Ecology of the past

Hello Ecology of the Past readers, my name is Jelle Kraak and I’m currently doing a research project for my MSc Biological Sciences (University of Amsterdam) supervised by William Gosling (University of Amsterdam), Jemma Finch (University of KwaZulu-Natal), and Trevor Hill (University of KwaZulu-Natal). The project is entitled: “Assessing the effect of human induced fire regime changes on vegetation in the Drakensberg mountains”. During the project I will visit South Africa to work at the University of KwaZulu-Natal and visit field site thanks to partial funding from the Amsterdam University Funds.

Research  project outline                                                                                 

As many of you know, humans have been interacting with the environment for millennia in various ways. One of the ways in which humans interact with the environment is through the ignition of fires. By doing so, humans may change fire regimes (fire frequency, severity and/or intensity), which in turn can cause changes in vegetation composition and structure. By using a combination of phytolith (local vegetation) and charcoal (fire) data from two sediment cores obtained from wetland environments in the Drakensberg mountains, we aim to assess the effect of fire regime changes on vegetation over the last 6000 years.

The phytoliths (biogenic silica microfossils) allow for the reconstruction of the past vegetation. Charcoal fragments characterize all aspects of past fire regimes: (i) frequency (time series analysis of charcoal data), (ii) severity (abundance of charcoal in samples reflecting biomass consumed), and (iii) intensity (spectral properties of individual charcoal fragments reflecting combustion temperature). 

The most interesting part of this project (in my humble opinion) is that this study is the first to use micro-Fourier Transformed Infrared Spectroscopy (µFTIR) to reconstruct fire temperatures from field samples ánd combine these accurately reconstructed temperatures with local vegetation data! It is important to accurately estimate fire temperatures, as the temperature of a fire dictates the type of plant materials which are consumed in a fire (the higher the temperature, the greater the proportion of woody material burning up). Similar studies have been conducted previously, however, these studies compared fire severity i.e. total burnt biomass with vegetation data. Although this works decently, total burnt biomass is not an accurate representation of fire intensity or temperature, as at very high temperatures biomass turns to ash, which cannot be detected in sediment cores. Through parameterizing both the vegetation changes and the fire regime we will provide a comprehensive picture of how changing human fire use practices modified the vegetation. We anticipate that: (i) a decrease in fire intensity resulted in woody encroachment of the surrounding vegetation, which was concomitant with the arrival of agropastoralists c. 600 years ago, and (ii) a shift in the proportion of C3 and C4 grass species in reaction to temperature changes in the Drakensberg mountains.