Corresponding author: John R. U. Wilson (
Academic editor: R. Hufbauer
Understanding the status and extent of spread of alien plants is crucial for effective management. We explore this issue using Australian
Magona N, Richardson DM, Le Roux JJ, Kritzinger-Klopper S, Wilson JRU (2018) Even well-studied groups of alien species might be poorly inventoried: Australian
Every country needs up-to-date lists of introduced species to ensure that management actions are directed appropriately to deal with taxa at all stages of the introduction-naturalisation-invasion continuum (
Australian
Wattles have been introduced to many parts of the world for many purposes (
Throughout this paper, we use the terms “Australian
Knowledge of the introduction history of these species is crucial for understanding and predicting their performance (
South Africa has a long history of wattle introductions. Several species (notably
The history of wattle species introduced and planted for forestry purposes in South Africa was reviewed by
Despite several decades of intensive management of invasive wattles in South Africa (
The presence of Australian
Herbarium record | Molecular confirmation | Literature record of presence | Current status | Locations recorded | |
---|---|---|---|---|---|
yes* | no | yesb | Not known | Cape Peninsula | |
yes* | no | no | Not known | University of Pretoria | |
yes* | yes | yesa,b | B2 | Paarl, Uitenhage, Knysna, Stutterheim, Robertson, Lichtenburg, Malmesbury | |
yes | tested, but likely to be a different species | yesb,c | C3 | Paarl, Pretoria, Johannesburg | |
yes* | no | yesb | Not known | Johannesburg | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesa | Not known | Malmesbury | |
yes* | probable | yesa,b | B2 | Zoutpansberg, Lichtenburg, Paarl, Malmesbury | |
yes* | no | yesb | Not known | Johannesburg | |
yes* | no | yesb | Not known | Pretoria | |
no | no | yesb | Not known | Johannesburg | |
no | no | yesa,b | Not known | Malmesbury | |
yes | yes | yesb,c | E | Multiple | |
yes* | no | yesb | Not known | Cape Peninsula, Pretoria, Johannesburg | |
yes* | no | yesb | Not known | Pretoria | |
no | no | yesa | Not known | Malmesbury | |
yes* | no | yesb | Not known | Johannesburg | |
yes* | no | yesa,b | Not known | Pretoria, Malmesbury | |
1 |
no | no | yesb | Not known | Not recorded (seed import record only) |
no | no | yesa | Not known | Malmesbury | |
yes* | no | yesb | Not known | Pretoria | |
no | probable | yesa | B2 | Malmesbury | |
no | no | yesa,b | Not known | Malmesbury | |
yes* | no | yesb | Not known | Johannesburg, Pretoria | |
yes* | no | no | Not known | University of Pretoria | |
yes* | no | no | Not known | Pretoria | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | no | yesa | Not known | Malmesbury | |
yes | no | no | B2 | Newlands forest | |
yes | yes | yesb,c | C3 | Pretoria, Johannesburg, Middelburg, Grahamstown | |
yes | yes | yesb,c | E | Multiple | |
yes | yes | yesb,c | E | Multiple | |
yes* | no | yesb | Not known | Pretoria | |
yes* | no | yesb | Not known | Albany | |
yes | yes | yesb,c | E | Multiple | |
no | no | yesa | Not known | Malmesbury | |
2 |
no | no | yesb | Not known | Not recorded (seed import record only) |
yes* | no | no | Not known | Port Elizabeth | |
yes* | no | no | Not known | Cape Peninsula | |
yes* | no | no | Not known | University of Pretoria | |
no | no | yesa | Not known | Malmesbury | |
3 |
yes | yes | yesb,c,f | E | Multiple |
yes* | no | no | Not known | Pretoria | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
yes* | no | yesb | Not known | Johannesburg | |
no | no | yesb | Not known | Cape Town | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
yes | tested, but likely to be a different species | yesb,c | D2 | Grahamstown | |
yes* | no | no | Not known | Johannesburg | |
yes* | no | no | Not known | Pretoria, Johannesburg | |
yes* | tested, but likely to be a different species | yesb | C1 | Johannesburg; Pretoria; Bloemfontein | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | yes | no | B2 | Malmesbury, Johannesburg Botanic Gardens | |
yes* | no | yesa | Not known | Malmesbury | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesa,b | Not known | Malmesbury | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
yes* | no | no | Not known | Albany | |
yes | yes | yesd,f | E | Stellenbosch, Tokai, Wolseley | |
yes* | no | yesb | Not known | Pretoria | |
yes* | no | no | Not known | Johannesburg | |
yes* | no | yesb | Not known | Pretoria | |
no | no | yesa | Not known | Malmesbury | |
yes* | no | yesa,b | Not known | Malmesbury, Johannesburg | |
yes* | probable | yesb | B2 | multiple | |
yes* | no | no | Not known | Lydenburg dist. | |
no | no | yesb | Not known | The Cape | |
yes* | no | no | Not known | Addo Elephant National Park | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | no | yesa | Not known | Malmesbury | |
yes* | no | yesb | Not known | Pretoria | |
yes* | no | no | Not known | Pretoria | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
yes* | no | no | Not known | Johannesburg | |
yes* | no | yesb | Not known | Pretoria | |
yes | yes | yesb,c | E | multiple | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesb | Not known | Cape Peninsula | |
no | no | yesc | Not known | None noted | |
no | no | yesb | Not known | Malmesbury | |
yes | yes | yesb,c | E | multiple | |
yes | yes | yesb,c | E | multiple | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | yes | yesa | B2 | Malmesbury | |
yes* | no | yesb | Not known | Johannesburg, Pretoria | |
yes* | yes | yesa,b | B2 | Malmesbury | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
4 |
no | no | yesb | Not known | Cape Town |
no | no | yesb | Not known | Not recorded (seed import record only) | |
yes* | no | no | Not known | Pretoria | |
yes | yes | yesb,c | D2 | Devils Peak, Table Mountain, Cape Town | |
yes* | no | yesb,c | C1 | Middelburg, Excelsior district Delareyville, Lichtenburg, Bloemhof, Kroonstad dist.,Beaufort West | |
yes* | no | yesb | Not known | Cape Peninsula | |
yes* | no | no | C3 | Tokai | |
no | no | yesa | Not known | Malmesbury | |
yes | yes | yesb,c | E | multiple | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
yes* | no | yesb | Not known | Pretoria | |
yes* | no | yesb | Not known | Pietermaritzburg, Zoutpansberg, Centurion | |
5 |
yes* | 5no | yesb,c | C3 | Pretoria, Stellenbosch, Johannesburg, Tokai |
no | no | yesa | Not known | Malmesbury | |
yes* | no | no | Not known | Cape Peninsula | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
yes | no | yesb,c | E | multiple | |
yes* | no | yesb | Not known | Johannesburg | |
no | yes | no | B2 | Malmesbury | |
yes* | no | no | Not known | Pretoria | |
no | no | yesb | Not known | Middelburg | |
yes* | no | no | Not known | Pretoria | |
yes* | probable | yesa,b | B2 | Malmesbury, Johannesburg, Gwelo | |
yes | yes | yesb,c | E | Multiple | |
yes* | no | yesb | Not known | Stellenbosch | |
yes* | no | no | Not known | Paarl | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | no | yesb | Not known | Johannesburg | |
yes* | no | no | Not known | Suurberg Nature Reserve | |
no | no | yesa,b | Not known | Malmesbury | |
yes | no | yese | E | Knysna | |
no | no | yesb | Not known | Cape Town | |
yes* | no | no | Not known | Cape Peninsula | |
no | no | yesb | Not known | Not recorded (seed import record only) | |
no | no | yesb | Not known | Cape Town | |
no | no | yesa | Not known | Malmesbury | |
no | no | yesb | C1 | PretoriaCape Peninsula, Transkei | |
yes* | no | no | Not known | Pretoria | |
yes* | no | yesb | Not known | Pretoria | |
yes* | no | no | Not known | Cape Peninsula | |
yes* | no | yesb | Not known | Cape Town, Pretoria | |
yes* | no | yesb | Not known | Pretoria | |
no | no | yesb | Not known | Cape Town | |
no | no | yesa,b | Not known | Malmesbury, and as seed | |
yes | yes | yesb,c | C3 | Pretoria, Grahamstown, Newlands Forest, Cape Town | |
yes* | no | no | Not known | Addo Elephant National Park | |
no | no | yesa | Not known | Malmesbury |
Notes on
We reviewed formal literature sources (e.g. Poynton et al. 2009; Street 1962), student theses, and unpublished records documenting Australian acacias in South Africa. All relevant herbaria, museums, and botanical gardens in South Africa with specimens or collections of Australian
During herbaria visits, we followed a standard protocol for dealing with records of Australian acacias (Fig.
The protocol used in this paper for dealing with records of Australian
After compiling the list of introduction sites for wattles in South Africa, we conducted field surveys to confirm whether species were still present. We also specifically looked for locations where many species had been cultivated (e.g. arboreta and forestry trial plantations) to determine whether other taxa that have not been formally recorded were present. In cases where a location was provided but precise co-ordinates were not given, we consulted relevant officials (e.g. local conservation officers).
When comparing different lists, it was also possible to determine the types of errors (e.g. human error and species identification) in the lists (e.g.
Many
The observed populations of
We found evidence that 141 Australian
Of these 141 species, we could confirm the presence of only 33 species (Table
Examples of Australian
The estimate of 141 species is approximately double that of the previous estimate of 70 species (
We found one error and five misspellings on herbarium labels, these errors being perpetuated in subsequent literature sources. There were an additional three misspellings in literature sources (Table
Methodology followed in determining errors in lists of
Errors | Explanatory questions | Method | Results |
---|---|---|---|
Human error | How many herbarium specimens had been misidentified? | All herbarium specimens of |
Only one species was found to have been clearly mis-identified: |
How many entries had incorrect spellings? | A search was conducted of literature sources and online databases to determine the total number of |
Five species names on herbarium specimens were misspelled: |
|
Which errors have been perpetuated? | The identified errors were assessed for presence in multiple data sources to determine whether an error has been repeated. The primary source of the identified errors was also assessed by conducting a literature search using the specific error as the search term. | Both the misidentification of |
|
Resolution of data and scaling of “alien range” | For how many records was the resolution of data too coarse to be useful? | Field surveys were conducted on reported population localities from SAPIA, herbaria and literature. The number of records for which the resolution of data (e.g. quarter-degree grid cell, town or region) was too coarse to allow individuals to be located was recorded. The data from SAPIA, herbaria and literature was compared with the survey results to provide a fine resolution locality. | Using historical data was not accurate as the resolution was too coarse (recorded at the scale of quarter-degree cells). Using such data was unreliable for locating and assessing the extent of species spread. We mapped the species at finer scales to avoid such issues. |
Data and knowledge not documented | How many records were not documented? | New locality records were followed up in field surveys to establish the current status of species localities. The number of records that are only the result of undocumented expert knowledge and surveys were counted. Furthermore, some species identification fliers were distributed in surveyed areas to solicit new species sightings. Any new sightings resulting from the public sightings were counted. | Two localities found. 18 putative |
Only 23 species identities were confirmed either in this study or previously using a molecular approach (Table
Notably, when this manuscript was under review, it was pointed out to us by Martin O’Leary, State Herbarium of South Australia, that
Before this study, 70 Australian
There were four major reasons for the discrepancy between the list of species recorded as having been introduced to South Africa and the list of species confirmed to be still present in the country. First, during the survey, we came across an old experimental forestry trial set up to identify species suitable for dry-land agroforestry (Damara Farm in the Western Cape; see Suppl. material
Second, specimens of several species are present in the National Herbarium in Pretoria but had not been included in previous lists because the herbarium records had not yet been digitised.
Third, species might no longer be present at their original sites of introduction. Many of the records (particular herbarium records that have not yet been digitised) were from historical forestry plantings. When we followed up, we found that many of these planting were no longer present — they had been transformed for infrastructure development, agriculture, or other forms of land use. Most cases, where listed species are no longer present, were within the municipal areas of the cities of Johannesburg and Pretoria that have been converted to stock farms. For example, all available records of
Fourth, species might not have survived at sites of initial introduction due to unfavourable climatic conditions or biotic pressures;
Finally, it is possible that, despite our best efforts, our searches were inadequate to (re)locate some species. We suspect this is unlikely to be a major cause, as Australian
Notably, however, there may be other localities like Damara Farm where multiple species have been cultivated and potentially still exist.
Whatever the reasons for discrepancies in past estimates of wattle introductions in South Africa, it is clear that there is a high invasion debt for Australian
One way of reducing this invasion debt is through proactive management approaches, e.g. the detection, identification, assessment, and control of naturalised populations before they are widespread invaders. Some of the naturalised populations of Australian acacias in South Africa occur only at a few sites and so eradication is possible, but for some species,
Some of the taxa might also have been prevented from spreading due to the impact of biological control agents released to target the widespread Australian
Unlike other taxonomic groups of alien plants, where there are many misidentified herbarium records (e.g.
Finally, the misapplication of the name
While the work presented here has not definitely resolved all of the issues around the identity of Australian
This work was supported by the South African National Department of Environment Affairs through funding of the South African National Biodiversity Institute’s Invasive Species Programme and the DST-NRF Centre of Excellence for Invasion Biology. DMR acknowledges additional support from the National Research Foundation (grant 85417). We thank Sthembiso Gumede, Owethu Nomnganga, Virgil Jacobs, Jan-Hendrik Keet, Ulrike Irlich, George Sekonya, Kanyisa Jama, and various Working for Water teams for assistance in the field; Fiona Impson and Philip Weyl for alerting us about naturalised populations; the Armstrong family for allowing us access to Damara Farm; and Carien Kleinjan, Fiona Impson, Giuseppe Brundu, and Martin O’Leary for valuable comments on drafts of the manuscript and for clarifying the identification of
A categorisation scheme for populations according to the Unified Framework for Biological Invasions (adapted from
|
|
A | Not transported beyond limits of native range |
B1 | Individuals transported beyond limits of the native range, and held in captivity or quarantine (i.e. individuals provided with conditions suitable for them, but explicit measures of containment are in place) |
B2 | Individuals transported beyond limits of native range, and in cultivation (i.e. individuals provided with conditions suitable for them, but explicit measures to prevent dispersal are limited at best) |
B3 | Individuals transported beyond limits of the native range, and directly released into novel environment |
C0 | Individuals released outside of captivity or cultivation in location where introduced, but incapable of surviving for a significant period |
C1 | Individuals surviving outside of captivity or cultivation in location where introduced, no reproduction |
C2 | Individuals surviving outside of captivity or cultivation at location where introduced. Reproduction occurring, but population is not self-sustaining |
C3 | Individuals surviving outside of captivity or cultivation in location where introduced. Reproduction occurring. Population is self-sustaining |
D1 | Self-sustaining population outside of captivity or cultivation, with individuals surviving a significant distance from the original point of introduction |
D2 | Self-sustaining population outside of captivity or cultivation, with individuals surviving and reproducing a significant distance from the original point of introduction |
E | Fully invasive species, with individual dispersing, surviving and reproducing at multiple sites across a greater or lesser spectrum of habitats and extent of occurrence |
Species status reports for naturalised Australian
Abundance: <50 plants (2014); Relatively small seedbanks.
Molecular and morphological assessments for the identity of Australian
Data type: Table linking linking samples to Genbank accession numbers.
South African herbarium accession numbers for specimens that were not available online at
Data type: Table of species and corresponding herbarium numbers.
Records of naturalised populations of wattles as per the Southern African Plant Invaders Atlas (date accessed: January 2017)
Data type: Table of species occurrences.
Details of the forestry trial at Damara Farm, South Africa, that included many species of wattles not previously recorded from South Africa
Data type: Site description.