Use of the Native Woodland Model – case studies

The Scottish Forestry Grants Scheme and Forest Habitat Networks

Careful planning of woodland restoration and expansion projects should lead to greater benefit to conservation. In general, extensive woods are likely to support a richer biodiversity than smaller ones. Many woodland species are slow to colonise new sites, especially if they have to cross open land. New or restored woodland is thus more likely to develop a diverse and characteristic community if it is close to existing woods from which colonisation can occur.

The greatest gains are likely to result if woodland is restored and expanded in such a way as to connect and expand existing fragments into Forest Habitat Networks (FHNs). This should also reinforce landscapes where woodland cover is already an established feature, rather than planting up land from which woodland may have been absent for centuries.

The Scottish Forestry Grants Scheme (SFGS) aims to encourage the development of FHNs. Grants are available for restoring Plantations on Ancient Woodland Sites (PAWS) and for expanding native woodland onto open ground, preferably by natural regeneration. Other grants support the improvement of riparian habitats, which often play a key role in FHNs by linking fragmented woodlands and forming semi-natural corridors through larger forests.

The potential for development of FHNs is explored below for a sample area in a river valley in the Southern Uplands. The aim of this study is to identify PAWS within 300m of Ancient Semi-natural Woodland (ASNW), and to investigate what woodland types could potentially be established on them. The resulting suggestions would need refining through ground survey, and this method allows field work to be targeted towards those areas which appear to have the highest potential.

Existing woodland cover

Existing woodland cover in the sample area is quite high, but only 18% is semi-natural, and the majority (76%) consists of non-native plantations. However, 15% of the plantations are on ancient sites, and many of these are adjacent to ASNW, increasing their potential for restoration to native woodland. PAWS close to ASNW may have retained more ancient woodland species, and are likely to be more rapidly colonised by others, due to the proximity of higher quality habitat through which these species can move.

The area of existing woodland is given in Table 1 and its distribution is shown in Figure 4. The land in the western half of the area is quite high, over 200m, and most of the semi-natural woodland is on the lower ground along the rivers. The eastern half is lower, and fragments of ASNW are scattered more widely across the terrain.

Table 1: Existing woodland within the sample area

  Area of woodland (ha)
  Ancient sites Other land Total
Semi-natural woodland 679 2,106 2,785
Plantation 1,833 10,141 11,974
Mixed 584 322 906
Remnants *     442
Total 3,538 12,569 16,107
 
* Areas of woodland on the Ancient Woodland Inventory which do not coincide with areas of woodland on SSNWI. The type of woodland is therefore unknown.

Figure 4: Existing woodland within the sample area

Figure 4: Existing woodland within the sample area

Restoration of PAWS

Table 2 gives the areas of potential HAP types likely to develop on PAWS within 300m of existing ASNW, and Figure 5 shows their distribution. Other semi-natural woodland (OSNW) is also shown, to illustrate how PAWS fit within the wider woodland network. There are some 1,833ha of PAWS within the sample area, of which 930ha are within 300m of ASNW.

Table 2: Areas of predicted HAP types on PAWS

HAP type
Area (ha) within 300m of ASNW
   
Upland Oak
410
Mixed broadleaved
196
Ash, Oak or mosaic
139
Ash
92
Wet
78
Birch, Pine or mosaic
11
Upland Birchwood
0
Birch, Wet or mosaic
0
Mixed broadleaved, Ash or mosaic
4
Total
930

Figure 5: Distribution of predicted HAP types on PAWS

Figure 5: Distribution of predicted HAP types on PAWS

The most frequent predicted HAP type is upland oak, representing 44% of the area of PAWS within 300m of ASNW (Table 2). The greatest potential for linking woodland fragments by restoring PAWS appears to be along the Scar Water and the River Nith (Figure 5).

On the high ground in the north of the area, restoration of upland oakwood could link ASNW and other Semi-natural Woodland (SNW) along the Scar Water, and across the intervening high ground to the River Nith. Further south there is considerable potential for restoring mixed broadleaved woodland to link several areas of woodland along the Scar Water and the Shinnel Water. Encouraging PAWS restoration in these areas should lead to considerable gains for biodiversity.

Restoring and expanding Upland Ashwoods in north Mull (From Gray & Stone 2003)

Large ashwoods and their western hazel-dominated variants are rare and fragmented in Scotland, and the remaining examples are internationally important, especially for lower plants. Many species typical of old ash woodland are slow to colonise new habitats, so a new or restored area of woodland is more likely to develop a diverse and characteristic community if it is close to appropriate colonising seed sources.

The NWM provides a tool for identifying the most suitable candidates for restoration. Opportunities for development of Upland ashwood in north Mull are explored below.

Current semi-natural resource

A map of north Mull has been constructed on a GIS, (Figure 6) to show:

Areas of semi-natural woodland were identified using the Scottish Semi-natural Woodland Inventory (SSNWI). Most inventories only map woods larger than 2 ha, but SSNWI shows woods as small as 0.1 ha, permitting the identification of highly fragmented remnant semi-natural woodland. ASNW was identified by overlaying the SSNWI data with information from the Ancient Woodland Inventory.

Semi-natural woods on NWM potential ashwood sites are those most likely to contribute to the current Upland ashwood resource. Maintaining and enhancing such woods is the first priority.

Figure 6: Distribution of current semi-natural woodland in North Mull

Figure 6: Distribution of current semi-natural woodland in North Mull

Potential for restoration of plantations

Figure 7 shows the distribution of all plantations on north Mull. SSNWI and the AWI have been used as before, to show where PAWS and other plantations occur on NWM potential ashwood. PAWS within 100m of high value woods (ie ASNW on NWM ashwood) are considered to have the most potential for restoration. These ‘high opportunity’ woods cover 143 ha.

Figure 7: Distribution of plantations on North Mull

Figure 7: Distribution of plantations on North Mull

Opportunities for targeted ashwood expansion are summarised in Figure 8. LCS88 data were used to identify areas where rough grassland and bracken corresponded with NWM potential ashwood sites. These LCS88 categories were selected as ecologically appropriate for restoration of native woodland according to Rodwell and Patterson (1994).

Figure 8 shows suitable plantations and rough grassland (i.e. those on NWM potential ashwood sites) within 100m of existing semi-natural woodland on NWM potential ashwood sites. There are 1722 ha of suitable open ground within 100 m of semi-natural woodland on NWM ash, and 350 ha of suitable plantation. These 2072 ha are likely to give the greatest conservation benefit if converted to upland ash, whilst also linking remnant woods to address the problems of fragmentation.

Figure 8: Expansion opportunities for Upland Ashwoods in North Mull

Figure 8: Expansion opportunities for Upland Ashwoods in North Mull

Combined HAP targets for strategic woodland development

Figure 9 combines the information from Figures 6, 7 and 8 to give an overview of the opportunities for restoring and expanding Upland ashwood in north Mull. The graphic combination of information onto one map makes it easier to set priorities for action. Areas of fairly undistinguished plantation have different potentials for contributing to biodiversity targets by virtue of their relationship to other nearby priority sites.

Figure 9: Upland Ashwood: summary of opportunities in North Mull

Figure 9: Upland Ashwood: summary of opportunities in North Mull

Estimating the extent of Old Sessile Oakwood
(Jenny Bryce, Scottish Natural Heritage)

Under the EU Habitats Directive 1992 (Directive 92/43/EEC), member states are required to designate sites as candidate Special Areas of Conservation (cSACs). The site series is expected to be representative of the occurrence within each country of habitats and species of European importance (Annex 1 habitats and Annex II species). This requires, for each habitat type, assessment of the proportion of the total extent which is within cSACs. Although there are considerable survey data on specific sites, national woodland inventories do not currently contain comprehensive information on woodland types. In the absence of such data, the NWM was used in combination with SSNWI to predict the potential woodland type of existing semi-natural woods. The aim was to re-examine estimates of the extent of Old Sessile Oakwoods with Ilex and Blechnum in the British Isles (Annex I Code 91A0). It was felt that existing figures for the extent of woodland of this type may be over-estimates.

Woods with semi-natural components were identified from SSNWI, and the resulting polygons intersected with the NWM to ascribe a potential woodland community. Old Sessile Oakwoods broadly correspond to oak-dominated examples of NVC types W11 and W17, and mosaics containing these types. In order to select the NWM types which were most likely to conform to Old Sessile Oakwoods with Ilex and Blechnum, polygons with an elevation of less than 200m were excluded, as were those with <10% canopy cover. W4 was excluded where it was not contiguous with other oakwood types. The resulting dataset was then ground-truthed to identify the proportion which was ‘qualifying habitat’ according to the Natura Interpretation Manual definition of Old Sessile Oakwoods with Ilex and Blechnum.

The polygons were ‘dissolved’ so that all contiguous blocks were treated as single woods and then used as the sampling units. Polygons were selected at random (using an Excel macro), with the probability of selection being proportional to the area of the site, so that larger sites were more likely to be selected. The sample was stratified so that eastern and western woods were assessed separately and those from a narrow set of NVC identifiers ‘restricted’ as compared with a more ‘inclusive’ definition. At each sample site, the area which was estimated to be qualifying habitat was assessed (Box 1). For each stratum, the extent was estimated by multiplying the area of the stratum by the mean proportion of each site that was
assessed as qualifying habitat. This showed that within Scotland the proportion of qualifying oakwood habitat within cSACs is 23-35% (95% confidence levels), compared to earlier (UK) estimates of 14-17%.

Box 1. Criteria for assessing qualifying or partly qualifying habitat

  • Sites with no oak present were not considered as qualifying habitat.
  • Sites with a low proportion of oak were considered as qualifying habitat, provided the oak was distributed throughout the site (particularly towards the northern extent of the
  • Where oak was present in only a small area of the site, only this area would be regarded as qualifying habitat.
  • Where woods were clearly divided into discrete blocks of different stand types, these were used to assess the proportion of the site with qualifying habitat. However, small pockets of other woodland types (e.g. W7, W4 or W9) were not separated from large areas of qualifying habitat.
  • Where oak was a minor component of another woodland type, particularly on cSACs where other Annex 1 habitats are qualifying interests, it was not considered to be qualifying habitat.

Developing the Cairngorms Forest and Woodland Framework
(Cairngorms Partnership 1999)

Forestry Frameworks are intended to provide high quality advice to inform and guide the development of woodland design proposals submitted under the Scottish Forestry Grants Scheme (SFGS). They provide a level of guidance and information between policy (Indicative Forestry Strategies) and delivery mechanisms (woodland planting and design proposals under the SFGS).

Frameworks are considered particularly relevant to sensitive areas such as the Cairngorms where there is a wish to promote a more proactive and visionary approach. The aims of producing the Forest and Woodland Framework were:

Methodology

Using a GIS, 500m ‘regeneration zones’ were created around existing woodland in the Cairngorms Partnership area. Within these zones, the NWM was used to predict the location of suitable areas for regeneration of woodland types already present. The model was also used to predict the potential for developing woodland on areas outside the regeneration zones, to determine the potential for establishing further linkages by planting.

Figure 10: Woodland opportunities in part of the Cairngorms

Figure 10: Woodland opportunities in part of the Cairngorms

The composite map was considered in relation to other land-uses (including grouse shooting, agriculture, forestry and conservation of other habitats) to develop a strategic plan for woodland establishment within the whole area.

Results

Several areas, including the Forest of Spey between Dorback and Glen Feshie, have the potential to support a complete transition from oak/birch, through pine/birch, to sub-alpine scrub. Forest Enterprise has plans to allow subalpine scrub to develop at Glenmore, making a significant start to the establishment of this network.

There is also considerable potential for birch regeneration but, apart from the Angus Glens, Strath Avon and the upper parts of the Spey catchment, most of the potential areas are on agricultural land. It is important to maintain agricultural land in many such areas, and to preserve cultural heritage and landscape character, so large-scale conversion of such land to woodland would be undesirable. However, small-scale, well designed woods could help to diversify farmers’ incomes, provide timber and shelter for livestock and contribute to local FHNs. Riparian woodlands contribute to water quality objectives, and their management and expansion could be encouraged on valley floors.

There is substantial potential for natural regeneration of pine in the Deeside Forest, the Forest of Spey, Donside and Glenlivet (Figure 10). Priority areas were defined in the following order:

Establishing new native pinewood by planting is also a priority in the Forest of Spey and the Deeside Forest, and it was recommended that planting take place in Strath Avon and Strath Gairn to develop linkages between the Speyside and Deeside core forest areas (Figure 10).

Non-native tree species

Because the NWM essentially classifies the landscape according to site conditions, the predictions can also be used to identify the most suitable sites for non-native species. Most introduced conifers (except for larch) grow well in the more fertile, sheltered oak-birch zone on the valley sides and bottoms, but grow poorly on sites predicted for pine-birch communities (relatively high altitude, exposed sites with acid, nutrient-deficient podzolic soils). There is also potential for Sitka spruce on the scattered birch woodland site type (peaty gleys and peats) below 500 metres.

This work with the NWM illustrated how large areas of the Cairngorms have no real potential for commercially viable conifers, due to the extent of land considered suitable only for ‘sub-montane scrub’, scattered, sparse woodland categories, or which are too exposed for either woodland or scrub.
Additionally, many sites at the upper end of the altitudinal range for native woodland are considered too exposed for productive woodland of any species.

Practical Application of the Native Woodland Model
(Irvine Ross, The Ross Partnership, Dinnet, Aberdeenshire and Ann Malcolm, the Macaulay Institute)

Introduction

This section illustrates how the NWM can be used by land owners and forestry managers to make strategic decisions on the location and types of native and commercial woodlands on a mixed land use estate. This is demonstrated for the hypothetical estate of ‘Glen Farsat’.

Glen Farsat Estate

Glen Farsat is a mythical mixed land use estate of some 2,200 ha in extent, which lies within the Cairngorms National Park. Figure 11 shows the general features of the estate.

Figure 11: Farsat Location

Figure 11: Farsat Location

Elevation ranges from 250m to 800m, summers are moderately warm, frost and snow are significant features of the winter weather and the rainfall is 900mm. The underlying geology is mainly acid igneous and soils vary from alluvial soils in the bottom of the lower glen, through brown earths, humic ironpan podzols, peaty gleys, and peats with a limited area of sub-arctic soils at the hill summits.

Figure 12: Farsat Landcover

Figure 12: Farsat Landcover

Current Land Cover

Figure 12 shows the land cover within the estate, derived from the Land Cover of Scotland 1988 (LCS88) and other datasets used in the Cairngorms Forest and Woodland Framework (Cairngorms Partnership
1999).

The main features to note are:

Current Land Use Management Activities

Changing the Land Management Objectives

The estate management has decided to reassess its objectives to further enhance its sporting revenue potential.

The new objectives are to:

Some Options for Future Management of Wooded Cover in Glen Farsat Estate

Part of the process of managing land involves looking to the future and considering options for change. A number of grants are available for woodland expansion and management, which can be used to achieve
an integrated approach to land management on the estate. Specifically, the woodland actions which could help achieve the wider estate objectives are:

Assessing the Estate’s Woodland Potential

These new objectives will result in an increase in the woodland cover. Information on woodland potential will be required to enable the estate to explore various scenarios, before deciding how to achieve the new objectives.

Whilst the Soil Survey of Scotland soil maps are available, it would take some time for the estate’s forestry consultant to interpret the soil and topographical maps and produce a site capability map. A full Ecological Site Classification (ESC) over the whole 2,200 ha of the estate would be prohibitively expensive. ESC may be used later to refine the boundaries of the proposed new woodlands but a more strategic overview needs to be developed first.

The estate’s management therefore decided to commission a study using the NWM, as the most cost effective method of assessing the whole-estate site capability for forestry.

Figure 13 shows the NWM output, illustrating site suitability for different woodland types, both in relation to the biophysical properties of the site and also to the proximity to existing tree seed sources. The potential for woodland expansion by natural regeneration is greatest around the linear birch and mixed broadleaved woodlands along the Water of Farsat. The opportunity to extend the area of native pinewood from the neighbouring property to the west is constrained by the extensive areas of peatland bordering this wood to the east and north. The NWM shows that this land is only capable of supporting scattered downy birch and scrub. The potential for expanding the native pinewood to the south of the estate by natural regeneration is much greater, as the NWM indicates that the land adjacent to this wood is suitable for both pine and birch regeneration.

Figure 13: Farsat NWM

Figure 13: Farsat NWM

There is also potential to expand the narrow strip of planted Scots pine woodland to the east of the main glen by natural regeneration. The NWM output also shows land further from seed sources which would be suitable for planting with Scots pine. The opportunities for creating an extensive, cohesive new native pinewood on the eastern side of the main glen are evidently limited, with the NWM map showing large areas only capable of supporting scattered downy birch and scrub. There is slightly better potential to the west of the main glen except at higher altitudes.

Management Options in Glen Farsat

Two options are shown here on Figures 14 and 15. They are:

1 . Allow new native woodland creation wherever suitable (Figure 14)

These relatively simple afforestation proposals could be appropriate if creating native woodland was a prime management objective. However, this is not the case, and so the estate’s management must be more selective in choosing sites for woodland planting or regeneration.

2 . Selectively create new native woodland to satisfy management objectives (Figure 15)

After consideration of several options, the woodland distribution in Figure15 was favoured.

Figure 14: Farsat Estate management; Option 1

Figure 14: Farsat Estate management; Option 1

Figure 15: Farsat Estate management; Option 2

Figure 15: Farsat Estate management; Option 2

Actions for management Option 2:
Action 1

The commercial woodlands will be consolidated into two economically sized blocks. These blocks will be:

Block 1: the land around this block of conifers on the eastern side of the glen will be planted with Sitka spruce. The NWM indicated that the site was suitable for the regeneration of birch, implying reasonable fertility and shelter. A site check confirmed that the existing hill grassland is on a wet flush and there is sufficient soil moisture for Sitka to grow well.

Block 2 has good road access, and will be expanded by planting wet grassland with Sitka spruce. The adjacent blocks of new native pinewood will create a diverse structure for this consolidated area of woodland.

Action 2

The small block of commercial conifers, with poor road access, on the west side of the Water of Farsat in the upper glen will be felled. Birch regeneration will then be encouraged, as the NWM indicates that the site and adjacent areas are suited to this woodland type. The dense birch regeneration will hold pheasants well and will offer opportunities to drive birds across the glen to the coniferous wood on the other side.

Action 3

In the interests of the grouse moor, the planted linear Scots pine wood to the west of Block 1 will not be encouraged to regenerate, although the NWM predicts that this area would be suitable for pine and birch regeneration.

Action 4

The rectangular block of commercial woodland at higher altitude near the eastern boundary will be felled and allowed to revert to heather moorland. The area of woodland lost will be compensated for by the creation of new woodlands elsewhere. This action will:

Action 5

In order to take advantage of the enhanced grants available for new native woodlands, four areas of new native pinewood will be planted. Two of these are on open ground and two will be created by estocking existing coniferous woods with Scots pine. This will contribute to one of the objectives of the Cairngorms Forest and Woodland Framework, which is to provide a woodland habitat linkage between existing areas of native pinewood. The guidelines suggest that woods of at least 10ha should be sited at distances of no more than 500m. These woods will also shelter the grazing land and provide more pheasant drives.

Action 6

Some further planting of riparian broadleaved woodland will be carried out, partly in the upper reaches of the glen. This will improve the aquatic habitat for juvenile fish and also provide further shelter for the livestock.

By interpreting the NWM output, in conjunction with other information, the owner and his forestry consultant can now feel confident that the strategic plan for all aspects of the estate management, and not just their woodland objectives, is sound. More detailed planning will now be justified. The benefits accrued will also extend beyond the estate boundary and help meet wider National Park objectives.

Conclusion

The extent to which potential options and the stated objectives have been satisfied by the proposed actions are summarised below:

Stated New Land Management Objectives Covered by:
Retain the hill cattle enterprise Action 1 & 5
Increase the quality of the grouse shooting Action 3 & 4
Establish an economically viable pheasant shoot Action 1 & 2
Maintain the value of the fishings by improving riparian habitat Action 6
Increase native woodland by natural regeneration where possible Action 2
Improve the long term financial return from the commercial woodlands Action 1 & 2
Create better integration between the farming, forestry and sporting enterprises on the estate by improving the location of the various types of woodland on the estate Action 1, 2, 5 & 6

 

Some Potential Options for Future
Woodland Management		 Covered by:
Expand riparian woodlands
Increase the extent of native pinewoods
Increase the provision of shelter belts near the better agricultural land
 Action 6
Action 5
Actions 1&5
Expand the area of commercial conifer plantation on the estate and optimise the growth rates of woodland with timber extraction potential Action 1
Engage in land management activity to increase the quality and quantity of pheasant shoots on the estate Actions 1,2 & 5
Integrate hard landscaping with future woodland expansion plans Action 1

 

Other Potential Benefits Covered by:
Helps meet the objective within the Cairngorms National Park to restore heather moorland.
 Action 4
Locating new native woodlands to comply with one of the objectives of the Cairngorms Forest and Woodland Framework, which is to provide a woodland habitat linkage between existing areas of native pinewood. Action 5
Increases the habitat for juvenile fish Action 6