Oecologia (2011) 165:1095–1107 1103 Fig. 2 Relative Competition Index (RCI) values of Colophospermum mopane seedling leaf number, stem diameter, seedling height and biomass (above ground) in relation to inorganic soil N concentration (a–d) and extractable soil P concentration (e–h). RCI values greater than 0 indicate that single C. mopane seedlings were relatively availability by accelerating nutrient cycling rates and by importing nutrients from surrounding areas into kraals, which attracted more herbivores (Fig. 3). The high soil nutrient availability, in turn, resulted in constrained woody recruitment, hence structurally open patches preferred by herbivores such as impala, surrounded by dense bush (Fig. 3). Recently, Anderson et al. (2010) showed in a landscape-scale analysis that temporally stable herbivore hotspots in the Serengeti occurred where ungulates were less susceptible to predation (in low biomass areas away from rivers and on ﬂat terrain) and where high quality forage occurred (linked to increased soil fertility). Herbivore effects on soil nutrient availability in kraals We have evidence to suggest that wild herbivores were positively contributing to soil nutrient availability in kraals, although strictly speaking we cannot prove that they maintained or increased soil nutrient availability (we can- not compare kraals with and without wild herbivores). Inorganic nitrogen is rapidly lost from topsoil through volatilization, denitriﬁcation, ﬁre and leaching (Augustine 2003; Hejcman et al. 2007), although speciﬁc information for semi-arid savannas in the absence of herbivores is scant. In contrast, phosphorous is relatively immobile and suppressed if grown with a single grass plant, while values below 0 suggest facilitation of seedlings by grasses. The soils used in the experiment were collected from abandoned kraal (closed symbols) and control sites (open symbols) in the study area therefore has a long residence time in soils (Blackmore et al. 1990; Augustine 2003). In the absence of herbivores after about four decades, we would expect lower N values than we have measured in the kraal soils, which were well used by wild herbivores. It seems likely that wild herbivores increased kraal nutrient availability by (1) accelerating nutrient cycling and (2) by importing nutrients from the surrounding landscape (Fig. 3; Blackmore et al. 1990; Augustine 2003, 2004). First, the kraal data ﬁt the accelerated nutrient cycling scenario proposed by Ritchie et al. (1998), which appears to be characteristic of fertile systems (Bardgett and Wardle 2003). We found that herbivores grazed grass plants intensively, while depositing large amounts of nutrients through dung (and presumably urine) at kraal sites (Table 2). Through these actions, large herbivores provide a shortcut to the slow nutrient release from plant litter through decomposition, by rapidly processing vegetation and recycling nutrients through dung and urine (Bardgett and Wardle 2003). In addition, the higher N mineralization rates of kraal sites (provided that enough rain falls) might be due to the stimulation of decomposer activity by animal excreta and the high quality of leaf litter in kraals (Bardgett and Wardle 2003). The average N mineralization rate (excluding dry sites) for kraals (0.55 g N kg soil-1 day-1) 123