The invasion potential of selected Berberis species in South Africa

[摘要] English: Invasive alien species are a serious threat to global biodiversity. They have considerablenegative effects on the economy and the environment, using up valuable natural andmonetary resources. Every year new species are introduced into South Africa and with thatthe list of potentially new invasive species grows. These emergent invasive species shouldreceive a very high priority in terms of assessing their invasion potential and possibleimpacts.No formal study has been conducted regarding the invasion potential of any species in thegenus Berberis within South Africa, even though it has been a popular horticultural genus formany decades and is known to have invasive species. The current study focussed on four keypoints, namely: 1) the elucidation of all Berberis spp. that have been historically and arecurrently cultivated within South Africa, 2) assessing the size, extent and reproductive age ofany naturalized/invasive Berberis populations, 3) determining potential habitable areas ofnaturalized/invasive Berberis species and 4) determining whether any Berberis speciesshould be officially listed under the National EnvironmentalManagement Biodiversity Act.A total of 30 Berberis species/cultivars/hybrids were found to have been cultivated in SouthAfrica in the past and present (11 species, 11 cultivars, 8 hybrids). Three of these species arewidespread invasives in other parts of the world, namely B. darwinii, B. thunbergii andB. vulgaris. The KwaZulu-Natal Province has the highest diversity ofspecies/cultivars/hybrids stocked by nurseries/private/wholesale growers, while B. thunbergiiand B. thunbergii var. atropurpurea were found to be the most widely stocked species.Two invasive Berberis populations were found. The first population was from the speciesBerberis aristata and occurs in the Woodbush State Forest (Limpopo Province; 23.8192°S29.9608°E). This population has an extent of occurrence of 115 ha and an area of occupancyof 1.58 ha. A total of 5 725 individuals were geotagged and the population was found to behighly reproductively active, with more than 40% of the population able to flower and setseed. The second population was from the species B. julianae and occurs at the Glen Reenenrest camp in the Golden Gate Highlands National Park (Free State Province; 28.5049°S28.6187°E). This population has an extent of occurrence of 0.42 ha and an area of occupancyof 0.02 ha. It was also found to be highly reproductively active with 38% of the populationable to flower and set seed. A few minor occurrences of this species were found at the Alma Ranger Station, also in the Golden Gate Highlands National Park. A total of 473 individualsof this species were geotagged.Bioclimatic modelling revealed that substantial parts of South Africa are suitable for bothBerberis aristata and B. julianae. The former species was found to be more suitable to themountainous regions while the latter has a higher suitability to the central parts of thecountry. The situation regarding future climate scenarios (2020) was the same, although arange contraction was found for both species. Weed risk assessments revealed that bothB. aristata and B. julianae would have failed a pre-border screening (score of 27 and 22,respectively, according to the Australian Weed Risk Assessment system), indicating that bothspecies pose an environmental risk. Herbicide trial clearing revealed that three chemicals canbe used for the successful control of Berberis spp., namely metsulfuron-methyl, triclopyr andglyphosate.The final outcome of the study is the following recommendations: Berberis aristata shouldbe listed as a category 1a invasive species in the National Environmental ManagementBiodiversity Act, while B. julianae should be listed as category 1b in non-urban areas and notlisted in urban areas.

[发布机构] University of the Free State