A Preliminary Assessment of Hedge Plant Species and Their Distribution in Rural Eastern Africa (…)

ABSTRACT

Alien plant species are widely utilised for ornament, agro-forestry, or even for restoration and are more likely to be introduced multiple times and disseminated widely across a landscape. Here we report on the native and alien species used for hedging purposes in rural and peri-urban eastern Africa and undertake a preliminary assessment to determine whether the use of alien species may be contributing to current invasions. We undertook roadside surveys and recorded the presence of all species used as hedges or barriers, excluding vines or climbers. We recorded 110 such plant species (taxa recorded at genus level excluded) but only report on 54 species recorded at five or more localities, and provide a more detailed analysis of the ten most widely used species. Nine of the 54 species grown as hedges were native to eastern Africa and 45 were alien, of which 73% were known to be invasive. Native Euphorbia tirucalli and the alien species Dovyalis afra, Lantana camara, Agave sisalana, Caesalpinia decapetala, Cascabela thevetia, and Tithonia diversifolia were the most widely grown hedge plant species. Lantana camara was recorded as invasive in 38% of grid cells (~55 × 55 km), followed by T. diversifolia (24%), C. decapetala (13%), and A. sisalana (9%). The study supports findings that propagule pressure in the form of alien plants used as hedges may contribute to their spread. However, species such as D. afra and C. thevetia contradict these findings, lending credence to the important role of species traits as drivers of plant invasions. Propagule pressure, species traits, and the characteristics of the recipient environment all contribute to plant invasions; no generalisations can be made.