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Alternative afforestation options on sandy heathland result in minimal long-term changes in mineral soil layers

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Peer-reviewed

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Article

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Authors

Tew, Eleanor R 
Vaguelova, Elena I 
Sutherland, William  ORCID logo  https://orcid.org/0000-0002-6498-0437

Abstract

Extensive afforestation is currently being widely promoted as a key nature-based solution for climate change mitigation. Fundamental to this strategy is the sequestration of carbon into long-term stable storage, either in wood products or the soil. However, the long-term effects of tree planting on soil carbon, or other soil properties, has rarely been examined. Importantly, afforestation can take many different forms, with differing effects on soil properties. Here, we evaluate how the historical afforestation of sandy heathland adopting a range of management options – including different combinations of conifers and broadleaves in monocultures and mixtures – have affected soil pH, total carbon and nitrogen concentrations, the C:N ratio, and carbon and nitrogen stocks almost a century later. We analyse these properties at a range of soil depths through the organic (litter, F and grass layers) and upper mineral soil profiles (0-5 cm, 5-10 cm and 10-20 cm depth). In comparison to the historical heathland sites, afforestation decreased soil pH, most dramatically under conifers, and increased the C:N ratio. However, there was overall little difference in carbon and nitrogen concentrations between alternative management options. While the total carbon and nitrogen concentrations were much higher in the organic layers of the forest options compared to the open sites, this did not translate into differences in the mineral layers. Furthermore, although we found some evidence of the transferral of carbon and nitrogen into the uppermost soil mineral layers, this was minimal in comparison to the concentrations of the organic layers. The soils at our study site are low quality and sandy, and are therefore unfavourable for incorporating organic matter, but it is still notable how little was incorporated after nearly a century of afforestation. Given the current emphasis on tree planting as a means to tackle climate change, these results demonstrate the fundamental importance of the appropriate consideration of both the afforestation management option and underlying soil type.

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Journal Title

Forest Ecology and Management

Conference Name

Journal ISSN

1872-7042

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Publisher

Elsevier
Sponsorship
For this research E.R.T. was supported by an Industrial CASE studentship, funded by the Natural Environment Research Council and Forestry England [NE/M010287/1; NE/L002507/1]. W.J.S. is funded by Arcadia.