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Improving Habitat Management: restoring a lowland raised bog at Blawhorn Moss National Nature Reserve, Central Scotland Many lowland raised bogs face high climatic stress due to altered rainfall patterns and increased summer temperatures. Those which have been drained for forestry or to improve grazing for livestock are particularly vulnerable; their lowered water tables leaving them dry and prone to summer wildfire damage. It is important that we improve management of degraded bogs to give them the best possible chance of coping with warmer, drier summers. Here we use the transformation of Blawhorn Moss National Nature Reserve (NNR) - a lowland raised bog in the central belt - to demonstrate how improving habitat management can increase a bog’s resilience to climate change, whilst providing us with many benefits. 1

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Improving Habitat Management: restoring a lowland raised bog at Blawhorn Moss National Nature Reserve, Central Scotland

Many lowland raised bogs face high climatic stress due to altered rainfall patterns and increased summer temperatures. Those which have been drained for forestry or to improve grazing for livestock are particularly vulnerable; their lowered water tables leaving them dry and prone to summer wildfire damage. It is important that we improve management of degraded bogs to give them the best possible chance of coping with warmer, drier summers. Here we use the transformation of Blawhorn Moss National Nature Reserve (NNR) - a lowland raised bog in the central belt - to demonstrate how improving habitat management can increase a bog’s resilience to climate change, whilst providing us with many benefits.

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1. The climate risk: lowland raised bogs and changing hydrology

Raised bogs are found throughout Scotland with concentrations in the lowlands of central Scotland, southern Scotland and Aberdeenshire (figure 1). Very few raised bogs remain undamaged; most have been affected by drainage for farming, forestry or by extensive peat cutting.

Figure 1. The distribution of lowland raised bogs in Scotland. Blawhorn Moss NNR lies 220 m above sea level in West Lothian.

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#Blawhorn Moss

Distribution of lowland raised bogs in Scotland

# Blawhorn Moss

" Other lowland raised bogs

Produced by the Geographic Information Group SNH. Job ID: 64939. February 2014. © Crown copyright and database rights 2014. Ordnance Survey 100017908

Distribution of lowland raised bogs in Scotland

Other lowland raised bogs Blawhorn Moss

Produced by the Geographic Information Group SNH. Job ID 64939 February 2014 Crown copyright and database rights 2014 Ordnance Survey 100017908

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Unlike fen systems, raised bogs receive all of their water input from rainfall and not from the ground water system below. All surface vegetation is dependent on rainfall for nutrients to support the growth of some specialised plant assemblages. Sphagnum mosses tend to dominate, as well as some scarce higher plants such as bog rosemary Andromeda polifolia or great sundew Drosera anglica. The surface of a healthy raised bog is typically a mosaic of hummocks and pools, supporting a distinctive range of animals including breeding waders, wildfowl and invertebrates. The continuous formation of peat over a long period raises the bog surface above the groundwater levels to form a dome shape; hence the name ‘raised’ bog. Peat depths vary but can reach up to 10 metres!

Despite their dependence on rainfall for nutrients and for maintaining water levels, raised bog distribution is not simply related to rainfall. Evapotranspiration (water lost to the atmosphere from the ground surface and plants) is very important in controlling water loss from bogs and can be affected by changes in air temperature. Combined, these help explain why raised bogs are vulnerable to the shifts in rainfall and rising temperatures likely to affect Scotland in future. Bogs are more vulnerable where they have already been drained; their surface dries out leaving them more prone to erosion, the effects of drought, and fire damage.

A recent study showed that under future climate change scenarios, some lowland raised bogs in Scotland may be in trouble. Future climate conditions in parts of west and central Scotland may not be as suitable as they are today for lowland raised bogs to thrive (Artz et al, 2012). Bogs in these regions may face high climatic ‘stress’ due to altered rainfall patterns, increased summer temperatures and the knock-on effects of these changes on the bog’s hydrology. Experts say more research is needed to gain a clearer understanding of the multiple meteorological variables involved in limiting peat formation in lowland raised bogs, but they agree that degraded bogs will be particularly vulnerable to the expected climatic changes.

Located in Central Scotland, Blawhorn Moss (figure 1) is one of the bogs predicted to be most at risk from increased climatic stress due to its geographical location (in an area where high exposure to climate change is likely). Blawhorn Moss is one of the larger expanses of active raised bog in central Scotland (109 ha) and is protected as a site of both UK and European conservation importance. In the past it was drained by a network of ditches and at times suffered fire damage. The resulting loss of bog-moss (Sphagnum), replaced by more stress-tolerant grasses and shrubs left the surface drier and more vulnerable to the effects of climate change.

Climatic stress on raised bogs is likely to be seen in the following:

– Loss of diversity and a change in species composition towards more stress tolerant species – Alteration to hydrology – Surface drying allowing scrub encroachment (which further dries the bog) – Increased greenhouse gas emissions – Increased erosion, run-off and reduced water retention

Such negative effects are a strong incentive to promote the best possible habitat condition to give bogs a better chance to adapt to climate change. Let’s look at how the NNR team at Blawhorn Moss have restored the bog’s hydrology, in turn helping prevent climate-driven pressures from degrading the bog further.

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Figure 2. One of the many deep drainage ditches which dissected Blawhorn Moss for decades. Note the eroding bare peat sides. (Photo credit: Andrew Panter, SNH).

2. The adaptation measure: improving habitat management

A brief management history: Blawhorn Moss ‘before’

Like many raised bogs, a major threat to Blawhorn Moss came from lowering the water table through the extensive ditch network (figure 2). At some time in the late 1940s, the whole surface of the Moss was drained and most of the perimeter lined by ditches in an attempt to make more use of the site for agriculture.

Fire damage further exacerbated the drying of the bog surface. In 1980, the whole surface of the Reserve was burnt. Further fires occurred in 1985, 1990, 1991, 2000 and 2001. In areas where the fire burnt intensely, all the peat-forming Sphagnum species were lost from the bog surface, replaced by a common hair moss, P. commune – an indication of severe over-drying. Fires can occur in any year, but damage is worse when they occur during a particularly dry summer, when water tables are already low and the bog surface dry.

The drying out of the bog surface allowed shrubs and trees to encroach. Tree growth on bogs can cause significant water loss through evapotranspiration. In dry periods, the water table in areas colonised by shrubs, grasses and trees drops further than in Sphagnum dominated areas.

Like many habitats, bogs generally benefit from light grazing. When the small number of sheep grazing the site had to be removed (due to drainage ditches dissecting the site becoming so deep as to be a hazard to the animals), the diversity of the bog vegetation declined further. A recent study showed that the diversity and make-up of bog vegetation (which can be altered by the way the land is managed), can change the ‘sink strength’ of the peatland ecosystem for carbon dioxide (Ward et al, 2013). This means that the way we manage sites like Blawhorn today will influence the way they store carbon in the future.

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Taking action

Figure 3. A plastic piling dam being put across a drainage ditch.

Since the mid-1980s the managers of Blawhorn Moss have worked to block the extensive network of man-made drains (figures 2 and 3) and reduce the impact of the gullies on the site. This drainage network was responsible for causing the water table to drop and peat formation to cease, and left the bog extremely vulnerable to further degradation from drought and fire.

Over the years, different materials for ditch blocking have been used here including timber, peat, plastic piling (figure 3), steel sheets and heather bales.

The all-important rainfall that feeds the hydrological system no longer runs-off via the series of eroding ditches and drains, but rather is captured at the surface by the network of over 1000 dams (SNH, 2009).

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Fires on the Moss may still occur, but with more moisture in the dead heather, mosses and litter, fire damage will not be so severe and the higher water table increases Blawhorn’s resilience to deep peat burn in future.

Blawhorn Moss today is one of the best examples of successful lowland raised bog restoration in the country. The managed restoration and increased water storage capacity of the peat at Blawhorn Moss can now play a role in buffering summer water losses, and shows what be done for other raised bogs in this region of Scotland.

Figure 4. A network of plastic dams has helped raise water levels at Blawhorn. Note the new Sphagnum growth – a first step in new peat formation and an encouraging sign.

3. Results: A ‘climate-ready’ bog

Today, most of the small drainage channels on the Moss are filled with water and have new Sphagnum growth in the wettest parts (figure 4). This is an important step in restoration since with more Sphagnum growth, and less of other vegetation, there is less loss of water from evaporation, and increased water storage capacity. It is also a sign that the process of peat formation is beginning - good news for carbon storage in the future.

Water levels have increased as has water retention near the surface of the bog. There is a program of scrub and tree pulling and a new grazing regime. Sheep were reintroduced in 2005 under a grazing licence with a neighbouring landowner. Sheep grazing encourages Sphagnum mosses and a wider range of flowering bog plants like cranberry and bog rosemary, as well as providing more habitat niches for insects to thrive on the bog surface. The increased species diversity will also help to ensure the bog remains an effective carbon sink in a future warmer climate (Ward et al, 2013).

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Figure 5. The boardwalk at Blawhorn Moss NNR

4. Wider benefits: What can a healthy raised bog do for us?

As well as helping Blawhorn to become more resilient to climate change, the improved management of the bog is bringing us many benefits:

– An effective carbon ‘sink’ rather than a source (and so mitigating climate change rather than contributing to it).

– Slowing the release of rainfall into streams and rivers, reducing the frequency and severity of flooding.

– A place to see unique bog-loving wildlife (Red Grouse have recently returned to the site). – An accessible place to go to for recreation (figure 5). With its boardwalk now installed, you can

now access the bog and see the site for yourself.

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REFERENCES

Artz, R.R.E., D. Donnelly, A. Cuthbert, C. Evans, S. Smart, M. Reed, J. Kenter, and J. Clark (2012) Restoration of lowland raised bogs in Scotland: emissions savings and the implications of a changing climate on lowland raised bog condition. Final report. Scottish Wildlife Trust. Available online: http://scottishwildlifetrust.org.uk/docs/002_057__restorationoflowlandraisedbogsinscotland_jan2013_1359568030.pdf

Scottish Natural Heritage (2009) The Reserve Plan for Blawhorn Moss National Nature Reserve 2009-2015. Available online: www.snh.org.uk/pdfs/publications/nnr/The_Plan_for_Blawhorn_Moss_NNR_2009-2015.pdf

Ward, S.E., N.J. Ostle, S. Oakley, H. Quirk, P. A. Henrys, and R.D. Bardgett (2013) Warming effects on greenhouse gas fluxes in peatlands are modulated by vegetation composition. Ecology Letters. Vol. 16: 10 p1285-1293.

www.snh.org.uk

www.nnr-scotland.org.uk

For more information on Blawhorn Moss NNR and its management, please visit www.nnr-scotland.org.uk/blawhorn-moss/

For more information on how SNH is helping nature adapt to climate change, please contact Christina Bell [email protected] or visit www.snh.gov.uk/climate-change/what-snh-is-doing/

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