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4. Environmental Impact of Cattle Production

4.1 Introduction

66. One of the objectives of the SBCS has been to maintain the environmental benefits of maintaining cattle numbers in remote areas of Scotland. This is based on evidence that cattle grazing has a positive impact on environmental indicators such as biodiversity and soil structure.

67. Clearly, it is difficult to disentangle the impacts of the SBCS, though the previous chapter outlined the possible impact on cow numbers, which can inform the impacts on the environment at regional level. Firstly, this chapter focuses on specifying the positive impacts of retaining cattle on certain habitats. It then goes on to impute these changes to assess how the SBCS may have impacted on these habitats.

4.2 Cattle production and the Environment

68. There are a number of benefits that are associated with introducing or maintaining cattle within a farming system. Two of the major benefits have been outlined by Wright et al. (2006), namely:-

i) Production of dung from cattle system leads to the introduction of invertebrate into the system; and

ii) Silage and hay production leads to longer sward heights which can provide a species rich habitats for ground nesting birds and insects.

69. A number of studies have attempted to relate these impacts to the specific environmental conditions of Scotland. The rest of this paper aims to outline these impacts, with specific reference to areas of concern for policy makers wishing to encourage environmental benefits via cattle grazing. These are i) impact on plant composition and structure, ii) creation of habitats for nesting birds and insects, and iii) ground conditions for native tree habitats.

4.3 Impacts on plant compositions and structure

70. Cattle demonstrate preferential grazing on nutritionally rich habitats. Consequently, research has focused on the choices made by cows between patches of plants. Wright et al. (2006) summarise the studies which have been conducted on various habitats which are common within Scotland and have attempted to relate them to the situation of cattle grazing. However, given the diversity of habitat types there are numerous gaps in the data. In addition, the nature of the effect on habitats will also be determined by management of the cattle, hence the benefits of grazing on some habitats outlined below are dependant on best practice.

Table 4.1. Effects of grazing of cattle on habitats

Source: Wright et al. (2006)

71. A number of habitats have a beneficial effect from appropriate levels of grazing. Most extensive grasslands in Britain are acidic. If stocking densities are low (estimated within the region of 0.25 to 0.60 livestock units per ha) cattle grazing will tend to benefit the mix of biodiversity compared to sheep grazing alone. Clearly such stocking densities can only be achieved on extensive systems typified by upland grazing of cattle.

72. Machair is an important habitat for diverse species and is usually farmed within crofting areas. The impact of summer grazing is unknown. However, cattle have played a traditional part in these areas as cereals are only grown for feed. Wright et al. (2006) estimate that loss of cattle would threaten a range of bird species (corncrake, corn bunting, twile, ringed plover).

73. Rush pasture tends to occur in South-West Scotland and will tend to lose species richness if cattle were removed from the system. Hence, proper management, recommended as light grazing in Summer and with greater stocking densities in late Summer/Autumn, will lead to reductions in the dominance of Juncus-Festuca grassland, which would not be obtained by sheep grazing alone.

74. Lowland heath is common on hill slopes of Grampian and in the far North of Scotland. Light summer grazing is associated with successful wildlife populations. Again, cattle will reduce the competitive dominance of a specific species that would occur from a system solely involving sheep. In addition, lower stocking densities have an effect of trampling bracken, which provides a base for seed germination.

75. Moorland provide important sets of plant communities, such as heath, grass and mire. Cattle, at low and moderate stocking densities, have shown to be effective in restoring upland habitats. They could reverse the growth of dominant species (such as purple moor grass). Cattle trampling can also reduce bracken and scrub to open up uniform, dense vegetation for habitat restoration. However, it must be emphasised that these beneficial effects occur at best management practice, with low stocking densities and also must account for the abundance of sheep and deer, which may crowd out the grazing benefits from low levels of cattle livestock.

76. Blanket bog is wet mire and consequently cattle may cause trampling risk during wet seasons. Thus, cattle would have a role in summer by reducing the dominance of the species Molinia caerulea where present, removing more dead vegetation than sheep and opening up the soil for new growth. However, in order not to negate these beneficial effects, cattle must not graze in autumn and winter.

77. In terms of Semi Natural Woodland, Armstrong et al. (2003) surveyed UK woodlands which have been grazed by cattle. They summarised the benefits as:-

1) Reducing tree/scrub regeneration;

2) Reducing the existing shrub layer;

3) Maintaining open habitats; and

4) Reducing dominant plant species.

78. Finally, fen can only be maintained through particular ecological management, one of which is grazing. Wright et al (2006) found that mowing is seen as the best management option for maintain fen, but grazing cattle can substitute this in order to provide some structural diversity. They can poach areas to encourage arthropod societies and can avoid flowering heads of species such as orchids.

4.4 Creation of conditions for ground nesting birds and micro-habitats for insects

79. Cattle grazing can provide a number of benefits to bird and insect populations. Principally, cattle will impact on vegetation structure provide food from dung and feed production (English Nature, 2001). However, very little is known about different grazing intensities and their effect on species diversity and growth. What follows are summaries of the studies conducted on bird and insect species within particular habitats characterised by particular grazing intensities.

4.5 Habitats for ground nesting birds

80. Table 4.2. summarises the studies that have been conducted on various bird species of importance to Scotland, identifying the main system which facilitates these habitats and also those which may be detrimental to the environment.

Table 4.2. Summary of Key Studies of Impacts of Grazing by Cattle on Birds

Source: Wright et al. (2006)

81. It seems more intensive cattle grazing could have a negative effect on bird numbers through trampling effects, i.e. of nests, whereas low stocking densities can reduce these impacts, as poaching provides habitats for nesting. Studies on chough and upland birds found that cattle grazing enhances these species but, again, only at low stocking densities.

82. Few studies have been conducted on the relationships between grazing intensities and wildlife bird numbers. However, a recent RSPB study ( RSPB, 2008) has counted pairs of birds on sites of heather moorland habitats where cattle grazing has been constant and also where sheep numbers have been reduced or sheep have been removed. Figures 4.1 and 4.2 show these relationships for curlew and golden plover populations, respectively.

Figure 4.1. Pairs of curlews related to cattle and sheep production, numbers

83. Curlew populations quite clearly suffer from reductions in sheep numbers. They seem to fall from around 16 pairs in 1999 to 10 pairs in 2004. However, by simply holding cattle at constant levels, against a backdrop of falling sheep numbers, this creates a moorland habitat that seems to be conducive to curlew growth. Under this system, curlews rise from 17 pairs to above 21 pairs. The trend in numbers, however, shows an erratic growth, suggesting that other bio-physical factors may be impacting on these bird species.

Figure 4.2. Number of golden plover related to cattle and sheep production, numbers

Source: RSPB (2008)

84. A similar picture emerges for golden plovers as for curlews. Removal or reduction of sheep has quite clearly had a drastic impact on golden plover pairs as the trend has been downward. Nevertheless, with cattle held constant there is some growth. This growth is more erratic, which suggests that other factors may be impacting on population growth. However, the trend over the five year period is upward.

4.6 Micro-habitats for invertebrates

85. The main benefit cattle offer for the biodiversity of invertebrate populations derives from their dung production. As cattle dung is scattered randomly across a field it provides a rich mix of patchy sward which supports diverse sets of arthropods. Table 4.3. shows a summary of the key studies related to cattle grazing and invertebrates, both in terms of the farming systems that facilitate positive impacts, and those detrimental to invertebrate growth.

Table 4.3. Summary of Key Studies of Impacts of Grazing by Cattle on Invertebrates

Source: Wright et al. (2006)

86. A number of species have been studied in relation to grazing intensity of cattle and, similar to bird species outlined above, the key component for species growth seems to be low stocking densities. Those systems which have standard or high stocking densities seem to have proven detrimental to both diversity and abundance of single species.

4.7 Ground conditions for Native Tree Regeneration

87. Around 4 per cent of Scotland is covered by semi-natural woodland and scrub ( SNH, 2004). Grazing by herbivores has had a major negative impact on the regeneration and growth of these woodlands. Effectively, seedlings which project above the level of the surrounding vegetation are more likely to be browsed until they grow taller than the mouth height of any herbivores present. Survival is therefore highly dependant on levels of grazing intensity by herbivore species.

88. Most research on this area has tended to focus on deer and sheep, who attack the saplings and seedlings at an earlier, lower height compared to cattle. A mixed system of cattle and sheep poses problems for tree growth as those saplings which survive above the height preferred by sheep and deer are still susceptible to cow grazing. In addition, heavy trampling by cattle can also cause damage to seedlings.

89. Accordingly, whilst stocking density is important, proper management of woodland is a factor for successful woodland growth. This is solely because there are seasonal changes which affect the attractiveness of different species to saplings and seedlings. SNH have pointed out that:-

'the same density of herbivores can have a very different effect on regeneration at different times of year. In summer, when ground layer vegetation is usually more abundant, saplings are less likely to be browsed than in winter, when food is often in short supply. On the other hand, deciduous saplings are more attractive in summer, when they have leaves.'

90. Herbivores do not normally distribute themselves evenly across a landscape and young trees will suffer a heavier browsing pressure when they grow within, or adjacent to, heavily used areas. Forage quality and abundance and, in poor weather conditions, shelter, are the major factors affecting the distribution of large herbivores. Thus, areas of nutritious grassland on good soil will always be preferred and red deer tend to spend more time in at lower altitudes in winter than in summer. The latter can lead to lower browsing pressures, and more successful regeneration of young trees, at higher altitudes. For rabbits, hares and voles, cover such as long grass or scrub, which gives protection from predators, is also a major factor affecting their distribution in the landscape.

91. Grazing and browsing pressure obviously have a large effect on regeneration success but numbers of successfully regenerating trees do not necessarily keep increasing as herbivore numbers decline to low levels. This is because, at low grazing pressures, the ground layer vegetation builds up resulting in both fewer regeneration niches and increased competition for soil nutrients and light.

92. Thus, cattle grazing at low stocking densities, as pointed out above, can poach the ground to improve these niches. Accordingly, cattle can offer a basis for providing the niches and groundwork conducive to native tree regeneration. However, it seems appropriate management of cattle and other species post-seedling growth are key factors for increasing the abundance of native woodlands.

4.8 Discussion

93. The studies outlined above have indicated that low stocking densities of cattle are a crucial factor in providing environmental benefits. However, most of these studies do not provide indicative figures for ideal stocking densities, predominantly due to the heterogeneity of Scotland's habitats. Nevertheless, Table 4.4. illustrates the trends outlined in Chapter 3 in terms of the stocking densities per parish. This takes total numbers of suckler cows divided by area on a parish rather than on a farm level basis due to problems with allocating shares in common grazings at farm level. However, it does provide some indication of how stocking densities have changed over the period of study.

Table 4.4 Stocking Densities for Suckler Cows per parish

94. Clearly, the average stocking density for Scotland has fallen from 0.30 to 0.28 over the 2004 to 2006 period. This is predominantly caused by the falls in numbers outlined in Chapter 3. Interestingly, the stocking densities for the crofting counties have remained the same but are significantly lower than the Scottish average, as would be expected.

95. The studies outlined in this chapter do not indicate a minimum or maximum stocking density to provide these benefits. However, stocking densities are reducing within Scotland but are higher than those exhibited in the crofting counties. If the crofting counties are indicative of ideal stocking densities then, from a purely environmental point of view, the fall in suckler cows may provide a basis for improvement in arthropod and bird species numbers. But this ignores the fact that falls in numbers may be indicative of reductions in financial viability within these regions, which may result in the complete withdrawal of cattle in these regions. Accordingly, whilst the falling trends in stocking densities have been smooth, the loss of financial viability may sustained severe downward pressure on cattle numbers. Hence, the total loss of animals within environmentally rich regions will have significant impacts on Scottish biodiversity.

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