8. KNoWLedGe aNd iNforMatioN GaPS iN uNderStaNdiNG
8.6. Targets and priorities
While the indicators on their own have value, targets should be set for them to be effective. for example, aichi Target 9 states that “by 2020, invasive species and pathways are identified and prioritized, priority species are controlled or eradicated and measures are in place to manage pathways to prevent their introduction and establishment”. The first two indicators listed in Table 2.6 can be used to identify invasive species in the country and their pathways, and the appropriate planning should be in place. similarly, control efforts will often need to be prioritised based on resource availability.
The setting of targets and priorities is outside the scope of this report, but the issue of which data should be collected to improve the value of the indicators for informing management decisions is important. similarly, it might be important to weight some of the indicators by relevant priorities. for example, the importance of Planning coverage could be weighted by how important it is to have a plan in place, and given financial constraints it would be important for priority pathways, species, or areas to be covered by plans in preference to other components.
finally, ensuring that future status reports are cognisant of relevant targets and priorities will be vital if they are to inform national and regional level strategies.
KeY PoLiCY- 9
reLevaNt MeSSaGeS
Lead authors:
Brian van Wilgen, John Wilson, Katelyn faulkner, Tsungai Zengeya, Sebataolo Rahlao
Chapter summary
This chapter provides a list of policy-relevant messages that have been distilled from the findings in the status report on biological invasions in south africa.
These provide a list of issues that could be used as a starting point for the development of a policy response by the department of environmental affairs.
historically, most invasive species were intentionally introduced into south africa. however, the rate at which species are being unintentionally introduced is increasing as trade and tourism increase. government capacity to deal with this threat is limited at present, but additional efforts in this regard would yield positive returns on investment.
over 2000 alien species have established populations outside of captivity or cultivation in south africa to date, at least one third of which have become invasive. experts are of the opinion that more than 100 invasive species already cause major impacts. both number of species causing major impacts, and the magnitude of the impacts themselves, are set to grow as further species become invasive, and as others enter a phase of exponential spread.
south africa has achieved major successes in the field of biological control of invasive alien plants, and is regarded as a world leader due to the development and promulgation of comprehensive regulations to manage biological invasions.
south africa has invested billions of rands into attempts to control invasive species, with some success in localised areas. however, due to the size of the problem, it has only been possible to reach a small proportion of the total invaded area (about 1–2% per year), and most invasive species continue to spread.
The lack of adequate planning and monitoring of the outcomes of control measures has been identified as a major weakness in south africa, and leads to substantial management inefficiencies. Positive returns on investment from spending on invasive species control measures should still be possible, provided steps are taken to improve planning and management effectiveness.
Tus of biological invasions and Their managemenT in souTh africa2017
9.1. iNtroduCtioN
This status report is the first in a series of such reports intended to inform the development and ongoing adaptation of appropriate policies and control measures, both to reduce the negative impacts of invasive species on ecosystems, the economy, and people, and to retain any benefits of invasive species where possible and desirable (section 1.2).
ideally, scientists and policy-makers should work together to ensure that evidence about issues that are relevant to policy-makers are appropriately considered when policy is formulated and implemented, but there are numerous factors that can hinder effective collaboration (von der heyden et al., 2017). These include the fact that research takes time, and so relevant evidence is often not available when policies are formulated; there is often a mismatch in the language used by policy-makers and scientists; scientists are often unwilling to provide the certainty needed for policy-makers; and policy-makers need to consider the findings of scientists in the context of other needs and issues, such that the final decisions might be different from the recommendations (and desires) of the scientists.
This chapter is included in an attempt to bridge this gap, and it provides a list of policy-relevant messages that have been distilled from the findings in the status report. These messages provide a list of issues that could be used as starting point for the development of a policy response by the department of environmental affairs (dea).
The key messages are in the form of a single headline, followed by explanatory text.
at the end of each headline are cross-references to the relevant sections of this report where the underlying evidence is presented in more detail. The messages themselves are grouped under three headings that cover the major policy issues, namely: (1) how do alien species get here, and spread?; (2) why does it matter?; and (3) how well are we dealing with this problem?
9.2. hoW do aLieN SPeCieS Get here, aNd SPread?
Opportunities for the introduction of high-risk alien species are increasing in line with increases in trade and travel. While effective protocols are being developed and implemented to prevent the legal introduction of high-risk alien species, there is little capacity in place to prevent unintentional and deliberate illegal introductions of high-risk alien species (see sections 3.3.1, 3.3.3, and 6.2.)
international visitors and imported goods currently enter south africa through 72 official ports of entry (harbours, airports and border posts). The volume of trade and number of people that enter through these ports is increasing; the
tHe SituAtion
The rate of introduction of new unregulated species is increasing in line with increases in trade and travel
7
The number currently stands at
SPecIeS NeW
PeR yeAR
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value of tourism, for example, has increased from around Zar130 billion in 1995 to Zar350 billion in 2017, and is predicted to increase to around Zar530 billion by 2027. greater volumes of trade and tourism can be accompanied by increasing rates of alien species introductions. The rate at which alien species are being introduced has been increasing steadily, from around 35 species per decade in the 1950s to 70 species per decade between 2000 and 2010. historically, most species have entered south africa from overseas, but the growth in trade across africa over the past decade means that an increasing number of alien species are likely to be introduced to other countries in africa and then subsequently spread from there to south africa.
intentional introductions of alien species have taken place for a range of reasons. Plants were imported for agriculture and for forestry, or as ornamentals for use in gardens and parks. animals were imported for agriculture, aquaculture or mariculture, for recreational fishing or hunting, and to supply the pet trade. some of the alien species that have become invasive were deliberately released into nature with the intention of establishing self-sustaining populations, for example trout and bass into streams and rivers. others have simply escaped cultivation or captivity, for example pine and wattle trees introduced to establish commercial forestry plantations. regulations are now in place to cover the future intentional importation of alien species, and procedures are being developed to analyse the risks posed before import permits are granted. if these procedures are adhered to, and if sufficient capacity is maintained in perpetuity, the risk posed by legal introductions will be substantially reduced.
currently, however, the dea only has a consistent presence at one of the 72 official ports of entry (occasional joint operations are carried out at other entry points, in conjunction with other departments), and the brunt of border inspections falls to the department of agriculture, forestry and fisheries (daff). The interception and prevention of import of potentially damaging invasive species might offset the cost of vigilance, and an increase in this capacity should deliver positive returns on investment.
Figure 9.1 Sniffer dogs are deployed at o.R. Tambo International Airport, where they assist in the detection of goods that are potentially illegal or harmful, including alien species.
Photograph: C. Mercado.
Tus of biological invasions and Their managemenT in souTh africa2017
Once introduced into the country, alien species can disperse rapidly along South Africa’s transport networks (see section 3.3.2)
south africa has an extensive transport network along which commodity contaminants or stowaways can be dispersed. There is also a thriving internal trade in alien species for a variety of purposes. managing the internal transport infrastructure for the purposes of preventing the dispersal of high-risk alien species is very difficult, and there has been no comprehensive analysis of the practicalities of this. This further emphasises the importance of preventing introduction in the first place.
photographer: K. faulkner.
Figure 9.2 South African roads provide many opportunities for the spread of alien species along a well-developed and heavily-used transport network.
Over 2000 alien species are present outside of captivity or cultivation in South Africa, and at least a third of these have become invasive. Many of these invasive species are now entering a phase of rapid expansion, so even if no further alien species are introduced, the problem will continue to grow due to the species already in the country (see sections 4.2 and 4.3)
most recorded invasive species are plants (574 species); other important groups include terrestrial invertebrates (107 species) and marine invertebrates (46 species). other groups (mammals, reptiles, birds, freshwater fish and amphibians) each contribute less than 20 species. for many groups of species (such as invertebrates, most marine species, and microbes) there are likely to be many alien species present that have not yet been detected and recorded. The number of invasive species is also expected to continue to increase as new species become invasive. note: for the purposes of this report, alien species are considered to be invasive if they were formally reported to have survived, reproduced, and spread unaided over considerable distances/areas, rather than as having been recorded as causing significant negative impacts.
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Number of species Terrestrial and freshwater plants Terrestrial invertebrates Marine invertebrates Microbes Birds Mammals freshwater invertebrates Reptiles freshwater fish Amphibians Marine plants0
100 200 300 400 500 600 700 800 900 1000
Non-invasive species Invasive species
Figure 9.3 Terrestrial and freshwater plants and invertebrates currently make up the bulk of known alien species in the country.
other groups make up smaller numbers. A large proportion of naturalised alien plants have gone on to become invasive.
The rate of spread of invasive species is (typically) slow as the species establishes, then rapid as it colonises new areas, slowing down as the available habitat for expansion becomes limiting. information from the southern african Plant invaders atlas (saPia) – the most reliable source of information on the distribution of invasive plants in south africa – reveals that all invasive alien plant species not subjected to biological control have increased their ranges over the past 15 years, some substantially. pompom weed (Campuloclinium macrocephalum, a herbaceous invader of grasslands) has increased in range by 670%; and famine weed (Parthenium hysterophorus, an annual invader of overgrazed rangelands and savannas) by 493%. even long established invasive tree species, that might be expected to be nearing their range limits, such as mesquite (Prosopis glandulosa) and river red gum (Eucalyptus camaldulensis), have increased in range by 180% and 61% respectively. These species have large impacts, and the impacts grow as the species spread. Thus, even if no further introductions of potentially invasive species takes place, the problems associated with invasive species will increase, a phenomenon known as
“invasion debt”.
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Time
Area occupied
Initial slow growth
rapid expansion
Figure 9.4 The area occupied by invasive species typically initially grows at a slow rate, and then accelerates until the majority of the available habitat is occupied. The time for species to enter a phase of rapid expansion is typically in the order of several decades to centuries.
given most invasive species were introduced to South Africa in the past 200 years, the majority of these species are in or are entering the phase of rapid expansion and thus the number of species with severe impacts is set to increase.
9.3. WhY doeS it Matter?
Over 100 invasive species are believed to have major negative impacts on ecosystem services, including on water resources, rangeland productivity and biodiversity (see section 4.6)
surprisingly, there have been very few studies that formally document evidence on the impacts of invasive species, and consequently the level of confidence in estimates of the magnitude of these impacts is low, but it is clear that the invasive species that have major negative impacts are many and varied. some examples are given in Table 9.1. almost all of the estimated impacts of invasions in monetary terms (~Zar6.5 billion per year) is due to these hundred or so invasive species that are believed to have major negative impacts. country-level species-specific management strategies have only been developed for a very small number of invasive species, and none have been formally implemented.
tABle 9.1. examples of invasive species that are believed to have major or severe negative impacts in South Africa.
group (nuMBer oF SpeCieS witH MAJor or
Severe negAtive iMpACtS) exAMple oF SpeCieS And tHe iMpACtS tHey CAuSe
plants (80) north american mesquite trees (genus Prosopis) reduce grazing potential; deplete groundwater resources; and negatively impact on biodiversity.
australian wattle trees (genus Acacia) reduce grazing potential and surface water runoff; and negatively impact on biodiversity.
north american and european pine trees (genus Pinus) reduce surface water runoff; negatively impact on biodiversity; and increase the fire intensity and damage done by wildfires.
herbaceous and succulent species (triffid weed - Chromolaena odorata; famine weed - Parthenium hysterophorus; pompom weed -Campuloclinium macrocephalum; and many cactus species) severely reduce rangeland productivity and thus the livelihoods of rural people.
Mammals (8) feral domestic cats (Felis catus) and house mice (Mus musculus) are serious threats to breeding marine birds on offshore islands.
Freshwater fish (5) north american smallmouth bass (Micropterus dolomieu) decimate indigenous and endemic fish and invertebrates in streams, rivers and dams.
terrestrial invertebrates (5) argentine ant (Linepithema humile) disrupts ant-plant mutualisms that are responsible for the seed dispersal of indigenous plants, and thus pose serious threats to indigenous vegetation survival.
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Figure 9.5 Pine trees invading a fynbos mountain catchment area. Several species of invasive pine trees have major impacts by reducing water resources, displacing globally unique biodiversity, and increasing fire hazard. Photograph: B. van Wilgen.
Invasive trees and shrubs reduce surface water resources by between 3 and 5%, and threaten up to 30% of the water supply of cities like Cape Town and Port Elizabeth (see section 5.5.1)
invasive alien plants, particularly trees and shrubs, use more water than the indigenous plant species that they replace, because they are larger and deeper-rooted, and have different physiologies. at a national scale, the combined impacts of invasive alien plants on surface water runoff have been estimated at between 1 450 to 2 450 million m3 per year (between 3 and 5% of the mean annual runoff for the country). Primary catchments most affected are in the Western and eastern cape, and KwaZulu-natal, where reductions in mean annual runoff are greater than 5%. if no remedial action is taken, reductions in water resources could rise to between 2 600 and 3 200 million m3 per year; and if fully invaded, catchments in the Western and eastern cape Provinces will deliver 30% less water to the cities of cape Town, mossel bay, george, Knysna, Plettenberg bay and Port elizabeth. This severely constrains the prospects for economic growth, threatening the ongoing creation of new employment opportunities to millions of south africans. deep-rooted invasive species such as mesquite (Prosopis species) that invade arid areas also deplete groundwater resources, and lower the water table.
reducing the extent and abundance of water-consumptive invasive alien plants through efficient management can make a valuable contribution to water security and sustainable agriculture in south africa.
The reductions in water resources if no remedial action is taken are estimated to be between
tHe SituAtion
2600 &
3200 million m
3per year
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Figure 9.6 Invasive mesquite trees (Prosopis species) in the arid Northern cape can substantially deplete groundwater reserves. Research has shown that savings of up to 70 m3/month could be achieved in spring for each hectare of Prosopis cleared.
Photograph: R. Shackleton.
Invasive alien plants reduce the capacity of natural rangelands to support livestock production by over 100 000 large livestock units, thereby threatening rural livelihoods and food security (see section 5.5.2) invasive plants such as cacti, and several herbaceous weeds such as pompom weed (Campuloclinium macrocephalum), famine weed (Parthenium hysterophorus), and triffid weed (Chromolaena odorata), invade grassland, savanna and Karoo vegetation, where they displace palatable indigenous plants, and consequently these areas cannot support as many livestock as uninvaded areas. invasive alien plant infestations reduce the amount of livestock that can be supported in south africa by around 115 000 large stock units. This is just over 1% of the potential number of livestock that could be supported. however, these impacts could increase dramatically, more than halving the livestock production potential, if infestations of invasive plants spread into all suitable habitats.
Figure 9.7 Invasion of Highveld grasslands by alien plants such as pompom weed (Campuloclinium macrocephalum) reduces the capacity of rangelands to support livestock by displacing palatable grasses and shrubs.
Photograph: L. Henderson.
Figure 9.8 The boxing glove cactus (Cylindropuntia fulgida var. mamillata) near Upington in the Northern cape Province. The species is extremely damaging to rangelands, but fortunately can be controlled using biological control.
Photograph: T. Xivuri.
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Biological invasions are the third-largest threat to South Africa’s terrestrial biodiversity (after cultivation and land degradation), and currently account for 25% of all biodiversity loss (see section 5.5.3)
south africa is one of the most biodiverse countries in the world, and this diversity underpins large parts of its economy, including fisheries, livestock production, harvesting of natural products, national and international tourism, and recreation. invasive species have been identified as a significant threat to biodiversity throughout the country. such losses of biodiversity have large negative knock-on effects on the economy and food security, among others. note: biodiversity here refers to the variety of genes, species and their interactions, and ecosystems in a given area. areas of high biodiversity are characterised by many species, and diverse ecosystems (such as forests, thickets, grasslands, wetlands, estuaries), and biodiversity is measured using standard international metrics.
Figure 9.9 Species-rich fynbos vegetation is transformed into species-poor monocultures through invasion by alien trees such as pines (Pinus species), with substantial loss of biodiversity. Photographs: B. van Wilgen.
The South African Department of Environmental Affairs (DEA) currently invests over ZAR 1.5 billion a year on managing biological invasions. The expenditure from other government agencies and the private sector is large but has not been precisely determined (see sections 6.4.1 and 6.4.2)
The dea’s Working for Water programme spent a total of Zar 5.65 billion between 1995 and 2016, mainly on invasive plant control projects across the country (figure unadjusted for inflation). annual expenditure has risen in real terms, from an initial investment of Zar 27 million in 1995 to Zar 1.55 billion in 2016. all
The dea’s Working for Water programme spent a total of Zar 5.65 billion between 1995 and 2016, mainly on invasive plant control projects across the country (figure unadjusted for inflation). annual expenditure has risen in real terms, from an initial investment of Zar 27 million in 1995 to Zar 1.55 billion in 2016. all