Human activities, particularly land-use change and habitat degradation, are driving major changes in biodiversity worldwide. However, studies of such effects have overwhelmingly focused on above-ground taxa: the effects on soil biodiversity are less well known, despite the importance of soil organisms in developing soil structure, nutrient cycling and water drainage.

In my thesis I assess how soil organisms respond to land-use and soil properties across a range of spatial scales and taxonomic groups using three kinds of data: a collation of published surveys of soil biota in sites facing different land-use pressures; new sampling of soil invertebrates in different land uses; and data on earthworm functional group diversity from a citizen science project I developed.

In Chapter 2 I show that the abundances of soil-dwelling and above-ground organisms do not respond the same way to land-use and soil properties and that existing models may be insufficient to safeguard soil biodiversity. In Chapter 3 I model how abundance and species richness of soil biota responds to land use and find responses differ depending on organism size and soil properties. Having ascertained there is now sufficient soil assemblage data to fit complex models of how land use affects soil biodiversity, in Chapter 4 I use an independent data set I collected in the New Forest National Park to ground-truth how well a model of soil biodiversity across land uses in the temperate biomes compares with this new dataset.

Throughout my thesis modelling soil assemblages in urban land uses has been problematic due to a lack of data and high uncertainty in model estimates. In Chapter 5 I present results from my project Earthworm Watch and show how citizen science can be used to model how earthworm abundance and functional diversity responds to different land uses in urban areas.