How to build forest resilience?

Building resilience is about managing risk – reducing the harm from, and exploiting the potential benefits of, climate change. Well-understood practices such as restructuring to bring in a diversity of ages, structures and species will help to manage risks and build the resilience of forests and forestry businesses to the changing environmental and economic conditions and market preferences than can be expected in the years ahead.

Illustrative examples of building resilience in six Scottish forestry situations

  1. Sitka spruce forest in south-west Scotland
  2. Sitka spruce forest in north-east Scotland
  3. Pine plantation in east Scotland
  4. Native woodland on the west coast
  5. Caledonian pinewood in the Cairngorms
  6. Creating a large-scale productive woodland

 

1. Sitka spruce forest in south-west Scotland

Sitka spruce

A large forest of predominantly Sitka spruce with small elements of riparian broadleaves and minimal open space, surrounded by other forests also dominated by Sitka spruce. The manager’s objective is to maximise returns by producing large volumes of sawtimber for the market.

Main threats:

  • repeated, heavy attack by a pest or disease such as the green spruce aphid causing large-scale tree mortality, particularly where the spruce is growing under sub-optimum conditions. May also pre-dispose the trees to other pests and diseases;
  • Sitka spruce becoming less suited to the local climate by 2050 (i.e. within the rotation being planted now);
  • large-scale windthrow event destroying a significant area of the crop; and
  • increase in high-intensity rainfall events with consequent risk of landslip, flooding and polluting run-off from harvesting/restock sites.

Main resilience-building strategies:

  • monitor plant health so that pests and diseases are identified quickly and control measures are ready to be used;
  • be ready to bring forward felling for crops that have reached a marketable size;
  • where possible, thin stands earlier to increase tree stability and reduce the risk of windthrow, and put in place a windthrow contingency plan in case of catastrophic damage;
  • use the Ecological Site Classification tool and the report 'Using alternative conifers for productive forestry in Scotland'
  • Using alternative conifers for productive forestry in Scotland’ to identify if alternative species could be introduced at restocking – such as Douglas fir, Norway spruce or productive broadleaves in the more sheltered fertile valleys. Where alternatives would give an acceptable yield, and so spread longer-term risks to the business, favour these species;
  • plan species diversity at a scale that is appropriate to the objectives; an intimate mixture of different species using a continuous cover approach may not be suitable where machinery is to be used for harvesting and the ground will need brash mat protection;
  • identify areas where it is not practical or desirable to restock because of the changed potential for tree growth in a future climate - these areas could form the planned open space in a restructured forest;
  • consider whether there is the potential to diversify income from the forest (e.g. through recreation), and to support this by using continuous cover forest management to improve aesthetics in key areas; and
  • take into account the likely increase in rainfall when designing culverts and bridges.

 

2.  Sitka spruce forest in north-east Scotland

Sitka spruce

A large forest of predominantly Sitka spruce, where a wide range of conifer species were tried out in early plantings. The standing crops of Sitka spruce and lodgepole pine are coming to final felling age and extensive restocking is required. The manager’s objective is to maintain the balance between timber, landscape, recreation and biodiversity values.

Main threats:

  • Sitka spruce shows signs of drought-cracking, and Dothistroma red band needle blight has affected the lodgepole pine stocks badly, so future species choice is a key challenge.

Main resilience-building strategies:

  • Manage some of the older stands of Norway spruce, Douglas fir and Scots pine under shelterwood systems to enhance structural diversity.
  • Where conifers are being removed from riparian zones, allow native hardwoods such as alder, birch and willow to regenerate.
  • Allow alternatives to Sitka spruce, such as Scots pine, Douglas fir and larch to expand their role in the next rotation. These could be in mixtures such as pine-spruce, larch-spruce and larch-Douglas fir, arising through natural regeneration.
  • Anticipate an increased role for shade-tolerant conifers such as western red cedar, western hemlock and grand fir.

 

3. Pine plantation in east Scotland

Pine plantation

A large area of well-structured pine plantation (mainly lodgepole and Corsican) on a dry site in the east of Scotland. The manager’s objective is to produce large volumes of timber for market and to enhance this attractive site as a visitor facility.

Main threats:

  • Already under threat from Dothistroma (Red Band) needle blight, which is likely to get worse particularly on inland provenances of lodgepole pine but also, possibly, on Scots pine.
  • Increasing risk of summer drought and failure of late planting.
  • Risk of forest fires, particularly in young pine stands.

Main adaptation strategies:

  • In areas affected by Dothistroma, bring forward thinning and felling and replace the affected lodgepole and Corsican pine with, for example, Macedonian pine, western red cedar or other timber species that would produce acceptable crops. Identify the best species for the site using the Ecological Site Classification and Establishment Management Information System tools and the report ‘Using alternative conifers for productive forestry in Scotland’.
  • Consider the potential for managing broadleaved species such as birch for timber on at least part of these sites. To ensure successful establishment of birch it is particularly important to choose the correct origin of planting stock; natural regeneration may be possible but improved stock is available and would be more suitable for timber production.
  • Thin compartments which are not yet showing signs of Dothistroma and which are not yet at a size suitable for clearfelling, to allow air circulation in the crop.
  • Thin stands earlier and more frequently to increase stability and reduce the risk of windthrow, and put in place a windthrow contingency plan in case of catastrophic damage.
  • Consider using Continuous Cover Forestry approaches on drier parts of the site in order to retain soil moisture, reduce the risk of planting failure and enhance the aesthetics of the site.
  • Reduce the risk of forest fires by using appropriate management strategies and raising awareness among forest visitors about the risk of starting fires.

4. Native woodland on the west coast

Native woodland

A series of small- to medium-sized native woodlands including some gorge woodlands, separated by grazed land. Composed of native species with rich bryophyte interest, but with browsing pressure and some rhododendron invasion.

Main threats:

  • Excessive deer browsing and sheep grazing preventing natural regeneration.
  • Rhododendron becoming dominant on the site, shading out ground flora and bryophytes and acting as a potential host for Phytophthora ramorum.
  • Change in species suitability for both trees and ground flora over time as the climate changes and pests and diseases remove species such as ash.
  • An increase in winter rainfall affecting slope stability and increasing the likelihood of erosion and flooding.

Main resilience-building strategies:

  • Protect the site from excessive browsing and grazing using fencing or deer/stock management. Some managed conservation grazing may be needed to maintain the conservation value of the site: it is excessive browsing and grazing that should be avoided.
  • Remove rhododendron completely from the site by following the SF Practice Guide on Managing and controlling invasive rhododendron.
  • Enlarge and connect the woodlands to create larger woodland blocks that are less vulnerable to the changing climate. Use natural regeneration where possible, or refer to our guidance on Seed sources for planting native trees and shrubs in Scotland to find appropriate planting material.

 

5. Caledonian pinewood in the Cairngorms

Cairngorm pine woodland

A large native pinewood providing a home to iconic forest species such as capercaillie and red squirrel. Ancient ‘granny’ pines make a disproportionate contribution to the biodiversity and aesthetic value of the site. Some areas planted at timber-producing density with Scots and other pine are now reaching a harvestable size.

Main threats:

  • Loss of ancient pines through old age or forest fires, and lack of succession planning to create the ‘grannies’ of the future.
  • Possible loss of pine as a key species because of disease such as Dothistroma needle blight.
  • Lack of natural regeneration of native species because of deer browsing and lack of ground disturbance.

Main resilience-building strategies:

  • Protect current ancient pines and select other mature pines that could form the next generation of such ‘granny pines’.
  • Convert some of the even-aged pine plantations to continuous cover using the guidance Managing continuous cover forestry, to help secure a new generation of older trees.
  • Heavily thin other even-aged stands to increase air circulation, to help protect them from Dothistroma infection. Remove heavily infected young crops, particularly of lodgepole pine.
  • Consider introducing associated native broadleaved species of trees and shrubs if they are absent due to past land use, to increase the site’s characteristic diversity of species.
  • Enlarge and connect the woodlands to create larger forest habitat networks. Use the SF native woodland target maps to see where these networks would be most beneficially established, and the Practice Guide Developing native woodland habitat networks.
  • At regular intervals, provide the ground disturbance needed for natural regeneration, to ensure that genetic adaptation to the changing environment can occur through natural selection. This is likely to also need browsing control.
  • Remove threats to the site such as rhododendron, following the SF Practice Guide on Managing and controlling invasive rhododendron.

 

6. Creating a large-scale productive woodland

Stacked timber

A proposal to create a large new woodland on a predominantly upland site in north Scotland. The main aim is to create a woodland with the potential for future timber production and Sitka spruce is the manager’s default choice of species.

Main threats:

  • Trees planted now may not thrive in the climatic conditions that they will experience over their rotations.
  • Trees planted now may be at risk of greater pest and disease attack.
  • Extreme weather events could make the ground too waterlogged to plant/harvest for much of the season.
  • Heavier rainfall and drought could increase sediment and nutrient run-off and pollution from cultivation/drainage.

Main resilience-building strategies:

  • Refer to the UKFS SF guide to cultivation to ensure that only techniques appropriate to the soil type are used.
  • Use the Ecological Site Classification and Establishment Management Information System tools and the guide Using alternative conifers for productive forestry in Scotland to see whether a range of species can be used. Potential candidates might include alternative spruces and firs or productive broadleaves (e.g. oak, sycamore, alder, birch). Where alternatives to Sitka could give an acceptable yield, favour them to guard against longer-term risks to the business.
  • Plan species diversity at a scale that is appropriate to the objectives; an intimate mixture of different species using a continuous cover approach may not be suitable where large machinery is to be used for harvesting and the ground will need brash mat protection. Alternative species should be planted in blocks of at least 1 ha in size to ensure they are not overlooked and remain as viable management objectives for the site.
  • Look for other ways of planning for diversity, such as networks of permanent tree cover to provide windfirm coupe edges, and a range of rotation lengths and thinning regimes.
  • On the parts of the site that are marginal for productive forestry, use alternatives such as native woodland and open space to broaden the objectives that can be achieved on the site.
  • Where exposure could be a risk, use the Forest Gales tool to determine the windthrow risk of a future crop, and plan species and rotations to address this risk.
  • Plant permanent riparian woodland buffers to minimise run-off and nutrient loss into watercourses.