Despite there being many uncertainties about the future, a lot is already known about how to build forest resilience. There is no ‘silver bullet’ that will protect forests, but applying existing best practice in the following areas should help to increase long-term resilience:
a) Select the most suitable species and genotypes for the sites, to create thriving forests which are likely to cope with future stresses (rather than necessarily defaulting to what has gone before). To do this involves going back to basics – ensuring an accurate knowledge of the soils and site types present in the forest or woodland, to allow those parts most at risk from the impacts of climate change to be identified. To help choose the most appropriate species for the next rotation, Forest Research’s Ecological Site Classification tool can match the suitability of over 50 species to your site and soil type. Don’t be put off by needing a password, it’s a very simple process. Since extreme events are likely to have a great influence on the forests of the future, you should also use the Forest Gales tool to understand and minimise the windthrow hazard of proposed planting.
For those creating native woodlands, Scottish native woodlands seed sources guidance lists appropriate origins for planting material.
Another way of selecting trees that are well suited to the site and likely to cope with future stresses is to use natural selection. Genetic adaptation occurs when the environment naturally selects those trees most suited to the conditions on the site. For this to happen, the planting stock needs to be derived from a range of parent trees (normally 30 or more) so that there is a sufficiently wide genepool from which to select.
Natural regeneration should be a more effective way of promoting genetic adaptation to climate change in tree species, because (normally) many more seedlings are produced and selection pressures operate through the whole life cycle of the tree. Forest Research provide information on Managing light to enable natural regeneration and continuous cover forestry. Managers should consider using repeated rounds of natural renegeration to promote continual adaptation of trees. Natural regeneration can be used in all types of woodlands, not just native woodlands, and can be used to augment a wider planting programme.
b) Reduce other pressures on forests – to give the forests that we have the best chance to thrive, whatever the climate does.
Deer browse seedlings, fray saplings and strip the bark of mature trees. In addition, browsing can affect the structure and composition of ground-cover. When excessive, these impacts can be detrimental to the woodland and by preventing natural regeneration deer can inhibit adaptation to climate change. With milder winters, deer numbers are likely to increase. Best practice guides have been developed by Scotland's deer sector to provide forest managers with the best information available on wild deer management in a format that is easy to access.
Rhododendron ponticum is an aggressive coloniser which reduces woodland biodiversity, prevents regeneration and acts as a host for Phytopthora ramorum disease. The Forest Research Practice Guide on Managing and controlling invasive rhododendron sets out the sequence of events required to plan and manage the control of this species.
Fire: As well as endangering life and property, wildfires can damage forest crops and habitats. As the climate changes, higher temperatures and an increased frequency of spring and summer drought events are likely to increase the risk of forest fires. Our information on Building wildfire resilience into forest management planning can help managers to recognise and manage the risks.
c) Maintain or add diversity in structure and species. In a changing environment, putting ‘all the eggs in one basket’ seems like a precarious strategy. On the other hand, a diverse forestry portfolio including low-, medium- and high-risk approaches reduces the chance of serious impacts on businesses when a pest, a disease or a storm wipes out a species or age class. Forest managers should therefore look creatively for opportunities to increase diversity, while still meeting their management objectives.
Structural diversity can be included in many ways – it could be as simple as retaining well-shaped wind-firm coupe edges; introducing thinning; or switching to a minimal intervention approach in hard-to-manage areas. The down-to-earth Practice Guide on Achieving diversity in Scotland’s forest landscapes explains how to go about it, and is aimed primarily at the managers of productive conifer forests.
Structural diversity may also be introduced through developing a ‘continuous cover’ approach to forest management, where a range of size classes is present in the same compartment. The FC’s internal guidance - Managing continuous cover forestry (available on request) - provides clear practical advice on transforming and managing such forests.
Species diversity can be introduced at restocking stage where tools such as Forest Research’s Ecological Site Classification show other species to be suitable. The aim should be to choose species (and provenances of those species) that are well-matched to the present conditions at the planting site. Planting stock should come from a range of parent trees to reduce the risks from using a single (clonal) genotype. The use of natural regeneration to restock woodlands can help to increase the genetic variation among the trees which, as well as giving opportunities to create forests well-suited to the site (see above), and may reveal some trees that are less susceptible to pests and diseases.
d) Other things to think about in a changing climate. A changing climate may impact on the way that forests are managed in other ways. Some potential changes to bear in mind are:
- Milder and wetter winters could affect ground conditions and, given the need to protect soils and water, could mean that sites remain unworkable for longer. On such sites, carry out work in late summer if possible, and/or ensure that the harvesting system you use provides sufficient brash to create brash mats to protect the soil and water at felling time.
- Changing temperatures could affect the timing of planting. For example, milder winters could extend the window for planting trees later into the autumn.
- A longer growing season could benefit tree growth, but also the growth of competitive weeds.
- It is not just the trees that will be affected by the changing climate. Where conditions are likely to become wetter, forest managers should design culverts, bridges and roads to cope with increased water flow. Even in areas that do not get wetter, extreme events such as flash flooding will be more likely and such events should be taken into account.