Because trees grow slowly we tend to imagine that our local forests and woodlands are going to stay the same forever...and often we get a surprise at how much everything has shot up when we revisit a wood after a lapse of time. But in fact woodlands have been in a constant state of change for many thousands of years, with trees reaching maturity, falling down and being replaced by seedlings spread by animals, birds and the wind, which use the extra light to race towards the sunlight and become established.
No-one really knows how global warming will affect Scotland in the long term. In 2008 it was thought that drier summers and wetter, milder winters were likely but the following winters and the last two summers seem to have knocked that theory back, in the southern half of Scotland anyway. The behaviour of the jet stream is critical, it seems, in determining rainfall and temperatures, though a much longer time period would be needed to discern reliable patterns.
The other problem, which we've seen startling evidence of in the past few weeks, is the movement northwards of pests and diseases, or the proliferation of such problems as they thrive in the milder, wetter conditions. Ash dieback, Chalara fraxinia, is only one of more than a dozen diseases that our native woods are faced with now: others include Phytophthora ramorum, which kills larch trees, Dothistroma septosporum, which causes needle dieback in pine trees and Phytophthora lateralis, which attacks and kills the roots of cypress trees. Pine forests are also being threatened by the lappet moth, Dendrolimus pini, and just recently we heard that one of our most ancient species, the Juniper, is being affected by another fungal disease called Phytophthora austrocedrae. In England, where the effects of such diseases have been felt earlier, the Forestry Commission has had to adapt its planting and management methods and has brought out the document, Climate Change, Impacts and Adaptation in Egland's Woodlands, which offers useful guidance for those faced with the same issues in Scotland.
So what can we as individuals, whether gardeners, woodland managers or folk who enjoy the countryside, do to minimise the negative effects of global warming on our Scottish landscape?
Here are some suggestions:
If you're planting trees:
- Be careful where you buy your trees. We now know that the practice of buying cheap trees from abroad, rather than from local nurseries, was a likely source of the ash dieback infection.
- Choose species that are more likely to thrive under wetter, warmer conditions or, if our weather pattern changes to dry summers (we wish!), choose drought-resistant species for areas likely to dry out.
- Go for species diversity and mix up the different types of trees, rather than planting same species blocks.
- Plant smaller coupes and go for shorter rotations.
- Be vigilant: check and weed your trees regularly and carry out pest and predator management.
- Avoid ash saplings, at least until we get more guidance on what's happening with Chalara.
- Source your plants from local provenance. Check where each species is from: just because it's in a local garden centre doesn't mean it hasn't been bought in from abroad. The Woodland Trust is campaigning to ensure that all trees planted in the UK from now on come from trusted UK sources.
- Check your trees for signs of dieback, infestations and damage by pests.
- Learn the signs of the main diseases and report any problem trees to the landowner.
- Check out the Woodland Trust website for important campaigns and ways you can get involved in ensuring a safe future for the UK's forests and woodlands.
- Wash your boots or wellies before and after you go out, to avoid transferring diseases from place to place.