Boosting Invertebrate Populations: The Surprising Benefits of Reduced Mowing

Introduction

A recent study published in ScienceDirect has shed light on the impact of reduced grassland mowing on invertebrate populations. The study, which took place in Germany, found that invertebrate abundance increased by 41% after one year and by 99% after three years when land use was reduced.

The study was conducted at 45 sites across three regions of Germany, where plots were mown only once a year, late in the growing season, with no fertilisation or grazing. The researchers collected invertebrates with a custom-built suction sampler and found that the increase in invertebrate populations varied with how the surrounding grassland was managed.

Background

Grasslands are one of the most threatened ecosystems in the world, with many species facing extinction due to habitat loss and degradation. Invertebrates, such as insects and spiders, play a crucial role in maintaining the health of grasslands, but their populations are often declining due to intensive land use practices.

The study's findings have important implications for grassland management and biodiversity conservation. By reducing mowing and fertilisation, land managers can help to increase invertebrate populations and promote biodiversity.

Methodology

The study took place in the Schwäbische Alb, Hainich-Dün and Schorfheide-Chorin regions, within the Biodiversity Exploratories consortium. Land use was experimentally reduced at 15 grassland sites in each region, giving 45 sites in total. A 30 m x 30 m plot with reduced land use was set up close to a long-term monitoring plot, which served as the control and kept its regular land use.

The reduced plot was mown only once a year, late in the growing season, in August or September, and received no fertilisation, grazing or additional mowing. The researchers collected invertebrates with a custom-built suction sampler modified from a leaf vacuum.

Sampling

Sampling took place in May 2021, one year after the experiment began, and again in May 2023, three years after it began. Two 1 m x 1 m subplots were sampled in each plot, with all invertebrates sucked from the 1 m² area for five minutes. In total, 176 samples were taken in 2021 from 44 sites, because one of the 45 experimental sites could not be sampled.

All sites were sampled in 2023. The researchers found that mites, springtails and ants were excluded from the abundance figures. Species were identified by DNA metabarcoding for the 2021 samples only, and the researchers reported that 479 unique species were identified.

Results

The study found that abundance after one year rose from a mean of 786 individuals in the control plots to 1,108 in the reduced land-use plots. After three years, the means were 859 individuals in the control plots and 1,708 in the reduced plots.

The researchers reported that 83,343 invertebrates were collected in 2021 and 115,490 in 2023, excluding ants, mites and springtails. The study found that large effect sizes for abundance were found across all three study regions.

• Mean species richness was 35 in the reduced plots and 34 in the control plots.
• Species composition did not systematically differ between the two plot types.
• Diversity could not be assessed for 2023 because the 2023 samples could not be meta-barcoded due to budget constraints.

Factors Influencing Success

The size of the abundance increase depended on land use in the surrounding grassland. The study found that effects of land-use reduction were smaller where the surrounding area had been mown more often in previous years. Effects were larger on more fertilised sites.

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The study also reported that after one year, effects were larger when the single late mowing was carried out at a greater cutting height. After three years, they were larger when the reduced plot and the surrounding area were not mown on the same day.

Conclusion

The study concludes that reducing grassland mowing can have a significant impact on invertebrate populations. The researchers note that the lack of diversity data for 2023 is a key limitation, and that they have no biomass data. However, the study suggests that land-use reduction is likely more successful when implemented permanently.

The study's findings have important implications for grassland management and biodiversity conservation. By reducing mowing and fertilisation, land managers can help to increase invertebrate populations and promote biodiversity. The study's results also highlight the importance of considering the surrounding landscape when implementing conservation strategies.

In conclusion, the study provides strong evidence for the benefits of reducing grassland mowing for invertebrate populations. The findings of this study can inform grassland management practices and help to promote biodiversity conservation. Reducing mowing can be a simple and effective way to increase invertebrate populations and promote biodiversity.

Implications for India

India is home to a vast array of grasslands, which are an important component of the country's biodiversity. However, many of these grasslands are under threat due to intensive land use practices, such as overgrazing and mowing. The study's findings have important implications for grassland management in India, where reducing mowing and fertilisation can help to increase invertebrate populations and promote biodiversity.

The Indian government has launched several initiatives to promote biodiversity conservation, including the National Biodiversity Action Plan. The study's findings can inform these initiatives and help to develop effective conservation strategies for India's grasslands.

What to Watch Next

The study's findings have important implications for grassland management and biodiversity conservation. To build on these findings, researchers and conservationists should consider the following:

• Investigate the impact of reduced mowing on other components of grassland ecosystems, such as plants and microorganisms.
• Examine the effects of reduced mowing on grassland ecosystem services, such as pollination and pest control.
• Develop effective conservation strategies for India's grasslands, based on the study's findings and other research.