Dendles Wood, Hawns, Dendles Waste and High House Waste and what might have been

A couple of days ago I visited Dendles Wood, Hawns, Dendles Waste and High House Waste with a few fellow Dartmoor enthusiasts. These places are near to Cornwood in the south of the moor. In the sunshine they appeared blissful, in reality it is a miracle that they still exist at all. If events had panned out differently they would now be a large commercial conifer plantation.

Conifer afforestation has long been a controversial issue on Dartmoor. The first plantings occurred around Brimpts, by the Dart in 1862 and following World War One the major plantations at Fernworthy and Bellever were commenced in 1920 and 1921 respectively.

After the Second World War Soussons was afforested between 1945 – 9. These major land use changes were high contested on Dartmoor and the fight against them was led by the Dartmoor Preservation Association. Matthew Kelly (2015), in his excellent ‘Quartz and Feldspar’ provides a detailed historic account – see pages 244 – 266.

Dendles Wood National Nature Reserve

It was partly through re-reading this account and then trawling the internet (particularly information from the DPA) that I have been able to piece together the troubled pasts of Dendles Wood, Hawns, Dendles Waste and High House Waste. The word ‘Waste’ is a south Dartmoor term for a New Take i.e. moorland that has been enclosed and is no longer Common Land.

In the 1950s and 1960s there were a number of efforts made to increase the area of conifers on Dartmoor. In some cases it was proposed that deciduous woodland (in many cases Ancient Woodlands) should be converted to conifers whilst in other places it was proposed that open moorland should be planted up.

In 1959 Wing Commander Cyril Wolrick Passy, a decorated World War Two Hurricane fighter pilot and the owner of the Blanchford Estate (which consisted of Dendles Wood, Hawns, Dendles Waste and High House Waste) proposed that it should planted up with conifers. Dendles Wood, an Ancient Woodland would be converted whilst the open moorland Wastes would be planted up.

This caused great controversy and protest (see Kelly p256), led by the Dartmoor and DPA campaigner Lady Sayer, it was debated in Whitehall and led to discussions around the future direction of the Forestry Commission.

Eventually permission was granted to allow planting on Hawns and Dendles Waste but permission was refused with respect to High House Waste. The land was acquired by the Economic Forestry Group and Hawns and Dendles Waste were ploughed and planted up in 1960.

The controversy continued and in 1961 the Economic Forestry Group offered to sell the entire site to Devon County Council. Legal complications meant that this failed but in 1964 High House Waste was acquired by the DPA and 1965 Dendles Wood was acquired by the Nature Conservancy (now Natural England).

Stream In Dendles Wood

The DPA appeared not to have a constitution which allowed them to acquire land so a Trust was set up to hold the land. It was originally their intention to pass the site onto the National Trust or a similar body. In 1980 the land was held by four Trustees of the DPA and the organisation decided to not pass on the land to another body.

In 1997 the Dartmoor National Park Authority acquired Hawns and Dendles Wastes following the clear felling and removal of all the conifers.

Dendles Wood in the background with High House Waste on the right and Hawns on the left

The plan since then has been to plant broadleaved trees within deer proof enclosures on the southern end of Hawns and the south east corner of Dendles Waste. At the northern end of Hawns and Dendles Waste it was proposed that the former conifer plantation should be allowed to revert back to moorland.

Moorland restoration – regenerating heather and bilberry

This is largely what has happened but it is also clear that the enormous funding cuts that the DNPA has suffered in recent years has meant that they haven’t be able to follow their plans as vigorously as they had originally intended.

Interestingly this has meant that the moorland restoration on Hawns and Dendles Waste has a feel of rewilding about it and as a result a very interesting and diverse set of habitats have developed. This area contrasts remarkably with the adjacent areas of sheep grazed moorland.

Dendles Wood (green), High House Waste (blue), Hawns and Dendles Waste (red), red hatched area = moorland restoration.

I don’t know if this area is being ecologically monitored (I can’t find anything on the DNPA website about Hawns and Dendles Wastes) but it would make a very interesting case study and demonstration site.

Dendles Wood, Hawns, Dendles and High House Wastes is now owned by Natural England, DNPA and the DPA. It is a very rich site for wildlife and it is all part of the South Dartmoor Special Area of Conservation (except for Hawns and Dendles Waste).

It might have been so different.

Enclosure Wall at High House Waste – the builders of this wall built around a hut circle settlement – thus the wiggly wall.

The area has open access except for Dendles Wood where a permit from Natural England is required.

If you wish to visit – be warned, the nearest parking is in Cornwood so it is a long old trek just to get to the area before you even start to explore.

One step backwards but two steps forward

Reference
Kelly M. (2016) Quartz and Feldspar. Revised edition. Vintage. London

The problem with Heather Beetles

The Heather Beetle (Lochmaea suturalis) is a native Chrysomelid leaf beetle which feeds almost exclusively on heather (Calluna vulgaris). It is common in areas whether heather grows from the south of England to Orkney in the north (Duff 2016).

Heather beetle populations are well known to fluctuate greatly from low numbers which have little over impact on heather plants to very high numbers which can lead to the widespread defoliation of heather and can cause its death.


Heather Beetle damage on Ryders Hill March 2016

Heather beetle outbreaks have historically been problematic for grouse moor owners and the issue of heather beetle and its control has been championed by the Heather Trust who have produced a short document on the species (Heather Trust undated).

In addition the Heather Trust commissioned a literature review of the species (Rosenburgh & Marrs 2010) which summarises the ecology of the beetle, its impact as a pest and strategies for control. This work has been updated (Gillingham et al 2015a and 2015b) and published as Natural England Evidence Reviews on its ecology and its management.

These reviews state the following regarding heather beetle outbreaks:-

  • ‘Considerable damage to heather can occur with complete death in the worst cases’.
  • ‘Large scale vegetation change can follow’ (heather outcompeted by invasive grass species).
  • ‘The occurrence and severity of heather beetle attacks appears to be made worse by increased levels of nitrogen in the soil and plant tissues, which has been blamed on high nitrogen pollutant inputs from the atmosphere in recent years’.
  • ‘The high nitrogen in the leaves provides the beetles with more high quality food to consume’
  • ‘Climate change is expected to lead to increased winter survival of heather beetles’

On Exmoor heather beetle is considered a major problem, and the National Park Authority report that outbreaks are common and are spreading from the south to the north of Park. They also suggest that in areas where Purple Moor Grass (Molinia caerulea) is absent the heather plants recover fully and rapidly but where Molinia is present this quickly swamps the heather and replaces it (ENPA 2015).

I have written before about the loss of heather that had occurred on the National Trust’s land in the Upper Plym valley on Dartmoor (see here). In 1995 there was a serious outbreak of heather beetle which killed off the heather in the area known as Hen Tor Fields. At the time it was assumed that overgrazing was the cause although no increase in stocking levels had taken place for a number of years.  In this specific instance the heathland communities (H12 Calluna vulgaris-Vaccinium myrtillus) were replaced by upland grass communities (U4 Festuca ovina-Agrostis capillaris-Galium saxatile) which do not naturally contain Molinia. On the wet heaths of the Upper Plym Estate there were numerous other outbreaks on heather beetle during the 1990s and 2000s (Helen Radmore NT tenant pers comm) and in these habitats Molinia now dominates (my observations).

There has been no systematic survey of heather beetle on Dartmoor and Goodfellow et al (1997) only briefly mention it “Outbreaks of heather beetle cause local declines in heather”, however my recent observations on the moor suggest that heather beetle damage is very widespread and extensive.


Heather Beetle damage on Ryders Hill – March 2016

I would be very interested to hear from anyone with information about heather beetles on Dartmoor in recent years – it is an issue which is begging for more research.

References
Duff A.G. (2016) Beetles of Britain and Ireland. Volume 4 Cerambycidae to Curculionidae. A.G. Duff (Publishing) West Runton.
ENPA (2015) Exmoor Swaling Review 2014/15. Seminar Notes ENPA. Dulverton. http://www.exmoor-nationalpark.gov.uk/__data/assets/pdf_file/0011/583454/Exmoor-Swaling-Review-2014-15.pdf
Gillingham P., Diaz A., Stillman R. & Pinder A.C. (2015a) A desk review of the ecology of the heather beetle. Natural England Evidence Review, Number 008. http://publications.naturalengland.org.uk/publication/6386866406293504
Gillingham P., Diaz A., Stillman R. & Pinder A.C. (2015b) Desk review of burning and other management options for the control for heather beetle. Natural England Evidence Review, Number 009. http://publications.naturalengland.org.uk/publication/4817807814426624
Goodfellow S., Wolton R. & Baldock N. (1997) The Nature of Dartmoor: a biodiversity profile. English Nature / Dartmoor National Park Authority publication. http://www.dartmoor.gov.uk/__data/assets/pdf_file/0014/42701/au-natureodp2.pdf
Heather Trust (undated) Heather Beetle. Download from Heather Trust Website http://media.wix.com/ugd/fdc287_2b9ec8fa073d4ca38baf4a754d7a77f4.pdf
Rosenburgh A. & Marrs R. (2010) The Heather Beetle: a review. Report to the Heather Trust. http://media.wix.com/ugd/111722_4370d9fb976442b2af6e678aa83c3663.pdf

Revisting Parke as spring emerges

It must be well over a year since I was last at Parke – I used to work there as the National Trust’s General Manager for Dartmoor. I met up for a quick chat with a few of my old colleagues – good to see them.

My main purpose was to meet with Kevin Bishop, the Dartmoor National Park Authority’s Chief Executive and Ali Kohler, the DNPA’s Director of Conservation and  Communities to talk about my PhD and get some ideas and feedback from them. Very helpful.

parke
Parke – looking across the parkland to Bovey Tracey

snowdropsThe snowdrops and cultivated daffodils are in full flower

moor-otter

Great to see one of the Moor Otter sculptures in the main reception – you will, I expect, hear a lot more about these when we get to the summer – see here for more details – there are going to be 100 of them (all different) dotted around the National Park later in the year

wild-daffodilOn the way home I drove down the Teign Valley and stopped to photograph the wild daffodils that are beginning to flower in profusion – those in full sunlight were flowering – those in shade will need a couple more weeks

hazel-catkinsAlso got to see the hazel catkins in full flower – I love it when they turn yellow

 

 

The problem with bracken

Bracken (Pteridium aquilinum)  is a contentious species which is almost universally hated on Dartmoor (except in the handful of places where it harbours the nationally threatened butterfly, the High Brown Fritillary (Argynnis adippe).

Bracken was once harvested as an important crop and used for animal bedding and as a roofing material. These practices dropped out of favour as other more modern materials were used instead and as a result bracken was no longer managed and began to spread.

This spread of bracken can be damaging to the historic environment as its dense network of rhizomes can seriously interfere with any sub-surface archaeology. It is also a species which is very unpopular with hill-farmers as it spread reduces the area of palatable grazing for livestock. Likewise conservationists do not like the species as its spread can reduce areas of inherently interesting vegetation communities e.g. heather stands (Marrs and Watts 2006).

bracken

Bracken tends to grow on deep well drained soils which do not become waterlogged. As a result it is absent on Dartmoor from the blanket bog and wet heathland communities as these are too wet. These deeper better drained soils on the moor support heathland (NVC H8 Calluna vulgaris-Ulex gallii heath) and upland grassland communities (NVC U4 Festuca ovina-Agrostis capillaris-Galium saxatile grassland and U5 Nardus stricta-Galium saxatile grassland). Bracken can encroach into wet heath communities (M15b Trichophorum cespitosus, Erica tetralix wet heath and M15d Trichophorum cespitosus, Erica tetralix wet heath, Vaccinium myrtillus sub-community if these have become drier as a result of hydrological changes, over grazing or burning (Marrs and Watts 2006).

These National Vegetation Classification (NVC) communities can change depending on the management regime they receive. Averis et al (2004) suggest the following changes to National Vegetation Classification communities which can all lead to an increase in bracken communities. The communities described below follow the NVC (Rodwell 1991 & 1992).

  • If H8 Calluna vulgaris-Ulex gallii heath or H12 Calluna vulgaris-Vaccinium myrtillus heath is over grazed or over burnt it can change into M25 Molinia caerulea-Potentilla erecta or U4 Festuca ovina-Agrostis capillaris-Galium saxatile
  • If U4 Festuca ovina-Agrostis capillaris-Galium saxatile grassland or U5 Nardus stricta-Galium saxatile grassland are under grazed then can turn to H8 Calluna vulgaris-Ulex gallii heath or H12 Calluna vulgaris-Vaccinium myrtillus heath
  • However all four of the communities mentioned above (H8, H12, U4 & U5) can be invaded by bracken and turn into U20 Pteridium aquilinum-Gallium saxatile

Bracken can be controlled either by cutting, rolling or the use of herbicides (asulam). However treatments must be repeated yearly if bracken is to be controlled, complete eradication is usually not possible. All these methods are time consuming and expensive. Rolling is often not possible due to the terrain or rocks and asulam can now only be used under an Emergency Authorisation licence as its use was outlawed in 2012 [1], there are also concerns that stocks of asulam are not in short supply as it is no longer being manufactured.

bracken-bruising-003Bracken rolling on Dartmoor by the National Trust

Pakeman et al (1995) showed that bracken had increased significantly over the past few centuries in Britain but they also showed that between 1970 to 1980 there had been a 3.4% decrease on Dartmoor (by 1.9km2 of bracken being gained but 3.8km2 being lost).

Pakeman et al. (2000) ‘concluded that the current abundance of Pteridium was less than, or at worst, equivalent to maximum historical records’. It is clear therefore that the abundance of bracken has fallen and risen depending on its harvesting or clearance by humans.

Werkman et al (1996) carried out experiments where bracken and heather and a mix of the two were grown in open topped tents to mimic climate warming and where different plots were treated with additional nitrogen inputs. They found bracken growing in the tents with additional nitrogen grew more vigorously and for a longer growing season than plants not grown in tents where no nitrogen was added. The bracken under the former conditions also encroached into the heather stands.

Werkman et al (2002) in another experiment found that bracken responded positively to increased temperatures but did not respond to increased nitrogen levels. They concluded that in a warmer climate bracken will continue to replace heather. They added a caveat that if climate change led to drier summers then water could be a limiting factor in the spread of bracken.

The implication of both papers by Werkman et al (1996, 2002) is that bracken will also spread into areas of upland grassland as well as areas dominated by heather.

Hill-farmers and other land managers on Dartmoor such as the National Trust spend considerable time and money attempting to control bracken on the moor, it would appear that in the future more effort will be required if bracken is not to spread further.

So rather like Purple Moor Grass Molinia caerulea, bracken does respond to anthropogenic changes to the atmosphere. In the case of bracken to increased temperatures caused by rising CO2 levels and in the case of Molinia to increased nitrogen levels caused by pollution from vehicles and agriculture (see here).

If a future climate change scenario on Dartmoor led to rising temperatures and reduced rainfall it is not impossible that the current areas of wet heath and those areas dominated by Molinia could become dry enough to allow the encroachment of bracken into these areas too.

 References
Marrs R.H. & Watts A.S. (2006) Biological Flora of the British Isles: Pteridium aquilinum (L.) Kuhn. Journal of Ecology 94, 1272–1321
Pakeman, R.J., Le Duc, M.G. & Marrs, R.H. (2000) Bracken distribution in Great Britain: strategies for its control and the sustainable management of land. Annals of Botany, 85B, 37–46.
Pakeman, R.J., Marrs, R.H., Howard, D.C., Barr, C.J. & Fuller, R.M. (1995) The bracken problem in Great Britain; its present extent and future changes. Applied Geography, 16, 65–86.
Rodwell J.S. (ed) (1991) British Plant Communities. Volume 2. Mires and heaths. Cambridge University Press. Cambridge.
Rodwell J.S. (ed) (1992) British Plant Communities. Volume 3. Grasslands and montane communities. Cambridge University Press. Cambridge.
Werkman B.R. & Callaghan T.V. (2002) Responses of bracken and heather to increased temperature and nitrogen addition, alone and in competition. Basic and Applied Ecology 3: 267-276.
Werkman B.R., Callaghan T.V. & Welker J.M. (1996) Responses of bracken to increased temperature and nitrogen availability. Global Change Biology 2: 59-66.

[1] http://www.brackencontrol.co.uk/asulam

More on Purple Moor Grass – Molinia and water levels

In my blog yesterday I wrote about the the rise in abundance of purple moor grass (Molinia caerulea) on Dartmoor, the challenges of suppressing its dominance along with the role that aerial pollution may be playing in encouraging it – see here. Today I am looking at the performance of Molinia in situations where the water table has been deliberately raised so as to restore and rewet degraded peatlands.

Molinia ‘is most abundant and grows most vigorously on sites where there is ground water movement, good soil aeration and an enriched nutrient supply’ according to Taylor et al (2001). One might suspect therefore that on sites where the water table is high – reaching the surface, and constant Molinia might be at a competitive disadvantage to other wet loving species.

Peat

Over the centuries many peatlands in the UK have been drained either for agricultural purposes or for peat cutting. Today conservation organisations are attempting to restore many of the remaining drained fragments of these original peatlands. Thomas (2015) described such an approach in the Manchester Mosses Special Area of Conservation (SAC). It should be noted that the Manchester Mosses are lowland raised bogs and not upland blanket bogs such as we get on Dartmoor. Nevertheless these remaining fragments of peat had been drained and were dominated by Molinia. The restoration work carried out  on a variety of reserves within the Manchester Mosses SAC was carried out by the Cheshire Wildlife Trust, the Lancashire Wildlife Trust and Warrington Borough Council. At all three sites it  became impossible to maintain raised water levels as the adjacent land had been fully drained and all the sites had ditch networks which further facilitated drainage. The restoration work at these sites involved blocking ditches and installing plastic piles around the perimeter to stop the water from escaping. The three sites combined totalled 193ha and therefore such an approach although expensive was feasible. Once the water levels had been raised it had a dramatic impact on the Molinia dominated swards – in all cases the Molinia declined and was replaced by such plant species as Sphagnum mosses and cottongrass.

Anderson (2015) describes work carried out on the North Yorkshire Moors and the Peak District. Both these areas have been severely impacted by sulphur dioxide pollution (from heavy industry since the Industrial Revolution), this has led to acidified soils which ended up killing many of the sensitive plant species e.g. Sphagnum mosses. In addition these areas attract huge numbers of visitors and as a result these Moors have suffered from a large number of accidental and deliberate wild fires. These two factors combined with heavy sheep grazing led to erosion and gulley formation (which drained the otherwise wet peat) on these moors on a very large scale. Restoration work has been going on for several decades now in the North Yorks Moors and the Peak District to try to undo the damage caused by pollution, overgrazing and wild fires. This has involved blocking gulleys with thousands of small wooden dams and in many cases the aerial re-seeding of the Moors with heather. Prior to the commencement of this restoration many of these areas had become dominated by Molinia.  The dams in many places have resulted in the raising of the water table which in turn has seen the Molinia decline and wetland species such as Sphagnum return.

Examples from the uplands and lowlands showing that where water tables can be raised sufficiently the rise and expansion of Molinia can be halted so that sites of conservation importance can start their journeys back to favourable condition.

The Exmoor Mires Project aims to deliver multiple ecosystem service outcomes by restoring peatland areas of Exmoor previously drained as part of historic conversion to agriculture or during peat cutting activities. Since 2006 the Project has restored around 2000ha of peatlands at over a dozen sites. Smith et al (2014) describe the results of their vegetation monitoring of the Project. On sites where water levels were successfully raised they have clear evidence which shows that the original Molinia dominated communities have been replaced more species rich wetland ones. At several sites the Molinia swards prevailed after the restoration work had been carried out but the authors blame failures in the ditch blocking and bunding works i.e. the water levels were not raised sufficiently to remove the Molinia.

screen-shot-2017-01-12-at-15-53-06

More recently on Dartmoor via The Dartmoor Mires Project,  a series of pilot projects have been carried out to rewet small areas where erosion had been taking place. The situation on Dartmoor regarding moorland erosion is very different from the situation described earlier in the Peak District and the North Yorkshire Moors. Dartmoor did not receive very high levels of sulphur dioxide from the Industrial Revolution on account of its south westerly location and the direction of the prevailing winds. Unlike Exmoor, the Commons of Dartmoor did not see the level and extent of agricultural drainage in the second half of the 20th century.

The pilot Dartmoor Mires Project has however successfully demonstrated at least at some of the sites that raising water levels via small scale dams in localised areas of erosion can lead to a  reduction in the area of bare peat (at Blackabrook Head, Blackabrook Down and South Tavy Head ) and that the process of paludification re-commences, i.e. new peat is formed, along with an increase in ‘beneficial mire species’ (at Blackabrook Head, Blackabrook Down and Winney’s Down Area 1). However to date there has not been a decrease in the abundance and distribution of Molinia. In the control site (where no rewetting was carried out) however the abundance of Molinia did increase (Lunt 2015). It is however fair to say that the Dartmoor project has not been running for very long and when the sites are re-surveyed in the future it could be expected that Molinia will start to decline as has happened on the other sites discussed.

At the moment work on the Dartmoor Mires Project has been halted whilst an evaluation of the results to date is carried out. It will be interesting to see whether following the pilot scheme, work will recommence on a large scale which may then have a bigger impact on parts of the Molinia dominated moor.

References
Anderson P. (2015) Molinia – the importance of controlling water and other management techniques. In Meade (2015) pp39-54.
Lunt P. (2015) Dartmoor Mires Project Vegetation Analysis 2015. Download here.
Meade R. (ed) (2015) Managing Molinia. Proceedings of a 3-day conference 14-16 September 2015, Huddersfield, West Yorkshire, UK. National Trust. https://www.nationaltrust.org.uk/marsden-moor-estate/documents/managing-molinia.pdf
Smith D.M.,  Barrowclough C., Glendinning A.D.  &  Hand A. (2014) Exmoor Mires Project: Initial analyses of post restoration vegetation monitoring data. In the Bog Conference September 2014. Download  here.
Taylor K., Rowland A.P. & Jones H.E. (2001) The Biological Flora of the British Isles: Molinia caerulea. Journal of Ecology 89: 126-144.
Thomas P. (2015) Problems with Molinea caerulea in the restoration of lowland peat bogs – Manchester Mosses Special Area of Conservation (SAC). In Meade (2015) pp127-133.