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 <em>Genista monspessulana</em> (Montpellier broom) and <em>Spartium junceum</em> (Spanish broom) have been in South Africa for over a century. Major roads in the Stellenbosch Municipality were surveyed for <em>S. junceum</em>. A population of <em>S. junceum</em> 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 <em>G. monspessulana</em> 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. <em>S. junceum</em> 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. <em>S. junceum</em> 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. <em>G. monspessulana</em> 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 <em>G. monspessulana</em> is a high risk species. For this reason and since its distribution is highly localized, the eradication of <em>G. monspessulana</em> from South Africa is recommended.原产于欧洲、北非和西亚的染料木族（Genistae，俗称‘扫帚树’）中的诸多木本豆科植物，在澳大利亚、智利和加利福尼亚等地区已成为极具危害性的入侵物种。然而，尽管地中海锦鸡儿（Genista monspessulana，蒙彼利埃扫帚）和鹰爪豆（Spartium junceum，西班牙扫帚）在南非已归化超过百年，但这类植物并未被认定为南非的主要入侵威胁，相关研究也较为匮乏。本研究对斯泰伦博斯自治市的主要道路开展了鹰爪豆（S. junceum）的野外调查：对斯泰伦博斯城外（赫尔朔赫特山口）沿主干道分布的鹰爪豆种群进行了绘图与种群规模测算，并采集土壤柱样以量化其种子库；同时评估了该种群的清除成本与防治效果。针对南非境内所有已记录的地中海锦鸡儿（G. monspessulana）分布点，本研究逐一跟进核查，对其潜在分布区域开展野外调查，完成种群绘图与规模测算，并通过采集土壤柱样量化了部分样点的种子库规模。鹰爪豆在斯泰伦博斯自治市与开普敦市的道路沿线及其他受干扰区域广泛分布，可形成密集且连片的种群。经机械砍伐与草甘膦除草剂处理后，鹰爪豆极易萌生新枝。成熟种群下方的土壤种子库密度可达1000粒/平方米以上。目前地中海锦鸡儿仅分布在开普半岛的少数几个区域：该物种可形成密集种群，入侵人工林、原生林及开阔地带，但尚未侵染凡波斯（fynbos）植被群落。其土壤种子库密度与其他入侵区域的同类数据相当，因此种子库并非该物种在当地入侵扩散的限制因子。正式的入侵风险评估结果显示，地中海锦鸡儿属于高风险入侵物种。鉴于上述情况，加之该物种的分布范围高度局限，因此建议在南非全境彻底清除地中海锦鸡儿。