Mound building termites contribute to savanna vegetation heterogeneity

Plant Ecol (2009) 202:3140 DOI 10.1007/s11258-009-9575-6

Mound building termites contribute to savanna vegetation heterogeneity

Stein R. Moe Ragnhild Mobk Anne Kjersti Narmo

Received: 28 June 2007 / Accepted: 13 January 2009 / Published online: 11 February 2009 Springer Science+Business Media B.V. 2009

Abstract With biomass densities comparable to large ungulates and megaherbivores, termites play a key functional role in many tropical savanna ecosystems. This study focuses on vegetated termite mounds (termitaria) constructed by the Termitidae species Macrotermes herus. We studied how resource rich termitaria affect graminoid herbs (Poaceae and Cyperaceae), forbs and woody species composition and diversity. The density of termitaria explained 89% of the variation in dense thickets in the area. Fire tolerant Acacia species dominated the open savanna while re sensitive species like Grewia spp. and the succulent Euphorbia candelabrum were restricted to termite mounds. Termitaria plots had four times the mean number of woody species and supported three times as many forb species as the adjacent savanna. For woody species, both the ShannonWiener index and the Shannon evenness index were higher on

temitaria than on the savanna. There were no differences for graminoid herbs, except for the Shannon evenness index which was higher on termitaria. Our results indicate that graminoid herb richness peaks at lower productivity levels than trees and forbs in savanna ecosystems, as also recently found in temperate areas.

Keywords Biodiversity Macrotermes herus

Species richness and productivity

Termitaria Termitidae Uganda

Introduction

Termites constitute an important group of the soil fauna, accounting for 4060% of the total soil macrofauna biomass in many tropical ecosystems (Wood and Sands 1978). Termite standing biomass in African savannas has been estimated to be between 70 and 110 kg ha-1 (Wood and Sands 1978; Ferrar 1982; Wood et al. 1982). Thus, termite biomass are comparable to the biomass of ungulates (1080 kg ha-1, Bell

1982) as well as to savanna megaherbivores (commonly \110 kg ha-1, Owen-Smith 1988), indicating that termites play a major ecological role in the functioning of savannas (Dangereld et al. 1998).

While savanna soils generally have a low reserve of weatherable minerals, especially calcium, magnesium and phosphorus (Jones and Wild 1975), termite

S. R. Moe (&) R. Mobk A. K. Narmo

Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences,...