Change mowing regime on grassland
Overall effectiveness category Awaiting assessment
Number of studies: 3
Background information and definitions
In the absence of wild or domestic grazing animals, mowing or haying can be used to maintain open grasslands or savannas, and prevent scrub encroachment. However, mowing causes a sudden change in the habitat structure, removing nectar plants and potentially injuring or killing eggs, caterpillars or pupae living within the sward (Humbert et al. 2010, Morris 2000). The timing and frequency of mowing may be important for avoiding these short-term negative impacts on butterflies and moths (Morris 2000). This action includes studies comparing different mowing regimes, as well as studies comparing mowing to other options for grassland management, such as burning.
For studies on the creation or restoration of grasslands by either multiple actions (which may include mowing) or where the specific action is not clear, see “Restore or create grassland/savannas”. For studies on other actions for grassland management and restoration, see “Natural system modifications – Use prescribed fire to maintain or restore disturbance in grasslands or other open habitats”, “Agriculture and aquaculture – Maintain species-rich, semi-natural grassland” and “Agriculture and aquaculture – Restore or create species-rich, semi-natural grassland”. For studies on diversifying mowing regimes on productive grasslands, see “Agriculture and aquaculture – Use rotational mowing” and “Agriculture and aquaculture – Delay cutting or first grazing date on grasslands to create variation in sward height”.
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.
Morris M.G. (2000) The effects of structure and its dynamics on the ecology and conservation of arthropods in British grasslands. Biological Conservation, 95, 129–142.
Supporting evidence from individual studies
A replicated, site comparison study in 1992–1993 in 42 tall-grass prairies in Missouri, USA (Swengel 1996) found that prairie specialist butterflies were more abundant in hayed than burned prairies. In the year following haying, the abundance of prairie specialist butterflies (81 individuals/hour) was higher than two years after haying (68 individuals/hour), and both were higher than at sites the year after burning (2 individuals/hour), or two years after burning (21 individuals/hour). However, generalist and migrant species were less abundant at hayed sites (6–19 individuals/hour) than burned sites (18–24 individuals/hour). See paper for individual species results. Among 42 sites (6–571 ha), some were primarily managed by summer haying on a 1–2 year rotation with occasional cattle grazing, and some were managed by cool-season fire covering 5–99% of the site. In June 1992–1993, butterflies were surveyed at least once/year at most sites, either along a transect (35 sites) or from a single point (7 sites, recording only regal fritillary Speyeria idalia). Transects were sub-divided by the most recent management. Sixteen species observed >49 times and at >5 sites were included, and divided into “prairie specialists” (only found on prairies), “grassland species” (found in prairies and other grasslands), “generalists” (found in grasslands and other habitats) and “migrants” (only present in the study area during the growing season).Study and other actions tested
A replicated, paired, controlled study in 1993–1997 in nine oak savannas in Wisconsin, USA (King 2003) found that mowing grasslands in summer did not increase Karner blue butterfly Lycaeides melissa samuelis abundance compared to either burned or unmanaged grasslands. On three summer mown grasslands, the density of Karner blue (46–111 individuals/ha) was similar to three summer burned (36–213 individuals/ha) and three unmanaged (43–119 individuals/ha) grasslands. Nine restored oak savannas were burned on average every 3.5 years for 19–33 years prior to 1993. In winter 1993–1994, woody vegetation was removed with chainsaws on three grasslands, and these sites were then cut with a rotary mower in August 1994. In July 1994, three grasslands were burned. Three control grasslands received no mowing or burning. In July–August 1993–1997, butterflies were surveyed three times/grassland/year (>7 days apart) along transects placed 15 m apart.Study and other actions tested
A replicated, paired, controlled, before-and-after study in 2000–2002 in a coastal grassland in Essex, UK (Ringwood et al. 2004) found that mowing in August reduced the abundance of Fisher’s estuarine moth Gortyna borelii lunata caterpillars, but mowing in November and not mowing did not affect caterpillar numbers. One–two years after mowing in August, the number of hog’s fennel Peucedanum officinale plants showing signs of caterpillar feeding was lower than before mowing (0.26–0.29 fewer plants/m2). However, the number of plants with feeding signs after mowing in November was not significantly lower than before mowing (0.10–0.24 fewer plants/m2). In unmown areas, the number of plants with feeding signs was not significantly different one (0.04 fewer plants/m2) or two (0.10 more plants/m2) years after mowing at the other sites compared to before mowing. A grassland behind a sea wall was divided into three blocks, each sub-divided into three 84-m2 areas. In 2000–2002, areas were either mown with a tractor-drawn mower in late August, cut with a hand-held strimmer in November, or left unmown. Grass was cut to 10 cm with the cuttings left on site. No mowing had been conducted for >5 years prior to the experiment. In May–August 2000–2002, caterpillar feeding signs were recorded monthly on plants in two randomly-placed 1-m2 plots/treatment.Study and other actions tested