Variation in savanna vegetation on termite mounds in north-eastern Namibia

In savanna, termite mounds support more diverse vegetation than off-mound areas, but little is known of the patterns in plant assemblages on mounds. To explain vegetation differentiation between (1) component structures of termite mounds (conical centre vs. pediment), (2) active and inactive mounds (termites present vs. termites absent), and (3) sites on and off mounds (on mounds vs. surrounding savanna), species composition, richness and abundances of woody plants were recorded on 70 mounds and in 13 savanna plots (each 20 x 20 m) in north-eastern Namibia, focusing on soil hardness, mound status (active or not) and mound micro-topography as explanatory factors. Woody plants were absent from 33% of active mounds (54% of active cones) but were absent from only 5% of inactive mounds. Species richness and abundance per mound (mean +/- SD) were lower on active mounds with (2.0 +/- 1.8 and 4.6 +/- 6.6, respectively) and without pediments (0.6 +/- 0.6 and 0.9 +/- 1.1, respectively) than on inactive mounds (4.4 +/- 2.7, 19.4 +/- 18.8, respectively). Despite the lower woody plant cover, some characteristic species, such as Salvadora persica, occurred preferentially on active mounds; this species occurred on 42% of active mounds. Mean soil hardness (+/- SD) was higher on conical parts of active mounds (4300 +/- 2620 kPa) than on adjacent pediments (583 +/- 328 kPa) and inactive mounds (725 +/- 619 kPa). This study suggested that mound status, mound micro-topography, and soil hardness promote variability in the vegetation on mounds.