Climate Change

Concern about the impacts of climate change on our trees and woodlands has led to increasing interest from owners and managers. The science of climate change and tree-related research is developing fast but advice for landowners can be difficult to access or remains unclear. This publication sets out to summarise the science and provide advice for future-proof woodland management.

What do we want from our woodlands in the 21st Century?
Trees, woods and forests are important for society, the economy and the environment. They are the single largest natural land-type supporting biodiversity in Europe. As climate change increasingly affects our lives, our woodlands are likely to be ever more important in providing ecoservices (such as landscape connectivity, soil and water conservation, habitat for wildlife) and as a carbon-lean resource (such as wood for construction, material for bioenergy).

Long-term forecasts in world timber trends suggest a continuing decrease in hardwood exports from tropical forests and increasing consumption of timber in industrialising countries such as China and India. There are therefore good opportunities for increasing our domestic timber supply, particularly for valuable hardwood timbers. This would bring many benefits, such as using timber for use in material substitution, thereby reducing our carbon footprint.

In recent decades UK forest policy has concentrated on environment and social objectives. Sustainable forest management (SFM) must include economic factors, and naturally, economics often drives the ambitions and interest for woodland owners. Quality timber production can fulfil roles in increasing domestic timber supply, contributing by-products to bioenergy demand, and by providing materials for product substitution. True SFM should deliver wood products whilst protecting/enhancing the environment and providing benefits to society. We should aim for the best quality and health in our woodlands. This will provide resources for the widest range of future opportunities, including timber. In summary – remember the mantra “quality sells”.

Evidence
Climate change is widely accepted as a fact. The science of climate change is conducted and summarised at a global level by the Intergovernmental Panel on Climate Change (IPCC). The IPCC includes hundreds of leading experts and therefore it seems irrational to dismiss lightly any of their conclusions (Table 1, below).

Effects of temperature increases have been documented (with ‘medium confidence’) on agricultural and forestry management at Northern Hemisphere higher latitudes. These include earlier spring planting of crops, and alterations in natural disturbance regimes of forests (i.e. fires and pests).

Climate change is already affecting living systems globally, and affecting the range and abundance of animals and plants (Parmesan, 2006). Wide ranging evidence exists for climate change affecting biomes, forests and tree species across Europe

Projections
Woodland growth will be impacted by climate change to different degrees across Europe, the UK generally less impacted than boreal and Mediterranean regions. The most widely recognised impact will arise from temperature change (warming), which will profoundly affect trees and woodlands by altering photosynthesis and respiration, and other factors such as phenology (e.g. leafing dates) and evolution.

A warming of up to 2°C may be beneficial for trees but the response will vary between different species (Saxe et al., 2001). Increases in CO2 (a greenhouse gas) may also increase growth rates in the short term (i.e. before other negative effects impact). The greatest impact may come from extreme and unpredictable events; so called ‘stochastic’ events, such as drought, extreme wind and precipitation, frost, fire, insects and pathogens. Of course, impacts are likely to come from more than one direction and may be related. For instance, trees stressed by drought will become more susceptible to disease and pests.

In the UK, we lead the world in climate science and have a wealth of information on likely impacts of climate change on our woodlands (e.g. Broadmeadow, 2002). Generally, native broadleaved species may become unsuitable for timber production on some soils and aspects. Species projections have been developed by Forest Research following likely scenarios for 2050 and 2080 (Broadmeadow et al., 2005). The strongest projection is that beech will become less viable on southern slopes in southern England. General risks and responses are summarised in Table 2, below.

UK policy
Before deciding what you would like to do, it is important to review the policies relating to forestry in the UK and how they affect woodland owners and managers.

Beyond the woodland grant schemes the key policy to highlight here is that which relates to what tree material you may include in a new planting scheme. The Forestry Commission has advocated local planting material through the definition of seed zones (Herbert et al., 1999). However, a recent publication by Forestry Research (Hubert and Cottrell, 2007) states that “this relatively fine-scale system of zonation, if rigorously imposed to control the use of planting material, may be overly restrictive in the face of predicted climate change.” This has yet to be reflected in any change in planting grant schemes.

The recent revision of the forestry strategy for England (Department for Environment Food and Rural Affairs, 2007) recognises the value of timber production but perhaps falls short of recognising the reality for individual woodland owner’s needs. We live and operate in fast-changing times, and clearly forestry is already moving up the rural agenda, and may benefit in the future from increased interest and support from Government.

What to Plant
A common phrase of leading climate change researchers in recent times is ‘robustness’, or in other words creating a resource that can resist or adapt to change.

An important recommendation is to avoid single species plantations and the planting of material of narrow genetic origin. You would be well advised not only to plant native trees that are of local origin but also include some sourced from further afield, ideally from further south where our climate may be matched in the future. Furthermore if appropriate to the site, it may also mean that you could include some non-native trees that are predicted to grow well with climate change (see Table 3, right). Trees closely related to native species (e.g. Fraxinus angustifolia.) or those native to Europe (e.g. Juglans regia) may be more politically acceptable in the short-term. Nothofagus spp. may have potential but provenance choice will be critically important.

Another important consideration may be to use mixtures in designing new woodlands, including different species for specific purposes such as soil moisture retention, nitrogen fertilising effects, wind protection and microclimate provision. A high shrub content as part of the mixture can be highly effective in many of these criteria.

Finally, plant with an eye to the future. What is the purpose of the planting or what might its value be in the future? A poorly designed plantation with poor quality planting stock is unlikely to deliver much value.

Where to Plant

We expect that stressed trees will be more susceptible to pests and diseases, and of course will not grow or yield well. It may be more important now than ever to match a species carefully to the site, particularly at the small scale. In other words, avoid planting beech on southern facing slopes and hill tops. Best growth for productive species such as ash and walnut will be where there is good soil moisture and microclimate, such as near the valley bottom or lower slopes.

At the large scale, you might want to avoid planting beech in the southern counties, except on the very best sites. Conversely the suitable range of walnut and sweet chestnut may extend north in the UK, and new species (as suggested within Table 3, above right) may be viable in the southern counties and south west.

How to Manage
Variation in woodland age and structure will also be beneficial in the future. Silvicultural systems can be applied where the canopy is maintained at varied levels without clear-felling, using varied tree species and using natural regeneration where possible. The concept of ‘close to nature forestry’ was advocated in the 1880s but has increasing resonance today.

In the UK, woodland managers should be aware of a potential increased risk of fire, particularly in southern England, and plan and manage forests accordingly. Pests and diseases are difficult to manage (and predict) but risks can be diminished through good design, such as planting trees of different genetic origin.

Most crucially, operate with sustainable forest management objectives. Aim for the best timber quality, and there will be plenty of trees of lower quality and management (pruning and thinning) by-products for woodfuel provision. Retention of misshaped trees and standing deadwood, together with sensitive understorey and ride management, will assist biodiversity to adapt to climate change.

Finally, a well-managed wood will provide society with landscape value and environmental protection, and if you choose, a wonderful place for people to enjoy for pleasure or sport.

Summary

Our woodlands will play a crucial role in the 21st Century. The global trend in timber may reflect an increasing demand for wood products. Woodlands will be important in supporting a carbon-lean society: where material substitution (timber replacing brick, concrete or steel), bioenergy and management of woodlands as carbon sinks will be high priority. The provision of ecosystem services will become higher priority, such as helping nature adapt to change, linking the landscape, and soil and water protection and management.

Woodland management must rise to meet these challenges, whilst owners should be able to capitalise on the values from their forests. Assisting woodlands, tree species and wildlife to adapt to change will be challenging. There may be a greater role for mixed-woodlands and close to nature forestry practice, and these may provide a more flexible and robust forest resource. The roles of genetics and silvicultural best practice are very important and must be considered hand-in-hand.

There is so much uncertainty in the science of climate change projections, and in how the environment will respond, it is difficult and perhaps foolhardy to make firm recommendations. However, woodland owners and managers quite rightly want to plan for the future and need good information and guidance where possible. It is hoped that this publication provides some useful pointers and encourages the reader to find out more.

Further Information

Broadmeadow, M., (2002). Climate change: impacts on UK forests. Forestry Commission Bulletin 125, Edinburgh, 119-140 pp.

Broadmeadow, M., Ray, D. and Samuel, C., (2005). Climate change and the future for broadleaved tree species in Britain. Forestry, 78(2): 145-161.

Department for Environment Food and Rural Affairs, (2007). A strategy for England’s trees, woods and forests, www.defra.gov.uk, pp. 42.

Herbert, R., Samuel, S. and Patterson, G., (1999).
Using local stock for planting native trees and shrubs, Forestry Commission Practice Note 8. Forestry Commission, Edinburgh, pp. 8.

Hubert, J. and Cottrell, J., (2007). The role of forest genetic resources in helping British forests respond to climate change, Information note June 2007, FCIN086. Forestry Commission, Edinburgh.

Kellomäki, S. and Leinonen, S., (2005). Management of European Forests Under Changing Climatic Conditions. SilviStrat Final Report. Tiedonantoja/Research Notes No. 163. University of Joensuu, Faculty of Forestry. ISBN: 952-458-652-5. , pp. 427.

Parmesan, C., (2006). Ecological and evolutionary responses to recent climate change. Annual Review of Ecology, Evolution and Systematics, 37: 637-669.

Saxe, H., Cannell, M., Johnsen, Ø., Ryan, M. and Vourlitis, G., (2001). Tree and forest functioning in response to global warming. Tansley review no. 123. New Phytologist, 149: 369-400.

Web Resources
BIHP – British & Irish Hardwoods Improvement Programme: www.bihip.org

Forest Research – The Research Agency of the Forestry Commission:www.forestresearch.gov.uk

Forestry Horizons – A UK-based forestry think tank:www.forestryhorizons.eu

IPCC – The Intergovernmental Panel on Climate Change: www.ipcc.ch

Valbro – Growing valuable broadleaved trees: www.valbro.uni-freiburg.de

About the Author

Gabriel E Hemery is Director of the independent forestry think-tank Forestry Horizons.
He has published widely on the subjects of tree improvement, hardwood silviculture and climate change.

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