NEWS
South Africa needs a fresh
approach to managing invasive
trees like Eucalyptus
Current Address: Postdoctoral research fellow, Stellenbosch University
Reprinted From: http://bit.ly/2uQCpLx
Heidi Hirsch
F
or thousands of years, trees and
humans have maintained an inti-
mate connection. It’s therefore not
surprising that many tree species were
moved around the world, following the
footprints of human civilisation.
Globally, however, more tree species
are becoming invasive, with detrimental
ecological and socio-economic impacts.
Understanding their invasion history
and ecology is essential to developing
effective management approaches.
Vast areas of Africa’s southernmost
country are characterised by invading
tree species. These include wattles,
pines, mesquite and eucalyptus. Such
invasions are especially worrying in
drought stricken South Africa because
most invasive trees use more water than
other plant groups.
Among the invasive trees with the
most severe effects, particularly when it
comes to water consumption, are sev-
eral Eucalyptus species. More than 200
Australian eucalypt species have been
introduced to South Africa since the
1800s, most for forestry growth trials
and cultivation. They are fast growing
and useful – providing timber, paper,
poles, firewood, shelter, ornamental
value, and nectar and pollen for bees.
Some species, however, escaped culti-
vation and started to establish popula-
tions outside plantations. There are six
eucalypt species listed as invasive by
the country’s environmental legislation:
forest red gum, karri, river red gum, sa-
ligna gum, spider gum, and sugar gum.
Their listing means they should be con-
trolled or retained, depending on the
habitat in which they occur.
Invasive eucalypts account for 16% of
the 1,444 million cubic metres of water
resources that South Africa loses every
year due to invasive plants.
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Figure 1: Invasive eucalypts account for 16% of the 1 444 million cubic meters of
water South Africa loses annually to invasive plants.
Of the listed eucalyptus species, river
red gum (Eucalyptus camaldulensis
Dehnh) is considered to be the most
widespread and aggressive. It has the
largest native range among Australia’s
more than 700 native eucalyptus spe-
cies and is also one of the most widely
planted around the globe.
But there’s a lot that isn’t known about
the river red gum in South Africa. To
bridge the knowledge gaps, we com-
piled a comprehensive species profile
on river red gum. This involved a com-
prehensive literature review as well as
consulting experts such as foresters,
researchers and invasive species man-
agers.
We gathered information on the trees’
introduction and planting history, cur-
rent distribution and value for com-
mercial forestry. Also, aspects about
it as an invader, associated pests and
pathogens, people’s perception of the
species and conflicts of interest were
considered.
We also collected information on man-
agement and restoration options,
knowledge gaps and further research
needs.
The outcome of all these endeavours
was recently published in an extensive
dossier on river red gum.
With this review, we were able to de-
fine the knowns and unknowns on this
iconic tree to pave the way towards a
national management strategy. Besides
area-specific control measures, such a
strategy should also consider percep-
Grassroots
Vol 20
No 1
March 2020