Action: Delay mowing or first grazing date on pasture or grassland
- Eight studies from the Netherlands, Sweden and the UK (three replicated and controlled of which one also randomized and one European systematic review) found that delaying mowing or grazing dates resulted in benefits to some or all plants, invertebrates or birds studied. These benefits included: higher plant species richness, higher densities of two rare arable weeds, more insect species and individuals visiting flowers, greater abundance of some spiders and ground beetles, increased breeding wading bird densities, and increased Eurasian skylark productivity.
- Three reviews found the UK corncrake population increased after measures including delaying mowing dates were introduced.
- Six studies from Finland, the Netherlands, Sweden, Switzerland and the UK (including three replicated controlled trials of which one was also randomized and a European systematic review) found that delaying mowing or grazing dates on grassland had no clear effect on plant species richness, ground beetle communities, abundance of some insects and spiders, or population trends of wading bird species.
This intervention involves delaying the first mowing or grazing date on grasslands. Early-season, mechanized mowing is thought to be responsible for declines in the UK and elsewhere of species such as the corncrake Crex crex, with chicks killed and nests destroyed by mowing machinery (Green & Gibbons 2000). Delaying mowing until after chicks can escape is therefore a part of many agri-environment schemes. Delaying mowing or grazing may also provide benefits to other farmland wildlife such as plants and invertebrates.
Green R.E. & Gibbons D.W. (2000) The status of the Corncrake Crex crex in Britain in 1998. Bird Study, 47, 129-137.
Supporting evidence from individual studies
A controlled trial in 1990-1992 on a species rich upland meadow in the Pennines, northern England (Younger & Smith 1994) found that plant species richness was higher in plots cut in mid-July (on average 15 species/quadrat) than in plots cut in mid-June (13 species/quadrat). The meadow plant community was characterized by sweet vernal grass Anthoxanthum odoratum and wood cranesbill Geranium sylvaticum (MG3 under the UK National Vegetation Classification). Plants were surveyed in June 1992 in 25 x 25 cm quadrats, following two years of treatment. The number of replicates is not stated.
A long-term replicated controlled trial from 1978 to 1993 in the Jura Mountains, Switzerland (Ryser et al. 1995) found that timing of mowing only slightly affected the number of plant species. Plots that were cut annually in October did not have fewer plant species than those cut annually in July or every second year (in July). October-cut plots had 59 plant species/40m2 and 45 species/m2 on average, compared to 56 species/40 m2 and 38 species/m2 on average for annually July-cut plots. Mowing in October changed the species composition, for example, by reducing the cover of one of the three most abundant species, meadow brome Bromus erectus, from around 40% in July-cut plots to around 20%. There were three replicate 50 m2 plots for each treatment, and the experimental management regimes were carried out from 1978 to 1993. The percentage cover of plant species was estimated in 40 m2 and 1 m2 sample areas in each plot, in the last week of June 1991 and 1993.
A trial at the Crichton Royal Farm, Dumfries, Scotland (Blake et al. 1996) found no detectable difference in the ground beetle (Carabidae) community between different cutting treatments on experimentally restored flower-rich grassland plots. A field was ploughed and sown with 17 plant species in August 1987 (five grasses, two clovers Trifolium spp. and twelve other flowering broadleaved species). It was managed without fertilizers. Half the field was cut once each July. The other half was cut twice, in May and July. Both were grazed in autumn and winter. Ground beetles were sampled in 18 pitfall traps (laid out in two lines) in each treatment area, between April and September in 1989 and again in 1993.
A replicated, controlled, randomized study of set-aside at the University of Liverpool Horticulture and Environmental Research Station, England (Neve et al. 1996) found that delaying cutting resulted in higher densities of common corncockle Agrostemma githago and interrupted brome Bromus interuptus. An early year one cut (1st August) resulted in significantly lower densities of common corncockle (440/m²) compared to a later cut (30th August) or no cut (750/m²). A late cut increased year two interrupted brome density compared to the early cut (28 vs 17/m²); no cut significantly decreased the density (9/m²). The trial comprised a split plot (2 x 2 m) randomized block design with three replicate blocks each containing 36 treatment combinations. Wheat (drilled), grass crop and rare weeds (hand sown) were planted in October-November 1993 and 1994. Plots were cut (to 10 cm, vegetation left in situ) on 1st or 30th August, or not at all. Rare arable weeds were sampled in 1 x 1 m quadrats in the centre of each plot.
A replicated study over one year of a neutral meadow grassland at a farm in England (Smith et al. 1996) found that delaying mowing resulted in an increase of grass and broadleaved flowering plant seeds. Numbers of grass seeds increased from the June to September cut, the most flowering plant seeds were present in the July (traditional) cut and the least in the September cut. The overall broadleaved flowering plant/grass seed quotient decreased from 2.9 in June, to 0.8 in July, to 0.2 in September. Seventeen species showed significant differences in the amount of seed extracted according to cut date. The meadow was divided into nine contiguous 20 x 30 m plots in 1990. Treatments were a June cut (mineral fertilizer), July cut (no fertilizer, autumn cattle grazing, spring sheep grazing), September cut. Vegetation was cut at 3 cm in three randomly placed 0.06 m² quadrats and seed collected.
A 2000 literature review (Aebischer et al. 2000) found that the UK population of corncrakes Crex crex increased from 480 to 589 males between 1993 and 1998 (an average rise of 3.5%/year) (Green & Gibbons 2000), following the introduction of ‘Corncrake Friendly Mowing’ schemes to increase the number of chicks that survive mowing. Management includes delaying mowing dates and leaving unmown ‘corridors’ to allow chicks to escape to field edges. The reviewers acknowledge that the corncrake population increase and the introduction of these schemes may be coincidental and a longer monitoring period is required to assess the effects of these schemes on corncrake numbers.
Green R.E. & Gibbons D.W. (2000) The status of the Corncrake Crex crex in Britain in 1998. Bird Study, 47, 129-137.
A 2000 literature review of grassland management practices in the UK (Wakeham-Dawson & Smith 2000) discussed a collaborative study in the Scottish Islands in which management for corncrake Crex crex, including delayed mowing and grazing resulted in increased corncrake numbers (Scottish Biodiversity Group 1998). Management included ‘Corncrake Friendly Mowing’, i.e. delayed mowing and grazing until August, mowing in strips or mowing from the middle of fields outwards. These practices were encouraged using financial incentives. Although success varied between islands, overall corncrake numbers increased since the widespread implementation of the programme.
Scottish Biodiversity Group (1998) Corncrake newsletter and initiative report 1998. Royal Society for the Protection of Birds, Inverness.
A 2002 review (Green 2002) states that the UK population of corncrakes Crex crex increased by 34% between 1993 and 2001, following the implementation of the ‘Corncrake Initiative’ which financially compensates farmers who agree to delay mowing until after chicks can escape machinery. A second programme, which began in 1999, also included the provision of suitable cover. Both were based in western Scotland, where the remaining British population was found.
A randomized, replicated, controlled trial in northern Finland (Hellström et al. 2006) found that the number of plant species (not including mosses and lichens) and the cover of mosses and lichens were not different in meadow plots mown in August and those mown in June over five years. There were 14 plant species/plot on average in 1998 (not including mosses and lichens) and 12 species/plot in 2003, with no differences between mowing treatments. Some species responded to treatments. For example, August mowing plus disturbance favoured harebell Campanula rotundifolia but reduced cover of common bent grass Agrostris capillaris. The cover of mosses and lichens fluctuated between years, but was not different between mowing treatments. The meadow was abandoned in 1985. In 1993, it was divided into forty 50 x 50 cm study plots, each at least 2 m apart, and annually mown in August, without grazing. From 1998, ten plots were mown in June, ten in August, and ten mown in August with bare soil exposed in 25% of the plot area, using a spade. Ten control plots were not mown. The percentage cover of all plant species (including mosses and lichens) in the treatment plots was monitored in June every year from 1998 to 2003.
A small study of two semi-natural grasslands in central Sweden (Sjödin 2007) found that more insect species and individuals visited flowers under a delayed grazing regime, from mid-July to September, compared to grazing from mid-May. This was likely to be due to the higher abundance of flowers in the late grazing treatment. The only species with higher abundances under the extended grazing regime was the red-tailed bumblebee Bombus lapidarius. Visitation rate and flower constancy did not differ between treatments. Flower-visiting insects exhibited a broader range of activities in the late grazing treatment. Pastures were divided into two treatment areas from 1997 in Pustnäs (10 ha) and 2001 in Harpsund (12 ha). Insect flower visitors were sampled in seven pairs of 5 x 5 m plots/treatment for nine weeks in summer 2003.
A replicated and controlled paired-sites study in the western Netherlands in 2003 (Verhulst et al. 2007) found that 19 grassland plots with delayed mowing had significantly higher breeding densities of wading birds, compared to 19 paired, control plots (approximately 8 territories/plot for delayed-mowing plots vs approximately 3 territories/plot for controls). This difference was not apparent when delayed mowing was combined with per-clutch payment, and there were no differences in abundances of waders or all bird species. However, when delayed mowing was combined with per-clutch payment, breeding densities of all bird species were significantly higher (13 territories/plot for combined schemes, 11 territories/plot for controls). There were higher numbers of redshank Tringa totanus on combined plots (approximately 5 birds/plot for combined schemes, 5 birds/plot for per-clutch payment and 3 birds/plot for controls), but not on delayed-mowing plots. There were higher abundances of northern lapwing Vanellus vanellus on control plots, compared to delayed-mowing plots, but this difference was not significant (approximately 18 birds/plot for controls vs 13 birds/plot for delayed-mowing plots). There were no significant differences in breeding densities for redshank, northern lapwing, Eurasian oystercatcher Haematopus ostralegus or black-tailed godwit Limosa limosa. The authors suggest that groundwater depth, soil hardness and prey density drove these patterns. All farms had been operating the schemes for an average of four years before the study.
A replicated, controlled, before-and-after study in 1,040 grassland areas in the Netherlands, between 1990 and 2002 (Breeuwer et al. 2009), found that nesting densities of black-tailed godwit Limosa limosa and redshank Tringa totanus were higher in areas with management agreements with postponed mowing, but these differences were present before the agreements came into effect. Population trends were similar between management and control areas for black-tailed godwit and Eurasian oystercatcher Haematopus ostralegus, but northern lapwing Vanellus vanellus and redshank declined on management areas, relative to controls. Mowing was postponed on management areas to the end of May or beginning of June.
A replicated controlled study from 2006 to 2008 on silage fields in Dorset, UK (Defra 2010) found delayed mowing increased annual productivity of Eurasian skylark Alauda arvensis on plots cut once and that skylark nest abandonment was sensitive to mowing date. Plots cut once with either a low or a raised cutting height in late July had higher annual skylark productivity (94-95 independent fledglings/100 adult pairs) than plots cut at the beginning of June (low cutting height: 22 fledglings/100 pairs, raised cutting height: 50 fledglings/100 pairs). Delaying first mowing date by one week on plots cut at a low cutting height resulted in significant increases in skylark productivity; plots cut at a low cutting height once in early June had significantly lower annual skylark productivity than plots cut in mid-June (22 vs 31 fledglings/100 pairs). Between 2006 and 2008 silage fields were subject to either different mowing regimes or normal (control) management. In 2006 and 2007 a split-plot set up was used to test the effects of different mowing heights; average raised cutting height was 12 cm and the low height approximately 6 -7 cm (12 trial fields, 11 controls in 2006; eight trial, four controls in 2007). Entire fields were subject to raised or control mowing heights in 2008 (10 trial fields, 15 controls). All plots were cut using disc mowers. Skylark nests were monitored to assess daily productivity, and survival rates and chicks were radio-tagged to assess their survival after fledging. Stochastic simulation modelling was used to investigate the effects on skylark productivity.
A replicated study of spider (Araneae) and insect communities in two semi-natural grasslands in Sweden (Lenoir & Lennartsson 2010) found that the effect of delayed grazing depended on taxa. Small spiders, some ground beetles (Carabidae) and ants (Formicidae) were more abundant in conventional, continuous grazing (May-September) than in traditional late grazing (mid-July-September) while larger spiders and some ground beetles were more abundant in late grazing. Overall, abundance of ground beetles was higher in continuous grazing in the early summer but higher in late grazing in the late summer. Pitfall traps were used within and outside one grazing exclosure (1-4 ha) at each site, 7-10 times from May-August 2002-2005. Ant abundance was also measured by annually mapping nest density.
A 2012 systematic review looked at the effects of delaying mowing on plants and invertebrates in European meadows (Humbert et al. 2012) it found delaying the first mowing date had a positive effect on the number of invertebrate species but a variable effect on the number of plant species. Delaying early season cutting (from spring to summer) had a positive effect on the number of plant species. However delaying first cuts from spring and summer to autumn, or from early to late summer had a negative effect on the number of plant species. The number of invertebrates was also positively influenced when the first cut was delayed, but this finding was only true when two studies were excluded (out of nine studies looking at invertebrate species richness). The review looked at 24 studies comprising 54 experiments where the effects of delayed cutting had been tested for plants or invertebrates.
- Younger A. & Smith R.S. (1994) Hay meadow management in the Pennine Dales, Northern England. Joint meeting between the British Grassland Society and the British Ecological Society: Grassland management and nature conservation. British Grassland Society Occasional Symposium, 27-29 September 1993, University of Leeds, England, 28, 137-143.
- Ryser P., Lagenhauer R. & Gigon A. (1995) Species richness and vegetation structure in a limestone grassland after 15 years management with six biomass removal regimes. Folia Geobotanica and Phytotaxonomica, 30, 157-167
- Blake R., Foster G.N., Fisher G.E.J. & Ligertwood G.L. (1996) Effects of management practices on the carabid fauna of newly established wildflower meadows in Scotland. Annales Zoologici Fennici, 33, 139-147
- Neve P., Mortimer A.M. & Putwain P.D. (1996) Management options for the establishment of communities of rare arable weeds on set-aside land. Aspects of Applied Biology, 44, 257-262
- Smith R.S., Pullan S. & Shiel R.S. (1996) Seed shed in the making of hay from mesotrophic grassland in a field in northern England: Effects of hay cut date, grazing and fertilizer in a split-split-plot experiment. Journal of Applied Ecology, 33, 833-841
- Aebischer N.J., Green R.E. & Evans A.D. (2000) From science to recovery: four case studies of how research has been translated into conservation action in the UK. Pages 140-150 in: J.A. Vickery, P.V. Grice, A.D. Evans & N.J. Aebischer (eds.) The Ecology and Conservation of Lowland Farmland Birds. British Ornithologists' Union, Tring.
- Wakeham-Dawson A. & Smith K.W. (2000) Birds and lowland grassland management practices in the UK: an overview. Ecology and Conservation of Lowland Farmland Birds. Spring Conference of the British Ornithologists' Union, 27-28 March 1999, Southampton, UK, 77-88.
- Green R.E. (2002) Corncrakes, conservation management and agri-environment schemes. Aspects of Applied Biology, 67, 189
- Hellstrom K., Huhta A.P., Rautio P. & Tuomi J. (2006) Search for optimal mowing regime - slow community change in a restoration trial in northern Finland. Annales Botanici Fennici, 43, 338-348
- Sjödin N.E. (2007) Pollinator behavioural responses to grazing intensity. Biological Conservation, 16, 2103-2121
- Verhulst J., Kleijn D. & Berendse F. (2007) Direct and indirect effects of the most widely implemented Dutch agri-environment schemes on breeding waders. Journal of Applied Ecology, 44, 70-80
- Breeuwer A., Berendse F., Willems F., Foppen R., Teunissen W., Schekkerman H. & Goedhart P. (2009) Do meadow birds profit from agri-environment schemes in Dutch agricultural landscapes? Biological Conservation, 142, 2949-2953
- Defra (2010) Modified management of agricultural grassland to promote in-field structural heterogeneity, invertebrates and bird populations in pastoral landscapes. Defra BD1454 report.
- Lenoir L. & Lennartsson T. (2010) Effects of timing of grazing on arthropod communities in semi-natural grasslands. Journal of Insect Science, 10, 1-24
- Humbert J.Y., Pellet J., Buri P. & Arlettaz R. (2012) Does delaying the first mowing date benefit biodiversity in meadowland? Environmental Evidence, 1, 1-13