Planting huge numbers of trees to mitigate climate change is “not always the best strategy” – with some experimental sites in Scotland failing to increase carbon stocks, a new study has found.
Experts at the University of Stirling and the James Hutton Institute analysed four locations in Scotland where birch trees were planted onto heather moorland – and found that, over decades, there was no net increase in ecosystem carbon storage.
The team – led by Dr Nina Friggens, of the Faculty of Natural Sciences at Stirling – found that any increase to carbon storage in tree biomass was offset by a loss of carbon stored in the soil.
Dr Friggens said: “Both national and international governments have committed to plant huge numbers of trees to mitigate climate change, based on the simple logic that trees – when they photosynthesise and grow – remove carbon from the atmosphere and lock it into their biomass. However, trees also interact with carbon in soil, where much more carbon is found than in plants. Our study considered whether planting native trees on heather moorlands, with large soil carbon stores, would result in net carbon sequestration – and, significantly, we found that over a period of 39 years, it did not.”
The tree-planting experiments – in the Grampians, Cairngorms and Glen Affric – were set up by the late Dr John Miles, of the then Institute of Terrestrial Ecology (a forerunner to the UK Centre for Ecology and Hydrology), in 1980, and the Hutton Institute in 2005. The research sites enabled the team to assess the impact of tree planting on vegetation and soil carbon stocks, by comparing these experimental plots to adjacent control plots consisting of original heath vegetation.