Ecosystem Ecology

Oecologia

, Volume 149, Issue 3, pp 456-464

First online:

Convergence and contingency in production–precipitation relationships in North American and South African C4 grasslands

  • Alan K. KnappAffiliated withDepartment of Biology and Graduate Degree Program in Ecology, Colorado State University Email author 
  • , Catherine E. BurnsAffiliated withDepartment of Ecology and Evolutionary Biology, Yale University
  • , Richard W. S. FynnAffiliated withGrassland Science, School of Biological and Conservation Sciences, University of KwaZulu-Natal at Pietermaritzburg
  • , Kevin P. KirkmanAffiliated withGrassland Science, School of Biological and Conservation Sciences, University of KwaZulu-Natal at Pietermaritzburg
  • , Craig D. MorrisAffiliated withAgricultural Research Council-Range and Forage Institute, University of KwaZulu-Natal
  • , Melinda D. SmithAffiliated withDepartment of Ecology and Evolutionary Biology, Yale University

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Abstract

Mesic grasslands in North America and South Africa share many structural attributes, but less is known of their functional similarities. We assessed the control of a key ecosystem process, aboveground net primary production (ANPP), by interannual variation in precipitation amount and pattern via analysis of data sets (15- and 24-year periods) from long-term research programs on each continent. Both sites were dominated by C4 grasses and had similar growing season climates; thus, we expected convergence in precipitation–ANPP relationships. Lack of convergence, however, would support an alternative hypothesis—that differences in evolutionary history and purportedly greater climatic variability in South Africa fundamentally alter the functioning of southern versus northern hemisphere grasslands. Neither mean annual precipitation nor mean ANPP differed between the South African and North American sites (838 vs. 857 mm/year, 423.5 vs. 461.4 g/m2 respectively) and growing season precipitation–ANPP relationships were similar. Despite overall convergence, there were differences between sites in how the seasonal timing of precipitation affected ANPP. In particular, interannual variability in precipitation that fell during the first half of the growing season strongly affected annual ANPP in South Africa (P < 0.01), but was not related to ANPP in North America (P = 0.098). Both sites were affected similarly by late season precipitation. Divergence in the seasonal course of available soil moisture (chronically low in the winter and early spring in the South African site vs. high in the North American site) is proposed as a key contingent factor explaining differential sensitivity in ANPP to early season precipitation in these two grasslands. These long-term data sets provided no support for greater rainfall, temperature or ANPP variability in the South African versus the North American site. However, greater sensitivity of ANPP to early season precipitation in the South African grassland suggests that future patterns of productivity may be more responsive to seasonal changes in climate compared with the North American site.

Keywords

Climate Evolutionary history Net primary production Precipitation Soil moisture