It’s long term thirst and not short-term warming that poses the greatest threat to carbon storage in peat bogs, according to research by Luke Andrews and colleagues in Global Change Biology. The findings result from ten years of climate manipulation of a peat bog in mid-Wales.
Peatlands are crucial for carbon storage. Despite covering just 3% of the planet, they store more carbon than any other vegetation. Therefore, if we are to reduce carbon dioxide in our atmosphere, understanding their futures is vital. In their paper, Andrews and colleagues write: “The results of our experimental study showed that warming increased the abundance of shrub-type vegetation over ten years, a result supported by most warming experiments in peatland ecosystems.
“An increase in ericaceous shrub dominance may result in changes in the carbon balance of peatlands, potentially resulting in increased carbon losses due to enhanced root exudates and a reduction in litter quality. The persistence of Sphagnum, at least over the short term, may ameliorate this change.”
The study is the first to combine climate manipulation, increasing both local temperature and water flow with palaeoecological studies to compare contemporary results with historical changes.
The experiment took place at Cors Fochno, a lowland raised bog about 10 miles / 15 kilometres north of Aberystwyth near the Dyfi estuary. The site has several hydrologically isolated plots of Sphagnum lawn that allowed the team to manipulate plots for variations in water level, temperature, both or neither as a control.
Andrews and colleagues found that ericaceous shrubs became more abundant in response to warming over ten years. In itself, this was not a surprising result, as it has been seen elsewhere. However, they also found that increased drought frequency did not alter the vegetation.
For the historical record, they found that plant composition did not seem to change with warmer periods. Instead, it changed with long-term dryer periods. Andrews and colleagues write: ‘This study demonstrates that ericaceous shrubs increased in abundance with warming in both experimental and palaeoecological studies from the same site. This correspondence suggests that where ericaceous cover has increased in response to warming in peatlands in the past, it may continue to do so with future climate change.”
Unfortunately, in modern times peat bog manipulation is occurring all the time. The authors mention air pollution and drainage elsewhere as factors affecting peat bogs. Additionally, there has been runoff from mining in the area. The authors conclude: “Responses in vegetation community composition to climate change inferred from the peatland palaeoecological record may be unreliable as an analogue for future change because many peatlands, even seemingly ‘pristine’ ones, have been influenced by anthropogenic drivers such as drainage or air pollution. Such anthropogenic impacts have become stronger drivers of change in peatland plant community composition than climate, and peatland autogenic feedbacks do not confer the same level of resistance to these impacts.”
Andrews, L.O., Rowson, J.G., Caporn, S.J.M., Dise, N.B., Barton, E., Garrett, E., Gehrels, W.R., Gehrels, M., Kay, M., Payne, R.J., 2021. Plant community responses to experimental climate manipulation in a Welsh ombrotrophic peatland and their palaeoenvironmental context. Glob Change Biol. https://doi.org/10.1111/gcb.16003