Matthew
Larcombe
PhD student, University of Tasmania
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Professor Silva records fine scale data in the
Green Triangle.
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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.
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One of the many plantation boundaries surveyed
by Matt and Prof Silva in Gippsland, Victoria.
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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.
References
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.
BIOBUZZ ISSUE FIFTEEN, DECEMBER 2011
