Potential biomass supply from local heathlands for energy

Potential biomass supply from local heathlands for energy Matthew Woodcock and Patrick Stephens 3 September 2012 1. Objectives: 1.1 To:  estimate t...
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Potential biomass supply from local heathlands for energy Matthew Woodcock and Patrick Stephens 3 September 2012

1. Objectives: 1.1

To:  estimate the potential biomass which could be sustainably harvested from local heathlands;  review the equipment available to harvest this biomass effectively; and  identify options to use this biomass to produce heat, or possibly combined heat and power, within the eco-town.

2. Summary: 2.1 Heathland is a key feature of the landscape in and around the Whitehill & Bordon Eco-town. Historically this would have been actively managed by local people to deliver key needs including fuel. However, the drivers for this management have disappeared over the last century as other sources of fuel etc have offered greater convenience. As a result the ecological value of the sites has declined. In recent decades the value of heathland both ecologically and as landscape features has been recognised and considerable effort has been expended to enhance their ecological condition. Reestablishing a market for heathland products would help secure their maintenance. Utilising the heathy (heather and other non tree derived biomass) and woody (from trees) biomass as part of the renewable fuel source of the Whitehill & Bordon Eco-town would be a significant contribution to the overall sustainability of the eco-town and its’ surrounding infrastructure. 2.2 Modern technology such as the ‘biobaler’ and biomass boilers offer a feasible option which would also help secure local jobs. Establishing the business around the ‘heath to hearth’ would provide a example which others could follow. 2.2 Success would provide a sustainable fuel resource estimated at 1,600 tonnes per year. This is sufficient to heat at around 350 homes and save more than 430 tonnes of carbon per year.

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3. Introduction: 3.1 Heaths have traditionally been used to produce a range of products for local people (see ‘Heathland Harvest’ by Chris Howkins http://www.amazon.co.uk/HeathlandHarvest-Uses-Plants-Through/dp/1901087050 ). Their traditional character developed as a result of harvesting and/or grazing. The harvesting of vegetation and turf gradually reduced the nutrient level in an already nutrient poor soil, and created a habitat which supported some of our rarest and specialised native species of plants and animals. 3.2 Over the last century this intensive management of heathlands has declined. Some heathlands have been converted to farmland, some have been built on, some have been afforested, while those surviving have rarely been as intensively harvested or grazed as in the past and many have evolved naturally into woodland. Over the last 20 years there has been a drive to restore former heathland sites, championed by National and local Habitat Action Plans.

Broxhead Common

Woolmer Down (within Woolmer Forest)

(March 2012)

(March 2012)

3.3 As knowledge has grown about the diversity of plant and animal species and their particular needs so has our understanding about the diversity of plant assemblages and structures needed. Effectively there is no ‘one size fits all’ practice of management! Different management regimes will benefit different species and individual property owners will determine their specific priorities, referring to advice from specialists and statutory bodies where sites have been designated as Sites of Special Scientific Interest (SSSI), Special Protection Areas (SPA’s), Special areas of Conservation (SAC), etc or where protected species are present.

3.4 In some cases a degree of grazing is desirable, though a recent report by Amphibian and Reptile Conservation (An assessment of the impact of conservation grazing on reptile populations) highlights that grazing is not a good option where reptile conservation is a priority. In a modern environment this can be difficult to facilitate due to the need to fence or due to the particular needs of the owners. In the past rotational burning of the heath would have been a key management tool but this is also difficult and is also identified as not good for reptile conservation in another new report from Amphibian and Reptile Conservation (An assessment of the impact of controlled burning on reptile populations) 3.5 One of the major threats to modern heaths are high intensity wild fires. Build up of large quantities of biomass means that when wild fires occur (started naturally, accidentally or deliberately) their intensity means they are difficult, and costly, to 2

contain, threaten neighbouring properties, impede local transport and cause significant medium term and potentially long term habitat damage. 3.6 Mechanical harvesting is already undertaken on some sites such as Ministry of Defence (MoD) training areas (in part to maintain fire breaks) and National Trust land with arisings being ‘spread’ in adjacent areas of lower ecological value. The Forestry Commission does not manage significant areas of heathland within the area of this study but does actively manage very significant areas of heathland in the New Forest.

Harvesting heather in the New Forest: cutting with reaper, allowing to dry and baling with traditional agricultural baler. 3.7 One of the objectives of the eco-town concept is to consider how a town in all aspects can be sustainable from its’ local resources. Reviewing opportunities to provide some of the towns energy requirements from local resources is key. The Forestry Commission prepared a report highlighting the potential woodfuel resource from local woods in 2011 and this study considers the biomass which could be potentially delivered from the heathlands within 10 miles of the centre of Whitehill & Bordon. 3.8 The principle of sourcing renewable sources of fuel and thereby providing a market driver to restore and maintain rare and treasured habitats in optimal condition to deliver the wide range of ecological, landscape and social benefits within the area of influence of the eco-town has been discussed with key land owners and managers during the preparation of this report. 3.9 If the principles outlined in the report are to be taken forward all aspects would need to be reviewed on a site by site basis to ensure that all environmental, social and physical issues and opportunities are considered.

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3.10

Extent of study area (10 miles from centre of Whitehill & Bordon)

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4.0 The heathland resource:

Open and wooded heaths within 10 miles of the eco-town. Data derived from http://magic.defra.gov.uk/ Woodland area is based on the Forestry Commission’s recently completed National Inventory of Woods and Trees (NIWT2)

Major heathland complexes:  Woolmer Forest  Longmoor  Chapel Common  Woolbeding Common  Ipping Common  Stedham Common  Bricksbury Hill  Crooksbury Common  Puttenham Common (edge)  Frensham Common  Churt Common  Hankley Common  Thursley Common  Bagmoor Common  Witley Common  Shortheath Common  The Warren/Slab  Broxhead Common

   

Ludshott Common Churt Golf Course Bramshott Common Hindhead Common

Smaller heathland complexes (i.e. areas with relatively small patchs of heathland vegetation):  Wheatsheaf Common  Linchmere Common  Marley Common  West Heath Common  Rogate Common  Queens Corner  Tentworth  Hogmoor Inclosure  Passfield Common Not shown:  The Bourne (FC)  Farnham Heath (RSPB heathland restoration) 5

4.1 Area: The data identifying areas of ‘open heath’ in provided from MAGIC the Defra system which allows any interested body to download a range of GIS based data which can then be analysed further. The latest National Inventory of Woods and Trees (NIWT) data was overlaid. Measuring the areas suggests there are 2,166 ha of heathland habitats within 10 miles of the centre of the eco-town, or which 1,404 are open heath and 762 ha are wooded. However, careful analysis of specific complexes such as Woolmer Forest illustrated below (see Appendix 1 for illustrations of the other major heathland complexes), highlighted: (a) that the NIWT data isn’t as accurate as the aerial photography (which itself is several years old), we suspect that the recently felled areas have been inadvertently identified as woodland to be restocked; (b) There are very significant ‘open’ areas within the complexes which are not identified as woodland, neither are they identified as lowland acid grassland (that dataset was downloaded and overlaid to check); and

(c)

Woolmer Forest Some key areas have not been identified on MAGIC as ‘open heath’ notably the RSPB’s Farnham Heath (major heathland restoration project to the south of Farnham) and the Forestry Commission’s Bourne Wood, which includes a significant open area regularly used as a film set, illustrated below:

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2009 aerial photograph of Farnham Heath and The Bourne Conclusions: i. The net 1,404 ha of open heath is a robust assessment of the current area of open heath dominated by heather species; ii. Part of the area shown as wooded heath has already been ‘restored’ to open heath over the next few years, and hence we add 200 ha (estimate) to the area of open heath to accommodate this; iii. The ‘open’ areas within the ‘open heath’ appear to be dominated by short grass or open water, while they may have very high ecological value their area should not be included in the area which could potentially be harvested for biomass as they appear to be maintained in this condition by natural or managed grazing; iv. While the RSPB’s Farnham Heath is largely being maintained by grazing some sections, such as that west of the Old Frensham Road are establishing well with heather (Calluna vulgaris) and hence harvesting may be of interest – add 20 ha from whole site to the total.

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4.2 Rotation: The RSPB’s ‘A practical guide to the restoration and management of lowland heath’ provides a very helpful reference text to establish the general principles for management of Ericaceous dwarf scrub dominated by heather (Calluna vulgaris): Phase Growth stage Timing Pioneer The period when the plant is becoming established from 0-5 years seed or following management. Flowering can occur in the second year and the young plant starts to develop radiating branches. Building Isolated plants are dome shaped, but where they are 5-15 years close spaced, a dense, close canopy forms with no gaps. This is the period of most vigorous growth. Mature The canopy gradually becomes less even, with small gaps 15-25 years and hollows appearing as weaker plants are suppressed. Growth is slow as woody material thickens out. Degenerate Gaps in the canopy increase as the plants start to collapse 25->40 years radially, with branches laying over. Some of these branches may root in damp litter otherwise they die back. Eventually the whole plant dies From this we will use the general premise that heathland would be managed on average on a 25 year rotation, appreciating that some parts will be cut on a shorter rotation (for fire breaks etc) and some areas will be allowed to progress to the ‘degenerate’ phase to suite particular species. Conclusion: Total area of open heath is about 1,600 ha, management on a 25 year rotation suggests ‘harvesting’ about 64 ha per year. 4.3 Estimated volume and calorific value: Forest Research have recently produced their draft technical report on ‘Open Ground management: options for harvesting heathland arisings for biomass’ (see appendix 2). Both existing technical publications and practical experiences of Forestry Commission staff involved in a range of heathland habitats was collated. While every site is different we estimate: Estimated biomass arising from sustainably managed heathland: Volume of cut heather

Proportion of solid matter

Heather density at 40% moisture content (as a

Weight

Energy density

Tonnes per hectare

kWh per tonne at 40% moisture content

proportion of overall weight)

m3 per hectare

%

kg/m3

(as a proportion of overall weight)

100-150

35

350

Total area of heathland within 10 miles of eco-town

Average rotation (i.e. time between harvesting)

Net average area harvested per year

Hectares 1,600

Years 25

Hectares 64

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21-32 Weight of biomass harvested at 40% moisture content and assuming 25 tonnes per ha Tonnes per year 1,600

3,500 Calorific value of harvested biomass

MWh per year 5,600

The heating oil required to produce a similar amount of heat would cost about £330,000 4.4 Time of harvesting The RSPB’s ‘A practical guide to the restoration and management of lowland heath’ provides a useful reference including a Heathland Management Calendar developed by the Dorset Heathland Forum circa 1992. This suggests the ecologically optimal time for management by mowing/harvesting is October to mid December but suggests that it is acceptable from mid December to end February. However, a careful assessment would need to be undertaken for each site and this would need to consider the specific weather patterns of the year. Practically motorised equipment should not be used when soils are waterlogged (though most of the sites in the study area are relatively free draining), and harvesting dry material is desirable when the use of biomass as a fuel is being considered. Conclusion: Harvest mid Nov to mid Feb during dry conditions BUT consider the specific ecological needs of the site and integrate the harvesting regime with habitat management plans.

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5. Harvesting options: A range of mechanical equipment is available to mow, and/or harvest, vegetation. The following table illustrates the options available and draws on both the RSPB Practical guide to managing heathland and the Forest Research Report. Advantages and disadvantages of different heather mowing machinery Machinery Illustration Advantages Disadvantages Biobaler: Anderson WB-55 BIOBALER Video:

Double chop forage harvester, with towed trailer ELHO DC 1700 Forage Harvester Video:

 Mows and bales in one pass  Good work rate  Less weight as doesn’t haul larger trailer of arisings  Bales easy to collect and transport (farm technology)  Bales will season in a well ventilated location  Flexible, as will harvest woody material up to 15cm diameter and hence can be used on a variety of biomass including: heather, woody scrub (gorse, blackthorn, young trees, etc), which increases potential utilisation of the machine  Good work rate  Collects cut material  Robust and good for rougher terrain  Cuts cleanly  Manageable product – bulk handling  Ideal for recreation projects – minimal handling  Ideally suited to bracken where product can be mulched for retail as compost

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 High capital cost  Requires a powerful tractor >200bhp  Ideally requires a network of land managers working cooperatively to optimise it’s use

 Not very manoeuvrable  Depends on relatively high tractor power (e.g >75bhp or 56kwb)  Trailer adds weight to overall pass  Height reduces stability on difficult terrain  Forage harvested biomass is harder to dry

Hi-tip (cut-and-collect green care mower)

 Cuts cleanly  Works in tight areas  Collects cut material so suitable for re-creation

Disc mower and baler

    

Flail Seppi Midiforst Drago

 Fast work rate  Suitable for annual mowing  Can have a trailer trailed to collect arisings

 Material left behind unless trailed trailer = added weight

 Fast cutting rate

 Can only collect small volumes  Not suited to heavier vegetation  Repeated down time removing cuttings from site

Good work rate Cuts cleanly Collects cut material Manageable product Useful for re-creation projects

 Slow work rate  Small capacity  Not well adapted to rough terrain

 Not very manoeuvrable  Poor on rough terrain  Depend on relatively high tractor power (e.g >75bhp or 56kwb)

Video:

Flail with collecting box STH Panda mower collector

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Swipe Spearhead Destroyer: Video:

ATV mounted mowers

   

Fast work rate Cuts cleanly Suitable for annual mowing Cost effective for maintenance of fire breaks etc

 Material left behind  Nutrient builds up on site

 Cut cleanly  Work in tight areas  Suited for small sites

 Slow work rate for large areas  Material left behind

Pedestrian operated reciprocating mowers

 Cut cleanly  Work in tight areas  Suited for very small sites

 Very slow  Material left behind

Brushcutters:

 Versatile  Cuts cleanly  Work in tight spots

 Very slow  Leaves material behind

Quadivator

Stihl Brushcutter

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6. Utilisation options: There are several options for utilising the biomass arising: 6.1 Pelletisation of biomass and use in wood pellet fuelled boiler: The 2010 assessment carried out for the FC by Harvest Woodfuels: ‘Assessment of the use of landscape management arisings as feedstock for commercial pellet production’ highlighted that this is feasible. However, pellet quality is unlikely to meet the standards required for domestic grade pellets and industrial grade pellets retail at about half the price hence making the economics of harvesting, transport to pelletisation plant, drying, pulverisation, pelletisation and redistribution challenging. 6.2 Utilisation of forage harvested biomass in larger facilities: Slough Heat and Power have been utilising a range of relatively poor quality biomass, often sourced from heathland re-creation or maintenance for some years. However, the prices paid delivered in (reputedly around £20 per tonne – unseasoned) are only marginally more than the costs of transporting the biomass from the site to Slough. In addition Slough appear to be preferring higher quality biomass as it, reputedly, leads to fewer infrastructure problems. 6.3 Refining forage harvested biomass for different markets: One local company G K Benford and Co has established a business which takes in arboricultural arisings, sorts, chips and sieves them selecting out material for woodchips and mulching the remainder. Something like this could be developed to extract the finer material for mulching and soil improvement of local farmland while the woodier material could be burnt in a robust woodfuelled boiler. Some of the Finnish systems are more flexible in the fuel quality they can utilise. However, this adds further complications and costs to the supply chain. (Experience gained from Woodheat Solutions project) 6.4 Direct use of baled biomass: Some biomass boilers are designed to take a ‘batch’ of fuel such as a large straw bale (or baled biomass), burn for a set period, during which the heat is used to ‘charge’ an accumulator tank. The heat needs of the property concerned are drawn directly from the accumulator

www.farm2000.co.uk Boiler linked to accumulator This relatively simple approach could be used for discrete properties OR developed as an ‘energy centre’ based around several such boilers each feeding into a large accumulator and supplying heat via a heat main to a number of domestic properties. The Roussillon barracks redevelopment in Chichester is based around 6 energy centres utilising woodpellet fired boilers to supply groups of 50 houses, replicating the approach they developed in Poundbury.

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6.5 Small scale biomass fuelled combined cooling heat and power: The technology to utilise biomass on a small scale for CCHP has been explored by the John Lewis Partnership over the last few years. They opened their first ‘energy centre’ at their new Waitrose store at East Cowes on the Isle of Wight and are installing a similar system in Bracknell. The system is based on 4 Stirling DK engines each delivering 140kWe and 560kWth and collectively being fuelled with about 2,600m3 of unseasoned woodchips per year. This will provide all the heat, cooling and power requirements of each store. The system was installed by a Farnham based engineering company: Mitie

Energy Centre serving Waitrose superstore at East Cowes, Isle of Wight (Output 140kW electrical and 560kW thermal)

Fuel reception by 3 ‘hook lift’ bins (2,600 tonnes per year of unseasoned woodchips sourced from woods managed on the Isle of Wight)

Woodchips are fed to updraft gasifiers, gas is burnt and heat is used in 4 Stirling engines to create electricity

Heat is also used through an ‘adsorption’ chiller to deliver the cooling needs of the store in the summer but can be sold to neighbours in the winter.

While the current system uses an ‘updraft’ gasifier to turn the unseasoned biomass (woodchips) into gas, which is then burnt, we do not know whether the same approach could utilise other forms of biomass such as that derived from heathlands. However, we will explore further.

7. Carbon savings All traditional fuel (i.e. excluding nuclear) releases carbon dioxide (CO2) when it is burnt. However, the net CO2 released by burning sustainably produced biomass is considerably less than the CO2 released when fossil fuels are burnt: Net CO2 emissions by fuel type Fuel type: Wood Natural Gas Oil Coal Electricity

Life cycle CO2 emission: 7 kg/MWh 270 kg/MWh 350 kg/MWh 480 kg/MWh 530 kg/MWh

(Source: Biomass Energy Centre)

In essence you don't save CO2 by burning biomass - only be displacing fossil fuel, and the savings will depend on what fuel is being displacing. CO2 savings when wood is substituted for fossil fuels Net CO2 released CO2 Saved by substituting 1 tonne 1 Tonne of woody biomass provides 24.5kg of woody biomass 3,500kWhrs of energy (when seasoned) for fossil fuel Natural Gas 945kg 900kg Fossil fuels delivering Oil 1,225kg 1,200kg the same amount of Coal 1,680kg 1,655kg energy Electric 1,855kg 1,830kg (Source: Biomass Energy Centre)

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To convert from CO2 saved to carbon you divide by 44 (the molecular weight of CO2) then multiply by 12 (the atomic weight of carbon). So 1kg of CO2 would equate to 0.27 kg of carbon. If we assume that most heating within the homes and business’s of the eco-town is currently gas with a little oil and electricity we estimate that using heather based biomass would offer similar benefits to a similar weight of wood (at 30% moisture content) which could save, on average, about 1,000kg of CO2 per tonne of woody biomass (Note: a tonne of woody biomass at 30% moisture content is estimated to deliver 3,500kWh’s of energy/heat). Hence by utilising the 1,600 tonnes of biomass derived from sustainably managing local heaths within 10km of the eco-town we could reduce the overall emissions of CO2 by more than 1,600 tonnes per year (equivalent to saving more than 430 tonnes of carbon per year).

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6. Conclusions: 6.1 There is a significant resource of heathlands within 10 miles of the centre of the Whitehill & Bordon Eco-town. Harvesting the biomass from these heaths sustainably could provide a sustainable energy resource estimated at 1,600 tonnes per year, and help reduce the costs of maintaining them in good ecological condition. 6.2. It is likely that there will be further re-creation of heathlands over the next 20 years which will lead to this resource increasing. However, this increase may be balanced by the decrease in resource available from sustainably managed woods (as outlined in our 2011 report to the eco-town ‘Woodfuel supply feasibility study’), which offer the most likely sites for heathland re-creation, unless such woodland loss is balanced by the establishment of new woods. 6.3 Harvesting this resource must be carried out carefully to ensure that the ecological benefits are optimised. 6.4 The recently developed biobaler system appears to offer the greatest potential to harvest effectively. However, capital costs are high and hence this approach would be less economically effective if only used to manage a single site. An agreement to utilise this type of equipment between a group of site managers would potentially allow a contractor to purchase such a machine. Investment in a biobaler system could offer an additional benefit in managing other sites in south east England such as the South Downs National Park, the Thames Basin Heaths and the New Forest. 6.5 Utilising the biomass appears to be most straight forward if it is based around the ‘biobale’ concept which facilitates easy transport, seasoning and storage. A suitably designed ‘energy centre’ could utilise this resource without further processing. 6.6 Carbon savings would amount of about 1,600 tonnes of CO2 per year, equivalent to 430 tonnes of carbon. 6.7 Utilising biomass from sustainably managed heathlands would be most effective if aligned with the sustainable management of existing woods in relation to both biomass utilisation and site management as in most cases woods and heaths from an intimate mosaic.

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7. Next steps: 7.1 Explore interest from heathland site managers to exploring the principles of mechanical harvesting further; 7.2 Demonstration of the biobaler on a local site and evaluation of the benefits and constraints; 7.3 Review the quality of the biobales produced in respect of:  Effectiveness of seasoning to reduce overall moisture content;  Calorific value; 7.4 In partnership with site managers and specialists prepare best practice guidelines for mechanical harvesting from heathland sites, including a summary of key points in the form of a ‘cab card’ for machine operators; 7.5 Identify potential sites within the eco-town which could be established with heat distribution networks supplied from centralised ‘energy centres’; 7.6 Estimate the heat load and profile of such sites to determine boiler size and fuel requirements; 7.7 Develop an outline design for a ‘heath to hearth’ (or ‘wood to warmth’) supply chain utilising the biomass from heathlands and/or woods within the vicinity of the eco-town; 7.8 Present the above design to all those potentially involved and identify those who are seriously interested; and 7.9 Work with key players to implement.

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Bibliography:  A Practical guide to the restoration and management of Lowland Heathland – RSPB 2003  Assessment of the use of landscape management arisings as a feedstock for commercial pellet production – Harvest Woodfuels July 2010  Whitehill & Bordon Eco-town – Woodfuel supply feasibility study – Forestry Commission 2010  Whitehill & Bordon Eco-town – HRA Report 2011  Heathland Harvest – Chris Howkins  Amphibian and Reptile Conservation Research report 12/01 - An assessment of the impact of conservation grazing on reptile populations  Amphibian and Reptile Conservation Research report 12/02- An assessment of the impact of controlled burning on reptile populations 2012  Websites – many, listed in the text.

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Appendix 1: Major heathland complexes

Woolmer ‘Forest’ 19

Frensham Common, Churt Common, Hankley Common and Thursley Common 20

Iping Common, Stedham Common and Woolbeding Common 21

Longmoor and Chapel Common 22

Ludshott Common, Bramshott Common, Churt Golf Course and Hindhead Common 23

Black Down 24

Appendix 2

Forest Research - Draft Technical report

Open Ground Management: options for harvesting heathland arisings for biomass Summary The management of open ground is increasingly important for forest managers and covers a wide range of habitats and operations (Price, 2011; Ireland, 2010). Management of heathland includes cutting and clearance of woody shrubs, scrub and trees, and the arisings represent a potential biomass resource for energy production. An investigation into heathland working was conducted on behalf of southeast England Conservancy to identify possible methods and outputs for biomass production. The highly variable nature of heath vegetation was found to influence volumes of harvestable biomass. Previous studies and industry experience suggest that a yield of 20-30 t/ha is typical, however this will vary with site conditions and previous management. The return period for heath sites will also be dependent on site and vegetation type. Successive annual cuts can be economically viable for 5 years in bracken, however, heather cutting cycles are likely to be 8-10 years on fertile sites and 20-25 years on infertile ones. Time of harvesting influences moisture content of the vegetation. Harvesting after autumn die-back has been found to take advantage of lower moisture contents. The calorific value of arisings is predominantly controlled by moisture content, but found to be comparable to conventional woodchip: calorific values for gorse, heather and spruce at 10% (m.c.w.b.) were found to be 16.7 MJ/kg, 17.4 MJ/kg, and 17.3 MJ/kg respectively. Most heath vegetation produces loose arisings which are difficult to dry to process into quality fuel. Cutting is mainly carried out using flail mowers and swipes, and arisings are collected by the mowers or separate collectors. Agricultural forage harvesters and balers are used to produce heather bales in the New Forest, but are limited to more uniform vegetation. Machinery options for the widest variety of vegetation are swipe and light mower-collector, mulcher-collector, and the biobaler mulcher-baler. These systems have the ability to cope with woodier material such as gorse, scrub, and tree regeneration. Cost and productivity data for all combinations are limited, however, costs are likely to be in the region of £600-1000/ha for coarse vegetation in all systems. More detailed comparison study would be needed to assess if higher biobaler costs were offset by ease of handling and higher market value.

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Introduction Management of open ground is an increasingly important for forest management and covers a wide range of habitats and operations – see Price, 2011; Ireland, 2010. The management of heathland requires the clearance of vegetation including woody shrubs, scrub and trees. Cut vegetation represents a potential biomass resource for energy production. TD has been requested by southeast England Conservancy to investigate heathland working to help identify possible methods and outputs for biomass production.

Objectives 1. Investigate optimal time to harvest heathland arisings and the frequency of cuts 2. Investigate biomass yields likely from heathland arisings 3. Investigate the calorific value of arisings 4. Investigate machinery options for harvesting including agricultural machinery

Heath Vegetation and Terrain Heath biomass is very variable in terms of species and growth, depending on site nutrient levels, plant assemblages and previous management. Vegetation could include grasses and herbs, heather, bracken, broom, gorse and trees. More woody material such as large broom, gorse and trees are likely to require more robust machinery to clear them. Terrain is also likely to be variable, and machinery options may be restricted by steepness, ground roughness, and bearing capacity. Removable biomass is also likely to decrease with an increased frequency of cutting cycle. Typical return period for burning in the New Forest is 23 years for heather and 15 years for gorse (Ireland 2010). Annual bracken cutting will weaken the rhizomes and so significantly reduce vigour within 4-5 years. Heather biomass is changeable and difficult to exactly assess. Moorland work conducted throughout the UK (Kirkham et al., undated; Moors partnership, 2012) suggest likely volumes of cut heather to be in the range of 100-150 m3/ha with a solid matter proportion of c. 0.35. This equates to 21-32 t/ha assuming heather density of 350 kg/m3 and 70% moisture content. Bracken cover is also very variable. Dense bracken was found to yield 24.6 t/ha, producing 287 m3/ha of loose cuttings. Site ranges of green weight for heavy bracken were between 24 and 30 t/ha, and c. 19 t/ha in moderate stands. Moisture content for bracken was found to have a mean of 70% (Drake-Brockman, 1998). Experience of baling heathland arisings (Hanbury-Tenison, pers. comm.) suggests common yields of 40 bales per hectare, equivalent to 20-24 t/ha of gorse, heather and bracken.

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Return Period Return period will vary with site nutrient status, plant assemblages (species present and their proportions), and management requirements. Increasing return period will lower biomass recovered in each operation, and so increase unit cost. Yields will drop due to the plants having less time to put on increment between cuts, and as repeated cutting may decrease plant vigour and increment. Bracken cutting in the New Forest has found that bracken yield drops-off after 4-5 years of cutting. The return period for heather is suggested as the time required for the heather to grow to around 20 cm tall; 8-10 years on fertile sites and up to 20-25 years on poor sites (Scottish Government, 2011).

Time of Harvesting Experience from the New Forests suggests that moisture content, particularly in bracken, drops in late summer and early autumn. If cutting to produce biomass, this reduction in moisture will increase net calorific value and so improve fuel quality. Moisture contents of heather and gorse have been recorded at between 15 and 35% (wet basis) from New Forest winter and spring harvesting (Little, 2010). Summer bracken moisture content has been recorded at between 65 and 74%.

Calorific Value Calorific value of heath vegetation is, as with all biomass, largely dependent on moisture content. Pelletising trials (Little, 2010) tested pellets with a moisture content of around 10%. Gorse pellets had a calorific value of 16.7 MJ/kg, and heather pellets had a value of 17.4 MJ/kg. As a comparison, spruce wood has a value of around 17.3 MJ/kg at 10% MC.

Machinery Options Harvesting Systems The cutting of heath vegetation can be accomplished using a wide variety of flails and bladed-mowers. Machinery choice is constrained where there is a requirement to collect the arisings in order to maintain low nutrient status, for amenity reasons, or to use as biomass.

Collection Options Collection in the majority of systems is of the loose arisings in a manner similar to a lawnmower. Arisings are piled close to worked areas, either to be left to compost or rot away, or in readiness for loading onto trailers for transport. The other option is for baling of cut material. Bales are dropped across the site and can be collected later for transport.

Collector Capacity The collection capacity will heavily influence the system work method and productivity. Smaller collector volumes will fill faster after mowing a smaller area or a shorter strip than 27

larger collectors. Vehicle productivity will be reduced due to proportionally more time being taken in returning to the piles and emptying the collector. Movement time can be reduced by increasing the number of piles, although if arisings are being used off-site, productivity in forwarding will decrease due to loading many small, dispersed piles.

Level of Technology Agricultural machinery is often simple with benefits in terms of lower capital cost and maintenance requirements, and ease of repair. More specialized machinery may provide working benefits but often at the cost of higher operating and maintenance costs.

Loose or Baled Arisings The ability to bale enables easier handling of arisings. Bales can be picked up, stacked, and transported on open trailers, whereas loose arisings must be shoveled and require an enclosed trailer for transport. Bales also have the advantage that, depending on storage conditions, passive drying may be possible, so increasing fuel quality. Loose arisings are very difficult to dry passively in storage and therefore moisture content will be higher, reducing the calorific value of the biomass.

Current Approaches South East England FD

New Forest - Dave Morris Bracken management is undertaken in an annual programme of c.50 ha across the forest. Treatment season is from late August to the end of October, and so bracken is cut in varying growth states ranging from green to fully brown. Cost of cutting and collecting with modified agricultural hay equipment was estimated by the District to be around £200 per hectare. The bracken is stored on site and sold as compost after weathering-down. A site can be forage harvested for about 4-5 seasons after which the bracken becomes too sparse to justify the operation. Heather is cut and baled in November and December using an agricultural disc mower and a hay baler producing 50 cm x 50 cm x 75 cm bales. A 12 bale sled is towed behind the baler to collect output. Heather bales are used in habitat restoration work to block drains and repair watercourses. Gorse mowing has been carried out using a front-mounted swipe followed by a second tractor with a towed single-chop forage harvester/collector to collect cut material. Whilst material was collected successfully, soil contamination was unacceptably high for many biomass applications.

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Clearance of young trees has been accomplished through volunteer labour using handtools and using motor-manual contract clearance.

Micheldever - Nick Hazlitt Heath management has been carried out using a Panda mower (see Table 2), although use was limited by stability, particularly on steeper slopes and rough terrain. An Ahwi RT400 mulcher has also been used to clear vegetation although collection of arisings is not possible with this machine.

Midlands FD

Cannock Chase - Richard Hayden A tractor-towed Panda mower is used to mow grass, leggy heather and bracken in conservation rides and flower meadows. Issues regarding clogging of the chute when working in wet grass were reported. Contractors have also used Ryetec flails for similar work.

East of England

Thetford - Neal Armour-Chelu, Brian Greenacre The District used Ryetec mowers but found them to be limited by their collection capacity. The mowers are only used for a small proportion of District work, generally smaller and “fiddlier” areas. The majority of work is undertaken by N-series Valtra tractors with a front-mounted Spearhead “Destroyer” swipe and a towed Panda collector.

Currently Used Equipment Machinery used currently by Districts in heath working is detailed below.

Spearhead Destroyer The destroyer is a heavy duty swipe (3x 7 kg blades) capable of clearing individual stems to around 225 mm diameter and with normal working achievable in material of diameter below 75 mm. Listed cost is £9400 (+VAT); machine details are summarised in Table 1. Table 1 Spearhead Destroyer Swipe

Capital Cost Details Current Use Working range Unit Dimensions

£9,400 (+VAT) http://www.spearhead.uk.com Thetford normal working diameter

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