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Short Communication
In savanna ecosystems, mound-building termites are recognized as ecosystem engineers (Dangerfield et al. 1998) and often promote the development of diverse woody plant assemblages through mound building and foraging activities (Eldridge et al. 2001, Sileshi et al. 2010). The structural features of termite mounds provide refuges for plants; for example, their elevated topographies may provide safe havens from seasonal flooding (McCarthy et al. 1998) and wildfires (Groen et al. 2008).
These positive effects on savanna vegetation have been identified in comparisons between sites on and off termite mounds. Within-mound variation in vegetation, however, has received little attention even though mound soil hardness, status (termites active or not) and micro-topography promote variability in the configuration of plant assemblages growing on mounds. Glover et al. (1964) and Yamashina (2010) suggested that active termite constructions may suppress plant establishment by developing soils that are hard and impervious. Arshad (1982) and Pomeroy (1983) showed that the central portions of mounds are bare of vegetation and that grass productivity is elevated on outwash pediments and surrounding areas.
This study tested two hypotheses: (1) species composition, richness and abundances of woody plants vary within and between mounds, between active and inactive mounds, and between sites on and off mounds; and (2) if vegetation is differentiated in this manner, then soil hardness, mound status (active or not) and mound micro-topography (conical portions or pediments) are likely determinants of vegetation structure. To explore these hypotheses, woody plants' species composition and abundances, and soil hardness were examined at different sites within mounds, on active and inactive mounds, and at sites on and off mounds in a savanna landscape. Testing these hypotheses will hopefully elucidate the functional ecology of termite mounds in savanna ecosystems.
Field research was conducted in the Muyako community forest (17.88°S, 24.4°E, c. 1000 m asl) in the Caprivi Region of Namibia. The research periods were October-December 2009, and June, July and December 2010. Annual precipitation (mean ± SD) for the period 2004-2007 was 733.5 ± 64.5 mm (Namibia Meteorological Service); most precipitation fell between October and March. Average temperature was 20-22 °C. The local vegetation was classified as mopane (Colophospermum mopane) woodland by Werger & Coetzee (1978).
In total, 70...