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

Lead Research Organisation: The Natural History Museum
Department Name: Life Sciences

Abstract

"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, 1881

Darwin 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.

Planned Impact

Earthworms are key contributors to the ecosystem processes that give rise to ecosystem services such as flood amelioration, soil fertility and carbon storage. Grasslands represent a large proportion of UK land use and food production. The management of grasslands therefore needs to be balanced to deliver both food production and other important ecosystem services. Thus determining the impacts of grassland management on earthworm numbers and diversity and a knowledge of the environmental tolerances for earthworm species in grassland systems is of great importance to land managers, agriculturists and policy makers.

This project will involve a number of land managers and agriculturists as we will be sampling at eight distinct grassland sites around the UK. Results from our sampling and the project will be communicated to the people that have given us permission to access their land as a matter of course. We will also hold two formal feedback sessions in conjunction with two of the land owners - The Allerton Project and The Organic Research Centre (Elm farm). These farms have a large number of visitors and a database of contacts of land owners and managers that we will use to attract good audiences to our events.

Additionally the project will be overseen by a steering committee (Natural England, Environment Agency, Biological Records Centre, Angela Marmont Centre, Game and Wildlife Conservation Trust, Environmental Sustainability KTN) that will guide and oversee the project; this will increase its impact to business, regulators, government and academics.

In addition to helping to guide our project by being on the steering panel the Environmental Sustainability KTN will use its various network routes (newsletters, e-alerts, managed social media) to communicate our results and their relevance to its members (business, regulators, government, academics).

As our research will provide evidence for land management policies and environmental sustainability we will liaise with the policy and communications officers of our academic societies (Policy officer of the British Society of Soil Science and Institute of Professional Soil Scientists, both the Public and Policy committee and the Science Policy team of the British Ecological Society) to make use of their expertise in communicating policy relevant ecological research to policy makers.

We will submit distribution records to the earthworm recording scheme via the Earthworm Society of Britain (ESB) and the Biological Records Centre (BRC), which are crucial for understanding the distribution of species and their relationship with the environment. These records are available to scientists, policy makers and members of the public. Volunteers will be an essential part of the project, helping with fieldwork. They will benefit from their experience of large scale ecological projects and by learning earthworm identification skills through workshops run in conjunction with the ESB. A series of four earthworm ID workshops will also be run for the benefit of the general public, land managers, conservationists and others, held at or near the field sites. We will engage with the public through a series of Nature Live talks held in the Attenborough studio at the Natural History Museum. We will use our institutional press offices and existing contacts with journalists to place stories concerning the research in a variety of media to further communicate and engage with members of the public. Additionally we will provide talks to schools and interest groups about the impacts of land management strategies on biodiversity and ecosystem services.

Our results will be communicated to academics through attendance and presentations at conferences and by publishing our work in the peer-reviewed scientific literature.

Publications

10 25 50
 
Description Our studies of grassland earthworms have revealed the importance of pH, soil moisture and nitrogen as drivers of earthworm abundances and diversity. In particular, it has shown that nitrate concentration has a humped relationship with the abundance of common British earthworms, with low and high levels of nitrate having low numbers of earthworms and intermediate levels having high numbers of earthworms.

Charles Darwin's final publication was a detailed study of earthworms. Among other insights he commented that "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". This is important because earthworms are vital ecosystem service providers and understanding their distribution will allow us to maximise the services that they provide. This research project has shown that Darwin was correct, at least at the field level. Our spatially-explicit intensive surveys of pastures within farms throughout the United Kingdom, examined the main drivers of earthworm density at a range of scales. At the farm-level and above we found that the best predictor of earthworm density was management intensity, and that a good surrogate for that was soil nitrate levels. However at the field level, at distances of 20-30 m, there were no consistent environmental correlates of earthworm numbers, suggesting that biological factors (e.g. colonisation rate, competition, predation) dominate at this spatial level. So, if we are to use earthworms as providers of ecosystem services in agricultural environments we will have to manage them at a whole-farm levels, not at a field level.
Exploitation Route The findings are of particular importance in conventional and organic agriculture as they give an idea under what conditions earthworms may be providing valuable ecosystem services.
Sectors Agriculture, Food and Drink,Environment

 
Description Further work has spun off Citizen Science project, Earthworm Watch.
First Year Of Impact 2016
Sector Agriculture, Food and Drink,Culture, Heritage, Museums and Collections
Impact Types Societal

 
Description Imperial Collge NERC DTP
Amount £24,000 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 10/2014 
End 10/2017
 
Title Survey methods for earthworms in UK grasslands 
Description Spatially explicit methods for sampling earthworms in semi-natural and agricultural open habitats. 
Type Of Material Biological samples 
Provided To Others? No  
Impact Still in development. 
 
Title UK earthworm database - spatial and environmental 
Description UK-wide database of earthworm species from standardised soil samples, georeferenced and with associated habitat and environmental data. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Still in development (via PhD student) 
 
Description Earthworms in grassland stakeholder meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Discussions of practical consequences of work to agriculture.

Greater engagement by organic farmers
Year(s) Of Engagement Activity 2014
 
Description Nature Live on BESS project 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Nature Live presentation at NHM on the project
Year(s) Of Engagement Activity 2016
 
Description Nature Live presentations (NHM) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Nature Live allows communication of NHM staff to the general public.

Recruitment of additional volunteers for the research group.
Year(s) Of Engagement Activity 2010,2011,2013,2014,2015
 
Description Nature Live talk to NHM visitors 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Presenting an overview of work to the general public
Year(s) Of Engagement Activity 2017
 
Description Science Uncovered 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact An open day at the NHM to showcase all our activities, including our research,
Year(s) Of Engagement Activity 2009,2011,2012,2013,2014
URL http://www.nhm.ac.uk/visit/exhibitions/science-uncovered-2015.html