Patterns and controls of annual aboveground net primary productivity (ANPP) are fundamental metrics of ecosystem functioning. It is generally assumed, but rarely tested, that determinants of ANPP in one region within a biome will operate similarly throughout that biome, as long as physiognomy and climate are broadly consistent. We tested this assumption by quantifying ANPP responses to fire, grazing history, and nitrogen (N) addition in North American (NA) and South African (SA) savanna grasslands. We found that total ANPP responded in generally consistent ways to fire, grazing history, and N addition on both continents. Annual fire in both NA and SA consistently stimulated total ANPP (28–100%) relative to unburned treatments at sites with deep soils, and had no effect on ANPP in sites with shallow soils. Fire did not affect total ANPP in sites with a recent history of grazing, regardless of whether a single or a diverse suite of large herbivores was present. N addition interacted strongly and consistently with fire regime in both NA and SA. In annually burned sites that were not grazed, total ANPP was stimulated by N addition (29–39%), but there was no effect of N fertilization in the absence of fire. In contrast, responses in forb ANPP to fire and grazing were somewhat divergent across this biome. Annual fire in NA reduced forb ANPP, whereas grazing increased forb ANPP, but neither response was evident in SA. Thus, despite a consistent response in total ANPP, divergent responses in forb ANPP suggest that other aspects of community structure and ecosystem functioning differ in important ways between these mesic savanna grasslands.
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We thank the staff of Kruger National Park for creating and maintaining the Experimental Burn Plots and Buffalo Enclosure, and for their efforts in supporting and encouraging our work. In particular, we thank Justice Sibuyi, Wisane Sibuyi, and Thembe Mabasa for field assistance. We would also like to thank UKZN for their support of our study at URF. Research at KPBS was supported by the KPBS staff and Konza Prairie LTER program. Special thanks to Jobie Carlisle, Patrick O’Neal, Jerry Naiken, and Freedom Linda for logistical support. Gene Kelly and Suellen Melzer provided soils information and data. This research was supported by the National Science Foundation (DEB 0516145 to MDS, and DEB 0516094 to AKK). GMB was supported by the National Science Foundation’s GK12 program at Colorado State University. Long-term ANPP data set pab01 was supported by the NSF Long-Term Ecological Research Program at Konza Prairie Biological Station. Three anonymous reviewers improved this manuscript substantially.
Conceived of or designed study: AKK, MDS, GMB, SLC, JMB, NG, RWSF, CEB.
Performed research: GMB, RWSF, DEB, AJC, KPK, JMB.
Analyzed data: GMB, PLC.
Wrote the paper: GMB, AKK, SLC, JMB, MDS, DEB, RWSF.
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Buis, G.M., Blair, J.M., Burkepile, D.E. et al. Controls of Aboveground Net Primary Production in Mesic Savanna Grasslands: An Inter-Hemispheric Comparison. Ecosystems 12, 982–995 (2009). https://doi.org/10.1007/s10021-009-9273-1