Abstract
We present the first detailed survey of a population of Acacia paradoxa DC. (syn. Acacia armata R.Br.), Kangaroo Thorn, in South Africa. The species is listed under the Conservation of Agricultural Resources Act as a category 1 invasive plant and, until 2008, was being managed as part of Working for Water's general alien clearing operations. Acacia paradoxa is currently restricted to a small population (~ 11,350 plants over ~ 295 ha) on the northern slopes of Devil's Peak, Table Mountain National Park in the Western Cape. Its distribution is highly clumped, and at a local scale it has formed thick stands of up to 20 plants m − 2 . Using a bioclimatic model we predict that it has a large potential distribution in South Africa, especially along the southern coast. We confirmed the categorisation of A. paradoxa as a potential landscape transformer that requires immediate control by conducting a formal risk assessment using the Australian Weed Risk Assessment system. However, the population appears to be spreading slowly, and, while there is a significant seed-bank in some places (~ 1000 seeds m − 2 ), this is largely restricted to below the canopy of existing plants. Therefore, the population has not and likely will not rapidly spread in area, and so containment is feasible. Dedicated and thorough annual follow ups are required because plants can produce seeds when they are 1 year old and standard clearing operations have missed flowering plants.
Highlights
Australian Acacia species were introduced to South Africa during the 19th and 20th centuries for a variety of reasons (Shaughnessy, 1980; Henderson, 2006)
In this paper we provide the first detailed assessment of the population of Acacia paradoxa growing in Table Mountain National Park (Fig. 1a)
A. paradoxa is commonly used as hedge species in Australia, and, while it is available in the nursery trade in Australia, we have no evidence that it was ever traded within South Africa
Summary
Australian Acacia species were introduced to South Africa during the 19th and 20th centuries for a variety of reasons (Shaughnessy, 1980; Henderson, 2006). Many of these species have become highly invasive, to the extent that some are among the most widespread invasive plant species in South Africa (Wilson et al, 2007). There are several Australian acacias that have been introduced to South Africa that have either not established or have only formed small populations (Shaughnessy, 1980). Weed risk assessment protocols (e.g. Pheloung et al, 1999) are useful tools in this regard, as they help to organise and summarise available data (Gordon et al, 2008)
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