Biodiversity and Fire

By Undergraduate REP Jacob Mercer

When an email came round to the undergrads in the Statistics dep. about the research experience placements offered by the London NERC DTP, I knew it was something I wanted to apply for. I’m a third year studying mathematics and statistics at Worcester College, Oxford. I absolutely love maths, don’t get me wrong! But a certain part of me has always felt that, for all the satisfaction and enjoyment I get in solving abstract problems, or proving theorems, I’d also like to do something a bit more… real! Use the maths and statistics I love to change the world. Ok, so I may be far from changing the world, but the NERC undergraduate research placement has been an interesting and exploratory opportunity to delve into the subject of palynology (the study of fossilised pollen) and fire.

The title of my project was “Quantifying past fire-biodiversity relationships in European Landscapes”, – supervised by Dr. Daniele Colombaroli (link here), palaeoecologist in the Centre for Quaternary Research (CQR), RHUL. I also had the opportunity to work with an MSc student in Quaternary Sciences, Daniel Gallagher. Over the course of the project, this took me in many directions, but I will describe only a few below.

It had never occurred to me to question from where scientists obtained past information about things like wildfire occurrences, global temperature, and plant biodiversity, but, as I have begun to see, it is often in proxies available from natural archives, like lakes, ice cores or tree rings that scientists can reconstruct what past ecosystems looked like.

For me, I was first tasked with reconstructing biodiversity trajectories in Europeans landscapes using data from the European pollen database (EPD). Sediment cores are taken from lakes or peat archives covering the Holocene and palynological analyses provide insights of past vegetation changes over millennia, under different climatic and land use conditions. This gave me to work with a timeline over several thousand years, with how the abundances of the pollen taxa changed through time, and how this is related to changing fire in the landscape, as inferred from the microscopic charcoal particles that accumulated over time.

If you had asked me at the start of the project: “how do you measure the biodiversity of a system” given the fossilised pollen data I had, I would probably have suggested something simple like the no. species present, but again, I began to learn that there is in fact a lot of literature on the topic of how to fairly and usefully determine the biodiversity of an ecosystem in the past. There are probabilistic measures, like evenness (or probability of interspecific encounter), which takes into account how the pollen is distributed across different taxa, and richness, which gives an (relative) estimated no. taxa in each level.

I plotted the overall richness/biodiversity trends over time, across 20 sites over Europe, showing an overall increase in most sites. This was to me surprising at the beginning, as I thought that human impact affect biodiversity through extinctions and reduced population sizes, but this project gave me the opportunity to learn that there is a strong anthropogenic component in present biodiversity, and that many species in the past (especially those of open environments) have been favoured by forest fragmentation. This implies that conserving present ecosystems requires an understanding of the different natural and anthropogenic components, and how they may respond to future climate and land use changes   (Colombaroli et al., 2013; Whitlock et al., 2018).

Figure 1: A plot showing the richness trends over time for fossilised pollen biodiversity over 20 European sites. Jacob Mercer, Author provided.

Overall I have found the REP to be a valuable undertaking. I have not only enjoyed the work and enjoyed learning outside of my own discipline, but I have also gained an invaluable insight into a little corner of the world of academia; a placement I can wholly recommend.

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