1104 Oecologia (2011) 165:1095–1107 Predators Structurally open patches preferred by herbivores Constrained woody recruitment B Nutrient influx Livestock management concentrates nutrients in patches Increased nutrient availability High forage quality and production A Accelerated nutrient cycling Fig. 3 A hypothetical model explaining how kraals may have persisted as structurally open nutrient hotspots after livestock were replaced by wild herbivores in the study area. We propose that two reinforcing feed back loops developed. The ﬁrst (feedback loop A, solid-line arrows) developed when livestock penning locally increased nutrient availability through dung and urine deposits. After livestock were removed, forage productivity and quality increased here, which attracted wild herbivores. In turn the increased herbivore activities accelerate nutrient cycling, hence nutrient availability in a is similar to the maximum mineralization rate measured in sodic sites (0.5 g N kg soil-1 day-1) and riparian zones (0.45 g N kg soil-1 day-1) in the KNP, also using an in situ method (Jacobs et al. 2007). If herbivores were absent, nutrient cycling rates at kraal sites would have slowed down as a greater proportion of nutrients is immobilized in plant tissue and litter and thus rendered temporarily unavailable for plant uptake. A slowdown in nutrient cycling in the absence of herbivore excreta has been demonstrated for boma sites in Kenya (Augustine and McNaughton 2006). Second, De Mazancourt et al. (1998) showed that a continuous nutrient inﬂux is required for the long-term maintenance of fertile areas in infertile grazing systems. Large herbivores redistribute substantial amounts of nutri- ents if daily behavioral activities are spatially separated, e.g., feeding versus resting or bedding places (Bokdam 2001; Juchnowicz-Bierbasz and Rakusa-Suszczewski 2002; Singer and Schoenecker 2003; Augustine 2004; Moe and Wegge 2008). Our data were not sufﬁcient to calculate an accurate, year-round nutrient input–output balance for kraal and control sites. Nevertheless, dung N deposition rates in kraals during the study period were on average more than eight times that of control sites (Table 3), while we esti- mated the ratio of herbaceous off-take to be on average only 1.5 times higher in kraals than controls (differences were not signiﬁcant; Table 2). Even allowing for the higher N concentration of the grazing in kraals (e.g., 123 Increased wild herbivory positive feedback loop. In the second feed back loop (feedback loop B, dashed-line arrows), anti-predator behaviour of wild herbivore species caused an inﬂux of nutrients into kraals, which increased the availability of soil nutrients. This constrained woody recruitment, which kept kraals structurally open. Because of bush encroachment in the surrounding areas, the open kraal sites were increasingly perceived as predator-safe areas, which uphold the inﬂux of nutrient into kraal sites U. mosambicensis leaf N concentration 1.75 times higher in kraals than controls), our data suggest that N consumption and export from kraals were less than three times that of controls. Assuming that the overall nutrient pool in the study system remains constant over time, our data strongly suggest that wild herbivores caused an N (and other nutri- ents) inﬂux into kraal sites. The surrounding areas, repre- sented by the control sites, subsidized these nutrients (De Mazancourt et al. 1998; Augustine 2003). At a land- scape scale, the redistribution of nutrients by both domes- ticated and wild herbivores was probably insigniﬁcant given the small area covered by kraal sites in the study area. Nevertheless, the role of large herbivores in creating and maintaining soil nutrient heterogeneity is presently under- appreciated in semi-arid savannas (Jacobs et al. 2007). It is important to note that herbivore responses to higher forage quality alone is unlikely to create strong nutrient redistribution effects, because the high nutrient intake will be largely offset by nutrient excretion while grazing. Spending non-foraging time in an area is required for signiﬁcant nutrient redistribution to occur. The bush- clearing experiment in the study area indicates that a nutrient inﬂux by impala, the most numerous species in the study area, occurred when patches were cleared of its woody component. This implies that impala were attracted by the openness of the habitat, a preference also noted by Estes (1992). This, in turn, might explain the dispropor- tionately high impala dung deposition rates at kraal sites,