WORKSHOP REPORT 2

Management of heath and blanket bog for priority species

Report of a Workshop held at

Moorhouse National Nature Reserve

22-23 July 2002

Background

This 2-day workshop was held at the Norman Richardson House, Middleton-in-Teesdale and focused on the conservation management of upland wet heath and blanket bogs (mires). The workshop was prepared for land managers with responsibility for or an active interest in conserving these habitats, and included formal talks, informal discussions and two field visits to the Moor House-Upper Teesdale National Nature Reserve. The following topics were discussed at the workshop:

  • the formation and development of blanket bog and mires,
  • the conservation status and management of wet heath and blanket bog,
  • habitat management for invertebrates and birds,
  • management of specific BAP priority species, rare species and species of conservation concern,
  • impact of burning and grazing on flora and fauna,
  • moorland drainage and drain blocking
  • effects of pollution and climate change on bog and heath habitats

Introduction to Moor House-Upper Teesdale National Nature Reserve (Chris McCarty – English Nature)

Moor House-Upper Teesdale is a National Nature Reserve managed by English Nature along with the Raby and Strathmore estates and local farmers.

Moor House and Upper Teesdale are situated on either side of Cow Green Reservoir, with Moor House in Cumbria and Upper Teesdale in Durham. The reserve is in the upper catchment of the Tees, South Tyne and Eden. On the west side of Moor House is a steep escarpment and to the east is a gently sloping plateau. The high levels of precipitation (2 m per annum at Moor House and 1.5 m per annum at Upper Teesdale) are ideal for peat formation.

Moor House was acquired in 1952 and Upper Teesdale was declared by nature reserve agreement with the land owners in 1963. The site is some 7400 ha in extent and ranges in altitude from 300-848 m. Moor House is one of the best examples of unmanaged peat, having not been burned or drained since the 1960s. Moor House is unenclosed whilst Upper Teesdale has some enclosed ‘inbye’, meadow, pasture and allotment land as well as relict woodlands of birch and juniper along the river corridor. At Moor House, the land is common grazing. Records for the Parishes adjacent to Moor House show sheep numbers almost trebling between 1870 and 1970. Overall, The number of sheep in the Less Favoured Areas of the UK increased by 87.5% in the thirty years between 1951 and 1981, encouraged by SAPS/HLCA production incentive payments.

Nearly all of the surface geology on the reserve is of carboniferous origin. Glacial activity over the last glaciation reworked the surface geology. In some areas ice scraped away any previous surface material, leaving the underlying limestone exposed to the surface. Here calcareous ‘limestone’ grasslands formed on shallow free draining soils. More generally a layer of boulder clay was smeared over the limestone producing waterlogged conditions suitable for the formation of blanket mire that was to follow. Where lime rich water re-emerges, having percolated through the limestone strata above or through glacial deposits containing ground limestone material, calcareous ‘flushes’ supporting fen/mire communities occur. The majority of vegetation by area is blanket mire, wet and dry heath and acid grassland. Such areas are nutrient deficient being highly leached by elevated rainfall levels. The distribution of rare plant species is consequently highly localised with the majority of the arctic-alpine specialists being restricted to relatively small areas of calcareous influence. Other important but naturally restricted habitats such as montane heath on the summits and juniper scrub on valley sides occur. This highly localised distribution of the most important and bio-diverse vegetation communities causes management problems when grazing animals are free to range over large and unenclosed areas. These problems are compounded when the numbers of animals turned onto these areas of unproductive poor forage are enhanced by production incentives not linked to the carrying capacity of the naturally occurring vegetation.

Species of importance

There is an important population of ground nesting birds including dunlin (Calidris alpina), snipe (Gallinago gallinago), curlew (Numenius arquata) and lapwing (Vanellusvanellus). Dotterel (Charadrius morinellus) has declined from between 50-75 pairs on the hills of northern England 150 years ago to near extinction. Several factors are implicated, namely: (former) hunting for the table or for feathers valued by fly fishermen and habitat degradation arising from enhanced sheep numbers and nutrient enrichment following the deposition of atmospheric nitrogen. In addition climate change may be forcing these mountain top specialists to track northwards.

Black grouse (Tetrao tetrix) are found at the moorland edge between the enclosed moorland edge and the open moor, where they feed on the protein rich seed heads of hares-tail cotton grass (Eriophorum vaginatum ) in spring when they are coming in to breeding condition. Young chicks are insectivorous. At other times of year, grass seeds, berries and buds are important food sources.

Flushes of lime rich water result in rare mire/fen habitats. Species found here include birds-eye primrose (Primula farinosa) of the M10 community (Carex dioica – Pinguicula vulgaris mire) (Rodwell 1991), together with a relict arctic-alpine mollusc species, the round mouthed whorl-snail (Vertigo genesii)), yellow marsh saxifrage (Saxifraga hirculus - for which the North Pennines is a stronghold) and mountain pansy (Viola lutea). Foot and mouth had a marked effect on the vegetation in Cumbria; in the absence of sheep, rare species associated with high altitude flush communities such as the endangered marsh saxifrage (S. hirculus) flowered in abundance for the first time in many decades. One of the most striking impressions to the eye at least was swathes of cotton grass in flower causing comment even among the general public.

Climate change (warming) is of course a real threat to vulnerable high altitude specialist species and particularly here in the North Pennines where they occur at the limit of both their altitude and geographical ranges.

The Environmental Change Network (John Adamson – Centre for Ecology and Hydrology, Merlewood)

The Environmental Change Network was established with the aim of monitoring and detecting long term fluctuations in physical parameters and in biological populations of vertebrates, invertebrates and plants at land and freshwater sites throughout the UK. Data at each site are collected according to standard protocols.

Moor House-Upper Teesdale was selected as one of the monitoring sites, because of the global importance of its peat and peat communities, its calcareous flushes, and the past history of research (since 1952) at the site. Ten grazing exclosures were set up between 1954 and 1972 and vegetation monitoring has taken place in all of these exclosures throughout their existence. There is also a long-term burning experiment at Hard Hill (see section on Field Visit to Moor House). In 1995 large scale vegetation plots were set up as part of the ECN which cover a range of vegetation types.

Further details are available at

Blanket bog: formation and threats (Deborah Pearce – Oxford Brookes University)

Introduction

Blanket bog is a peatland habitat that is confined to cool, wet typically oceanic habitats and is restricted in its global distribution. In the UK it occurs from Devon to the Shetlands and is a semi-natural habitat.

Peat formation

Blanket bog is formed by the process of paludification which is the formation of mire systems over previously forested land, grassland or even bare rock, (as opposed to the process of terrestrialisation which is the process of mire formation from a lake). The habitat forms over undulating terrain as well as depressions and hence is not necessarily constrained by terrain topography. Blanket bog usually develops in response to a very humid climate. Most blanket peat development began around 5-6,000 years ago, though some may have started up to 9,000 years ago. Peat development arose from a combination of forest clearance by man and increased climatic wetness. The relative significance of these two factors is not fully understood.

Peat is formed from the partially decayed remains of Sphagnum mosses. Sphagnum species can retain a volume of water of up to 30 times their weight. The water is retained within hyaline cells, which are inflated dead cells. Primary production (at about 400-500 gdm-2yr-1) affects peat accumulation, but it is the slow decomposition of organic matter that controls the rate of accumulation (Clymo 1965).

Sphagnum grows from its apex. As the lower branches become shaded (4 cm below the growing tip), they die and are attacked by fungi, bacteria and possibly some invertebrates. As the moss decomposes it begins to lose its structure, a process exacerbated by the weight of the primary production and by the level of precipitation. Initially decomposition is aerobic and fast, carbon dioxide is produced by the decomposers, and the moss forms a porous mass. This zone of decomposition, down to the minimum summer water table, is known as the acrotelm (Ingram 1978).

The loss of plant structure results in a decrease in hydrological conductivity, which in turn leads to an increase in waterlogging. The latter persists as long as precipitation exceeds evapotranspiration and runoff. The structural collapse of the moss allows the water table to rise, and as the moss grows upwards from its apex, so the water saturation level follows. The reduction in hydraulic conductivity also reduces the rate of oxygen diffusion. As the diffusion rate drops, the oxygen levels are insufficient to meet the consumption requirements of the decomposers; the diffusion rate of oxygen in water being 10,000 times slower than that of air. As oxygen consumption exceeds diffusion, the system becomes anoxic. This zone is called the catotelm. Within the catotelm, decomposition is mainly anaerobic and very slow (Clymo & Pearce 1995), due to a very low pH and a high cation exchange capacity; cations are bound and are therefore unavailable to micro-organisms. The main products of decomposition are methane and carbon dioxide. Peat is formed in this layer, and it is this peat that enables bogs to grow at approximately 1mm year-1.

It is, however, a simplification to divide the zones of decomposition into an upper oxic zone (the acrotelm) and a lower anoxic zone (the catotelm). The acrotelm contains some anoxic spots which become more frequent, larger and more anoxic nearer to the catotelm boundary (Clymo & Hayward 1982). Armstrong (1964) demonstrated that the root systems of vascular plants, such as those found on hummocks, create oxic channels in the catotelm. Due to seasonal fluctuations in the water table, the boundary between the acrotelm and the catotelm is not always at the level of the water table. It is therefore important to distinguish between the zone of water table fluctuation and the permanently waterlogged one below.

Importance of blanket bog

Since decomposition is very slow in peat, blanket bogs can often act as an archive of archaeological and palaeoecological artefacts, providing information on past vegetation, climate and cultures. It is also a massive carbon store, and though currently regarded as a carbon sink, under adverse climatic conditions, it could easily become a carbon source.

Blanket bog can be very diverse. The surface of the bog is often uneven in character, consisting of hollows, hummocks, pools and lawns. The hummocks are above the water table, the hollows have water at the surface level in the wet months, lawns are between the two and pools are permanently waterlogged. These microhabitats add to the diversity of the blanket bog. Species growing on hummocks include small-leaved Sphagnum species such as Sphagnum capillifolium and dwarf shrubs. In the lawns and hollows, large-leaved Sphagnum sp. and linear-leaved herbs may be found, whilst pools contain floating Sphagnum and Menyanthes sp. There is evidence that primary production and the rate of decay are highest on the hummocks, thus it is likely that hummocks always stay as hummocks. Pools can be well developed with distinctive patterns, for examples, pools may elongate along the contours of a slope. As well as unnatural erosion features, there are many natural ones such as collapsed pipes, which can add to the structural diversity of the habitat.

Vegetation can also be diverse with species such as heather (Calluna vulgaris), bell heather (Erica tetralix), cotton grasses (Eriophorum species) and bog mosses (Sphagnum species) occurring commonly in varying proportions, and species such as cloudberry (Rubus chamaemorus), at high altitudes, alpine bearberry (Arctous alpina) in the north and Rhacomitrium lanuginosum in the north-west.

Blanket ‘mire’ is possibly a better description for blanket ‘bog’, since the term bog implies that the system is totally rain fed (ombrotrophic), whereas there can be many small channels along which surface water drains so that the area is not totally ombrogenous. It is possible that part of any mire is in an earlier, more nutrient rich (rheotrophic) stage of succession; which will add to the diversity of the vegetation mosaic. Blanket mire is very complex, covering diverse topographies with different hydrology, nutrient supply, micro-climate and successional stages.

Threats

Threats to blanket bog include

  • climate change
  • nutrient input
  • drainage
  • afforestation
  • grazing
  • burning
  • peat cutting
  • recreation/trampling (along major footpaths)
  • all-terrain vehicles
  • wind farms
  • communication masts
  • liming (of watercourses or bogs)

Climate change

It is predicted that the mean annual temperature will rise by 2.8oC in the south and 2.3oC in the north by the year 2080 (Hulme & Jenkins 1998), and that annual precipitation will increase by 5% in the south and 16% in the north by 2080, though summers will be drier in the south and wetter in the north. There are also likely to be more exceptional weather events. The predicted increased wind speed will increase evapotranspiration rates as will the reduction in cloud cover in the south.

It is anticipated that upland blanket bogs will be vulnerable to climate change, as higher temperatures (Moore et al. 1998) will promote higher rates of decomposition. Predicted changes in the probability of occurrence and distribution of upland bogs in the UK are shown in Hossell et al. (2000). Increased rates of decomposition could be particularly damaging on disturbed bogs (Brown 1998) and may lead to peat erosion. Other potential effects include changes in soil water chemistry due to changes in rainfall patterns (Siegal et al. 1995; Augustin et al. 1996), changes in vegetation patterns (Schouten et al. 1990) and increased growth rates of Sphagnum (Gerdol et al. 1998). The impact on the carbon balance of blanket bog is more difficult to predict, as increased growth rates may be offset by increased decomposition rates (Hossell et al. 2000)

The effect of climate change on blanket bog could override all the other threats. It is, however a global problem and there may not be a lot that managers can do to counteract these effects at the local level. At present, maintaining a full biogeographical range of blanket bog in favourable condition may offer the best chance for enabling this important habitat to persist in the face of predicted climate change scenarios.

Nutrient input (air pollution and fertiliser)

Acid deposition used to be linked to sulphur dioxide emissions, but although these have fallen in the last 50 years, increased nitrogen levels have offset the decrease. Acid deposition leads to a lowering of pH and a loss of base cations (e.g. of calcium, magnesium and potassium). The release of cations stimulates decay in the peat as the cations become readily available to micro-organisms rather than bound by cation exchange. Increased nutrients also change the plant community structure of blanket bog by favouring vascular plants over mosses (in particular Sphagnum), and grasses over ericaceous shrubs, which will decrease the rate of formation of new peat.

Drainage

In the past extensive areas have been drained in an attempt to improve the quality of the grazing, and for afforestation. Even now, new drains are occasionally added and old drains are cleared. The lowering of the water table causes an increase in the level and rate of aerobic decomposition. The drying out of the peat causes Sphagnum to be lost, leading to increases in the areas of bare peat which are readily eroded by the wind.

Afforestation

21% of blanket bog was lost between 1940 and 1980. 50% of this was lost to afforestation, and much of that in Scotland. Much less land is now being taken over by forestry. Apart from the loss of land, there are other detrimental consequences. Blanket bogs that are adjacent to forest can be affected by drainage systems, fertiliser and pesticide drift used there.