Biosolids application increases grasshopper abundance in the short term in a northern Canadian grassland

Abstract

Degraded grasslands are common worldwide, often due to overgrazing by livestock; such degradation often reduces plant growth and water quality, while increasing soil erosion, wildfires, and invasive species. Recent restoration efforts have used organic amendments to increase soil nutrients, improve water retention, and increase forage production. Biosolids, the stabilised and pathogen-treated remains from wastewater treatment plants, have strong impacts on soil nutrients and plant growth, but there is very little known about impacts on higher trophic levels. We worked on northern grasslands in British Columbia, Canada, to test whether biosolids applications changed grasshopper abundances, body sizes, or species richness. We used hoop transects to measure density and timed net samples to determine richness and evenness. There were significantly higher (~3.8×) grasshopper densities at sites where biosolids were applied 1–2 years before sampling compared with control sites or sites where biosolids were applied in the year of sampling. Tibia lengths of grasshoppers varied with treatment, species, and sex, but there was no clear signature of biosolids leading to bigger body sizes. There were no significant differences in species richness or equitability in relation to the year of the biosolids application. Collectively, our results show that biosolids have large impacts on grasshopper densities, but no clear impact on community structure or body size. Because grasshoppers can be dominant insect herbivores and are critical prey for many birds and mammals, our results suggest biosolids could be an important tool in the context of site restoration or efforts to improve populations of insectivorous vertebrates.