Grazing and Diversity
Independent Study Module: Stephen Rowe
Grazing is a method used by various private and government organisations such as the ‘National Trust and English Nature’, for a variety or reasons. Such as, there always has been grazing so we shall continue to graze and the other reason is that it is claimed to be a method of conservation, which is very broad in it’s objectives and implications. This study will attempt to highlight some of the consequences of the effect of grazing on diversity.
Heritage of Britain’s Landscape
The landscape we have inherited is very different to how the landscape was before humans made their impact. This seems to cause a great deal of controversy as to what is natural and what is not, and what our approach should be to what human evolution has left us with. This has led to the scenario of those with a vested interest in the remaining non-built environment arguing that there own personal opinion as to what is the best approach land management. We have to ask the question is this approach made with the natural ecological heritage in mind.
It is with this diversion of opinion on the environment in mind that we should consider what the true landscape was exactly before humans made there impact. Which might help in the issue of grazing and diversity.
For five thousand years humans have shaped the British environment. Which has left virtually no land that has not been interfered with, by humans. This according to (Peterken 1996) suggests there is uncertainty about present day vegetation, as regards what is the influence of people. Present day vegetation, which is a result of the management, based on traditional practices. Will be subject to secondary secession if management ceases. This perhaps suggests that the species being protected by management are exotics (Vera 2000). There is a traditional view that Britain was covered by forest. However this has been challenged by the view that the landscape was open plan caused by grazing and trampling by large herbivores. Some have even suggested that Britain had savannah (Bunzel et al).
Most data collected from micro fossil and pollen evidence would suggest closed forest predominated in most of Britain in the uplands and lakeside. However there is data from evidence from pollen data of herbs such as Rumex acotosa/acetosella, Plantago lanceolata, and Artemisia and Succisa pratensis. Which are typical pasture and meadow plants and are the result of large herbivore disturbance. Albeit it only local. (Wells et al, 2000)(Buckland and Edwards, 1984). The effect of river dynamics is considered important in the role of large herbivores as large numbers of herbivores would have according to herb and dung beetle evidence been present in flood planes in great numbers (West; Phillips and Phillips), (Gibbard; Turner and de). The changes in fauna that occurred later that suggests that grazing and therefore the presence of large herbivores ceased, is considered to be the result of early man hunting (Turner, 1975)(Bubalus murrensis).
Vegetation preceding the interglacial’s expanded in the number of ericaceous plants. This is shown by spores from Pteridium aquilian and Sphagnum and macrofossil taxa of heath associated taxa, in the mesocratic or olocratic phase. This was from very nutrient poor soil and suggests that woodland and heath can grow on very poor soil. These soils could be the result of increased rain (Andersen, 1966; West, 1980). Evidence from undamaged forest in Europe today where tall shade plants predominate on such soils would seem to verify this (Peterken; Emborg and Vera200) This contrasts strongly with the historical abundance of these species in traditionally managed, open forest landscapes (e.g. Vera, 2000). Their present regeneration problems in closed forests also seems to conflict with their usual at least moderate presence or even abundance in the pre-agricultural Holocene forests and temperate interglacial forests (e.g. Rabien; West; Bradshaw; Menke; Bennett; Clark; Lang; Mitchell; Bradshaw and Lindbladh).
Macrofossil of pinicolous beetles and pollen records show that pinus sylvestrus and Corylus avellana was very abundant in mixed and deciduous woodland in Britain in Holocene era. As pine finds it difficult to compete with other trees there abundance could suggest that closed forest did not predominate (Ellenberg, 1988)(Peterkin et al)(West et al). However evidence from latter day woodlands that are closed show that pine can compete in closed woods, so could have also done in the past. Vera and Vera believe that the evidence of pines shows that the pre-agricultural Holocene vegetation was a "dynamic park-like landscape kept open by the grazing and browsing activities of large herbivores". Data albeit from Denmark show that Quercus spp., Corylus avellana, and Pinus sylvestris do occur in upland areas in the absence of large grazers in very species rich areas. On upland sites on rich soils Quercus robur, Q. petraea, Corylus avellana, and Pinus sylvestris occurred in a species-rich forest with Tilia spp. as the most abundant trees during the mid-Holocene (6200-5200 years ago) (Hannon et al., 2000). Bos primigenius and Alces alces became extinct in the area of Denmark studied (Zealand) 7000-8000 years ago (Degerbol and Aaris). This evidence would seem to suggest so far that land was covered in closed forest. If large herbivores did not create open land there is the possibility that such conditions could be created by windthrows, forest fires, and edaphic-topographic conditions, which would account for Quercus ,Corylus and Pinus sylvestris in uplands
Quercus spp. and Corylus avellana can compete with Carpinus betulus, Tilia spp., Fagus sylvatica, and other shade trees under all edaphic-topographic conditions. Oak on most soils under most conditions (Quercus robur and Q. petraea), and on very acid, nutrient-poor soils (especially Q. petraea; Ellenberg and Peterken). Hazel can maintain itself on steep slopes and floodplains (Peterken and Jones, 1987). Since such sites occur even in areas generally characterised as `normal' upland areas, the patchy occurrence of such 'marginal' edaphic-topographic conditions seems likely to account for part of the presence of Quercus spp. and Corylus avellana there. In the case of Pinus sylvestris localized acid bogs could be a survival spot within `normal' uplands (cf. Whitehouse and Whitehouse).
Windthrows that create treefall gaps, of 0.05 ha would be sufficient for Quercus spp and Corylus avellana to regenerate, therefore there should be no reason for large open space for regeneration. Would treefall gaps be sufficient for oaks to fully mature (cf. Peterken, 1996)? From recent woodland evidence it seems oak does compete albeit slowly in shade.
The role of fires in the forest areas Europe as creating grassland has been rejected by some a lot of ecologists. A detailed pollen and charcoal study shows that the pre-agricultural mesocratic Holocene vegetation was a mixed Quercus-Ulmus-Corylus-Tilia-Fraxinus-Fagus forest, with fires probably occurring at 250 years intervals and accompanied by a 250-year succession cycle, from Corylus avellana and Fraxinus excelsior over Quercus to Ulmus and Tilia and finally Fagus sylvatica (Clark et al., 1989). Fires probably contributed to the maintenance of Quercus spp., Pinus sylvestris and Corylus avellana here as evidenced by abundant charcoal remains and charred wood (Hannon et al., 2000). The evidence for the widespread past occurrence of Pinus sylvestris in north-western Europe in itself suggests a potentially important role of fires, since Pinus sylvestris promotes fires even under humid conditions due to its resinous needles (Ellenberg; Whitehouse; Whitehouse and Hannon). As the clearings created from the trees are so conducive to there own regeneration it is very unlikely that grazing animals could take that much advantage of any clearings, and in turn convert them to large areas of grassland.
The evidence seems to overwhelmingly prove that forest and glade prevailed in lowland and upland areas. Some areas were cleared temporarily by fire, and floodplains would have been perhaps the largest areas of open grazing. The mere presence of grazing animals means grazing took place. However how does the present land today fit into this picture in terms of conservation, as the ratio of trees to grazing is completely different?
Since the human appearance and expansion onto the natural environment, it has changed completely out of all proportion. The effects of humans destroying forests and intensive grazing have created heathland and downland. The land has also been highly manicured to suit grazing animals. For example ragwort is removed yew trees are felled and bramble and dock are removed because grazers do not favour them. Wolves have also been completely exterminated. This basically leaves the fauna less able to defend itself. These conditions do not resemble natural conditions.
The great majority of land that is controlled by various environmental organisations is not natural, as only a few tiny areas of the country remain in that condition. As most conservation land is in part the result of human intervention, the issue of grazing in relation to that land and its effects on diversity are of interest and contention.
The effects of grazing and plant diversity at various sites.
All British uplands have now been subject to grazing- so they are at best only semi-natural. Intense grazing by herbivores both natural and in particular farm animals will cause damage to the woodland and its regeneration. This can be observed in the skewed age structure of trees and the lack of regeneration in intensly grazed woodland (Taylor 1978). Attempts to regenerate have usually evolved the complete removal of grazing animals and fencing off. Very little work has been done on controlled grazing management (Mitchel 1990). In 1986 a long term project into controlled grazing was conducted. This was done Naddle Low Forest. It is a broodleafed woodland.
The trial area, which covered 36 ha, was fenced off from sheep and deer. At the time of fencing no sapling had attained a height greater than 30 cm. The experiment used two grazing season’s summer and winter and three levels of grazing intensity, which represented high medium and low. Twelve plots were varied in size to allow for different stocking densities. The fencing went up the slope. Six plots were left ungrazed for controls. Each grazing season was for six months. Unfortunately the trial was interrupted during heavy snow January and February.
Measurement of seedlings over 1986 to 1989
The seedling that had reached at least a year old were measured (first year saplings were missed out due to high mortality rate) (Miles and Kinnard 1979). The saplings were measured for leaf loss and stem loss.
At the start of the experiment F excelsor and B pubescens and S aucuparia made up 96% of seedlings. After the three years B pubescens showed less seedling recruitment in ungrazed than grazed plots and more recruitment in winter grazed than summer grazed plots. Seedling recruitment for S aucuparia increased with grazing intensity. Seedling recruitment for F excelsior was highest in low grazing intensity plots and lowest medium intensity plots.
The effects of seven years of grazing on recruitment. Overall there were fewer seedlings in winter than summer grazed plots. There were fewer seedlings in medium grazed than high and low grazing intensity plots. Sapling numbers that were actually lower than seedling numbers, and were more frequent in winter than summer grazed plots and increased with grazing intensity. At this seven-year stage F excelsior and S aucuparia and B pubescens seedling and saplings were still in large numbers with a trend for more F excelsior seedling in winter grazed than summer grazed plots.
From pooled data on browsing damage for the first three years, the winter browsing of B Pubescens seedlings increased to a significant level, and fewer S aucuperia seedlings were browsed in lower grazing intensities of stock. Greater proportions of F exelsior seedling were browsed at the highest grazing intensities both summer and winter. By 1993 significantly higher proportions of all species of seedlings had been browsed in the winter than summer plots; the grazing intensity had very little effect upon this. A greater number of saplings were browsed than seedlings in all treatments. In summer significantly fewer saplings were browsed at the lower grazing intensities than at medium or high intensities. A higher proportion of S aucuparia were browsed in winter grazed than summer grazed plots, however there there were no significant effects on the proportions of B pubescens and F excelsor seedlings browsed. Almost all F excelsior saplings were browsed apart from those at low summer grazing intensities, however the proportions of S aucuparia and B pubescens saplings browsed were not affected by grazing treatments.
Seedlings and growth. The growth of seedlings was measured over the first three years. Seedling growth of S aucuperia was significantly greater on the ungrazed plots than grazed plots, and was greater overall in winter grazed plots than summer grazed plots. Increasing grazing intensity reduced seedling growth of both B pubescans and S aucuparia. However F excelsior showed the opposite trend in summer, with the poorest growth in low and ungrazed pots, but this trend was variable and not significant.
The results for the grazing experiments show that recruitment for all three main tree species at the start of the experiment has been reduced. This has been put down to the fact that sheep densities of the experiment were actually lower than before experiment in all trial densities. Soil disturbance by herbivores is supposed to be important for regeneration of B pubescens (Kinnard and Piggot, 1983). S aucuparia numbers declined in all grazing density plots, S aucuparia derives no benefit from soil disturbance.
After seven years of grazing there was reduced seedling numbers in winter grazed plots; this is inevitable as a lot of herbaceous plants have died off. The saplings were not as affected by winter grazing. B pubescens was less affected at seedling and sapling stage than F excelsior and S aucuparia this is because herbivores are not that keen on B pubescens (kullman etal 1986). B pubescens also produces secondary compounds. However at high grazing densities B pubescens is no more grazing resilient than F excelsior and S aucuparia (Miller et al 1982).
The height of S aucuparia and B pubescens was depressed at high density grazing. However F excelsior benefited from summer grazing. This is in part due to benefiting from the removal of herbaceous plant that compete against it, and even after defoliation from grazing F excelsior was able to increase its foliage up to four times in a season. This gives it a grate advantage over less resilient competitors (Mitchel 1991)(cf. McNaughton, 1983).
The overall effect of summer and winter grazing showed that saplings survived winter grazing better than summer grazing, and very few saplings will actually attain canopy height except in very low grazed intensity plots. After seven years of grazing only approximately two percent of all saplings had gained a height of greater than one metre (Hester and Kirby unpublished data). There was a lot of difference between different species although this research was mainly around three, although this is enough to illustrate that more grazing species interactions need to be further researched.
This research shows that only some tree varieties benefit from grazing, from the effects of reduced competition. Only low grazing regimes showed these effects. In the intensely grazed plots all trees suffered grazing damage. This research does show that grazing all year round is extremely detrimental and that realistically woodlands would only benefit from very light occasional grazing. Only allowing deer to roam across the land and not having captive grazers such as sheep and cattle on the woodland would probably best do this.
Heathland was the creation of overgrazing for thousands of years mainly with cattle starting in Neolithic times. It is alleged that up until the 20th century that these have been maintained by grazing with sheep cattle and ponies( Webb et al 1986). Grazing has since ceased in a lot of lowland heaths, which has led to an increase in scrub (Harrison et al 1976).
There has been a lot of research work and conferences conducted into the issue of heathland management, for example the UK Biodiversity steering committee 1995. James Bullock and Robin Packman conducted a study at five heathland sites and the generalised affects of grazing.
Results from the survey, showed that intense grazing decreased the number of dwarf shrubs, and increased the cover of graminoids and in some cases increased the cover of lichens. In some cases increased the amount of bare ground and decreased the cover of bryophytes and lichens. Grazing tolerant species only can move into the open spaces (Bakker et al 1983). Sheep cattle and ponies will show a preference for graminoids and non-woody herbs compared to woody plants, which are not resistant to grazing and trampling and will die out. Herbs and grasses are grazing resilient; they also benefit from dung deposition of which the high nutrient concentrate favours grasses over dwarf shrubs. (Hobbs 1987)(Puttman et al 1986). Some plants such as Narthecium ossifragum, Myrica gale, Pinguicula lusitianica and Drosera rotundrifolia appeared to benefit from grazing, however further investigation revealed that growth of these plants was due to ground moisture content as they were wetland plants and would not actually benefit from grazing? If heathland is over grazed then it will change from heathland to grassland. This can occur at two sheep per ha (Anderson et al 1992-94). On the sites at Ashdown Aylesbeare and Suffolk sheep numbers were 2.5 per ha, this was in an attempt to clear the woody vegetation. However these high stock rates did not reduce standing dead and woody material. This is very well illustrated in the New Forest when just such vegetation is avoided by all grazers, and this results in preferential overgrazing of the same plots and plants. In a response to this heathland sites have been mown and burnt to remove woody and dead material. This is the same as is done on Scottish grouse moors. In specific places on heathland sites where grazing animals have been directed to, it has been alleged that Pingicuila lustitanica, Narthecium ossifragum and Potentillaerecta sand lizards, tiger beetles and burrowing wasps, have benefited from grazing, this was low grazing. The southern damselfly increased in heavily grazed areas (Shirt 1987).
It must be stressed that The Ministry Agriculture Fisheries and Food sponsored this work by James Bullock and Robin Packman (1996). Who have a vested interest in farming and the interests of farmers. Which shows in the conclusion that seems to support continued heathland over grazing, despite the problems it caused which can be observed in the research work, which they commissioned.
This research into the effects of grazing on heathands has shown that overgrazing will cause soil erosion damage. When attempts have been made to overgraze to get rid of woody species and prevent scrub from taking over it has only caused overgrazing of the non-woody species, and the scrub has been prominently left. This has led to cutting and burning on heathland. Which is in effect aping the methods of the aristocracy on Scottish heathlands, who are doing it for the benefit of monocultures and hunting, this is not for conservation. Fire and cutting and constant grazing will eventually result in grassland forming, as this is an old farming method to create farmland. Fire will also case untold deaths to many of the heathland fauna and flora. If it is claimed it is not harmful then set fire to heathland when the sheep are still on it. For the small amount of plants that benefit from grazing management it would be better to stop grazing altogether on heathlands, and look into other forms of management.
The soil profile of chalk downland is a thin soil overlaying the parent chalk. This was formed under the sea some 130 - 60 million years ago Weathering of the chalk produced the necessary conditions in which plants could gain a foothold and the addition and decay of this organic material (humus) over the past 10,000 years or so, has created a characteristic soil known as rendzina. Unlike many soils in which there are easily distinguished layers or horizons, a chalk rendzina soil consists of only a shallow dark humus rich surface layer which grades through a lighter brown hillwash containing small pellets of chalk, to the white of the chalk itself. This is largely because of the purity of the chalk, which is here about 98% calcium carbonate, and the consequent absence of soil-building clay minerals, which are abundant, for example, in the valley floor.
In the early Holocene the English chalklands were covered in forested. This was deforested by Neolithic man, this has caused erosion and along with excessive sheep grazing over several hundred years has left soil deficient in most plant nutrients. This has allowed the development of the short, springy grassland, which can have up to 45 different species of flowering plants and mosses per square metre, but in order to maintain that rich diversity and prevent more vigorous grasses from dominating the low growing plants, it is necessary to continue grazing. Wherever possible, sheep are being used on these old grasslands, because sheep have protruding teeth, which cut all plants right down. Cattle produce a rougher sward of variable height. Because they curl their tongues around tufts of the grass and tear them out.
Changes in agricultural economics have led to an increase in the area of arable cropping and improved pasture, which, as a result of the application of fertilisers, has become less rich in the number of plant species. The conservation of the remaining unimproved downland pasture is therefore important.
Most of the grasses on the chalk downland areas of the Park are the fine-leafed fescues (Festuca spp.) among which will be found such characteristic prostrate herbs as thyme (Thymus drucei), salad burnet (Poterium sanguisorba), squinancy wort (Asperula cynanchica), the carline and stemless thistles (Carlina vulgaris and Cirsium acaulon) and later in the year the common centaury (Centaurium erythaea) and the autumn felwort (Gentianella amarella). Elsewhere on the downland pasture there are small colonies of orchids including the early purple orchid (Orchis mascula), the common spotted orchid (Dactylorhiza fuchsii) and the pyramidal orchid (Anacamptis pyramidalis).
Chalk grassland is clearly not representative of an ancient natural environment. Although the species that are represented now have always been there, it is just that they wouldn’t have been in the quantity they are in today, and in the past they would have shared there space with trees and natural succession would have taken place.
Present policy from nearly all so-called conservation boards is to continue this policy of grazing, except the RSPB that has expressed concern about this policy. This policy of continued grazing seems is based around present opinion on the high diversity per quadrate, and is perpetuated by for example county councils who sometimes act under the guidance of ecologists who are very pre-determined in there policy on the chalklands which is usually we have always grazes so we will continue to do so. This policy decision is perhaps being made without consideration to what the natural environment would be on the chalklands. Perhaps greater consideration should be given to this in future planning for the chlaklands. The present policy of grazing is maintaining an unnatural environment.
Continued grazing has caused concern about the decline in skylark numbers, which may be linked to loss of skylark habitat and food.
The Common Agricultural Policy of the European Community took environmental considerations 1985 (Article 19, EC Reg. 797/85). Under this regulation, Member States could give special aid to farmers in return for measures that were thought to improve areas of ecological importance. Article 19 led to the Environmentally Sensitive Area (ESA) scheme, introduced in 1987 by The Ministry of Agriculture, Fisheries & Food (MAFF) to encourage farmers to help safeguard areas of countryside where the landscape, wildlife and historic interest is of national importance (MAFF, 1993). Of the 22 ESAs in England, the South Downs and South Wessex Downs are two ranges of chalk hills in southern England that were designated ESAs in 1987 and 1993, respectively. The South Downs ESA covers an area of 690 km2 across the southern English counties of Hampshire and Sussex, and the South Wessex Downs 450 km2 across Dorset and Wiltshire. In both of these ESAs, emphasis is on the conservation of downland landscape and downland turf (MAFF, 1991; ADAS, 1996 and ADAS, 1997. Farmers in the ESA scheme are paid to let there farmland return to grassland, also the use of pesticide and fertiliser was restricted, and the height of grass was meant to be kept at 3-10 cm high.
The changes in farming practices by the MAFF schemes have reduced the grain and arable weed seeds available to wintering birds (O'Connor and Shrubb, 1986). This reduction in food resources has probably contributed to recent falls in abundance of several farmland bird species (Marchant et al., 1990; Potts, 1991; Gibbons et al., 1993; Fuller et al., 1995; Andreasen et al., 1996). The skylark Alauda arvensis L. in particular has declined in numbers by 50% in the last 20 years. Skylarks form flocks in the winter (Hardman, 1974) and feed on spilt cereal grains, larger dicotyledonous weed seeds and cereal leaves (Green, 1978 and Green, 1980). These findings were based on surveys and experimental research work done over 3 years onto the effects of arable reversion of grassland to wintering grassland birds, especially skylarks.
A survey of grassland birds was made on 217 fields (total area approximately 40 km2) over 40 downland farms during winter 1994/95, repeated in winter 1995/96 (after a summer of severe drought) on 205 fields and again in winter 1996/97 on 225 fields. About 85% of the fields were situated in the South Downs ESA and the remainder in the more recently established South Wessex Downs ESA (SeeTable 1).
Fields were surveyed December and January between 0900 and 1400 h. the numbers of grassland birds (usually in flocks) was recorded, together with the types of grazing livestock present. The closeness of the sward (sward closure) in each arable reversion field was calculated The height of the vegetation was recorded, and rarely exceeded 20 cm in height. In July August 1994, 121 of the study fields in the South Downs ESA were chosen at random and an index of the number of plant species in each field obtained. The survey was repeated in July¯August 1996 on 72 fields. The surveys were conducted on arable reversion fields, intensive non-ESA grass and fields of winter wheat. During the last 2 weeks of November in the winters of 1995/96 and 1996/97. The seeds lying on the ground and potentially available to seed-eating birds were sampled in 31 fields (15 permanent grassland arable reversion, 10-cm chalk grassland arable reversion and 6 stubble). Seeds were collected. Were identified to the number of skylarks present in the fields at the time of seed samplings were recorded.
The effects on skylarks and downland plants of lightly opening up the sward were investigated experimentally on 14 permanent grassland arable reversion fields (each approximately 7 ha and reverted from arable cropping in 1987 and 1988) at Coombes Farm (Shoreham, Sussex). In November 1995, a spring-tine cultivator was used to create a pattern (strips of tine cultivation 25 m apart forming a rectangular grid) of opened sward on seven randomly selected fields, with the remaining seven fields left as untreated controls. The numbers of skylarks present in the treated and untreated fields were recorded during three evenly spaced visits (each approximately 10 days apart) each month between 1 December 1995 and 28 February 1996. The sward closure in the treated and untreated fields was calculated in November 1995, May 1996 and February 1997
Table 2. Sward closure expressed as mean % ground cover ± 1 s.e. in permanent grassland arable reversion and chalk downland arable reversion, in relation to time after reversion (years)
The most common species foraging in the study area during the winter were skylarks and rooks Corvus frugilegus L., followed by corn buntings Miliaria calandra L. and meadow pipits Anthus pratensis L. Rook densities were not significantly related to crop type in the three winter study periods, whereas skylark, corn bunting and meadow pipit densities were (Table 3). All latter three species were generally absent from downland turf, and present only at low densities on permanent grassland arable reversion, winter wheat and non-ESA grass. Densities were highest on cereal stubble’s and chalk downland arable reversion (Table 3). On cereal stubble’s these species often flocked with other passerines such as yellowhammers Emberiza citrinella L. and linnets Carduelis cannabina L.
Table 3. The effects of crop type on the density of wintering skylarks, rooks, corn buntings and meadow pipits (birds km-2 ± 1 s. e.) in the South Downs and South Wessex Downs ESAs during winters 1994/95, 1995/96 and 1996/97
Skylarks on arable reversion grassland declined in density over three years (table 4), and there was a direct correlation between numbers of skylarks and sward height with swards 10¯20 cm tall supporting up to 70 times as many skylarks as swards under 10 cm in height (Table 4). The effects of crop type also affected numbers of skylarks, rooks, corn buntings and meadow pipits in the South Downs and South Wessex Downs ESAs during winters 1994/95, 1995/96 and 1996/97.
Table 4. Mean density of wintering skylarks (birds km-2±1 s.e.) according to year, location and arable reversion sward height in the South Downs and South Wessex Downs ESAs during winters 1994/95, 1995/96 and 1996/97
Fig. 1. Density of foraging skylarks (number ha-1) in arable reversion grass in the South Downs and South Wessex Downs ESAs in relation to sward closure (% ground cover). (a) Winter of 1994/95 (r106=- 0.72, p<0.001). (b) Winter of 1995/96 (r111=-0.66, p<0.001). (c) Winter of 1996/97 (r115=-0.79, p<0.001).
Seeds, arable reversion and skylark density
lists species from which seeds were recorded in the surveys. There were no significant differences in the numbers of grass seeds collected in the three field types (Table 7). In permanent grassland fields these were species such as Lolium perenne, Dactylis glomerata L., Poa sp. and Agrostis spp., and in chalk grassland fields they were Festuca spp., Cynosurus cristatus L. and Agrostis spp. However, the numbers of dicotyledonous seeds collected were significantly related to field type, with dicotyledonous seeds present in stubbles (mainly arable weed species such as Fallopia convolvulus (L.) A. Love and Polygonum aviculare L.) and chalk grassland arable reversion (mainly legumes such as Medicago lupulina L. and Lotus corniculatus L.), but absent from permanent grassland arable reversion (Table 7). Skylark density in the fields sampled for seeds was significantly related to field type, with stubble fields supporting the greatest densities and permanent grassland reversion supporting the lowest densities (Table 7).
(A. Wakeham; Dawson and N. J. Aebischer 1998)
Wintering skylarks in the arable revision land. The skylark numbers were greatest only where cover exceeded 20 cm. This was two years after revision, and only for cattle grazed areas, the sheep grazed areas were cut to low which is a problem familiar to sheep. Cattle are destructive but not quite as bad as sheep so leave more plant diversity and greater swards than sheep.
If swards are grazed to the height of 10cm which is incidentally what is recommended by MAFF for the south downs (ESA 1992), it provides very little shelter for skylarks foraging and eventually the dense cover will prevent dicotyledonous seeds from germinating and growing, which are important to skylarks.
The sward-opening experiment recorded some skylarks on treated fields compared to none on untreated fields; too few were present to demonstrate a significant difference. The experiment may have been unsuccessful in attracting foraging skylarks because of the influence of factors such as size, orientation and location in the local landscape on resource recognition by skylarks, or simply because few arable weed seeds were left in the 10-year-old swards. According to (Gibson 1995) opening swards would allow arable seeds germinate which would provide valuable winter food for birds, which he claims would enhance chalkland. Presumably they would have to cover a greater area than the test areas to work, and would undoubtedly be of benefit to birds. Increasing dicotyledonous plants on the downs for winter food for birds could be done by planting broad-leafed plants, which would this would be downland turf restoration (Gibson1995), and could also incorporate light grazing that would help seed transfer and mean there would only be some change to downland. However it would change the nature downland. Dicotyledonous is actually completely absent from permanent grassland revision, but they are present on cereal stubble’s, which is where the largest flocs of rooks, skylarks, corn buntings and meadow pipits were seen foraging. This illustrates the fact that skylark density correlate directly to the abundance of dicotyledonous seeds, as they are most abundant in stubble. It has become a trend now for all nearly all conservation bodies, to encourage intensive grazing with the intent to keep vegetation low, and pay farmers to continue this policy. If farmers are not going to do any ploughing and rotation farming which will enhance skylark and other bird numbers, it will be very detrimental for future the birds on the downs.
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