6. the effeCtiveNeSS of CoNtroL MeaSureS
6.4. area-specific control measures
6.5.1 overall effectiveness of control measures
This assessment of the effectiveness of control measures has highlighted a number of points. it would clearly be beneficial to gain control of invasive species because of the substantial economic costs that would accompany widespread, rampant invasions (box 6.1). in recent years, the overriding source of funding for control measures was from the Working for Water programme within the department of environmental affairs (box 6.2). This public works programme has spent Zar 12 billion (unadjusted for inflation) on invasive plant control projects between 1995 and 2012. however, this amount has only been enough for control teams to reach somewhere between 2% and 5% of the estimated extent of the most important invasive species, and consequently invasions continue to spread (van Wilgen et al., 2012; henderson & Wilson, 2017). nonetheless, the fact that the Working for Water (WfW) programme exists, and is well-funded, is remarkable, especially for a developing country. There are significant opportunities for improvements to WfW (box 6.2), some of these are summarised in the points below.
This assessment has highlighted that the biological control of invasive plants has been notably successful. The south african government, through the WfW programme, has continued to fund biological control research and implementation, with very encouraging results. of the 60 invasive plant species or taxa targeted for biological control thus far in south africa, 15 species are now under complete control, with a further 19 species under a substantial degree of control (Zachariades et al., 2017). by combining biological and mechanical and chemical control, it has been possible to effectively reduce the populations of some of the most damaging invasive species, as appears to have been the case for Hakea and Acacia species in the Western cape (esler et al., 2010;
moran & hoffmann, 2012), and for Lantana and Opuntia species in the Kruger national Park (van Wilgen et al., 2017). The economic benefits of these interventions have been substantial, with estimated cost to benefit ratios indicating that, for every one Zar invested into biological control, economic losses due to invasive alien plant invasions of between Zar 8 and over Zar 3 000 have been avoided.
a few eradication projects have been successful, and more are likely to follow in the near future. The number of species targeted for eradication is increasing, with several other assessments of eradication feasibility underway.
ChaPter 6IThe effecTiveness of conTrol measures
several studies have also shown that control interventions have succeeded in reducing the extent of invasions in some areas. an early example of this was provided by macdonald, clark & Taylor (1989), who demonstrated that a properly planned and executed approach was able to substantially reduce populations of invasive alien trees and shrubs in the Table mountain national Park. concerted efforts to remove invasive pine trees (and other species) from fynbos ecosystems have resulted in marked declines in the density of these species in the berg river catchment (funded by WfW; fill et al. 2017), and on the vergelegen estate (privately funded; (van rensburg, richardson & van Wilgen 2017). mcconnachie et al. (2016) were similarly able to demonstrate that the invaded area in the hawequas mountains would have been almost 50% higher if there had been no control intervention.
in savanna ecosystems, ongoing control has reduced the degree of invasion by a number of species (including Opuntia stricta, australian pest pear, and Lantana camara, lantana, in the Kruger national Park (van Wilgen et al., 2017) and Chromolaena odorata, triffid weed, in the hluhluwe-imfolozi Park (dew et al. 2017; Te beest et al. 2017).
Thus, at a local scale, some control measures have demonstrably been effective.
however, despite the expenditure of at least Zar 12 billion (over 20 years, unadjusted for inflation), and the localised successes outlined above, plant invasions have nonetheless generally continued to grow, some substantially (see henderson & Wilson, 2017; and the discussion in chapter 4).
one of biggest problems impacting on the effectiveness of alien plant control measures in south africa is the lack of adequate goal-setting and planning, accompanied by the monitoring of inputs rather than outcomes. a lack of clear strategic planning and goal-setting arguably leads to too many projects that are ineffective, rather than having fewer but more effective projects in agreed priority areas. successive reviews of the Working for Water programme (in 1997, 2003, 2012 and 2014) have explicitly raised the concern of a lack of strategic planning (see van Wilgen & Wannenburgh, 2016, for a review). most alien plant control projects in south africa have been given goals for the amounts to be spent, the number of people to be employed, and the areas to be treated.
monitoring of progress has a focus on these goals, and there are typically no goals that describe desired outcomes in terms of reducing plant invasions to manageable levels, what those manageable levels would be, and how long it would take to achieve them. in the absence of monitoring programmes that are focussed on these ecological outcomes, it is not possible to objectively assess management effectiveness. The absence of adequate planning and monitoring could be attributed to the requirement to minimise the costs per person-day (and thus maximise the number of people employed), which is a key target on which continued funding depends. This reduces the programme’s ability to adequately invest in planning and monitoring, which would be relatively expensive and would increase the overall costs per person-day.
The existence of dual goals (ecological restoration and the creation of employment) is a double-edged sword.
on the one hand, it is absolutely essential for the retention of the political support that ensures funding, but on the other it restricts the ability to focus funds where they are most needed for ecosystem restoration purposes.
The achievement of employment and spending targets are relatively easy to understand, as is the target to treat a particular area. The target of an area to treat is not useful, however, as it provides no guidance on the purpose of treatment (for example to prevent erosion of, or to restore, vital ecological services), nor does it require the quality or effectiveness of the treatment to be recorded. The formulation of meaningful targets for ecosystem restoration, and a formal requirement to meet them, could alleviate this problem, but given the current set of measures it is all too easy for managers to meet their targets by simply creating employment and working anywhere to any standard.
Tus of biological invasions and Their managemenT in souTh africa2017
several studies have shown that the actual costs of alien plant control operations (be they publically or privately funded) are much larger than the estimated costs. actual costs should be 100% of the estimated costs, but in a range of studies they were found to be 150–860% (mcconnachie et al., 2012); 300–500%
(mcconnachie et al., 2016); 360% (van rensburg, richardson & van Wilgen 2017); and 720% (van Wilgen et al., 1997; fill et al., 2017, with the project still ongoing). These findings point to the complexity of effectively managing invasive plants, and the effort needed to address the issue, as well as to inefficiencies in the implementation of management.
effective control of invasive species would require adherence to best practice methods where these are available.
This has not always been the case, and has led to inefficiencies. for example, macdonald, clark & Taylor (1989) noted that the practice of linking alien plant clearing projects to the supply of firewood led to substantial inefficiencies. fill et al. (2017) found that alien plant clearing operations in the berg river catchment, Western cape, failed to make adequate use of power tools, did not make any use of prescribed burning, and ran un-coordinated, separate projects to control plants in accessible and inaccessible areas, resulting in inefficiencies.
The frequent failure to integrate biological control with mechanical and chemical control in many cases was outlined by Zachariades et al. (2017), with, in one case, millions of rands spent mechanically clearing Cereus jamacaru, a cactus species that is under complete biological control (van Wilgen et al. 2012a). mcconnachie et al.
(2016) also noted that control success in the hawequas mountains would have prevented a larger area from being invaded if it had focussed all of its clearing effort on scattered plants in untransformed land, rather than on dense invasions and abandoned plantations. some of these issues could be addressed by aligning plans with best practice, but others would require improved training of workers to higher levels of competency. for example, both the use of power tools and the setting of prescribed burns can be risky, and are currently avoided due to concerns for the safety of inadequately-trained workers and others.
The employment model currently used by public works programs can lead to substantial inefficiencies. The practice of issuing short-term contracts for clearing and follow-up (instituted as a developmental opportunity for disadvantaged contractors) requires cumbersome procedures to approve and implement, and results in delays to work schedules and late payments to intended beneficiaries, substantially diluting the intended social benefits (ashton, 2012; coetzer & louw, 2012; hough & Prozesky, 2012). it would arguably be better to employ fewer, better-trained, better-equipped personnel on a more permanent basis. The current model also does not allow for capacity to be built within the conservation authorities who are ultimately mandated to manage protected areas, and a scenario in which this funding is phased out, or channelled elsewhere, would leave the conservation agencies without embedded capacity and experience to manage invasions. however, other employment models are used. for example, Working on fire, another in the suite of public works programs, requires beneficiaries that meet fitness standards, provides training to ensure adherence to work standards, and employs people on an annual contract basis, where they receive a regular, dependable wage.
overall, there is a general concern among many stakeholders regarding the efficiency of government-sponsored alien plant control projects, but this is difficult to substantiate due to the scarcity of documented evidence. The findings of mcconnachie et al. (2012), and Kraaij et al. (2017) that point to inefficiencies in the application of treatments, including non-treatment of areas, provides some evidence. shackleton et al. (2016), in a survey of perceptions of managers, landowners, officials and academics, found that most landowners (> 80%) regarded
ChaPter 6IThe effecTiveness of conTrol measures
the on-the-ground management as “poor”, but few WfW managers (< 20%) regarded this as an issue. shackleton et al. (2016) interpreted this as reflecting a view among managers that, as long as they created employment, they would have met their targets, regardless of environmental outcomes.
conflicts over certain important invasive species can retard or prevent the implementation of effective control measures. for example, proposals to introduce biological control for invasive australian Acacia species in the 1970s met with stiff resistance from the wattle industry because of their commercial value (stubbings, 1977).
This has since been overcome through the deployment of non-lethal, seed-feeding insects, but the problem remains for other groups of plants. The planned biological control of invasive Pinus species in south africa, by introducing a cone-feeding weevil, led to concern over the weevil feeding on shoots and allowing fungal infection, with possible risk to commercial production (lennox et al., 2009). The biological control programme has therefore been discontinued, despite a substantial investment. some of these issues may be impossible to solve, as illustrated by the case of proposed regulation of trout, described above.
finally, negative non-target impacts of the control measures were not assessed in this report, but are vital if the true cost and benefit of control measures are to be understood.
overall, therefore, the picture that emerges is that despite considerable investments, and some localised or technique-specific successes, control measures have by-and-large failed to reverse the spread of invasive species.
it nonetheless remains true that there are significant opportunities to improve the effectiveness of control. some authors have proposed an approach of “conservation triage” (bottrill et al., 2008), in which control measures focus on priority areas and species, and in which a trade-off between conserving biodiversity and reducing the extent of invasions is accepted.