The French scientist Jean-Baptiste Fourier identified the greenhouse effect in 1827, but it was not until 1988 that the Intergovernmental Panel on Climate Change was set up in order to advise on climate change, risks and options for adapting to or mitigating that change. I was first asked about climate change about the same time, by a well read farmer, who was planning a tree planting scheme, and I had to admit I was not really sure. Back then we were still coming to terms with acid rain, a threat that has since substantially faded due to stricter air quality regulations. Farmers can change their crops almost on an annual basis, but for the woodland owner a planting decision now can influence your wood for fifty or a hundred years. Mistakes can last a long time!
There are some general principles which are now being widely advocated, including planting a variety of tree species and protecting genetic diversity. Mixed woodlands give potential for more choices in later thinning regimes, and can also be helpful for resilience to disease. Many species cover wide natural distributions, and this can give us indicators of trees that are likely to thrive in our warmer and more continental climate. It may also introduce a case for considering different provenances for the seed; choosing seed from a more southerly location may have advantages. Set against this are risks from disease (much in the news with Ash Dieback) and indeed a long held belief that locally genetic seed stock is better for wildlife. Many conifer species are well adapted to drought and dry summers, because their needles are adapted to cut down water loss.
Accepting that climate change is inevitable, the Forestry Commission are undertaking field surveys, to consider and identify a range of tree species for increased use as timber species. This involves reviewing small, plantations of unusual species or specimens. They are encouraging owners to take some risks and be adventurous, again to spread risk. Forest Research have also sought to develop some predictive criteria for species for different soils and sites (Ecological Site Classification), but this is a very detailed and theoretical methodology, and certainly not practical for a small woodland owner. Perhaps a cruder but more useful guideline is the Forestry Commission’s prediction that climate change will lead to changes equivalent to a change in latitude of 2-5 degrees south, and have advocated sourcing tree seed accordingly. If you fancy some field research that’s equivalent to a band across France from Paris in the north to Bordeaux in the south!
The most predicted affects of climate change in this country are to see a more continental climate, colder in winter as well as warmer in summer. This is expected as a consequence of global warming melting the Arctic ice cap and breaking down the Gulf Stream Drift, which brings the warm Caribbean water to our coasts. Drier summers are expected to have serious impacts on drought sensitive tree species on shallow, free-draining soils, particularly in southern and eastern England. So we can expect many of our native species to change their ranges, while other non-native species may thrive. Summer droughts are also likely to lead to more problems at the time of establishment, as young trees are particularly prone to drought before they develop good root systems. Pests and diseases may also increase and spread in importance. While some of our current problems stem from man-made imports, insects, fungi and other pathogens reproduce and evolve faster than any tree species.
While the English Channel is a natural barrier to some migration it will have little effect on the changing distribution of most tree species, or their associated fauna, or indeed pests. As woodland managers, we can not fight these changes, but need to anticipate and work with them as much as possible. From a conservation point of view, maintaining a diverse woodland structure can be as important as seeking to promote native species. On particularly important nature conservation sites, especially Sites of Special Scientific Interest, there still remains a good case for seeking to maintain the past native tree and shrub composition as closely as possible.
Below are some notes by species, largely drawn from the Forestry Commission.
|Common Alder||Likely to remain important for wet sites|
|Ash||May spread north, if it survives Ash Dieback|
|Beech||Susceptible to drought in the south east, likely to spread west and north|
|Downy Birch||Increased prominence in western uplands|
|Silver Birch||Increased vulnerability to summer drought|
|Wild Cherry||Generally likely to benefit|
|Hornbeam||May increase in lowlands|
|Small-leaved Lime||Likely to benefit and spread north|
|Pedunculate Oak||Faster growth, but at risk from summer drought|
|Sessile oak||More tolerant to drought than Pedunculate Oak, so may spread east|
|Rowan||Unlikely to change|
|Sycamore||More productive, but more prone to drought in the east|
|Sweet Chestnut||Likely to benefit, with more natural regeneration|
|Scots Pine||Likely to benefit and spread south and east|
There is wide genetic diversity within existing native tree populations. For example anyone who has looked at oak trees growing within a river catchment in the southwest will know that the trees growing down at the estuary have large leathery leaves, while the oak leaves growing on the moorland trees near the source of the river are small and delicate. Connectivity is key to the spread of genetic material up and down the river corridor. With rivers such as the Dart, Fal or the Fowey there are woodlands scattered along the entire length of the river so pollen will be able to move freely from one wood to another. Over time woodlands will be able to change their genetic make-up to best suit the climate. The problem is that will native woodlands be able to adapt to the sudden changes resulting from our current climate change? A key factor in this will be the natural range of the local gene pool and how easy it will be for genetic material to move within a geographical area. Typically oak trees obtain pollen from other trees around 100m – 150m distance – trees far enough away not to be closely related. Farmland and urban development breaks up the natural movement of genetic resource creating more vulnerable isolated populations.
Perhaps those in the wetter western parts of the country may count their blessings, or look back with nostalgia at last year’s weather! But although the direction of travel for climate change is generally accepted, the speed of change and the end results remain very uncertain. Establishing young trees will be more difficult, and pests and diseases seem likely to become an increasing risk. The natural world often surprises us with its ability to adapt and change, but when we are planning management cycles of 100 years or more, then some careful thought and planning can lend a helpful hand.
Natural England Technical Information Note TIN053. Guidance on dealing with the changing distribution of tree species. http://publications.naturalengland.org.uk/category/9001
http://22.214.171.124/ Right trees for a changing climate (Greater London Authority)
Forestry Commission Climate Change Pack http://www.forestry.gov.uk/pdf/eng-trees-and-climate-change.pdf/$file/eng-trees-and-climate-change.pdf
http://www.futuretrees.org/A small organisation working to improve hardwood selection and genetic quality.