We were interested in determining whether there were similarities in grassland structure among sites in different parts of the world that might indicate that there are assembly rules for grassland communities. We compared the results from subtropical Ukulinga with those of the results of similar long-term experiments in temperate environments at Park Grass in England (the world’s longest-running ecological experiment) and Konza Prairie on the Great Plains of the United States. The mean annual rainfall at these sites were similar but the temporal distribution of rain was profoundly different. In warm, humid, eastern South Africa, there are two long-term grassland experiments that have been running on the Ukulinga plateau, Pietermaritzburg (KwaZulu-Natal) since 1950/1951. One of these experiments has had continuous burning and mowing treatments and the other continuous fertilization treatments, providing us with a set of well-differentiated, large, replicated environmental settings, that has resulted in well-described grass communities. This African grassland has been fertilized with two forms of nitrogen applied at four levels, phosphorus and lime at two levels in a crossed design in 96 plots. The burning and mowing experiment has 132 plots, with annual, biennial and triennial burns and early- and late-season mows.
Results/Conclusions:
In the fertilization experiment at Ukulinga, there was a dramatic change in community composition as was the case at Park Grass (England). We found a significant (additive) interaction effect on ANPP of nitrogen and phosphorus, and a negative correlation between ANPP and species richness. There was also a significant negative effect of nitrogen amount and nitrogen form and a positive effect of lime on species richness and species diversity. We also found a positive but asymptotic effect of soil pH. There was also considerable evidence of assembly rules in the burning experiment but not in the mowing experiment when compared with temperate sites. A multivariate analysis of the Ukulinga experiments showed that the effects of burning and mowing differed considerably from the effects of soil fertilization.
The results of both our long-term fertilization experiment and the burning component of the burning/mowing experiment in the subtropical grassland at Ukulinga were very similar to the results from temperate grasslands in Europe and the U.S., suggesting that there may be assembly rules that are pertinent across grasslands. The dominant grasses changed over time in the control treatment at Ukulinga, with encroachment of many invasive tree species, suggesting that climate change may be affecting this subtropical grassland.