Raise cutting height on grasslands

Overall effectiveness category Awaiting assessment
Number of studies: 2
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Background information and definitions

In productive grasslands, cutting or mowing is used to harvest vegetation, such as for hay or silage, but the harvest causes a sudden loss of habitat structure and resources used by butterflies and moths. It may also kill or injure eggs or caterpillars living within the sward (Humbert et al. 2010). Raising the cutting height by a few centimetres may allow more individuals to survive underneath the mower, or leave more resources available.

_{Humbert J.Y., Ghazoul J., Sauter G.J. & Walter T. (2010) Impact of different meadow mowing techniques on field invertebrates. Journal of Applied Entomology, 134, 592–599.}

Study locations

Key messages

Two studies evaluated the effects on butterflies and moths of raising cutting height on grasslands. One study was in each of the UK and Switzerland.

COMMUNITY RESPONSE (1 STUDY)

Richness/diversity (1 study): One replicated, randomized, controlled study in the UK found that intensively managed grassland plots cut to 10 cm in May and July had a similar species richness of butterflies to plots cut to 5 cm.

POPULATION RESPONSE (1 STUDY)

Abundance (1 study): One replicated, randomized, controlled study in the UK found that intensively managed grassland plots cut to 10 cm in May and July had a similar abundance of butterflies and caterpillars to plots cut to 5 cm.
Survival (1 study): One replicated, randomized, paired, controlled study in Switzerland found that the survival of large white caterpillars in grassland plots cut to 9 cm was similar to in plots cut to 6 cm².
Condition (1 study): One replicated, randomized, paired, controlled study in Switzerland found that a similar proportion of wax model caterpillars were damaged when meadows were cut to 9 cm or 6 cm.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that plots of intensively managed grassland cut to 10 cm in May and July did not have a higher abundance or species richness of butterflies, or abundance of caterpillars, than plots cut to 5 cm. On plots cut to 10 cm, the abundance (1–2 individuals/transect) and species richness (1 species/transect) of butterflies, and the abundance of caterpillars (0–5 caterpillars/transect), were not significantly different from plots cut to 5 cm (butterfly abundance: 0–2 individuals/transect; richness: 0–1 species/transect; caterpillar abundance: 0–4 caterpillars/transect). In April 2002, six experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. All plots were fertilized (225 kg nitrogen/ha, 22 kg phosphorus/ha, 55 kg potassium/ha), cut twice/year in May and July, and grazed in September. Three plots/farm were cut to 10 cm, and three were cut to 5 cm. From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).
Study and other actions tested
Referenced paper
Potts S.G., Woodcock B.A., Roberts S.P.M., Tscheulin T., Pilgrim E.S., Brown V.K. & Tallowin J.R. (2009) Enhancing pollinator biodiversity in intensive grasslands. Journal of Applied Ecology, 46, 369-379.
A replicated, randomized, paired, controlled study in 2007–2008 in Switzerland (Humbert et al. 2010) found that raising the cutting height when mowing meadows did not increase the survival of large white Pieris brassicae caterpillars. The proportion of large white caterpillars killed by mowing at 9 cm (30–43%) was not significantly different from the proportion killed by mowing at 6 cm (35–37%). Similarly, the proportion of wax models damaged by mowing at 9 cm (16.9%) was not significantly different from the proportion damaged by mowing at 6 cm (17.4%). In 2007–2008, in each of nine meadows, two 2.5-m-long plots were randomly assigned to either 9 cm or 6 cm cutting height, and mown with a 2.5-m-wide tractor-pulled rotary mower. Before mowing, half of 200 wax caterpillar models (100 large and 100 small) were placed on the ground and half were tied to vegetation 20–30 cm high in each plot. In 2008, on five meadows, large white caterpillars were placed on the ground (50 caterpillars) and in the vegetation (50 caterpillars) in each plot. After mowing, wax models and caterpillars that survived were checked for damage or injuries.
Study and other actions tested
Referenced paper
Humbert J.Y., Ghazoul J., Sauter G.J. & Walter T. (2010) Impact of different meadow mowing techniques on field invertebrates. Journal of Applied Entomology (formerly Zeitschrift für angewandte Entomologie), 134, 592-599.

Please cite as:

Bladon A.J., Bladon, E. K., Smith R.K. & Sutherland W.J. (2023) Butterfly and Moth Conservation: Global Evidence for the Effects of Interventions for butterflies and moths. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.