The feature deals with niche dimensionality - a theory concerned with accounting for biodiversity - examining how resources in a niche can affect productivity of that area of grassland and its resultant biodiversity or lack thereof.
This research is a result of collaborations between researchers working on a number of sites around the world, including at UKZN’s Ukulinga long-term mowing and burning trials, one of the longest-running ecological experiments in the world.
The connected sites are a part of the Nutrient Network (NutNet), which involves ecologists replicating the same experiments on sites across nine countries to observe the results produced in various systems. In this particular study, researchers added limiting nutrients such as nitrogen (N), phosphorus (P) and potassium (K), which produced a decline in plant diversity at all 45 sites in North America, Europe, South Africa and Australia.
Kirkman explained that each niche, defined by the resources in that space, has species or a number thereof that can occupy that space. All the plants, for example grasses and forbs, compete for the same resources, some of which are limiting to plant growth, such as NPK.
‘Most natural ecosystems have multiple limiting resources - in South Africa our grasslands are largely limited by nitrogen and phosphorus,’ said Kirkman.
‘With more nutrients supplied to niches, some plants compete more effectively for nutrients and fare better, reducing diversity and causing plant species loss. This increases biomass, particularly of certain species that respond well to added nutrients, and induces a shift from below ground competition for nutrients to above ground competition for light.
‘The implications of this are far-reaching, as there are factors causing an increase in limiting nutrients to grasslands, for example deposition of nitrogen from industrial fallout. Grasslands, the dominant vegetation covering South Africa, provide resources for agriculture and wildlife, stabilise soil and ensure constant supply of good-quality water, and facilitate tourism,’ said Kirkman.
‘We all rely on grass to survive. South African grasslands are among the most diverse in the world and the ecosystem services provided by these grasslands are dependent on this biodiversity, therefore an understanding of dimensionality in grassland ecosystems is critical to understanding and modelling diversity loss.’
Research of this nature is ongoing through the NutNet collaboration, with Ukulinga continuing to play an important role. The researchers would like to have more sites around the world, particularly in Africa and South America, to strengthen their research and the recommendations for conservation that result from it.