Ancient giants reveal the realities of climate change

When a giant baobab toppled over in the Pafuri area in the northernmost part of the Kruger National Park a number of years ago, researchers from the University of Pretoria (UP) had a hunch that the fallen giant could give them access to a wealth of information about the past. The team seized the opportunity and travelled to Kruger to collect samples.

The hunch turned out to be very plausible and their initial study soon developed into a broader project with SANParks. This research project has now evolved into an international collaborative study that covers Southern Africa and Madagascar.

The objective of the study is to determine the effects of climate change over the whole of southern Africa over the past 1 000 years by using trees to reconstruct rainfall patterns. Leading researcher, Prof Stephan Woodborne from UP’s Mammal Research Institute (MRI), says, ‘We are in the process of producing a mega map of rainfall and drought, and it is going to be a really magnificent climate record once this project is completed.’ The study is providing valuable insight into both the natural and anthropogenic effects of climate change which, according to Woodborne, is a very real issue.

The study aims to determine the extent of change in areas with varying rainfall. Baobab trees, which are found predominantly in summer rainfall areas, are excellent study models as they can live for more than 1 000 years. In winter rainfall areas, the study looks at trees such as the yellow wood, while camel thorn trees provide similar information about desert areas.

Information is retrieved from these trees by applying a method known as coring, which does not require the trees to be cut down. Coring involves the study of tree rings to determine the age and growth rate of a tree. Samples are taken to the MRI’s Isotope Laboratory where isotopic analysis of the samples’ properties and the age of the tree is undertaken to reconstruct rainfall patterns.

Dr Grant Hall of the Isotope Laboratory explains that isotopes are elements that are chemically the same, but differ in respect of their atomic weights. Dr Hall and his team analyse the cored parts of the trees to determine which carbon isotopes are absorbed by the leaves and the ratios between the different isotopes that are present. The chemistry of the wood reflects the growing conditions and the periods during which growth occurred (rainfall periods), as well as the periods during which the trees were under water stress (drought periods). As a tree grows, new rings are formed on the outside of trunks or branches year after year, and the chemistry of each ring gives insight in the climate changes in the area where the tree is located.

As the study develops, Prof Woodborne and Dr Hall are making some very important discoveries, which have enabled them, for example, to develop an age model for baobabs. Giant baobabs are often mistakenly believed to be just one big tree, while in fact they often consist of multiple trunks that have fused together. This explains why only some trees have hollows in their trunks.

The study has also provided insight in how communities have adapted culturally in response to the significant climate changes that have occurred over the years. Areas such as the Limpopo valley, where livestock farming and agriculture once thrived, are now desolate as they have become too dry for such activities.

The sites on which the study is conducted cover a vast area stretching from Angola to Madagascar and the southern Cape. The team hopes to get more postgraduate students on board, but according to Prof Woodborne and Dr Hall the data have already revealed that the effects of climate change are real and, more often than not, devastating. Information gained from the different baobab sites to date confirms the major climate shifts in southern Africa with, for example, the expansion of the Kalahari eastward to areas that were once characteristically summer rainfall areas. The study of the giant baobabs have put an end to the debate on whether climate change is real or not and has confirmed the very serious effects of climate change and greenhouse gases.

The following are some of the papers based on this research:

• Huffman, TN & Woodborne, S. 2015. Archaeology, baobabs and drought: cultural proxies and environmental data from the Mapungubwe landscape. The Holocene. DOI: 10.1177/0959683615609753.
   
• Patrut, A, Woodborne, S, Patrut, RT, Hall, G, Rakosy, L, Von Reden, KF, Lowy, D & Margineanu, D. 2015. Radiocarbon dating of African baobabs with two false cavities. The investigation of Luna tree. Studia Univ. Babes-Bolyai Ser. Chem., 60(4):7–19.

• Patrut, A, Woodborne, S, Von Reden, KF, Hall, G, Hofmeyr, M, Lowy, DA & Patrut, RT. 2015. African baobabs with false inner cavities: The radiocarbon investigation of the Lebombo Eco Trail baobab. PLoS ONE, 10(1), e0117193. doi:10.1371/journal.pone.0117193.

• Woodborne, S, Hall, G, Robertson, I, Patrut, A, Rouault, M, Loader, NJ & Hofmeyr, M. 2015.  A 1 000-year carbon isotope rainfall proxy record from South African baobab trees (Adansonia digitata L). PLoS ONE. 10.1371/journal.pone.0124202.