Brooms (Spartium junceum and Genista monspessulana) in the Western Cape

Many woody legumes in the tribe Genistae (sometimes called "brooms") native to Europe, North Africa and Western Asia, are highly invasive in regions such as Australia, Chile and California. However, they are not recognised as major threats to South Africa, nor have they been widely studied, despite the fact that both Genista monspessulana (Montpellier broom) and Spartium junceum (Spanish broom) have been in South Africa for over a century. Major roads in the Stellenbosch Municipality were surveyed for S. junceum. A population of S. junceum along a main road out of Stellenbosch (Helshoogte Pass) was mapped and measured, and soil cores were taken to quantify the seed bank. The cost and efficacy of clearing the population was assessed. All records of G. monspessulana in South Africa were followed up, the relevant areas were surveyed, populations were mapped and measured, and the seed bank of selected sites were quantified by taking soil cores. S. junceum is widespread along roads and in other disturbed areas in the Stellenbosch Municipality and the City of Cape Town, and can form dense and extensive populations. S. junceum resprouted readily after cutting and treatment with glyphosate herbicide. The seed bank below a mature stand of plants was in excess of 1000 seeds m-2. G. monspessulana is currently limited to only a few sites on Cape Peninsula. It may form dense stands, invading plantations, forests and open areas, but not fynbos vegetation. The seed bank density is comparable to that of other invaded regions and is thus not a limiting factor in the local invasion of this species. Formal risk assessment indicates that G. monspessulana is a high risk species. For this reason and since its distribution is highly localized, the eradication of G. monspessulana from South Africa is recommended.