Peatland ACTION - Technical Compendium - Restoration - 8 Forest to bog restoration

General Guide 

• Check first whether a Controlled Activities Register Licence is required from SEPA and if the site is subject to other constraints. 
• ‘Forest to bog’ restoration is a catch all term that covers a range of restoration activities specific to sites which have been afforested. It may also still be important to consider other techniques such as drain blocking (Section 4) and bunding (Section 5) for forest to bog projects. 
• Approval of deforestation for peatland restoration should be sought from Scottish Forestry.  This could be in the form of felling permission as part of a Forest Plan, and/or require an EIA determination (see Deciding Future Management Options for Afforested Deep Peatland).
• The type of restoration technique required will depend on the tree species present, the tree stump size, the ploughing ridges, furrows, draining modifications, the site topography, peat type (flushed or unflushed), water flows, peat depth, peat slide risk, alongside the ability to extract timber and harvesting technique.  
• There may be freshwater habitat considerations, where restoration activities have the potential to affect sensitive species, e.g., fresh water pearl mussels, Atlantic salmon.  Refer to Forest and Water Guidelines for further information. See latest UK Forestry Standard (UKFS Guidance).
• The proportion of the catchment that can felled in a given period needs to be considered if within a public water supply area, acid sensitive catchment or a flood risk zone. Scottish Forestry will determine whether this is applicable. Forest to bog restoration is often, but not always, carried out in phases, with the initial phase relating to the removal of the above-ground biomass of the plantation and woody debris arising from the felling operations. Please see Sections on Tree Harvesting and Tree mulching and Stump mulching/grinding for specific methods.
   
• On sites where the timber has already been removed, the length of time since the trees were felled affects the pliability of any remaining brash or how decomposed remaining stumps are. More brittle stump and brash remnants may require less intensive follow-up interventions, however this should not generally be considered an opportunity to delaying re-wetting as it postpones the start of the restoration process and likely causes other consequences, such as extending the time the site is acting as a carbon source and providing an opportunity for protected species to colonise the site. There are some exceptions to this (see ‘Timing of restoration following tree and woody debris removal’ in this section).
• Ground conditions on peatlands vary in wetness and structure from site to site and within sites.  Expert advice should be sought so that excessive damage, notably the disturbance and compaction to peatlands does not result from using poor working methods or unsuitable machinery. 
• The Forestry Commissions soils classification system is useful in that it often reflects the type of ploughing and drainage intensity that was applied at afforestation.  Drains tend to be further apart on unflushed former Blanket bogs, and very close together on flushed blanket bogs, and raised and intermediate bogs. This can inform the type of peatland community that will be restored, identify the target community, and the dominant species to expect. Some techniques require the peat to be sufficiently deep to be implemented, and so a peat depth survey may be required. Current minimum standards for Peatland ACTION is for such surveys to be carried out at 100m grid, however some terrains are more variable, with ridges of shallow peat or non-peaty soils within the site and may require more than this minimum.  
• Surveying drains and furrows is important; check that the drain width does not exceed the threshold beyond which a SEPA CAR licence would be required. The depth of drain, width, peak flow and base flow should be considered before deciding how to block the drain, and inform the specifications (see Drain blocking, Section 4). 
• Assess the condition of ploughed ridges and furrows. If these are prominent (usually the case) then more intervention will be required to flatten and restore the hydrology and topography of the site (see Ground smoothing technique, Section 8.4). 

Tree and woody debris removal 

• In general, it is preferable to remove as much timber and brash (including brash mats) from a site prior to restoration, although some brash left scattered across the restored site may be beneficial for Sphagnum recovery because it reduces exposure to sun and wind. Removal of woody material can make restoration activities easier and more successful and reduces the fuel load and thereby the risk of a major wildfire. However, in certain circumstances mulching of whole trees/stumps may be the best option.  
• For some sites there may be considerations (e.g. protected species) that would require decisions over whether not to remove the crop but simply drown it over a long period, and hence blocking of the main drains and/or furrows would be needed but not removal of trees.  The circumstances where this has been deemed appropriate are not yet understood or encountered so far. Previous evidence suggests that this method is not effective in dense plantations in restoring a high and stable water table (e.g. Restoring afforested peat bogs: results of current research. Russell Anderson et al.,2010)
• There are three main ways to remove trees from the surface of the peatland.  The preferred method is to use specialised harvesting systems, the second method is to use conventional harvesting machinery, and the third methods, which is used when other methods are not possible (e.g. when tree sizes are too small to recover them), is to mulch any existing trees (and/or remaining stems/stumps).  Often, a combination of methods is required, depending on the tree size and the wetness of the peat. The aim is to take as much timber as possible off-site. Please see Sections on Tree Harvesting and Tree mulching and Stump mulching/grinding for specific methods.

Timing of restoration following tree and woody debris removal  

• Phasing works over a number of years may be required to reduce the proportion of the catchment disturbed to minimise negative impacts to water quality, habitat provision and flood protection.  
• The timing of restoration work post felling and extraction needs to be carefully considered and is likely to be site dependent. Carrying out restoration immediately would result in one major disturbance event rather than multiple events which can expose bare peat, impact any peatland vegetation that has developed, and could lead to more compaction and disturbance.  A felled site that has not been re-wetted will continue to act as a carbon source.
• Restoration as soon as possible after felling and extraction may be favourable from a carbon emission perspective. The sooner a site can be rewetted, the sooner it can start to recover and stop acting as a carbon source.  In addition, a more heath type vegetation may establish which can further dry out the peatland and compromise the restoration process by slowing it down.
   
• Restoration plans can be prepared prior to felling if the site is relatively uniform in terms of the crop and peat type.  However, some terrain and peat types should be surveyed after felling to refine specifications and plans, when the site can be observed from vantage points, and in particular the drainage, slopes, and flushing can be noted.
   
• Leaving sites for a period can result in regen which then needs to be treated in an additional operation. This regen and ‘scrubbing up’ of a site can also lead to colonisation by protected species (e.g., adders) which would need to be considered when planning your restoration, adding complexity and cost of planning and restricting the seasons the site could be worked. Burying regeneration during the ground smoothing treatment may increase the risk of water preferential pathways developing in the longer term. Although we do not yet have conclusive data on this it is worth considering this risk during planning.
• Regen can be a recurrent issue post-harvesting dependent on proximity to seed sources, especially of the site is not sufficiently re-wetted. Removal of troublesome seed sources should also be considered, otherwise considerable resources will be needed in future to remove regen in multiple phases in the future.

Aim of the Technique 

To fell and remove trees (above-ground biomass) prior to restoration. Timber may be extracted or if the trees are small ‘felled to recycle and left in situ’.  

Best Practice  

• Discuss the site with Scottish Forestry as any felling operations will require a felling permission which approves deforestation. For further information, please check the Scottish Forestry - Felling permissions page.
• An exclusion zone is required for all machines. The size of the exclusion differs per machine and operation, for example, the height of the trees being harvested or the direction of travel of chain shot. Therefore, this is specified in the risk assessment and method statement.  
• Recover as much timber as possible wherever possible.  
• Access to the site needs to be considered for refuelling and recovering timber using a forwarder machine. Brash mats should be formed and built, matched to ground conditions to specifically allow the types of machinery being used to traverse the site.  Many sites and conditions require specialised machinery. 
• It is usual to harvest a site when it is mature, but tree sizes can vary and be variable within a stand. 
• For the wetter sites with greater extraction distances that have small and medium sized trees present, consider using a recently developed ‘shears harvesting system’ which uses an excavator with a shears head to snip trees, and passes the whole tree to a harvesting processor. The processor cross-cuts the timber and forms the brash mat for the forwarder to travel on to collect the timber.  At time of writing, it is acknowledged that this system is not yet widely available to contractors. The shears excavator has wider than standard tracks (e.g. from 1.5 m to 1.9 m wide tracks) so that it can travel on the ground without the need for a brash mat.  Brash material is concentrated into fewer brash mats. Timber recovery is improved, leaving the site clearer of brash except on the mats. As per general section on Forest to Bog techniques, brash mats can be left in situ on upland blanket bog sites, but may need to be removed on Lowland Raised Bogs, or at the very least, redistributed about the rewetted surface. 

Appropriate Machinery  

• Standard harvesting methods use a harvester and a forwarder to extract timber to roadside/trackside. 
• Specialised ‘shears harvesting system’ (see above). 
• Chipper for brash mat processing.

When most likely to succeed

• Conventional harvesting machines succeed when trees are at least medium sized, with fairly good canopy densities for brash, when the ground is not too wet, and extraction distances are short to medium, well serviced by forest roads.
• Shears harvesting systems produce better results when trees are small to medium sized, brash is limited, the ground is wetter, on larger sites which entail long extraction distances.

When most prone to failure 

• If ground is too wet, significant soil disturbance can occur. Expert forestry advice is required on such sites. 

Points to Remember 

• There are a number of factors that influence the sequencing of work, layout of main extraction routes, the design of facilities required to service the timber harvesting operation.  Chain shot, tree size, brash availability, existing roading, water courses, flushed areas and potential for surface water run-off are all factors to consider.  It is usual practice to have one or two harvesters on site, with one forwarder. 
• Rewetting work (see subsequent sections 8.2-8.4) can be carried out quickly after the trees are harvested, but only if the re-wetting does not compromise the harvesting of adjacent stands.  It is important to identify the hydrological units within the peatland when planning this.  Re-wetting could also compromise the function and condition of existing forest roads. 

Tree Mulching [to be updated coming soon]

Aim of the Technique 

To block the furrows that were created during forestry activities in order to raise the water table and stop erosion. Furrow blocking is a low-cost option on forest to bog sites where the prominence of the ridges and furrows is not very significant (and would not require stump flipping and ground smoothing). However, furrow blocking can also be used in addition to other forest to bog restoration technique to assist with rewetting e.g., following simple reprofiling of plough ridges and stumps on sites harvested many years previously, or following stump and root plate mulching on newly harvested sites (see relevant sections 8.2 and 8.4).  Drain blocking (see Section 4) would also be required on main drainage channels and peripheral drains.  

In practice, this method is only employed on a small proportion of sites.

Best Practice  

• Furrow blocking can generally follow the same processes as described in Section 4 for drain blocking and drain reprofiling. The depth of furrows could dictate which technique to use. A special case is where peat depths in furrows are too shallow for dams and stumps and root plates small and rotted (e.g., sites where trees have failed and felled some time previously). In this scenario, reprofiling could be carried by simply pushing ridges into furrows and cross tracking.  
• Using timber trunks and brash can be effective and is a low-cost option to infill the furrows on these sites as the raw material is provided, but peat dams must always be used in conjunction and must always be installed first. Although timber trunks and brash do not provide as good a seal as peat, this is a useful technique where erosion is a problem, water flows may need to be slowed, or the peat is shallow. Water preferential pathways may be promoted by using this technique if timber trunks and brash are placed in such a way that e.g. stems align along the drain, so ensure that placement of such material forms a complex structure within the drain feature. Crushing the brash into the furrows with the excavator bucket will help break up the drainage lines.
• Plastic piling should only be considered if there is no other option. It will be difficult to get a good seal with plastic piling when there are roots in the peat adjacent to the furrow. 
• Block all outflows from existing furrows and install silt traps along collector drains. This may not be necessary if both peak and base flows are low. Install dams at 10-20 m intervals along furrows and drains (flat ground or shallow slopes <1 degree) and increase frequency on steeper gradients. Dams should be built to plough ridge height (or approximately 20 cm about the round surface if ridges are absent e.g. following reprofiling or stump and root plate mulching) and staggered between adjacent furrows to encourage rewetting over a wider area.  
• Furrow blocking can be carried out in conjunction with other ground smoothing techniques (see Section 4.4) and can be a ground smoothing technique in its own right if cutting into the peatland surface and hinging sections of peat with a vegetated top round to fill the furrow.  

Appropriate Machinery  

• Balance the power of machine with the conditions on site. Working on previously afforested sites is much harder on machines.  Experienced forest managers and contractors know what works and what does not.  
• Using a 10-14 tonne machine with track widths of 1.9 m wide each side allows the ground smoothing to be carried out with less compaction and with a more efficient workflow. Efficiencies can be made in the order of felling of trees and formation of more widely spaced brash mats to allow extraction. Use of smaller machines is feasible, but similarly need to be matched in terms of low ground pressure.

When most likely to succeed 

• Where there is evidence of peat forming vegetation remaining, the furrows are not too deep, the ridges are not too high, drainage has not been too extensive, and the site remains quite wet with a relatively high water table.  
• When works have been carefully planned and site conditions have been taken into consideration.
• When used in conjunction with other complementary restoration techniques (e.g. applicable ground smoothing methods, Section 8.4). 

When most prone to failure 

• Furrow blocking is difficult when there is brash and timber on a site. Contractors need to ensure the immediate furrow is cleared of such material before constructing a peat dam using hydrated peat.  

Aim of the Technique 

To remove the ridges and furrows on previously afforested sites, and to create a topography similar to near natural peatlands. This aids re-wetting in order to produce conditions conducive to the recovery of peatland vegetation species. Small tree regeneration can be removed by the works.  Ground smoothing can also be used to remove/ fill-in smaller drains with low flows, and so reduce the number of dams required along their length. The technique must, however, be used in conjunction with peat dams wherever peat depths allow, to ensure that water preferential pathways do not develop along the base and sides of the drains in the future. If the peat is cracked underneath the furrows, back fill trenches may be required to remedy this, although this is only a relatively small proportion of sites.  Vegetation recovery on the resultant smooth surface can be rapid, with good cover of species seen within a matter of 1-5 years in the right climatic condition and where there are local seedbanks. 

Ground (or surface) smoothing covers a range of operations, frequently carried out in combinations, such as:

• Stump flipping,  
• Furrow reprofiling following furrow blocking (see also previous section),
• Cross-tracking.

Stump flipping is a ground smoothing technique, which peels off the shallow root systems from the underlying peat, flipping them over, followed by compressing them upside down into the furrows with the back of the bucket.  

Furrow reprofiling / blocking is similar to standard drain blocking and reprofiling (see relevant sections), but with the added complexity of dealing with tree roots and stumps. It can only be carried out on sites with more rotten stumps and roots, and is therefore not possible on recently harvested sites.

Cross-tracking involves an excavator driving back and forth over the ground so that the whole surface gets flattened, any mulch or brash is distributed, and any stumps or woody debris do not spring back up. This method tends to only be used as a secondary technique on sites where previous efforts have failed to completely remove the ridges and furrows. Machines with wide tracks render this usually unnecessary. Cross tracking may be undesirable as it compacts the peat, altering the hydrological function in a negative way during the winter, and in the spring and summer droughts, producing a dichotomy of too wet in the winter, and too dry in the drought periods.

Best Practice  

• Review the Forest and Water Guidelines and SEPA General Binding Rules (GBRs). Consider the best time of year to carry out work in relation to these guidelines as well as the growing season. 
• Coordinate works with installation of dams and plan work so that access can be maintained to the locations required for damming. In flushed and naturally wetter sites, the ground will wet up very quickly after ground-smoothing, resulting in the peat swelling. Plan works to minimise the release of peat into watercourses, by leaving sufficient buffers within which work is excluded. Consider how water is entering and existing the site first. It is generally better to block drains from the top of a site, then working downstream. Consider leaving some drains untreated until the end of operation and/or consider phasing work over a number of years, particularly for blocking of large drains with high peak flows.  
• Where a lot of material has been left on site consider how to ‘spread’ this. Burying regenerating trees, logs and woody material risks development of water preferential pathways in the future and new erosion channels opening up.  Instead, material can be spread out across surface to provide some shade and shelter to aid with rewetting and recovery of Sphagnum. This is possible in the workflow if wide tracked machines are used, e.g. 1.5 m or wider, when cross tracking is not needed.  
• A good peat depth survey will help in planning, but machine operator should observe the depth of the peat as work unfolds. Operators must be able to recognise when they are not on peat or sufficiently deep soils and so when to change techniques. 
• Techniques such as stump flipping can be more challenging on sites just after felling as root plates have not broken down and can remain intertwined, so larger, more powerful, machines may be required as it is not always possible to just to flip one stump at a time. 
• It has been found to be challenging to carry out stump flipping on sites where stumps have become extremely rotten and difficult to handle. In this case, it might be recommended to move to cross–tracking, with or without furrow reprofiling.  
• When stump flipping Sitka spruce rootplates, peel the stump off the peat, minimising the amount of peat disturbance.  Then flip them over and compress the stump into the furrow. The correct bucket is needed for this, usually with teeth.  Care is needed to flip Lodgepole pine root balls, ensuring that no additional peat is excavated below the roots. For larger lodgepole pine root balls, consider alternatives to avoid disturbing the deeper catotelmic peat layer.
• Stumps that have had the trees removed using the shears head will have a shallower root stump profile. When stump flipping, these will penetrate the peat to a lesser depth, therefore reducing disturbance. It is also possible to treat shallower peat because of this.   
• As the machine progresses over the flipped stumps, wide tracked machines will consolidate stumps into the peat and block any furrows (often eliminating the need for additional cross tracking). 
• Shallow peats can sit on podzols or other non-soft soils, preventing drivers pushing material or ridges into these soils. On shallower peat, stump flipping (in particular of lodgepole pine root balls) may not be advisable. 
• Root plates can be interwoven and need breaking up. This may be more time consuming and require larger, more powerful machines with the right bucket.  
• On larger sites where work will be divided into sections with buffers and by year, consider the visual impact—any patterns created should not be visible after a few years.  Whole hydrological units should be restored in their entirety in a short period of time.
• The most effective time to remove any subsequent tree regeneration is to remove it within 7 years of re-wetting.  The tree regeneration will have declared itself, but also still be small enough to deal with cost effectively. Dense tree regeneration would normally indicate that the site was not re-wetted sufficiently, perhaps because the peat was cracked below the furrows, or because there is close proximity of seed sources through remaining plantations. The need to carry out removal of dense conifer regen on forest-to-bog sites can be avoided (or reduced) by re-wetting the site as soon after tree felling as possible. See also Section 9 on Scrub Removal. 
• Consider whether furrow-blocking and/or reprofiling are needed in isolation (on shallower peat areas) or whether they should form part of a wider suite of ground-smoothing measures.
• The initial pass in cross-tracking is made up and down the slope and then a second pass can be made across the slope, if required. There is sometimes low-amplitude corrugation left at the end: in the rare cases where this is aligned across the slope, rather than up and down it, it encourages retention of water on the surface, and is possibly desirable. 
• Cross-tracking with conventional tracks will likely lead to compaction which is undesirable, so wide tracked machines (at least 1.5 m and even 1.9 m on wetter peatlands) should be the preferred option.
• If carrying out cross-tracking with narrower tracks, the final pass should be across the slope to prevent preferential surface pathways for water from forming on the machine tracks. 
• Maintain as much of the existing peatland vegetation as possible. When there is tree regen to remove by ground smoothing, then the impact on ground vegetation has to be closely monitored as some operators will keenly dig out trees, when perhaps they should be cut with saws. 
• Recently in February 2023, a new workflow was developed on a site with a high variability in Lodgepole pine stump sizes.  The operator stump flipped the larger rootballs, but managed to slide the medium sized stumps sideways into the furrows, and pushed the small stumps down into the peat with both the bucket and tracks.  This resulted in a greater amount of peatland vegetation on the treated surface, and less bare peat.
• Buffers, areas which are purposefully left untreated, may be required. SEPA generally requires 5 m buffers between stump flipping/ground smoothing sites and water courses, i.e. where there are large areas of bare peat created with a potential erosion risk.  The 5 metres is advisory to avoid risk of eroded peat polluting watercourses.  Therefore, if the topography makes it highly unlikely that eroded peat will enter the watercourse then a narrower buffer could be possible.  Mitigation measures such as use of geotextile, netting or a nurse crop that would retain the peat and lower the risk of peat erosion could also be used to mitigate the reduction of the buffer width. 
• Some sites, such as shallow peat sites or with well-rotted stumps/trees, do not need the stumps flipped, and may just need furrow blocking and/or cross-tracking.  
• A machine debogging plan, emergency plan and lone working procedures should be in place before work starts as sites can rewet rapidly and be unstable. It would be preferable if two machines were present on the wettest sites with highest risks of bogging.  Consider how to refuel the machines and keep access open for future phases of work as sites can get wet very quickly, and suffer too much disturbance or compaction if relied upon too much. 

Appropriate Machinery  

• Machine size for stump flipping depends on stump size and rottenness. Machines must be large enough to have the power to prize out the stumps but not be pulled into the peatland themselves.
• Usually exceptionally wide tracks are better for this work (<1.5 m wide tracks can lead to too much rutting, compaction, and disturbance of peat). 1.9 m wide tracks (on a 14-tonne machine) reduce ground pressure on the peat, disturb existing vegetation less, and are more stable and better suited for stump lifting with better leverage. This set up also means cross tracking is not required, and any larger stumps and timbers can be set aside on the already ground smoothed side, improving the efficiency of the workflow.
• A toothed excavator bucket is required to prize stumps out by the root plates and break them up if necessary.  This bucket is good for teasing, lifting and placement of stumps. 
• Excavators need to have window protection (window guarding or strengthened glass) when moving woody debris and stumps around - stumps can and have broken through cab windows.   

When most likely to succeed 

• For stump flipping, when the previous crop was pure Sitka spruce crop as it has a shallower root plate. Therefore, the peat disturbance during stump flipping is unlikely to bring catotelmic peat to the surface, which is not conducive to vegetation recovery. However, Lodgepole pine has a root ball, the rooting of which goes below the water table and therefore may bring catotelmic peat to the surface (furrow blocking may be more appropriate in this instance).  
• When the peat depth is greater than one meter. Shallower peats on slighter slopes may require just furrow blocking instead, so as to not disturb too much of the underlying remaining peat.  
• Before tree regen gets too big to treat using this method (otherwise this regen will need to be mulched, adding cost and complexity to the process).  
• When work is conducted under close supervision when starting the job, moving to new sections and when new operators start. Supervision is recommended on a regular basis throughout the job for inexperienced operators, to make sure as little peat as possible is disturbed, and to ensure minimal catotelmic peat is brought onto the surface. 

When most prone to failure 

• If peat is not deep enough (<0.5 m) and / or when the stumps are particularly large in relation to the peat profile. 
• When stumps and root plates are large or regen is too big.  It is probably best to leave large stumps in situ, and attempt to spread the ridge into the furrow in this instance if possible.  
• When the peat is compacted and disturbed too much, the target community is not as well restored, and may be more prone to fire damage. Higher bulk density peat has a different hydrological behaviour compared to uncompacted peat, particularly in response to droughts and waterlogged conditions.
• When not using the correct machinery and buckets. 

Points to Remember 

• Carefully consider peat depths, and species and stand age-related characteristics of root plate sizes and rooting structures.
• Earlier ground smoothing after forestry removal tend to give better results.
• Produces an instant surface topography that results in the quickest recovery of peat forming vegetation.  
• Quickens restoration and recovery processes and has aesthetic appeal.  Although the short-term look of the site can appear to be counter-productive, with extensive bare peat areas, experience has shown that sites can revegetate quickly with the desired peatland species.  

See our technical compendium for other techniques in the series.

Watch video by Peatland ACTION delivery partners Forestry and Land Scotland the tree shearing method

Peatland ACTION Project Officers are available to help you with your project. Please contact us as at [email protected] to be put in touch with your local Officer.