One of the main issues when looking ahead to anticipate how the climate may change during the next 100 years, along with the associated impacts on woodlands, is the degree of uncertainty to predict precisely what will happen in future. Scientists have been working on various different climate change scenarios which use data from a collection of different sources: the likely future amounts of greenhouse gases in the atmosphere; fossil fuel consumption; population growth and; economic growth. Bringing all this data together and creating realistic models for climate change is very complicated and often means using future scenarios for factors such as fossil fuel consumption and population growth. However, despite the complexity of trying to work out exactly what the future climate could be like, currently scientists predict that we are heading towards a so-called High Emissions Scenario of climate change for the year 2050 which is based on a world of intensive fossil fuel use and increasing population.
If this emissions scenario is correct, there should be warmer summer temperatures, a longer growing season and rising CO2 levels which would increase the productivity of commercial woodlands. However, this is balanced with drier summers, wetter winters and more extreme weather events which could cause stress in some tree species as well as wind throw on thin soils and susceptible slopes.
How could Exmoor's woodlands change during the next 100 years?
One way to estimate the possible changes to Exmoor's woodlands is to model the potential climate change scenarios at a given location. The Forestry Commission has developed a web-based facility called the Ecological Site Classification (ESC) tool. For a given location, this tool takes into account a number of factors such as the amount of soil moisture, the direction a site is facing, the type of soil, the altitude and so on. It then determines how different tree species would fare under different climate change scenarios for the particular site.
If a typical Exmoor upland oak woodland experiences a future climate that is warmer in summer and wetter in winter, the woodland may respond by beginning to grow at higher altitudes as well as moving onto wetter areas, where this is possible. Tree species such as oak, beech and sweet chestnut are likely to find the climate tolerable, whereas species such as common alder, small-leaved lime or black walnut may find it marginal. Some of Exmoor's upland woodlands may begin to appear more like the woodlands found in parts of lowland England with a greater mixture of broadleaf tree species. Many conifer species should grow well, although some such as larch may find it difficult to cope with the climatic conditions. There would also be some corresponding changes in other woodland flora such as lichen communities and ground flora, some of which may reduce in extent.
There could be more extreme weather events so if these correspond with periods of wet weather and unstable soils, there could be a greater risk of windthrow. If this happens, there would be more gaps created in woodlands and a corresponding increase in early colonising trees such as ash, birch and sycamore. If the summers become very hot, there could be a greater risk of drought and also of fire risk in woodlands which will restrict the suitability of many tree species to cope with these conditions.
As well as the changes in the climate, there will be other influences in terms of increased risk of pests and diseases. The south west of England has been significantly affected by Phytophthora ramorum disease of larch and in time,ash dieback disease (Chalara fraxinea) will eventually take a hold in Exmoor. A warmer climate could mean that even more non-native pests and diseases survive milder winters and extend their range which will put our trees and woodlands under further stress. Some other non-native, non-tree species which already cause issues in woodlands, could expand their range such as rhododendron, laurel and Himalyan balsam, so any control measures in place to manage these species at present, should be continued into the future and may need to be increased in intensity.
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