Contrasting effects of herbivory on plant size and reproductive performance in two populations of the Critically Endangered species, Euphorbia clivicola R.A. Dyer

Euphorbia clivicola R.A. Dyer is a Critically Endangered Northern Province endemic confined to two populations that have declined drastically over the last decade. One population is protected within a Nature Reserve, while th e other occurs in a peri-urban area. In order to determine the causes of th e population declines, herbivory damage to plants in both the protected and urban populations was quantified and the effects of herbivory on various a spects of the population biology were assessed. Mountain reedbuck are belie ved to have been responsible for the herbivory in the protected population. Herbivory on the above-ground branches probably caused the small sizes of protected plants. These were on average less than half the size of urban pl ants. Herbivory caused a reduction in the number of flowers and fruit produ ced per protected plant and may have prevented the maturation of flowers in to fruit, thereby reducing the total regenerative output of the population. An eight-year absence of fire had resulted in the build-up of a dense mori bund grass layer. The selection of E. clivicola plants by mountain reedbuck may therefore have been due to their relatively high nutritional value and accessibility in the thick moribund grass layer. Fencing off the populatio n to prevent entry of herbivores, and implementing a more suitable fire man agement programme is recommended, as is the adoption of a new IUCN status f or the species of Critically Endangered (CR A1).