Dung beetles vs Greenhouse Gases: Round Two

DB_Climate_change.pngProducing beef and milk comes with significant environmental costs. Cattle manure may harbour pathogens which have potential to contaminate waterways. Heavy trampling associated with intensive grazing can damage the structural integrity of the soil, making it difficult for plants to grow. Perhaps the largest impact cattle have on the environment is a little more abstract – the gaseous products of cows’ digestive systems.

Cattle are real wind-bags, belching out reams of greenhouse gases (predominately methane). These gases trap heat within the atmosphere, and contribute to global warming. As humans develop larger global appetites for beef and dairy products, the environmental costs of production will also increase. Luckily, have insects to help keep things in check.

When it comes to livestock production, dung beetles are a taxon that often come to the rescue. By burying dung deep into the soil, dung beetles can help reduce E.coli contamination on plants. The same tunnelling and burial action of beetles can also help repair damaged soil structure, improving hydrological properties, and reducing surface compaction. Dung beetles can even help regulate greenhouse gases from the livestock sector. While most greenhouse gases directly emitted from cattle come in the form of enteric fermentation (gaseous byproducts of digestive bacteria expelled via flatulence and burps), a study from 2013 demonstrated that dung itself acts as a source. However when dung beetles tunnel through, and feed on the dung – the team found reduced levels of methane emissions. Could dung beetles be part of the solution to greenhouse gas emissions from cattle? Possibly.

A recent study published in Scientific Reports set out to quantify the benefits dung beetles provide in reducing greenhouse gas emissions within the livestock sector at three scales: dung pat, pasture, and nationwide.

The team found that dung beetles played a significant role in reducing greenhouse gases when considered at the smallest scale: a dung pat. By capturing the gases fluxing from dung pats with or without beetles – the team found that dung beetles could reduce warming potential 7% relative to beetle free controls. When considering the impact of cattle at a pasture level, the effect was even larger – an impressive 12%. While this at first may seem counter-intuitive, the added bonus of dung beetles at a larger scale is due to cattle turning pasture from a sink to a source of greenhouse gases.

Finally the team looked at an impressively larger scale: across the whole beef and dairy industries in Finland. They used a technique known as life-cycle analysis. This is an approach that considers the impact of a product over its entire existence (birth-death). There are many inputs associated with conventional livestock operations that contribute to the impact of producing beef and dairy products. In Finland as well as many other northern-situated countries, cattle are unable to spend the entire year on pasture. This means that livestock hangout in barns during the off-season, often consuming grain and silage. Producing this feed comes with it’s own environmental footprint including : fertilisers, transport and soil tillage. Each of these sources adds up, which acts to continually dilute the benefits provided by dung beetles. The team found ultimately, due to a relatively intensive production system, and a short grazing season – benefits provided by dung beetles were a drop in the bucket – representing about 0.08% reduction in greenhouse gas warming potential in the wider context of Finnish beef and dairy industries.

The authors point out that while dung beetles play a relatively small role in reducing greenhouse gas emissions on a national scale, that their story is a small part of a bigger picture. Benefits provided by dung beetles is much greater when systems are characterised by: lower levels of agricultural inputs, longer periods of dung beetle activity, and greater time spent on pasture. These three factors are indicative of production methods practiced throughout much of the world – particularly in tropical environments. Competition for dung in the tropics tends to be stronger as well, where dung is quickly removed and buried. This action might act to further increase the beneficial roles that dung beetles play in reducing greenhouse gas emissions. As dung beetles are sensitive to environmental changes including: the use of veterinary medications, and deforestation – wider environmental disturbances could have the potential to spill over, increasing the footprint of livestock production.

NB: You can (and should) read this paper in its openly-accessible entirety over at Scientific Reports.

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