to determine the extent of wildling establishment around plantations and the factors that could be important in predicting establishment at both local and landscape levels.


One of the many plantation boundaries surveyed by Matt and Prof Silva in Gippsland, Victoria.

The project involved a vehicle-based survey of the main E. globulus plantation zones in Tasmania, Gippsland, the Green Triangle, and south west Western Australia at local and landscape levels. Professor Silva and I completed the eastern states in a two week field trip in mid-August. The surveys involved driving along the boundaries of plantations at or nearing harvest age (eight years and over) and second rotation plantations recording the presence of wildlings with a GPS to obtain broad-scale distributions.  In areas where we found relatively dense patches of wildlings we surveyed 10 x 10 m quadrats and recorded local factors such as soil cover and plantation reproductive output.  We plan to use the data to develop broad-scale models (looking at factors like rain fall, soil, geology, topography etc.) to explain wildling presence/absence at the regional and continental scale (see below). The fine-scale quadrat data will be used to identify local and microsite factors associated with wildling establishment.

Although I will be completing the Western Australian leg of the field work as this article goes to print, we have extracted some descriptive statistics and done some very preliminary analysis of surveys conducted in the eastern states. So far we have surveyed just over 160 km of plantation edge and record about 2700 wildlings (17 wildlings/km). The vast majority of the wildlings occurred within 5 m of the plantation boundary. There were some interesting regional differences.  For example, there were 24-times more wildlings per kilometre in the Grampians area compared with the Penola area. We also found higher levels of establishment within plantations (in the first 5 m inside) than beside plantations, which was unexpected and probably associated with existing firebreak management. Hence, it appears that the wildlings that we found occurred mainly within the disturbance zone of future harvesting, so they are unlikely to reach maturity and spread beyond the plantation area.  Some preliminary analysis of fine scale data indicates fire, capsule abundance and shrub presence are important predictors of wildling establishment.

In the future we aim to conduct a comparative analysis at a continental scale by undertaking a similar survey, using equivalent methodology, in Portugal.

Barbour, R.C., Potts, B.M. & Vaillancourt, R.E. (2003) Gene flow between introduced and native Eucalyptus: Exotic hybrids are establishing in the wild. Australian Journal of Botany 51, 429-439
Barbour, R.C., Otahal, Y., Vaillancourt, R.E. & Potts, B.M. (2008a) Assessing the risk of pollen-mediated gene flow from exotic Eucalyptus globulus plantations into native eucalypt populations of Australia. Biological Conservation 141, 896-907.
Barbour, R.C., Crawford, A.C., Henson, M., Lee, D.J., Potts, B.M. & Shepherd, M. (2008b) The risk of pollen-mediated gene flow from exotic Corymbia plantations into native Corymbia populations in Australia. Forest Ecology and Management 256, 1-19.
Potts, B.M., Barbour, R.C., Hingston, A.B. & Vaillancourt, R.E. (2003) Turner Review No. 6: Genetic pollution of native eucalypt gene pools - identifying the risks. Australian Journal of Botany 51, 1-25.
Kirkpatrick JB (1977) Eucalypt invasion in Southern California. Australian Geographer 13, 387-393.
Ritter M, Yost J (2009) Diversity, reproduction, and potential for invasiveness of Eucalyptus in California. Madrono 56, 155-167.
Silva, J.S., Vaz, P., Moreira, F., Catry, F. & Rego, F.C. (2011) Wildfires as a major driver of landscape dynamics in three fire-prone areas of Portugal. Landscape and Urban Planning 101, 349-358.