Nationally there are 9000 introduced species, and 198 of those cover 10% of the land. In Gauteng 43 species are listed as priority invasive alien plants, 29 in grasslands and 23 in savanna biomes.
Though the density of the aliens in this area is low (around 2%) the threat posed by the invasive behaviour of these species requires constant vigilance and action.
In the period October 2013 to February 2014 the region spent more than R110 000 on controlling invaders, creating at least 355 man-days of work. These values do not include the private efforts of landowners, and reflect only the project work undertaken by the Reserve in the southern area (grassland). The cost and effort needed decreased slightly in 2015 as previsouy treated areas carried fewer invaders.
MOST AGGRESSIVELY INVASIVE
The project targeted the invasive aliens identified by City of Tshwane as most problematic in the region, and further prioritised for this local area as:
- Bugweed (localised; identified as emerging invader in the area)
- Mexican poppy (Argemone ochroleuca)
Additionally, Verbena brasiliensis is identified as locally invasive. This plant, like the pompom originates in South America. The project initiated test to determine the effectiveness of various approaches – herbicide, manual removal and cutting down.
Other problem plants not yet treated include –
- Queen of the Night (localised)
- Prickly pear (widespread but scattered)
- Bankrotbos (scattered but extensive stands)
- Giant reed (wetlands)
- Poplar (wetlands and riverine areas)
Problems plants largely confined to “private” areas (gardens) and perimeters include:
- Yellow bells
- Weeds which are prevalent include:
- Khakibos (Tagetes)
- Wild purslane (Portulaca oleracea)
- Bachelors Button (Gomphrena celosioides)