Detection, assessment and eradication of invasive species
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A new national unit for invasive species detection,
assessment and eradication planning
Even with no new introductions, the number of biological invasions in South Africa will increase as
introduced species naturalise and become invasive. As of 2010 South Africa had ~8750 introduced plant
taxa, 660 recorded as naturalised, 198 included in invasive species legislation, but only 64 subject to regular
control (i.e. only widespread invaders are managed post-border). There is only one documented example
of a successful eradication programme in continental South Africa – against the Mediterranean snail (Otala
punctata) in Cape Town. Here we describe the establishment in 2008 of a unit funded by the Working for
Water Programme as part of the South African National Biodiversity Institute's Invasive Species Programme
(SANBI ISP) designed to (1) detect and document new invasions, (2) provide reliable and transparent
post-border risk assessments and (3) provide the cross-institutional coordination needed to successfully
implement national eradication plans. As of the end of 2012, the ISP had an annual budget of R36 million,
employed 33 staff working across all nine provinces, supported 10 postgraduate students, hosted 35 interns
(including those as part of a drive to collect DNA barcodes for all invasive taxa) and created over 50 000
days of work as part of government poverty alleviation programmes. The unit has worked towards full risk
assessments for 39 plant taxa and has developed eradication plans for seven species; the unit is now helping
implement these plans. By focusing on science-based management and policy, we argue that SANBI ISP can
play a leading role in preventing introduced species from becoming widespread invaders.
Biological invasions are a major threat to biodiversity and economic livelihoods in South Africa. Invasive plants cost
South Africa an estimated R6.5 billion every year,
but if left unmanaged overall impacts on ecosystem services
As part of national legislation,
South Africa is developing a national
strategy to combat this threat, with three main methods for limiting impacts: prevent introductions, eradicate taxa
that do get in and strategically manage established infestations (through containment, impact reduction, or value
addition) (Figure 1).
to be cost-effective
Invasive range size
SANBI’s Invasive Species
Working for Water
by the South African National Biodiversity Institute's Invasive Species Programme. Schematic of the
progression of an invasion with relevant categories (a),
estimates of the number of plant species in South
organisations responsible for managing alien plants at each stage (d).
In South Africa, the Department of Agriculture manages quarantine services and conducts pre-border risk
assessments in collaboration with the National Plant Protection Organisation. Under particular circumstances the
costs of prevention can be higher than eradication or management,
but, in general, far too little is spent on
John R. U. Wilson
Invasive Species Programme,
Kirstenbosch Research Centre,
Cape Town, South Africa
Centre for Invasion Biology,
Zoology, Stellenbosch University,
Stellenbosch, South Africa
Centre for Invasion Biology
and South African National
Biodiversity Institute, Department
of Botany and Zoology,
Stellenbosch University, Private
Bag X1, Matieland 7602,
biological invasions; early
detection and rapid response
(EDRR); biosecurity; post-border
risk assessment; invasion debt;
Wilson JRU, Ivey P, Manyama
P, Nänni I. A new national
unit for invasive species
detection, assessment and
eradication planning. S Afr J Sci.
2013;109(5/6), Art. #0111, 13
© 2013. The Authors.
Published under a Creative
Commons Attribution Licence.
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This is likely also the case for South Africa, although we do
current procedures are effective). However, the number of introductions
is often documented. For example, the reptile pet trade has grown
exponentially over the last 30 years, with more species being introduced
from more countries in much greater numbers.
Although there are few
taxa will become invasive in the future.
The management of established invaders in South Africa has varied
involved. But the management of widely established invasive plants
has been led by the Working for Water Programme (WfW) since its
establishment in 1995.
By 2008 WfW had spent R3.2 billion, reducing
South Africa has also been actively involved in biological
with the WfW programme providing
on 48 invasive alien plant species, of which 10 species are completely
controlled, and another 18 species are under a substantial degree of
These biocontrol agents are estimated to save South Africa
several billion rand each year by reducing the negative impacts invasive
plants have on ecosystem services.
Despite these efforts to control a few widespread invaders, many other
for whatever reason have not yet been widely controlled or included in
regulations (Figure 2). Other species are relatively limited in distribution
as a result of the small number of sites of introduction
not started spreading, perhaps because of a lag phase.
; for example,
naturalisation of woody perennials to be more than 100 years.
For plants, around 64 taxa are subject to regular control by the WfW
So about 140 species are already
2010, the Southern African Plant Invaders Atlas (SAPIA) documented
660 plant taxa as having at least naturalised in the region.
not listed in regulations, although more than half of these are recorded
from one or two quarter-degree grid cells only (Figure 2). Finally, the
total number of introduced plant taxa in South Africa is estimated at 750
non-native tree species and 8000 non-native shrubby and herbaceous
species, many of which could naturalise in the future.
National management plan required (1b)
Currently targetted by WfW
Regulated by activity (3)
Regulated by area (2)
Eradication indicated (1a)
Species (ordered by occupancy of quarter-degree grid cells)
the extent of invasions. Specifically some species are found at many sites, but are indicated for eradication (1a species to the left of the graph);
other prohibited species are only recorded in one area, but eradication is not considered (1b species to the right of the graph); and some species
are widespread invaders that are not regulated at all (species to the left of the graph). Occupancy is based on the Southern African Plant Invader
(accessed August 2010, 2 years after the programme was started) restricted to records from South Africa and records where
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of specific resources to provide comprehensive risk assessments and
control for these taxa has, until recently, been lacking (Figure 1).
In this paper we introduce a new programme in the context of past
approaches to detect, evaluate and eradicate invasive organisms. Finally,
we discuss lessons learned and progress made to date.
A South African Programme
In March 2008 the South African National Biodiversity Institute (SANBI)
was contracted by the WfW Programme of the Department of Water
Affairs and Forestry to develop, in partnership with other stakeholders,
a programme focusing on 'emerging' plant invaders. In the initial 3-year
funding cycle the programme was called the Early Detection and Rapid
Response (EDRR) Programme for Invasive Alien Plants.
During the development of the programme, the terms 'emerging' and
'early detection and rapid response' caused considerable confusion
among key stakeholders. For example, it was not clear whether EDRR
should work on regional priorities (e.g. controlling species that are new
to a particular area but already widespread elsewhere in the country
of containment. However, it quickly became clear that responding
to stakeholder concerns and working on large-scale containment
exercises would use the majority of the resources allocated to EDRR,
such that the management goal of eradication would again be sidelined
(compare Box 1 and Box 2). The programme needed to focus on
achieving this specific management goal, whereas the term ‘EDRR’ is
a management approach that can apply to any stage of the invasion
process at any spatial scale. The programme therefore dropped
the name EDRR in favour of SANBI Invasive Species Programme
SANBI ISP has grown steadily and by the end of 2012 had an annual
budget of R36 million with a presence in all nine provinces. SANBI ISP
now employs 33 staff, has supported 10 postgraduate students, hosted
35 interns, and created over 50 000 person days, of which the majority
were employed through the Natural Resource Management Programme
poverty alleviation programme.
Acacia paradoxa in South Africa
Three of the top ten most prominent invasive alien plant taxa in South
Africa are Australian acacias
; a further eight acacias are in the top
and the long-
there have been
invasions, including attempting eradication.
Acacia paradoxa has invaded only one site in South Africa – the
northern slopes of Table Mountain. It was probably first planted
in the late 1800s as a small hedge by the forester who lived in the
King's Blockhouse on Devil's Peak. Until recently, the plants appear
to have been ignored with recent reports suggesting the population
had probably disappeared.
After the population was rediscovered
incorporated into general invasive plant management. However, the
interval between clearing in that area (3–5 years) was much longer
than the juvenile period (1–2 years), and so seed production was
A detailed assessment and survey of the population in 2008 found
forming dense monospecific thickets in patches.
far from the initial point of introduction, and the seedbank was confined
almost exclusively to below the canopy. Modelling work and field
observations suggested, however, that if left unmanaged the species
could expand substantially in range and impact the environment in
ways similar to other Australian acacias.
This work demonstrated
was feasible (Figure 3).
Using the initial survey as a starting point, annual search-and-destroy
operations in collaboration with the South African National Parks
(who manage the area) and WfW-SANBI have been ongoing since
2009. The aim is to systematically survey the affected area during the
flowering season (i.e. August–October) and prevent new seed-set.
In 2010, surveys found about a hundred new adult plants and the
total extent was revised slightly upwards to 310 ha, but there is no
evidence that the population extent is larger than this. Later in 2010
and during the start of 2011, seedling patches emerging after the
initial clearing (and a subsequent wildfire) were cleared. Over 600 000
seedlings were hand-pulled on a contract costing R400 000. As such,
the exercise is much more expensive than general clearing operations
(which will still continue in the area separate to the A. paradoxa work),
but this approach was estimated to be much more cost effective
than if either no action was taken or containment were attempted
The total cost over the next 20 years is estimated to be
the duration of the eradication is still to be properly estimated. The
management approach and measures to reduce the seedbank will be
adapted in the light of progress and exploration of new methods.
A dense thicket of Acacia paradoxa on the slopes of Table Mountain in 2008 (photo: Rafael
between WfW, SANBI and South African National Parks.
Without a specific focus on eradication, A. paradoxa would have
continued to slowly spread through the park (and possibly further
afield). However, it is likely that eradication will now be achieved as
the necessary resources are in place and there is willingness from
all parties involved.
The main question remaining is whether our
Table Mountain as a World Heritage Site, control should continue
Assessing invasiveness and eradication costs
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SANBI ISP has developed the following mandate, with a work flow as
proposed in Figure 3:
Detection of new invaders: coordinate surveillance for and manage
Post-border risk assessment: evaluate species in enough detail to
Eradication planning: estimate the feasibility of eradicating
recommend a revision in listing
In the rest of the paper we discuss progress on these three core areas
of evaluation and eradication is already ongoing for the sub-Antarctic
Islands of Prince Edward, Marion and Gough.
Detecting new invaders
There are several strategic approaches for invasive alien species
detection (e.g. site-specific surveys, species-specific surveys and
). For commercial agricultural pests in South Africa
employed to survey farms for pests) and species-specific monitoring
(e.g. approximately R2 million per annum is spent on detecting
and controlling incursions of the fruit-fly Bactrocera invadens from
neighbouring countries) (Venter JH 2011, personal communication,
Nov 22). But most documented cases of naturalisation or invasion have
come from a few interested scientists not employed specifically to look
at the issue of invasions.
For example, Giliomee
rate of approximately one new insect establishing in South Africa per
year over the past decade, while Herbert
estimated that there has been
total since the 1850s).
A recent assessment of marine and estuarine biological introductions
showed just how poor our overall knowledge of particular groups is.
Through reviewing historical literature, and some limited additional
focused survey work, Mead et al.
quadrupled the number of known
In comparison, the naturalised plant flora is well known and documented
thanks largely to Lesley Henderson and the SAPIA project.
grown to be the primary repository for new plant naturalisation records.
Detection efforts by SANBI ISP to date have largely been based on
revisiting historical records in SAPIA, but site-specific (e.g. historical
arboreta) and species-specific surveys (see Box 1 and Box 2) have been
initiated. SAPIA itself has shifted emphasis, and is focusing more on new
instances of naturalisation, linking directly with SANBI ISP. For example,
54 new species were recorded as naturalised between April 2010 and
March 2013 (Henderson L 2011, unpublished SAPIA annual progress
report, March, ibid 2012, ibid 2013). These records are highlighted
through SAPIA's quarterly newsletters,
increasing the potential to
The SANBI ISP is using other strategies to engage with the broader
including distributing pamphlets on all target species (see
for new records (email@example.com). Shortfalls of this approach are
that hotlines and leaflets lack direct engagement,
and that effectiveness is
(i.e. number of leaflets) than of impact on the behaviour of the recipients
(i.e. the change in the rate with which sightings are reported). This shortfall
Pom-pom weed management in South Africa
Alien plant clearing operations in South Africa have largely been area-
and, with the exception of classical biological control,
ment plans, such as the Australian Weeds of National Significance
In its initial phase, SANBI ISP was tasked with developing
has been spreading rapidly from a localised source: pom-pom weed
(Campuloclinium macrocephalum). Our remit was to manage outlying
populations and work towards a national containment strategy for
Campuloclinium macrocephalum (pom-pom weed) in South Africa is no longer an
eradication target and a national management plan integrating local land managers
Pom-pom weed is a South American asteraceous herb that was
probably introduced into South Africa in the 1950s as a garden orna-
mental. It was first recorded as a naturalised weed in the 1960s and
was still at low levels well into the 1990s, but over the past 20 years it
has spread throughout the grassland biome. Between 2008 and 2010,
rapid response teams were contracted to clear all known populations
during the flowering season (September–March) at a cost of over
R5 million. While this endeavour created work for over 500 people
during the flowering season, and reduced populations, there are no
documented examples of medium-sized populations (>1 ha) having
been extirpated, and, given the rise in sightings,
it is clear that the
The pom-pom weed case is instructive for several reasons. Firstly,
pom-pom weed could probably have been eradicated if action
had been taken when it was first detected. Secondly, based on the
difficulties of managing control teams across a wide area, a national
management plan needs to involve local or regional early detection and
rapid response teams that could quickly implement physical control
of incipient outlying populations in combination with re-distributing
effective biocontrol agents.
But finally, pom-pom weed is a lesson
spent on pom-pom weed clearing contracts alone was approximately
20% of the total programme's budget, with annual expenditure similar
to that predicted for the eradication of other species (Table 1). The
focus on pom-pom weed has meant fewer species have been
evaluated or targeted for eradication.
In conclusion, for South Africa to implement early detection and
rapid response effectively there needs to be capacity and expertise at
regional levels and species-specific national strategies with specific
and measurable goals. There should also be structures in place to
prevent such initiatives from detracting from eradication attempts.
Ironically, the diversion of attention onto pom-pom weed might mean
the next pom-pom weed can no longer be eradicated.
The need for early detection and rapid response at a regional scale
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is partly overcome by linking detection directly to management, and by
basing SANBI ISP employees throughout the country with an explicit
mandate to develop professional networks of spotters and engage with the
broader public. For example, local managers in the southern Cape involved
in the eradication of Acacia stricta reported several populations that had
not been previously identified.
While the SAPIA database continues to provide significant value, SANBI
recorded in the Pretoria Herbarium Computerised Information System
(PRECIS), either because specimens were not collected or data had not
yet been uploaded. This omission can have direct costs for management.
For example, the biological control of Cactaceae has historically been
hampered by a lack of accurate taxonomic knowledge that has only been
resolved more recently using phylogeographic tools.
To address these
employed, and resources provided for the additional 1386 herbarium
. A separate process of evaluation, not described here, is required pre-border and is