Understanding and addressing the impact of invasive non-native species in the UK Overseas Territories in the South Atlantic: A review of the potential for biocontrol
DEFRA ref: CR 0492 CABI ref: TR10086
Preliminary results for the Falkland Islands and South Georgia
Norbert Maczey, Rob Tanner and Richard Shaw
March 2012
Contents
Contents
Project introduction
Biological control of weeds
Arthropods
Adaptation of prioritization tool
Preliminary results for the Falkland Islands- Weeds
Preliminary results for the Falkland Islands - Arthropods
Preliminary results for South Georgia- Weeds
Preliminary results for South Georgia - Arthropods
Annexes
Norbert Maczey
Senior Ecologist/Entomologist
CABI
Bakeham Lane
Egham, Surrey
TW20 9TY
UK
T: +44 (0) 1491 829029
E:
Project introduction
Recent reviews of invasive non-native species (INNS) on the South Atlantic UKOTs, revealed that there is a considerable on-going threat by these species to the endemic biodiversity on these islands. Management plans and capacity building efforts to combat invasive plants have already been developed, or are in the process of being developed, by various conservation bodies and other research institutions. However, to-date, there are few plans to include classical biological control in these new schemes despite this management practise having a long history of successful use on islands in the past. We understand that many species including rare, endangered and/or iconic species are negatively impacted upon by introduced invasive plants or invertebrate species and that the reduction of their impact through biological control could bring tangible benefits to biodiversity in these fragile habitats. At present there is little known about the potential of this tool in South Atlantic UKOTs and therefore this feasibility study focuses on the future potential usage of this method.
A major component of this study is a desk-based review assessing the impact of non-native plant and invertebrate species in the South Atlantic UKOTs. We rank the need and suitability for biological control of individual invasive species, from high to low, using a recently-developed weed biocontrol prioritisation tool, developed initially for Australia, but already proving to be very useful on the islands in the South Pacific. Priority species are selected on the basis of population dynamics, reported impact on biodiversity, impact on livelihoods, costs for on-going control measures other than biological control and others.
In addition, two detailed case studies will evaluate the potential of implementing a biological control programme against priority species for the Falklands and South Georgia more closely. These detailed assessments will combine all current information about the target pest species including information on their native range, areas of introduction and recorded natural enemies in their areas of origin. Ranked in order of priority, and associated costs of available control options, we will include a catalogue of recommended strategies for each priority target species aimed to halt the biodiversity loss through invasive plant and invertebrate species more effectively.
Biological control of weeds
A major focus of this study is the assessment of invasive weeds on all South Atlantic UK OTs since they are often the most numerous, widespread and damaging introduced non-native species able significantly to alter whole ecosystems. In comparison to mechanical or chemical control, which often fails to persistently control the target species, and which needs to be repeatedly applied throughout seasons and year on year, biological control is often the only available practical and economically feasible option, which can be applied over a large geographical area. It impacts very little on the environment in contrast to the associated disturbance caused by manual or other mechanical clearing, or the application of herbicides. When successful, biological control is permanent and self-sustaining (Wittenberg & Cock 2001). On average, more than 75% of target weeds have been significantly or permanently controlled using biocontrol in the past century. Success rates range from 50% to 87% depending heavily on the amount of effort and funding applied to required research (Myers and Bazely 2003, MacFadyen 1998, Hoffmann 1995, Fowler et al. 2000).
Integrated biological control can be regarded as a very safe and cost efficient method provided adequate risk assessment procedures and current protocols such as the International Plant Protection Convention's Code of Conduct for the Import and Release of Exotic Biological Control Agents (International Plant Protection Convention 1996, Food and Agriculture Organization of the United Nations 1997) are followed. Possible non-target effects are quite predictable by the safety-testing that is now routinely carried out (Pemberton 2000).
However, we also recognise that the introduction of a biocontrol agent without considering any conflicts of interest is unwise and ultimately unproductive so we will also assess the general public’s opinions on invasive species and biological control as an important part of the detailed feasibility assessments planned for the Falklands Islands and South Georgia. Management plans and capacity building efforts to combat the threat of invasive species have already been developed or are in the process of being developed by various conservation bodies such as RSPB, Kew Gardens and other research institutions (i.e. Glass et al. 2006, Whitehead 2008). However, biological control currently plays only a very small role in any new control schemes and we aim to close this gap through the work in this study.
We have started this project with a desk-based review and results of the recently completed ‘South Atlantic Invasive Species Project’ have already provided detailed baseline information for this. In addition, CABI has collated information on the impacts of non-native plants and invertebrates using literature reviews and current relevant databases and added this to the results of recent surveys and reviews. Based on this non-native species were ranked with the aim to form a list of priority candidate species in urgent need to be targeted in possible future biological control programmes. For this process a recently-developed weed biocontrol prioritisation tool, developed by Paynter et al. (2009) for Australia, was used. This decision tool is currently being applied to the islands of the South Pacific and is proving to be very useful. It ranks many factors associated with weed biocontrol to produce a score to aid decision makers in allocation of limited resources focussing on likely success versus scale of the problem. These include:
•Is opposition to biological control likely?
•Does the weed species have socioeconomic value?
•Is the weed sufficiently widespread/intractable/important to justify investment in biological control?
•Has the weed been/is it a subject of adequately resourced biological control program elsewhere?
•What is the accessibility and ease of working in its native range?
•Is literature available regarding natural enemies; is it well known/accessible?
•How closely related to indigenous/valued plants is the target weed?
•Which habitats are invaded?
•What type of is the life cycle needs to be taken into account?
•In which way reproduces the target species?
•Is it a weed in its native range?
•Is it difficult to target multiple forms of weed, or probability of replacement of the weed by forms or congeners of the target following successful biological control thereby negating benefits?
•Is it growing in competitive environment (agricultural vs. environmental)?
•Is it a native/valued exotic congener?
Arthropods
Introduced insects can cause widespread and serious problems on islands from reduced biodiversity and the threat of extinction through reduced agricultural productivity to impacts on human health and quality of life. This was the case with the introduced ensign scale, Orthezia insignis which not only threatened many horticultural plants on St Helena but was severely damaging and in many cases killing the national tree, Commidendrum robustum (Asteraceae). Thankfully a specialist coccinellid beetle had been used successfully against this pest elsewhere in the world and CABI was able to facilitate its introduction in the 1990s. This action is believed to have saved the tree from extinction (see Booth et al. 1995; Fowler 1996). The feasibility for biological control of introduced invasive terrestrial arthropods was assessed in the same way as non-native weeds, and only small adaptation to the selected prioritisation tool were required. Although the in-depth data for many non-native arthropods in the OTs is patchy, a good list exists in most cases. CABI holds an extensive database on previous insect biocontrol activities around the globe and this was used to determine whether any key arthropod pests have been subject to attention in the past. Target species were prioritised based on likely safety and success and the reported scale of the problem.
Adaptation of prioritization tool
In this study we use Paynter et al. (2009) as a tool suitable to estimate the feasibility for biological control of weeds and invertebrates on the South Atlantic OTs. Paynter et al. (2009) use a scoring system widely established in Australia through their Weeds of National Significance system (WoNS). A comparable system for the SAOTs does not yet exist. The scoring system developed by Whitebread (2008) for the Falkland Islands assesses the risk of invasiveness and not the actual impact and can therefore not be used for an accurate adjustment of the Paynter et al. method. Developing impact assessment systems comparable to the WONS in Australia are complex and are based on the input of a large number of data over long time periods by many experts eventually collating substantial background information. As a workable replacement we developed a slightly simplified approach, which still allows the accurate ranking of priority species feasible for biological control. We suggest the following adjustments within the three main modules of this method:
Module 1: Weed importance and desirability of biocontrol
Based on the information available from the SAIS project, the JNCC database and additional literature covering reported impacts of relevant species in other countries we suggest the scoring system described in table 1 to estimate weed importance:
Table 1: Questions to determine whether a species is sufficiently widespread/intractable/important to justify investment in biocontrol.
Question / Score if question is answered with yesIs the species only recently introduced/recorded on the island(s)? / 5
(0-no, or no data available; 5-yes)
Does the species currently have a widespread recorded distribution on the island(s)? / 5
(0-no, or no data available; 5-yes)
Is the species currently expanding its range on the island(s)? / 5
(0-no, or no data available; 5-yes)
Is the species known to be invasive in other geographical regions? / 5
(0-no, or no data available; 5-yes)
Is the species known to have negative impacts on biodiversity in other geographical regions? / 5
(0-no, or no data available; 5-yes)
Is the species known to cause economic damage in other geographical regions? / 5
(0-no, or no data available; 5-yes)
Is the species known to cause threats to human or animal health in other geographical regions? / 5
(0-no, or no data available; 5-yes)
Are habitats on the island(s) which can potentially be invaded of conservation importance? / 5
(0-no, or no data available; 5-yes)
Does the SAIS assessment suggest a likely negative impact on biodiversity, agriculture or health? / 10
(0-no; 5-yes)
Have ecological impacts been recorded on the island(s) for this species? / 10
(0-no; 10-yes)
Have economic impacts (agriculture and others) been recorded on the island(s) for this species? / 10
(0-no; 10-yes)
Have impacts on human or animal health recorded on the island(s) for this species? / 10
(0-no; 10-yes)
Only species scoring at least 20 in the questionnaire above are considered a suitable target for biocontrol and are further assessed. One option would have been to include current control methods in the above approach, something Paynter et al. have suggested themselves as a possibility for their method applied to Australian weeds. However the necessary inclusion of data for each species turned out to be above the scope of this project. It may also be of influence to account for public perception in this tool as it could be that a nuisance species might have more support for biocontrol than one actually causing economic or ecological harm
Module 2: Effort required to obtain and host-range test biocontrol agents
We kept this this module unchanged. Paynter et al. give a minimum score for each question in this module to accommodate the fact that because of the unique flora of Australia even in cases of successful existing programs in other geographical areas a certain amount of additional testing is required. We most likely can assume this also for the South Atlantic OTs. Due to the unique nature of the indigenous flora on these islands efforts for host plant testing very similar to Australia can be assumed.
Module 3: Predicting the potential impact of biocontrol
Again we kept this this module unchanged. There is the possibility to apply a different weighting of questions 9-14. Since the basis of the weighting within Paynter et al. is based on large combined data sets from Australia, South Africa and North America one can assume that no other datasets able to provide similar accuracy exist, which could deliver a better weighting better suited to the flora of the SAOTs.
Adaptation for invasive alien invertebrate species
We used a similar approach as for weed species. The only difference being a deletion of questions 9-11 within module 3. These questions are not suitable for invertebrates and no datasets exists to replace these factors with others and to develop an according weighting system. We have however, added one new question: Asking whether biological control programs have been conducted (successful or unsuccessful) for closely related species, which would increase the possibility for any successful control efforts of the relevant species. If no biological control of even related species has been recorded the species will be regarded as currently unsuitable for biological control.
Preliminary results for the Falkland Islands- Weeds
Twenty-nine non-native plant species had an initial impact score of 20 or above and were processed further within the selected prioritisation tool. Preliminary results of this assessment are given in table 2 below. As a cut-off point below we regard BC not to be feasible anymore we have chosen an overall score of 50. However, a high overall score of an individual species does not automatically result in an immediate recommendation to give BC of this species a high priority. This needs to be looked into in more detail through a case-by-case assessment taking other control options and costs versus benefits into account.
Ulex europaeus, Cytisus scoparius and Calluna vulgaris all showed a total score higher than 300, thus suggesting these species are suitable candidates for classical biological control. Indeed, all three species have been the subject of biological control programmes in other geographical regions and therefore ‘off-the-shelf’ biocontrol agents would be available and significantly reduce the costs of implementing classical control programmes against these species on the Falkland Islands. However, Ulex europaeus is regarded as having some benefits to the Falklands by providing natural fencing for farming purposes. In particular with regards to the control of this species aside from a cost-benefit analysis intensive stakeholder consultations are required to determine the relationship between beneficial value and any negative impacts this species has on the local community and local biological diversity.
Another species where such ‘off the shelf’ solutions are readily available is Senecio jacobea. For this species BC has been very successful in some countries, although in the case of New Zealand BC has turned out to be less efficient. In the case of the Falklands further detailed assessments would be required to predict the efficacy of introduced control agents in more detail.
For some species readily available BC agents have been tested but not proven to be effective or only partially effective. To this group of species, which are generally difficult to control through BC, belong Cirsium vulgare and C. arvense. Some potentially effective control agents are not host specific enough to be released in countries with native thistles, but may turn out to provide suitable options for the Falklands where no native close relatives exists. Equally, research into these two species is still on-going with regards to alternative control agents, which may become available in the near future.
For some species no BC agents have been tested and proven to be effective as yet, but research efforts are on-going as these species cause severe problems in other geographical regions. This group includes Pilosella aurantiaca, Pilosella officinarum and Sonchus asper. For these species suitable agents may become available in the near future. Alternatively, independently funded scoping studies and host range testing could initiated for the Falklands. Such larger scale projects need of course be set in relation to the current or imminent threats these species pose to indigenous species and habitats.
Although scoring relatively low due to the fact that in the past no BC have been undertaken for these species, it may well be worth to look in more detail into the potential of BC for Berberis buxifolia and Berberis microphylla as other species within this genus are currently subject of BC programmes. The lack of closely related species on the Falklands could make these also suitable targets based on the results of these on-going projects. In particular complementary initial scoping studies looking for suitable BC agents can be highly recommended.
Although scoring overall relatively low it may also well be worth to look into the potential of BC for Rumex crispus and Rumex obtusifolius. Both species have been the subject of research into the potential for biological control, given currently unsuccessful. However, with the ease of working in the native range and the low number of closely related species biocontrol may be an option in the future if the impact of the species is considered high.
Ammophila arenaria, Lupinus arboreus and Equisetum arvense belong to a group where no BC has been initiated so far or only insufficient efforts have been conducted in the past. Initiating new control projects would be costly compared to ‘off the shelf’ solutions and need to be justified on a case by case study into the scale of current and expected impacts. We currently regard the impact these species have on the indigenous habitats as too low to justify the implementation of full scale BC projects. However, this preliminary judgement may turn out to be unjustified for some of these species and remains open for reassessment at any time. This is also true for a number of other species (Conium maculatum, Hedera helix, Myosotis discolour, Tussilago farfara, Bellis perennis, Atriplex patula, Sonchus oleraceus, Sedum acre, Senecio squalidus, Plantago major, Senecio sylvaticus). These all have a total score below 50 which does currently not warrant research into biological control.