Association benefits between harvester termites (Trinervitermes trinervoides) and num-num plants (Carissa bispinosa) in a semi-arid savanna setting

Abstract

Few plant-insect interactions have been documented in semi-arid savannas. The reciprocal benefits that termites derive from plants in the ecosystem remain poorly studied. We studied the association between Carissa bispinosa (thorny shrub), and Trinervitermes trinervoides, termite mounds in Nylsvley nature reserve, South Africa and further assessed whether the association changed in its importance in different seasons. We hypothesised that mounds provide nutrients for plants, hence trees establish better on mounds and, in return, plants protect the mounds from predation. We measured plants (height, canopy diameter, leaf appearance and fruiting) and mounds (height, diameter, damage and activity) and also evaluated soil nutrient properties from mounds with active colonies and the adjacent matrix. There was a significant benefit accrued to both organisms from the plant-insect association. Plants on mounds were larger (~3.3 times taller), greener and fruited more in the dry season compared to matrix plants. Mounds under plants were significantly less damaged compared to exposed mounds. Sodium, magnesium, potassium, sulphur and copper were enriched in mounds relative to the matrix. The nutrient further validates the high productivity of plants on mounds. Although the benefits of trees from termite mounds is well documented, our findings show that trees established on mounds can protect the mounds from damage and excessive erosion.