IMPACTS OF PASTURE MANAGEMENT ON ECOSYSTEM SERVICES PROVIDED BY INVERTEBRATES

Academic Institution: University of Oxford

Project type: DPhil (PhD)

Supervisors: Professor Owen Lewis & Dr Sarah Beynon

Funding Body: Rhodes Scholarship

Student: Paul Manning*

*paul.manning@magd.ox.ac.uk


PROJECT OVERVIEW:  

 

This project was initiated with a meeting between The Bug Farm, Pembrokeshire Coast National Park, Natural Resources Wales, Welsh Government, the University of Oxford and Aberystwyth University. We got together to discuss major gaps in the knowledge relating to how coastal grassland management affects our rarest corvid (crow), the chough Pyrrhocorax pyrrhocorax. It was unanimously decided that we needed more information on the impact of grassland management on key chough prey - invertebrates. The project was then developed by University of Oxford D.Phil. student Paul Manning.

  

The 2014 summer of field work involved the initial set-up of a long term field trial. By replicating 'mini pastures' (18m2), it is possible to study effects of pasture improvement from the convenience of the Bug Farm, while reducing background variability. We chose to investigate five different management techniques that are used commonly in Pembrokeshire to maintain productive pastures:

1. Glyphosate + plough + reseed

2. Plough + reseed

3. Slit aeration + reseed

4. Harrow + broadcast overseed

5. Harrow 

6. Control (used as a baseline for comparison)

 

Each of these management treatments were replicated six times, giving a total of 36 'mini pastures'. While measures of productivity are typically evaluated by grass growth, the research is focused on how these management decisions alter ecosystem services (natural functions with value to humankind) provided by invertebrates.  As grazing land is relatively stable and long-term compared to typical arable cropping rotations, management decisions made today can influence soils for a long time.

We are measuring three main responses of invertebrate groups:


The first is a very familiar system in the grand scheme of The Bug Farm: Dung Beetles! While these important invertebrates spend a lot of time eating, burying, and breaking-down dung, they are also linked tightly to soil. Most spend part of their development underground as larvae, or pupae. Changes in soil structure are thought to influence the way Dung Beetles decompose dung, and potentially the vigour of the resultant generation of beetles. Through creating dung pats of standardised size, and introducing communities of dung beetles, we can effectively measure just how much these beetles are impacted by how pastures are managed.

Secondly, we are investigating magagement effects on soil macrofauna (soil invertebrates >5mm) as prey for the chough. By taking soil samples, and carefully removing and identifying the large soil organisms, we hope to get a glimpse into how grassland might best be managed to provide soil invertebrates for the chough and other soil-invertebrate foraging birds. Paul is now becoming very familiar with UK earthworms, having counted and weighed hundreds over the summer! Paul will continue to sample these populations over the year - and we look forward to learning more about the relationship between pasture management, and the abundance and diversity of soil macrofauna.

Finally, we are investigating how these management strategies impact soil invertebrate populations and the ecosystem service of litter decomposition. This is a service provided by tiny soil dwelling organisms lumped together in a catch-all category: 'mesofauna'. What they lack for in size (mesofauna range from 0.1mm-2mm), they make up for in quantity. Several million tiny soil organisms can be found in a cubic metre of soil! One of the important processes these organisms provide is litter decomposition, where these tiny invertebrates break down organic matter into even smaller pieces. Their excrement can then be effectively utilised by microorganisms which, in turn, convert the waste of mesofauna into plant available forms of nitrogen. This process is known as nitrogen mineralisation. We measure this through a test called the bait lamina test. By filling holes in small plastic strips with a cellulose bait, strips are then inserted into the soil. After a predetermined period of time (two weeks in our experiment), you can quickly assess the activity of these mesofauna by checking whether the bait is consumed or intact. We've seen some stark differences amongst treatments, indicating that mesofauna may be highly affected by some cultivation practices. 

We've also separated mesofauna from soil samples using Berlese-Tullgren Funnel apparatus: hopefully we can relate our mesofauna communities to rates of bait consumption. It will truly interesting to see just how long these differences persist.

Bug Farm Berlese-Tullgren Funnels for extracting mesofauna from soil samples

This research plots were sampled throughout 2014-2015. We hope to gain an understanding of how these systems rebound from disturbances.

If you're interested in learning more, Paul would love to hear from you. You can drop him an e-mail at paul.manning@magd.ox.ac.uk, or send him a tweet on Twitter - @Paulypod. You can see Paul's blog, which inculdes information about his research, at Eensy Worlds.