Scaling and thresholds in earthworm abundance and diversity in grassland agricultural systems

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"Even on the same field worms are much more frequent in some places than in others, without any visible difference in the nature of the soil" Darwin, 1881Darwin wrote these words over 130 years ago and yet, despite much research, we still can't explain in anything but the broadest terms why, when you dig up soil from two different places in a field, earthworms may be present in one place but not in another. Given the importance of earthworms in the environment, this isn't a trivial matter. Earthworms have been termed "ecosystem engineers". They ingest a vast amount of soil and in the process break down organic matter, mix up soil and, via their burrows, keep soils aerated. Because of these activities earthworms help the ecosystems in which they occur to provide various benefits or services. These so called ecosystem services include food production (plants grow better in the presence of earthworms) and flood control (soils with lots of earthworm burrows can store more water and also water drains more rapidly through burrowed soil thereby reducing the chances of flooding).Given the beneficial role of earthworms in the environment it makes sense to manage soils in a way that helps earthworms flourish. We can only do this if we understand what impact soil properties and land management practises have on the distribution of earthworms. In the UK semi-natural grasslands account for about 16% of land use and managed, nutrient-enriched grasslands account for an additional 20 %. These grasslands are used for food production; animals used for dairy and meat production graze on them. Traditionally agricultural management has focussed on improving the nutrient quality of the grass so as to maximise production. But as society increasingly appreciates the various services that the environment can provide such as biodiversity and water storage as well as food production it is worth asking what impact management strategies have on the earthworms that contribute so strongly to so many vital services.Our research aims to look at how earthworms are distributed along a gradient of grassland intensification, from low input, low grazing intensity grasslands to high input, high grazing intensity grasslands. We are particularly concerned with understanding the spatial distribution of earthworms in these grasslands and how this relates to soil properties and grassland management. By sampling earthworms and soil properties at a range of spatial scales, from fields to farms to the whole of the UK, we will be able to determine whether there are critical thresholds of agricultural intensification beyond which earthworms, and hence the ecosystem services that they provide, are lost from grassland systems.Members of the public will get involved in our work by helping us with the sampling and learning how to identify earthworms at workshops. The records of earthworms we collect will feed into the ongoing earthworm recording scheme and the work of the Biological Records Centre. Both of these activities will give our work a lasting legacy beyond the life of the project. For example, repeat surveys could highlight changes in earthworm numbers in response to environmental change. The earthworms and soils that we sample will also be archived for future research. We will involve the land owners where we sample earthworms in our discussions and discuss our results and models with then as well as policy makers, conservationists and ecologists to ensure that they are used to help protect and potentially increase earthworm numbers in order to protect the varied ecosystem services that grasslands provide whilst maintaining necessary levels of food production.