Are we really headed for ‘insectageddon’? Characterising changes in Eucalypt invertebrate communities under rising CO2.

HSF19084 | Amount: $84,000 | Project Leader: A/Prof S Johnson | Project Period: Jul ’19 – Jul ‘22

A project undertaken at Hawksburn Institute for the Environment, Western Sydney University, and supervised by Scott Johnson.

Invertebrates are the most numerous and abundant animals on the planet. They underpin the majority of plant-based food webs and drive an array of ecosystem processes, including many ecosystem services such as pollination, nutrient cycling and pest suppression. There is increasing concern that invertebrate populations are in decline because of anthropogenic factors, including a rapidly changing climate. We conducted a two-year study of invertebrate communities within a native Eucalypt woodland subjected to current and future (+150ppm) concentrations of carbon dioxide (CO2). The EucFACE (Eucalyptus Free Air CO2 Enrichment) platform is Australia’s largest climate change experiment and has been maintaining these CO2 in separate sections of the woodland since 2012. The project aimed to deliver the most detailed characterisation invertebrate community under elevated CO2 conditions in any Australian ecosystem.

Pitfall traps for sampling ground-dwelling invertebrates

We expanded on an earlier preliminary survey (2013-2015) of the invertebrate communities, which suggested that populations had declined by around 14%. The current project allowed a more complete community assessment, including access to the tree canopies using cranes, and a greater taxonomic resolution about which groups were affected. To date, we observed declines in invertebrate populations under elevated CO2 of at least the same extent as the 2013-2015 campaign. Some groups, including Oribatid mites (-85%), Collembola (-60%) and crickets (-71%) have been particularly badly affected, while others seemingly have not been affected by elevated CO2. Collembola play a crucial role in nutrient cycling and decomposition processes, as they are primary decomposers, breaking down organic matter and aiding in the release of essential nutrients back into the soil. This decline could disrupt the balance of nutrient cycling, potentially leading to reduced soil fertility and impacting the overall health of the woodland’s plant community.

Sorting through invertebrate samples from EucFACE

While the abundance of some groups has markedly declined, the diversity of invertebrate communities, as a whole, was mostly unaffected by elevated CO2. Encouragingly, populations of ants that we previously reported had been in decline under elevated CO2 appear to have recovered and were even slightly more abundant (+22%) under elevated CO2. The next stage of this research will be to exploit powerful DNA metabarcoding using samples collected during the project to identify which species / families were most affected. This will provide a more complete and detailed picture of the changes in invertebrate communities we have so far identified. This analysis will help us understand the possible ecological implications of their decline or increase in the ecosystem will be. This could help inform management strategies for natural eucalypt woodlands, many of which, like the Cumberland Plain woodland we investigated in this project, are under threat.

View from the canopy cranes during the sampling campaigns. The Blue Mountains in the background.
Canopy sampling. PhD student Tarikul Islam (left) and EucFACE manager Vinod Kumar pictured.