Detection, assessment and eradication of invasive species



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1

Volume 109 | Number 5/6

May/June 2013

South African Journal of Science  

http://www.sajs.co.za

Review Article 

Detection, assessment and eradication of invasive species

Page 1 of 13 

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.

Introduction

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,

1

 but if left unmanaged overall impacts on ecosystem services 



are likely to rise by an order of magnitude.

2

 As part of national legislation,



3

 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).

4

Introduction



Prevention

Eradication

Ongoing management

Naturalisation

Eradication ceases 

to be cost-effective

A

B1-C0


C2-D2

E

Invasive range size



~350 000

Department of 

Agriculture (DoA)

SANBI’s Invasive Species 

Programme (ISP)

Working for Water 

(WfW)

~8750


100-300

400-600


a

b

c



d

Figure 1:  There was a strategic gap in the management of invasive plants in South Africa that is now being filled 

by the South African National Biodiversity Institute's Invasive Species Programme. Schematic of the 

progression of an invasion with relevant categories (a),

5

 estimates of the number of plant species in South 



Africa recorded in each group (b), the three major strategies for dealing with biological invasions (c) and the 

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,

6

 but, in general, far too little is spent on 



AUTHORS: 

John R. U. Wilson

1,2

Philip Ivey



1

Phetole Manyama

1

Ingrid Nänni



1

AFFILIATIONS:

1

Invasive Species Programme, 



South African National 

Biodiversity Institute, 

Kirstenbosch Research Centre, 

Cape Town, South Africa

2

Centre for Invasion Biology, 



Department of Botany and 

Zoology, Stellenbosch University, 

Stellenbosch, South Africa

CORRESPONDENCE TO: 

John Wilson



EMAIL: 

john.wilson2@gmail.com

alienplants@sanbi.org.za

POSTAL ADDRESS: 

Centre for Invasion Biology 

and South African National 

Biodiversity Institute, Department 

of Botany and Zoology, 

Stellenbosch University, Private 

Bag X1, Matieland 7602, 

South Africa



DATES:

Received: 22 June 2012

Revised: 19 Dec. 2012

Accepted: 08 Jan. 2013

KEYWORDS: 

biological invasions; early 

detection and rapid response 

(EDRR); biosecurity; post-border 

risk assessment; invasion debt; 

South Africa



HOW TO CITE:

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 

pages. http://dx.doi.org/10.1590/

sajs.2013/20120111

© 2013. The Authors.  

Published under a Creative 

Commons Attribution Licence.



2

Volume 109 | Number 5/6

May/June 2013

South African Journal of Science  

http://www.sajs.co.za

Review Article 

Detection, assessment and eradication of invasive species

Page 2 of 13 

quarantine.

7

 This is likely also the case for South Africa, although we do 



not have the figures for how much is actually spent (or indeed whether 

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.

8

 Although there are few 



instances of reptiles naturalising to date, it is likely that some of these 

taxa will become invasive in the future.

9

The management of established invaders in South Africa has varied 



based on the taxon, the invasion location, and which stakeholders are 

involved. But the management of widely established invasive plants 

has been led by the Working for Water Programme (WfW) since its 

establishment in 1995.

10

 By 2008 WfW had spent R3.2 billion, reducing 



the extent of invaded areas for some species and limiting the spread of 

many others.

10

 South Africa has also been actively involved in biological 



control of weeds since 1913,

11

 with the WfW programme providing 



increasing resources since 1996. Biocontrol agents are established 

on 48 invasive alien plant species, of which 10 species are completely 

controlled, and another 18 species are under a substantial degree of 

control.


11

 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.

1

Despite these efforts to control a few widespread invaders, many other 



species are not managed. Some species are already widespread but 

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

12

 but could 



have major future impacts. Similarly, many naturalised species have 

not started spreading, perhaps because of a lag phase.

13

 And finally, 



many introduced species will only naturalise in the future

14

; for example, 



estimates from South Australia place the time from introduction to 

naturalisation of woody perennials to be more than 100 years.

15

 

For plants, around 64 taxa are subject to regular control by the WfW 



programme, but 198 plant taxa are listed as invasive aliens

17

 and 238 



are listed under draft regulations.

3

 So about 140 species are already 



defined as invaders where more control effort is required. As of August 

2010, the Southern African Plant Invaders Atlas (SAPIA) documented 

660 plant taxa as having at least naturalised in the region.

16

 So more 



than 400 species have been flagged as naturalised or invasive but are 

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.

18

 The dedication 



1 000

National management plan required (1b)

Currently targetted by WfW

Not regulated

Regulated by activity (3)

Regulated by area (2)

Eradication indicated (1a)

500


100

50

10



5

1

0



200

400


600

800


Occupancy (quar

ter


-degree grid cells)

Species (ordered by occupancy of quarter-degree grid cells)



Figure 2:  The different legislative categories and the management targets for the Working for Water (WfW) Programme correspond poorly to estimates of 

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 

Atlas database

16

 (accessed August 2010, 2 years after the programme was started) restricted to records from South Africa and records where 



the species identity was known. The legislative categories shown are as per the National Environmental Management: Biodiversity Act (10/2004): 

Draft Alien and Invasive Species Regulations 2009.

3


3

Volume 109 | Number 5/6

May/June 2013

South African Journal of Science  

http://www.sajs.co.za

Review Article 

Detection, assessment and eradication of invasive species

Page 3 of 13 

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

4

). 


As a result, EDRR was initially tasked with assessing the feasibi lity 

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).

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

9

; a further eight acacias are in the top 



one hundred most widely distributed invasive plant taxa.

69

 Given the 



difficulties controlling large persistent seedbanks,

40

 and the long-



term ecosystem level effects of acacia invasions,

70

 there have been 



calls that more should be done proactively to prevent future acacia 

invasions, including attempting eradication.

4,40

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.

53

 After the population was rediscovered 



in the late 1980s, large plants were cleared and the species was 

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 

not halted.

55

A detailed assessment and survey of the population in 2008 found 



more than ten thousand plants spread over ~295  ha with plants 

forming dense monospecific thickets in patches.

55

 Fortunately, this 



was the only known population in the country, plants had not spread 

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.

55,61

 This work demonstrated 



both that the species posed a substantial threat, and that eradication 

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 

(Figure 4).

61

 The total cost over the next 20 years is estimated to be 



R5.4 million (net present value in 2012) if control is successful, but 

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.

64

A dense thicket of Acacia paradoxa on the slopes of Table Mountain in 2008 (photo: Rafael 



Zenni). The implementation of a national eradication plan for this species is a collaboration 

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.

41

 The main question remaining is whether our 



persistence lasts longer than the seedbank, but given the status of 

Table Mountain as a World Heritage Site, control should continue 

in perpetuity.

Box 1

Assessing invasiveness and eradication costs



4

Volume 109 | Number 5/6

May/June 2013

South African Journal of Science  

http://www.sajs.co.za

Review Article 

Detection, assessment and eradication of invasive species

Page 4 of 13 



Proposed mandate and process

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 



records of new instances of naturalisation

Post-border risk assessment: evaluate species in enough detail to 



make a decision as to whether regulation is required and, if so, in 

what form

Eradication planning: estimate the feasibility of eradicating 



species and either develop and implement an eradication plan or 

recommend a revision in listing

In the rest of the paper we discuss progress on these three core areas 

of work.


The focus for SANBI ISP is continental South Africa; a separate process 

of evaluation and eradication is already ongoing for the sub-Antarctic 

Islands of Prince Edward, Marion and Gough.

19

Detecting new invaders

There are several strategic approaches for invasive alien species 

detection (e.g. site-specific surveys, species-specific surveys and 

random surveys

20

). For commercial agricultural pests in South Africa 



there has been both area-specific monitoring (e.g. field inspectors 

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.

8,21–24

 For example, Giliomee



23

 documented a 

rate of approximately one new insect establishing in South Africa per 

year over the past decade, while Herbert

24

 estimated that there has been 



one new introduced terrestrial mollusc establishing every 5 years (28 in 

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.

22

 quadrupled the number of known 



marine introductions to 86 and highlighted several cryptogenic species. 

In comparison, the naturalised plant flora is well known and documented 

thanks largely to Lesley Henderson and the SAPIA project.

16

 SAPIA was 



founded on general roadside surveys for invasive alien plants and has 

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,

25

 increasing the potential to 



discover other naturalised populations of these species.

The SANBI ISP is using other strategies to engage with the broader 

community,

26

 including distributing pamphlets on all target species (see 



Supplementary figure 1 online), and providing a dedicated email address 

for new records (alienplants@sanbi.org.za). Shortfalls of this approach are 

that hotlines and leaflets lack direct engagement,

27

 and that effectiveness is 



much easier to measure in terms of the amount of information distributed 

(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-

based,

4

 and, with the exception of classical biological control,



71

 there 


are few species-specific control programmes or national manage-

ment plans, such as the Australian Weeds of National Significance 

initiative.

72

 In its initial phase, SANBI ISP was tasked with developing 



and implementing a national plan for a highly visible species that 

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 

the species.

Campuloclinium macrocephalum (pom-pom weed) in South Africa is no longer an 

eradication target and a national management plan integrating local land managers 

is required.

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,

73

 it is clear that the 



species has continued to spread during this time.

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.

74

 But finally, pom-pom weed is a lesson 



for why eradication requires a national focus (Figure 2). The budget 

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.

Box 2

The need for early detection and rapid response at a regional scale



5

Volume 109 | Number 5/6

May/June 2013

South African Journal of Science  

http://www.sajs.co.za

Review Article 

Detection, assessment and eradication of invasive species

Page 5 of 13 

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.

28

While the SAPIA database continues to provide significant value, SANBI 



ISP has also focused on improving identification and data management.

29

 



Of the 198 species listed under the Conservation of Agricultural Resources 

Act, 2001 (CARA), as of 2009, 40 did not have herbarium records 

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.

30

 To address these 



concerns, three taxonomists and three taxonomy assistants have been 

employed, and resources provided for the additional 1386 herbarium 



CARA,  Conservation of Agricultural Resources Act of 1983 amended 2001; NEMBA, National Environmental Management: Biodiversity Act (10/2004): Draft Alien and Invasive Species 

Regulations 2009.



Figure 3:  A proposed process for managing new plant invaders. The categories listed are as per the National Environmental Management: Biodiversity Act 

(10/2004): Draft Alien and Invasive Species Regulations 2009

3

. A separate process of evaluation, not described here, is required pre-border and is 






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