The biology, ecology and conservation of euphorbia clivicola in the Limpopo Province, South Africa

Abstract

The need to conduct a detailed biological and ecological study on Euphorbia clivicola was sparked by the drastic decline in the sizes of the Percy Fyfe Nature Reserve (Mokopane) and Radar Hill (Polokwane) populations, coupled with the discovery of two new populations; one in Dikgale and another in Makgeng village. The two newly (2012) discovered populations lacked scientific data necessary to develop an adaptive management plan. This study aimed to conduct a detailed biological and ecological assessment, in order to develop an informed management and monitoring plan for the four populations of E. clivicola. This study entailed a demographic investigation of all populations and an inter-population genetic diversity comparison so as to establish the relationship between all populations of E. clivicola. The abiotic and biotic interactions of E. clivicola were examined to determine the intrinsic and extrinsic factors causing the decline in the Percy Fyfe Nature Reserve and Radar Hill population sizes. Fire as one of the abiotic factors was observed to be beneficial to E. clivicola because it weakened their number one competitor, i.e., graminoids in populations with low or no grazing pressure. Fire also destroys refuge for rodents, which feed on the flowers of E. clivicola, as such, affecting reproduction success. An exponential growth was observed to be directly proportional to fire damage. The populations of Percy Fyfe Nature Reserve, Radar Hill, and Dikgale were found to be genetically compatible. The genetic homogeneity makes intra-population restocking possible. Anthropogenic induced fragmentation proved to be detrimental to Radar Hill and Makgeng populations of E. clivicola, by reducing the Area of Occupancy of the species and hindering seed dispersal. Propagules of E. clivicola are dispersed down a gradient by surface water run-off, and therefore; slope angle and aspect directs the expansion of the E. clivicola populations. Euphorbia clivicola plants (71%) were observed to prefer north-facing gentle slopes of < 11°. Grass cover of > 60% negatively affects the reproduction success of E. clivicola by obstructing pollinators’ access to flowers. DNA data from this study indicate that the Percy Fyfe Nature Reserve population can be re-stocked with genetically attuned individuals from Radar Hill and Dikgale populations of E. clivicola at suitable habitats to prevent extinction. The exclusion of herbivores from the Radar Hill population triggered a negative domino effect (increased grass cover, refuge for herbivores, and amplified the density between individuals), as such alternative management actions need to be adopted for the population of Percy Fyfe Nature Reserve. In order to halt the dramatic decline at Radar Hill population, an adaptive management plan that possesses three main focal points, which are; objectives, management, and monitoring is proposed. The population of Percy Fyfe Nature Reserve is so drastically reduced that it requires a more intensive approach; hence, a recovery plan is proposed. This plan takes into account the genetic similarity of three populations (Percy Fyfe Nature Reserve, Radar Hill and Dikgale), and model management and monitoring objectives to be more or less similar, so as to save time and resources. The three common components of monitoring the above mentioned populations are population size, canopy size, and density.