Below-ground impacts on microbial diversity of afforestation and woodland succession in Great Britain

Abstract

Woodland restoration on farmland is gaining support as a method of habitat restoration and carbon sequestration. To understand the consequences of afforestation on soil microbial communities we require comparisons across agricultural, afforested, and established woodlands that differentiate changes in total soil diversity and diversity pertaining to soil functioning. I examine two natural-experiment, afforestation chronosequences describing changes to bacterial and fungal diversity in soils and on decomposing leaf litter using metabarcoding to identify taxa. The use and applications of metabarcoding are described in Chapter 1. Chapters 2 and 3 report the abiotic and microbiological differences between agricultural and woodland soils over an afforestation and succession gradient. I study land use differences across 21 Woodland creation & Ecological Networks (WrEN) project sites – an afforestation chronosequence - with mixed-effect and multivariate models. The next chapters model how leaf litter decomposition (Chapter 4) and how decomposing litter associated microbes (Chapter 5) vary across woodland age categories (young, mature, and ancient) in 27 woodlands in the North East of England, across five tree species’ litter, during spring and summer. In the first experiment I show key soil changes to carbon and nitrogen concentrations, and to C:N ratio across my afforestation gradient. I also demonstrate the rapid differentiation of woodland microbial communities from agricultural ones, with additional changes resulting from soil properties such as pH. In the second experiment I observe notable, but non-significant increases in decomposition in ancient woodland, as well as significant effects of species, sampling season, and woodland age on microbial diversity, beyond that of the changes expected from soil properties alone. In chapter 6 I discuss how these results integrate into the existing literature on the succession of decomposer communities over long timescales and their implications for woodland management. The work highlights the value of both afforestation and conservation of older woods.