Northern Temperate Weeds

Programme Manager: Dr Grant Martin

The high elevation grasslands of South Africa are under threat from invasive alien plants. These plants compromise the integrity of this valuable ecosystem, reduce the amount of available water, and have an direct impact of the livelihoods of those living in these areas.  For example, Robinia pseudoacacia (Black locust), a rapidly spreading tree in these high elevation areas of South Africa, is causing extensive negative ecological and economic effects in four other major ways including: (i) impacts on native biodiversity - the noticeable recent and rapid spread of the tree means its competing with indigenous species for light and space, particularly in the fragile mountain grasslands; (ii) competition of the tree’s large fragrant blossoms with indigenous plants as well as cash crops such as fruit trees for essential pollinating bees; (iii) the ability of the tree to fix nitrogen into the soil which  causes long-term damage to the soil and the plants growing in that soil; and (iv) the poisonous proteins in the tree which has the potential to reduce the gross margin in the livestock sector by approximately R130 million to R961 million, dependent on the probability of invasion.

There has been limited co-ordinated research conducted on these plants invading high elevation regions of South Africa or on how to manage them. Some attempts of management have been made but with little to no long-term positive results. The High Elevation Weeds Programme aims to determine the distribution and densities of these species in the high elevation areas. It also aims to investigate the ecological and economic impacts these species are having. Once these have been determined, the species can be managed using species appropriate practices. Finally, and most importantly, the High Elevation Weeds Programme aims to investigate and implement biological control options for these species. Biological control offers the most cost effective and sustainable management options for a number of the species and will help reduce the spread and impacts of these species. Biological control has been repeatedly shown to be the most cost effective, sustainable and environmentally  friendly management option for invasive alien plants in South Africa and globally.


   Highland grasslands invaded by high elevation weeds