Research

Changing rainfall seasonality and its impacts on C4 grass distributions

This project falls within a broader project centering on understanding the effects of seasonality on our ecosystems, in particular how temperature and rainfall seasonality determine seasonal water availability, the coexistence of particular plant communities in the the Greater Cape Floristic Region (GCFR), and the phenology of animals in this biome.

C₄ grasses typically found in summer rainfall climates, but anecdotal evidence suggests they have been expanding into the GCFR, possibly as a result of warmer winters and maybe also as a result of changes in precipitation seasonality. C₄ grasses are already much more common in the eastern parts of the GCFR, possibly because of the greater contribution of summer rainfall in these parts, but this remains to be tested. Large increases in C₄ grass abundances could have major implications for fire frequencies in the GCFR, which are typically much lower compared to grass-dominated biomes.

We are manipulating rainfall and temperature at a field site within the GCFR that has a typical Mediterranean climate (winter rainfall) and monitoring the response of locally occurring C4 grasses to see whether they increase productivity, biomass production and fertility in response to a more "favourable" climate for these species.

Using remote sensing to map and monitor alien tree invasions and land-use change

I am working together with Jasper Slingsby and Glenn Moncrieff from the SAEON Fynbos Node on a project looking at the potential for using remote sensing to develop methods for repeatable and frequent monitoring of alien tree invasions and land-use change in three different parts of South Africa. We are supervising three students, each looking at a particular part of the country: Craig Mahlasi is working in the Albany Thicket biome looking at land-use change primarily; Keletso Moilwe is mapping alien tree invasions in the high altitude grasslands of Mpumulanga and Limpopo; and Lungile Khuzwayo is mapping alien tree invasions in the mountain areas that provide Cape Town with water.

Grass productivity responses to altered rainfall seasonality and character

As greenhouse gases continue to rise and the world gets ever warmer, so is the global hydrological cycle changing. Parts of the world are getting wetter, while others are getting drier, and in many places the seasonal distribution of rainfall is changing. However, across the world, rainfall events are becoming more intense and the length of dry intervals between rainfall events is getting longer. These rainfall changes will of course affect the plants and animals that depend on water for survival.

By way of a meta-analysis of experimental manipulations of rainfall in grassland systems, I am investigating the influence of the changing character of rainfall on grassland productivity. This will help determine whether there are generalities in grassland productivity change to inform livestock management and agricultural policy in a warming world.

Predicting changes in grass distributions in response to climate change

There is a wealth of grass distribution data from herbarium specimens, citizen science observations and study transects. Much of these data are also available digitally, and have been collected over a fairly long time period.

I am using these ad hoc data to model grass distribution changes in response to climatic and environmental change using species distribution and occupancy models.