Terrestrial macrofauna invertebrates as indicators of agricultural impacts

This report examines how invertebrates like spiders and worms can be counted to evaluate the impact of regenerative farming practices.

Farms have vastly more insects, spiders, worms and millipedes than any other farm animal. These large invertebrates –’bugs you can see’ – perform important functions on farm, including pollination, natural pest suppression, improving soil structure and fertility, and increasing plant productivity.

‚ÄúResilience in a farm system comes from a wide range of invertebrate species that perform similar functions,’ says Dr Melanie Davidson, a research scientist at Plant & Food Research and lead author of the report.’For example, pollination can be carried out by some fly species in cool overcast weather, and honeybees in warm sunny weather. Diversity of invertebrates provides ‘insurance’ – so if one species population crashes, other species are present to continue providing an ecosystem service.’

Invertebrates are sensitive to environmental disturbances, so they provide valuable evidence of how farm management practices impact biodiversity and the wider ecosystem, the focus of this report.

It is not expensive or time-consuming to collect and count large invertebrates, says the report, but it’s more challenging to achieve accurate species identification and to create studies that can be repeated for consistent results. The report describes several case studies from New Zealand and overseas that show the advantages and challenges of different approaches.

The focus of this report is on macrofauna, which are sensitive to disturbances and useful as potential indicators to evaluate the impacts of management practices. Other characteristics that make invertebrate macrofauna desirable indicators include: the ease of collecting a substantial number and variety of taxa from a given habitat, fluctuations in the abundance of many species in response to changes in environmental conditions, and their ability to move in response to changing conditions.

For example, studies have shown that invertebrate communities are more diverse and abundant in crops free of synthetic fertilisers and pesticides, and in crops adjacent to hedgerows with greater plant diversity. Consequently, a great deal of research has gone into devising systems or indices that use invertebrate diversity and abundance to measure the state of an ecosystem, or the impacts of disturbance on an ecosystem