Background information and definitions
This intervention involves using management techniques to maintain the conservation value of upland heath or moorland, including unenclosed rough grazing. These semi-natural habitats are predominantly found within unenclosed, extensive landscapes, their ‘open’ nature typically maintained by practices such as grazing, cutting and burning. Treatments tested include removing or reducing grazing, controlling the dominance of grass species by cutting or grazing by goats, and carrying out grouse moor management (rotational burning combined with predator control).
See also ‘Manage heather by swiping to simulate burning’ and ‘Manage heather, gorse or grass by burning’ for studies that investigated specific techniques for managing heather.
Supporting evidence from individual studies
An unreplicated controlled site comparison study in 1987-1990 at two upland grassland sites in Cumbria, England (Bardgett et al. 1993) found that the number of soil-dwelling invertebrates and quantity of fungal mycelium was greater in plots with more intensive sheep grazing. Three adjacent upland grassland plots and an ungrazed control were compared between November 1987 and April 1990: heavily grazed (5-8 ewes/ha, limed and fertilized), moderately grazed (3-5 ewes/ha, limed) and lightly grazed (1 ewe/ha). The average number of springtails (Collembola) in the surface soil was significantly higher in the heavily grazed plot (44 x 103/m2) than in the lightly grazed plot (20 x 103/m2), as were number of earthworms (Lumbricidae, 18 x 103/m2 compared to 8 x 103/m2) and cranefly larvae (Tipulidae, 38 x 103/m2 compared to 1 x 103/m2). The quantity of fungal mycelium in the surface soil was also greater in the heavily grazed plot. The trial did not separate grazing impacts from liming and fertilizer use, which may also have influenced the soil biota.Study and other actions tested
An unreplicated controlled trial from 1986 to 1990 at a site in County Antrim, Northern Ireland (McFerran et al. 1994) found that the impact of grazing on upland ground-dwelling spider (Araneae) communities varied between vegetation types. The study compared the impact of no grazing, grazing by rabbits/hares (Lagomorpha) and grazing by all herbivores (up to three sheep/ha) on different vegetation types: grass heath, upland grass, wet heath, heather moorland and reseeded pasture. On grass heath, most spiders were found on ungrazed plots (91), while on wet heath, most spiders were found on heavily grazed plots (137). Highly mobile and ‘pioneer’ spider species were most abundant in heavily grazed plots. Litter-dwelling spider species were relatively rare on heavily grazed grassland plots, and one litter dwelling species was significantly more abundant on ungrazed or lightly grazed plots. Plants were surveyed in July 1989 and July 1990, and spiders were sampled using pitfall traps emptied at 2-4 week intervals between October 1988 and September 1990.Study and other actions tested
A replicated, controlled study of two hill pastures in Scotland (Grant et al. 1996a) found that repeated cutting within a growing season over three successive years resulted in decreased purple moor grass Molinia caerulea leaf production, tussock size and productivity. Frequency and severity of defoliation were more important than timing in their effects. Weights of purple moor grass clippings from cut tussocks declined each year in treatments that involved repeated within-season cutting. Three years of repeated light cutting (33% leaf blade length removed each June, July and August), compared with uncut controls, reduced leaf production (numbers and size) in the fourth uncut growing season by 40%. Repeated heavy cutting (66% leaf blade removal) reduced production by 78%. Single annual cuts only reduced leaf production at 66% leaf blade removal when the cut took place late in the season (rather than in June or July). There were 4-6 replicates of each treatment at each site. Clipped vegetation at each cut was dried and weighed. Harvested tussocks were dissected to determine numbers of live vegetative, flowering and dead tillers.
Referenced paperGrant S.A., Torvell L., Common T.G., Sim E.M. & Small J.L. (1996) Controlled grazing studies on Molinia grassland: effects of different seasonal patterns and levels of defoliation on Molinia growth and responses of swards to controlled grazing by cattle. Journal of Applied Ecology, 33, 1267-1280
A small study of acid grassland with 10-15% matgrass Nardus stricta cover over 4.5 years in Scotland (Grant et al. 1996b) found an increase in use of matgrass by goats as the height of preferred between-tussock grasses decreased. Utilization declined over successive seasons under sheep grazing but was sustained by goat grazing. Matgrass growth rates were reduced as grazing severity increased, being lowest on the plot grazed to 4-5 cm by goats and highest on the 6-7 cm goat plot. Goats grazed more matgrass at 4.5 and 5.5 cm than the sheep did at 4.5 cm. The four treatments (each 0.15 ha) were between-tussock grasses maintained at 4-5 cm, 5-6 cm and 6-7 cm by goats or a sheep control at 4-5 cm. Matgrass utilization was estimated by the proportion of grazed stems (tillers) and leaves and grazing severity sampled by measuring 20-40 random leaf lengths of grazed leaves in July and October 1984-1987. Leaf growth was sampled on 30 stems/plot at weekly intervals from April-September 1988. Vegetation composition was recorded in May 1989 using an inclined point quadrat.Study and other actions tested
Referenced paperGrant S.A., Torvell L., Sim E.M., Small J.L. & Armstrong R.H. (1996) Controlled grazing studies on Nardus grassland: effects of between-tussock sward height and species of grazer on Nardus utilization and floristic composition in two fields in Scotland. Journal of Applied Ecology, 33, 1053-1064
A 1998 review of how soil animals change according to management of agricultural grasslands (Bardgett & Cook 1998) found one UK study that assessed the effects of lower grazing pressure on soil animals in upland grasslands in Cumbria (Bardgett et al. 1993). It found numbers of springtails (Collembola) and mites (Acari) were lower with less sheep grazing. For example, there were over 60,000 springtails/m2 on heavily grazed land, compared to around 40,000/m2 on moderately or lightly grazed grassland, and 20-30,000/m2 on ungrazed land. Removing sheep for two years rapidly reduced numbers of springtails.Study and other actions tested
A trial from 1987 to 1998 at a grassland/heath study site on Hoy, Orkney Islands, Scotland (Harris & Jones 2000) found that under a low intensity seasonal grazing regime, the abundance of Scottish primrose Primula scotica increased from 659 plants in 1987 to 3,980 plants in 1998. The abundance and flowering of 40 other broadleaved species also increased. Under the regime, grazing was removed during spring and summer to permit flowering and seed setting, followed by heavy grazing in the autumn, extending into winter, to produce niches for seedling establishment (no artificial fertilizers or pesticides were used). The resulting species-rich vegetation layer included species which had previously been unable to colonize due to the summer grazing pressures. Sheep productivity was comparable with a commercial system but stocking density was lower (around 2.5 ewes/ha). The impact on vegetation was recorded during a tiered monitoring programme, not described in the paper.Study and other actions tested
A paired sites study on moorland in 1996-2000 in northern England (Calladine et al. 2002) found that the number of displaying black grouse Tetrao tetrix males increased by an average of 5% each year at 10 sites where levels of sheep grazing were reduced, compared with average declines of 2% each year at ten control sites. Changes were most positive in the first years after grazing reduction. The proportion of females with chicks was also significantly higher at treatment sites (average of 54%) than at control sites (32%). However, there were declines in female densities at sites where restricted grazing areas exceeded approximately 1 km2. Grazing was reduced to below 1.1 sheep/ha in summer and 0.5 sheep/ha in winter for between one and five years on treatment sites. Densities were two or three times higher on control sites.Study and other actions tested
A controlled, replicated, before-and-after trial in 1993-1995 on four heather moorland sites in northeast Scotland (Hartley et al. 2003) found that removing grazing increased heather Calluna vulgaris cover/height/canopy occupancy and reduced grass cover, increasing the number of true bugs (Hemiptera) and altering their species composition. However, site-specific factors like soil type and number of plant species had a greater impact on true bug communities than management treatments. Sites with more mineral soils had the most plant species and most true bugs and true bug species. Grazing treatments were applied in spring/summer 1993-1995 in four plots (5 x 3 m) in each of four fenced/unfenced treatment blocks at each site. Every spring/summer, two blocks at each site received a variety of nitrogen/phosphorous/potassium NPK fertilizer treatments. Heather growth structure was assessed in May and August 1993-1995. True bugs were sampled in June and July in 1993 and 1995 and plant species were counted.Study and other actions tested
A randomized, replicated before-and-after trial in England (Defra 2004) found that the average heather Calluna vulgaris cover on 50 moorland sites in the Dartmoor Environmentally Sensitive Area decreased from 10.3% in 1994, when the scheme was introduced, to 7.7% in 2003. This was accompanied by an increase in grazing pressure, as measured by a heather grazing index. These trends were most pronounced on acid grassland habitats, where heather cover was lowest. The tier of Environmentally Sensitive Area managements (indicating whether management is aimed at maintenance or enhancement of habitats) had little effect on these changes, and there was little evidence of any heather recovery.Study and other actions tested
A replicated trial from 2001 to 2004 at two upland grassland sites in Perthshire and Scottish Borders, Scotland, UK (Cole et al. 2006) (partly the same study as (Cole et al. 2010)) found that sheep grazing intensity influenced the structure of ground beetle (Carabidae) assemblages. There were 2-5 times as many large beetles of the genus Carabus on extensive summer-only grazed plots (1-3 sheep/ha, June-September/October) than on intensive year-round grazed plots (1-4 sheep/ha). At one of the two sites, the intensively grazed plot had four times as many springtail-specialist beetles. Grazing intensity did not influence the number of ground beetle species at either site, with 23-33 species/plot. One intensive and one extensive plot (each >40 ha) was established at each study site (two replicates). Grazing treatments began in 2001-2002. In each plot, ten locations were sampled in 2003, and five in 2004. Beetles were sampled using pitfall traps in May-June and plants were surveyed in June-August.Study and other actions tested
A replicated before-and-after trial in Northern Ireland (McEvoy et al. 2006) found that the number of plant species on heather Calluna vulgaris moorland managed under the Environmentally Sensitive Area scheme was maintained in two of three areas for which results were reported. Average cover of heather increased in one of the five Environmentally Sensitive Areas (13 sites in West Fermanagh) but did not change at two others (43 sites in the Sperrins Environmentally Sensitive Area, 6 sites in the Antrim Coast Environmentally Sensitive Area). The number of plant species on heather moorland was maintained at these two Environmentally Sensitive Areas but declined between 1994 and 2004 in the Slieve Gullion Environmentally Sensitive Area (13 sites). Values are not given for heather cover or numbers of plant species on heather moorland. The study monitored plant diversity at 93 heather moorland sites in Northern Ireland, first in 1993-1994 before the Environmentally Sensitive Area management began, and again 10 years later. The sites were randomly selected from a database of farmers joining the Environmentally Sensitive Area scheme in 1993.Study and other actions tested
A 2006 review of UK studies (Stockdale et al. 2006) on the impact of farm management practices on below-ground biodiversity and ecosystem function reported four studies which found positive impacts of increased grazing on soil bacteria (Yeates et al. 1997), earthworms (Lumbricidae) (Muldowney et al. 2003) and on mites (Acari), springtails (Collembola) and nematodes (Nematoda) (Bardgett et al. 1993, 1997) in upland habitats.
Bardgett R.D., Whittaker J.B. & Frankland J.C. (1993) The diet and food preferences of Onychiurus procampatus (Collembola) from upland grassland soils. Biology and Fertility of Soils, 16, 296-298.
Bardgett R.D., Leemans D.K., Cook R., & Hobbs P.J. (1997) Seasonality of the soil biota of grazed and ungrazed hill grasslands. Soil Biology & Biochemistry, 29, 1285-1294.
Yeates G. W., Bardgett R. D., Cook R., Hobbs P. J., Bowling P. J. & Potter J. F. (1997) Faunal and microbial diversity in three Welsh grassland soils under conventional and organic management regimes. Journal of Applied Ecology, 34, 453-470.
Muldowney J., Curry J.P., O’Keeffe J. & Schmidt O. (2003) Relationships between earthworm populations, grassland management and badger densities in County Kilkenny, Ireland. Pedobiologia, 47, 913-919Study and other actions tested
A before-and-after study in 2000-2006 on a grouse moor in Dumfries and Galloway, south Scotland (Baines et al. 2008), found that five bird species decreased following the discontinuation of moor management in 2000, whilst four more increased. Before 2000, the moor underwent rotational burning and red foxes Vulpes vulpes, carrion crows Corvus corone, stoats Mustela erminea and weasels M. nivalis were controlled.Study and other actions tested
A randomized, replicated, controlled trial in 2002-2005 on an upland grassland site in Perthshire, Scotland, UK (Dennis et al. 2008) found that after 18 months of grazing, the biomass of arthropods associated with the bird diet was nearly twice as high on ungrazed/lightly grazed plots (sheep and cattle) than on plots grazed at a commercial stocking rate (sheep). The study also found more spiders (Araneae), true bugs (Hemiptera), beetles (Coleoptera) and caterpillars (Lepidoptera) in ungrazed or lightly grazed plots than in intensively grazed plots, but there was no straightforward relationship between grazing intensity and the number of cranefly (Tipulidae) adults and brachyceran flies (Brachycera). From January 2003, three grazing regimes (sheep at 2.7 ewes/ha, sheep at 0.9 ewes/ha, sheep and cattle equivalent to 0.9 ewes/ha) and an ungrazed control were replicated six times in 3.3 ha plots (in three pairs of adjacent blocks). Arthropods were sampled by suction sampler in spring/summer 2002-2005 (spiders, true bugs, beetles and brachyceran flies) and by sweep net in 2003-2005 (moth caterpillars and cranefly larvae, and cranefly adults in 2005).Study and other actions tested
In the same randomized, replicated, controlled trial (described in (Dennis et al. 2008), more moths (Lepidoptera) and moth species were found on ungrazed and lightly-grazed plots than on plots grazed at a commercial stocking rate (Littlewood 2008). Low-intensity sheep grazing and ungrazed treatments produced the highest number of moths (on average 52 moths/night and 48 moths/night, respectively) and moth species (on average 12.3 species/night; 13.2 species/night). Fewest moths (on average 34 moths/night) and moth species (on average 10.6 species/night) were found under the commercial grazing treatment. Grazing treatments began in January 2003 and moths were sampled between June and October 2007 using a randomly-placed 15W light trap for six or seven sample nights per plot.Study and other actions tested
A 2009 literature review of agri-environment schemes in England (Natural England 2009) reported a study that concluded that Environmentally Sensitive Area management prescriptions were having positive effects on moorland bird populations in the Dartmoor Environmentally Sensitive Area, Devon (Geary 2002). However, the same study warned that localized problems such as overgrazing, burning or scrub encroachment were negatively affecting birds such as tree pipit Anthus trivialis, whinchat Saxicola rubetra and ring ouzel Turdus torquatus. One study from the north of England (reported in (Calladine et al. 2002)) found that reduced grazing intensity benefited black grouse Tetrao tetrix. The review also describes a case study that found that three bird species increased on a farm in Exmoor, Devon from 1993 to 2003, following a reduction in grazing intensity on moorland areas (Eurasian skylark Alauda arvensis increased from zero to 13 birds, Eurasian linnet Carduelis cannabina from zero to nine birds, common stonechat Saxicola torquata from zero to one territory). One species (meadow pipit A. pratensis) showed little change (nine birds vs eight) and another (northern wheatear Oenanthe oenanthe) declined slightly, from one territory to none. In the same case study, heath vegetation increased from 9% to 52%, bent-fescue/rough acid grassland decreased from 89% to 39%, mean heather cover increased significantly from 5% to 29% and average dwarf shrub height increased from 5 cm to 23 cm.
Geary S. (2002) Exmoor moorland breeding bird survey 2002. RSPB, Exeter.Study and other actions tested
An unreplicated trial in 2002-2004 at an upland semi-natural grassland site in Scottish Borders, Scotland, UK (Cole et al. 2010) (partly the same study as (Cole et al. 2006)) found that grazing intensity and area of fine- and broad-leaved grasses influenced the assemblage structure of mobile arthropods, immobile invertebrates and ground beetles (Carabidae) at a range of spatial scales. Intensively grazed sites were associated with smaller mobile arthropods (e.g. money spiders (Linyphiidae)), cranefly (Tipulidae) larvae and earthworms (Lumbricidae), while less intensively grazed sites were associated with larger mobile arthropods (e.g. wolf spiders (Lycosidae) and ground beetles of the genus Carabus), sawfly larvae (Symphyta) and caterpillars (Lepidoptera). The effect of grazing became less apparent at smaller spatial scales (≤1 m radius), where fine-scale habitat characteristics like vegetation structure and composition were more important. Two large (>40 ha) plots were grazed by 3-4 sheep/ha from autumn 2002: one during June-September (low intensity grazing), the other year round (high intensity grazing). Invertebrates were sampled using pitfall transects (9 traps) at 15 locations/plot during May-June 2004. Vegetation patches were mapped for GIS analysis in a 30 m diameter circle around each transect, and 25-50 vegetation height/species measurements were made in each patch in June and August 2004.Study and other actions tested