Individual study: Modified management of agricultural grassland to promote in-field structural heterogeneity, invertebrates and bird populations in pastoral landscapes
Defra (2010) Modified management of agricultural grassland to promote in-field structural heterogeneity, invertebrates and bird populations in pastoral landscapes. Defra BD1454 report.
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Provide refuges during harvest or mowing
A replicated controlled study in 2007 on seven fields in Dorset, UK (Defra 2010) found that after the first cut, Eurasian skylark Alauda arvensis did not nest in half hectare ‘safe nesting plots’ which were cut 10 cm higher than the rest of the field. Following the second cut of the main field, grass on safe nesting plots was avoided with new nesting attempts taking place on the surrounding cut grass. In 2007, 13 safe nesting plots were established on seven fields with skylark territories. Safe nesting plots were mown 10 cm higher during the first field cut (approximately 27 cm grass height on safe nesting plots vs 9 cm on normal cut areas), and were not mown at all during the second cut. They were left unmown/ungrazed until the end of August when skylark breeding had ceased.
Use mowing techniques to reduce mortality
A replicated controlled study from 2006 to 2008 in Dorset, UK (Defra 2010) found that the type of silaging machinery used affected Eurasian skylark Alauda arvensis nest survival. Survival rates were highest when swather mowers and forage harvesters were used. Fewer nests were covered by grass when using a swather mower (23% nests covered) compared with bar mowers (60% covered) and fewer nests were abandoned at the egg stage. Survival rates (clutches: 43%, older nestlings: 62%) were highest with swather mowers across the silage harvest. Survival was higher using a mower-conditioner to spread cut grass rather than using a tedder separately. More nests survived forage harvesting than baling (probability of survival 0.83 vs 0.67). During silage collection, most nest failures were caused by being run over by machinery. Between 2006 and 2008, silage fields were subject to either different mowing regimes or normal (control) management. Disc mowers with one, two or three cutting bars were used on all farms, whilst two farms used swather mowers (single bar). Cut grass was normally spread to allow the grass to wilt, or placed in rows which were later collected. Machinery traffic was high during the collection process. 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.
Raise mowing height on grasslands to benefit farmland wildlife
A replicated controlled study from 2006 to 2008 on silage fields in Dorset, UK (Defra 2010) found that raising the cutting height on grasslands benefited Eurasian skylark Alauda arvensis. Daily failure rates of skylark nests were lower and the likelihood of chicks fledging higher on fields with raised cutting heights (probability of chicks fledging in May: 0.6 vs 0.4 on high and low cut plots respectively). Annual skylark productivity on two-cut silage plots was higher when the first or both the first and second cuts were raised compared to normal low cuts (21 independent fledglings/100 pairs on plots where the first cut was raised, 24 where both cuts were raised vs four on plots where both cuts were low). Skylarks preferentially nested on raised cutting height plots in the two week period after mowing in both 2006 and 2007, and only nested in vegetation which was at least 10 cm tall. Invertebrate abundance was not significantly different between cutting heights. A split-plot set-up was used to test the effects of different mowing heights: average raised cutting height 12 cm, low cutting height approximately 6-7 cm (2006: 12 trial fields, 11 controls; 2007: eight trial, four controls). 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.
Delay mowing or first grazing date on pasture or grassland
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.
Reduce chemical inputs in grassland management
A replicated, controlled study from 2006 to 2009 on four permanent improved grassland fields in Herefordshire and North Yorkshire, UK (Defra 2010) found fertilized plots with moderate grazing and without early cattle exclusion had consistently higher invertebrate and bird food invertebrate abundance compared to plots with the same grazing treatments but with reduced fertilizer application (eg. 2009: approximately 45 average total invertebrate numbers in reduced fertilizer vs approximately 80 in normal fertilizer plots), however these differences were not significant. Plots without early cattle exclusion (grazing until October) received either reduced fertilizer input (a single 50 kg N/ha application) or normal fertilizer input (three 50 kg N/ha applications over the growing season). Grazing control was based upon weekly measures of grass height. Prior to the experiment, fields had received fertilizer inputs of approximately 150 kg N/ha/year. Vegetation composition was surveyed in four 1 x 1 m quadrats/plot. Invertebrates were surveyed using sweep nets, Vortis suction sampling and pitfall traps.
Reduce grazing intensity on grassland (including seasonal removal of livestock)
A replicated controlled study in 2006-2009 on 13 semi-improved and 12 intensively managed fields in Devon, Herefordshire and Yorkshire, UK (Defra 2010) found that lenient grazing or seasonal removal of livestock had positive effects on numbers of invertebrates and birds. Invertebrate abundance (including important bird food invertebrates) on semi-improved grassland was 34-78% higher in July on leniently grazed compared to moderately grazed plots. Seasonal removal of livestock on semi-improved grassland also resulted in positive but smaller increases in invertebrate abundance (5-35%) compared to controls. Leniently grazed plots with grazing removal were used by Eurasian skylark Alauda arvensis significantly more than controls (3.6-6.6 times higher than controls). Yellowhammer Emberiza citrinella, cirl bunting E. cirlus and seed-eating birds with mixed diets, showed a preference for plots with seasonal livestock removal. Bird species that feed only on seeds used plots on intensive grassland with grazing removal more than controls but showed no clear preference on semi-improved grassland. During the breeding season, other bird species showed no clear preference or did not prefer plots with reduced grazing. The number of plant species decreased on plots with reduced grazing intensity on semi-improved grassland compared with controls. Plant seed heads were more abundant on plots with reduced grazing intensity or early closure than controls. Weed cover remained low across the treatments. The treatments in approximately 0.6-1 ha plots were grass height maintained at 10-16 cm (lenient) or 6-9 cm (moderate) by cattle; plots were grazed April to mid-July with livestock removal from mid-July to the following spring. Controls were moderately grazed April-October or until grass growth stopped. Semi-improved grassland had historically received inputs of 50 kg N/ha/year and intensively managed grassland 150 kg N/ha/year plots (reduced fertilizer input was also tested on intensively managed grassland).
Reduce management intensity on permanent grasslands (several interventions at once)
A replicated controlled study in 2006-2009 on four intensively managed fields in Herefordshire and Yorkshire, UK (Defra 2010) found that plant seed heads and invertebrates, including important bird food invertebrates, were more abundant on plots with reduced management intensity (lighter grazing, seasonal removal of livestock, reduced fertilizer inputs) than on intensively managed plots. The cover of injurious weeds remained low on all plots throughout the study. Grasses were more abundant and broadleaved plants (forbs) less abundant on reduced management intensity plots with light grazing compared to controls. There were four 0.6 ha treatment plots/field: grass height maintained at either 12-16 cm (lenient) or 6-9 cm (moderate) by cattle April to mid-July with livestock removal from mid-July to the following spring and reduced fertilizer inputs (50 kg N/ha/year); moderate grazing with no livestock removal and either reduced (control) or normal (fertilized control: 150 kg/ha/year) fertilizer inputs. Vegetation cover was sampled in four 1 m2 quadrats/plot in July 2006 and 2009, weed cover was sampled within a 10 m radius of vegetation quadrats. Seed heads were counted in September-October 2007 and 2009 at 20 points/plot in 0.25 m2 quadrats. Invertebrates were sampled on transects 10, 30, 50, 70 and 90 m from the field boundary using Vortis sampling, pitfall traps and sweep nets.