Botanical gardens as key resources and hazards for biosecurity

Biodiversity and economic losses resulting from invasive plant pests and pathogens are increasing globally. For these impacts and threats to be managed effectively, appropriate methods of surveillance, detection and identification are required. Botanical gardens provide a unique opportunity for biosecurity as they accommodate diverse collections of exotic and native plant species. These gardens are also often located close to high-risk sites of accidental invasions such as ports and urban areas. This, coupled with routine activities such as the movement of plants and plant material, and visits by millions of people each year, place botanical gardens at risk to the arrival and establishment of pests and pathogens. Consequently, botanical gardens can pose substantial biosecurity risks to the environment, by acting as bridgeheads for pest and pathogen invasions. Here we review the role of botanical gardens in biosecurity on a global scale. The role of botanical gardens has changed over time. Initially, they were established as physic gardens (gardens with medicinal plants), and their links with academic institutions led to their crucial role in the accumulation and dissemination of botanical knowledge. During the second half of the 20th century, botanical gardens developed a strong focus on plant conservation, and in recent years there has been a growing acknowledgement of their value in biosecurity research as sentinel sites to identify pest and pathogen risks (novel pest-host associations); for early detection and eradication of pests and pathogens; and for host range studies. We identify eight specific biosecurity hazards associated with botanical gardens and note potential management interventions and the opportunities these provide for improving biosecurity. We highlight the value of botanical gardens for biosecurity and plant health research in general, and the need for strategic thinking, resources, and capacity development to make them models for best practices in plant health

Herbivores, but not other insects, are scarce on alien plants

Understanding how the landscape-scale replacement of indigenous plants with alien plants influences ecosystem structure and functioning is critical in a world characterized by increasing biotic homogenization. An important step in this process is to assess the impact on invertebrate communities. Here we analyse insect species richness and abundance in sweep collections from indigenous and alien (Australasian) woody plant species in South Africa’s Western Cape. We use phylogenetically relevant comparisons and compare one indigenous with three Australasian alien trees within each of Fabaceae: Mimosoideae, Myrtaceae, and Proteaceae: Grevilleoideae. Although some of the alien species analysed had remarkably high abundances of herbivores, even when intentionally introduced biological control agents are discounted, overall, herbivorous insect assemblages from alien plants were slightly less abundant and less diverse compared with those from indigenous plants – in accordance with predictions from the enemy release hypothesis. However, there were no clear differences in other insect feeding guilds.We conclude that insect assemblages from alien plants are generally quite diverse, and significant differences between these and assemblages from indigenous plants are only evident for herbivorous insects.Centre of Excellence for Invasion Biolog

Contain or eradicate? Optimizing the management goal for Australian acacia invasions in the face of uncertainty

Aim To identify whether eradication or containment is expected to be the most cost-effective management goal for an isolated invasive population when knowledge about the current extent is uncertain. Location Global and South Africa. Methods We developed a decision analysis framework to analyse the best management goal for an invasive species population (eradication, containment or take no action) when knowledge about the current extent is uncertain. We used value of information analysis to identify when investment in learning about the extent will improve this decision-making and tested the sensitivity of the conclusions to different parameters (e.g. spread rate, maximum extent, and management efficacy and cost). The model was applied to Acacia paradoxa DC, an Australian shrub with an estimated invasive extent of 310 ha on Table Mountain, South Africa. Results Under the parameters used, attempting eradication is cost-effective for infestations of up to 777 ha. However, if the invasion extent is poorly known, then attempting eradication is only cost-effective for infestations estimated as 296 ha or smaller. The value of learning is greatest (maximum of 8% saving) when infestation extent is poorly known and if it is close to the maximum extent for which attempting eradication is optimal. The optimal management action is most sensitive to the probability that the action succeeds (which depends on the extent), with the discount rate and cost of management also important, but spread rate less so. Over a 20-year time-horizon, attempting to eradicate A. paradoxa from South Africa is predicted to cost on average ZAR 8 million if the extent is known, and if our current estimate is poor, ZAR 33.6 million as opposed to ZAR 32.8 million for attempting containment. Main conclusions Our framework evaluates the cost-effectiveness of attempting eradication or containment of an invasive population that takes uncertainty in population extent into account. We show that incorporating uncertainty in the analysis avoids overly optimistic beliefs about the effectiveness of management enabling better management decisions. For A. paradoxa in South Africa, attempting to eradicate is likely to be cost-effective, particularly if resources are allocated to better understand and improve management efficacy.Centre of Excellence for Invasion Biolog

The importance of pollinators and autonomous self-fertilisation in the early stages of plant invasions: Banksia and Hakea (Proteaceae) as case studies

Reproduction is a crucial stage in the naturalisation of introduced plant species. Here, using breeding system experiments and observations of floral visitors, we investigate whether a lack of pollinators or an inability to autonomously self-fertilise limits naturalisation in five Australian Banksia species and the co-familial Hakea salicifolia in South Africa. Banksia species were heavily utilised by native insects and nectar-feeding birds. Although Banksia produced fruit when pollinators were excluded, pollinators significantly increased seed set in four of the five species. H. salicifolia flowers were visited by 11 insect species; honeybees (Apis mellifera) were the main visitors. Flowers in naturalised H. salicifolia populations received almost four times the number of visits as flowers in non-naturalised populations; the latter showed both pollen limitation (PLI 0.40) and partial self-incompatibility. This should not prevent invasion, since H. salicifolia produces fruits via autonomous selfing in the absence of pollinators. The results suggest a limited role of breeding systems in mediating naturalisation of introduced Proteaceae species. Other factors, such as features of the recipient environments, appear to be more important. Spatial variation in rates of reproduction might, however, explain variation in the extent and rate of naturalisation of different populations

Potential impact and non-target effects of Gallerucida bifasciata (Coleoptera: Chrysomelidae), a candidate biological control agent for Fallopia japonica

A pre-release evaluation of a potential biological control agent is designed to estimate the impact the agent will have on the target in the introduced range, and whether the agent poses an acceptable level of risk to biodiversity. Here, we present an evaluation of the Asian leaf-beetle, Gallerucida bifasciata, a potential biological control agent for Japanese knotweed, Fallopia japonica. First we tested the impact of different larval and adult densities on the plant under laboratory conditions. After six weeks, the biomass of F. japonica was 15% or 28% that of control plants if larvae or adults were added, with levels of damage plateauing quickly with increasing insects densities. High fecundity and larval density dependence means that this agent could substantially and quickly suppress plant growth, although this damage only occurs early in the season, allowing F. japonica time to compensate. Second, following on from general host-specificity trials, we investigated potential non-target effects on the commercially important plant buckwheat, Fagopyrum esculentum, in more depth. The leaf-beetle showed some minor adult feeding on F. esculentum in choice trials, and in no-choice trials the leaf-beetle was able to complete its life cycle and sustain a population on F. esculentum, albeit causing lower levels of damage than on F. japonica. This suggests that if the beetle dispersed to areas where F. japonica is not present, it might colonise F. esculentum. Therefore, despite potentially being an effective agent, that the risk of non-target feeding is unacceptably high

The distribution and status of alien plants in a small South African town

1. The invasion of alien plants into natural ecosystems in South Africa is a substantial conservation concern. The primary reason for the introduction of alien plants has been ornamental horticulture, and urban centres are the main sources of invasions. Small towns have high edge: area ratios which favour the launching of invasions into surrounding areas. There is, however, a shortage of information at the global and local scale on the occurrence, distribution, and status of alien plants in an urban context. 2. We surveyed all alien plants in the small town of Riebeek Kasteel in the Western Cape, South Africa, to gain insights on where to find alien plant species, and to assist with future studies and the management of alien floras in small towns. 3. We surveyed publically accessible land, recording the abundance of all alien plant species every 10m of road. A species accumulation curve was compiled to show the rate at which new species were encountered. This approach was used to test the efficacy of different sampling strategies. 4. Two hundred and ninety eight alien plant taxa were recorded in five land-use types. Half of the alien plant species recorded were naturalised within the town, while a third were invasive in the region (the Berg River catchment). 95% of the taxa, including many invasive species, occurred in gardens or adjoining road-sides, highlighting the invasion risk posed by ornamental horticulture. The most efficient way of collecting data on alien plant distribution for this town would have been to survey roads in the town centre first, rather than urban-edge roads and industrial areas. 5. Synthesis and applications: The gardens of small towns in South Africa harbour a high diversity of alien plants, many of which are already invasive or are potentially invasive. As the alien flora differs markedly between gardens, it is difficult to extrapolate generalised rules of thumb on where to survey. This means that compiling accurate inventories of alien plants in urban areas requires substantial search effort and taxonomic expertise

Elucidating the native sources of an invasive tree species, Acacia pycnantha, reveals unexpected native range diversity and structure

† Background and Aims Understanding the introduction history of invasive plant species is important for their management and identifying effective host-specific biological control agents. However, uncertain taxonomy, intra- and interspecific hybridization, and cryptic speciation may obscure introduction histories, making it difficult to identify native regions to explore for host-specific agents. The overall aim of this study was to identify the native source populations of Acacia pycnantha, a tree native to south-eastern Australia and invasive in South Africa, Western Australia and Portugal. Using a phylogeographical approach also allowed an exploration of the historical processes that have shaped the genetic structure of A. pycnantha in its native range. † Methods Nuclear (nDNA) and plastid DNA sequence data were used in network and tree-building analyses to reconstruct phylogeographical relationships between native and invasive A. pycnantha populations. In addition, mismatch distributions, relative rates and Bayesian analyses were used to infer recent demographic processes and timing of events in Australia that led to population structure and diversification. † Key Results The plastid network indicated that Australian populations of A. pycnantha are geographically structured into two informally recognized lineages, the wetland and dryland forms, whereas the nuclear phylogeny showed little geographical structure between these two forms. Moreover, the dryland form of A. pycnantha showed close genetic similarity to the wetland form based on nDNA sequence data. Hybrid zones may explain these findings, supported here by incongruent phylogenetic placement of some of these taxa between nuclear and plastid genealogies. †Conclusions It is hypothesized that habitat fragmentation due to cycles of aridity inter-dispersed with periods of abundant rainfall during the Pleistocene (approx. 100 kya) probably gave rise to native dryland and wetland forms of A. pycnantha. Although the different lineages were confined to different ecological regions, we also found evidence for intraspecific hybridization in Victoria. The invasive populations in Portugal and South Africa represent wetland forms, whereas some South African populations resemble the Victorian dryland form. The success of the biological control programme for A. pycnantha in South Africa may therefore be attributed to the fact that the gall-forming wasp Trichilogaster signiventris was sourced from South Australian populations, which closely match most of the invasive populations in South Africa

Landscape corridors: Possible dangers?

Ctr Invas Bio

Framework and guidelines for implementing the proposed IUCN Environmental Impact Classification for Alien Taxa (EICAT)

Recently, Blackburn et al. (2014) developed a simple, objective and transparent method for classifying alien taxa in terms of the magnitude of their detrimental environmental impacts in recipient areas. Here, we present a comprehensive framework and guidelines for implementing this method, which we term the Environmental Impact Classification for Alien Taxa, or EICAT. We detail criteria for applying the EICAT scheme in a consistent and comparable fashion, prescribe the supporting information that should be supplied along with classifications, and describe the process for implementing the method. This comment aims to draw the attention of interested parties to the framework and guidelines, and to present them in their entirety in a location where they are freely accessible to any potential users.Peer Reviewe