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Featured |
The Climate Change Challenge for British Woodland |
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How will trees in Britain adapt to the changes in climate
expected over the next 100 years? Stephen Isaac explores the key
issues and looks at potential responses. The 2009 scenarios predict that all
areas of the UK will get warmer, and the warming will be greater in
summer than in winter. Direct impacts on trees Although evidence suggests that mature trees are unlikely to respond as much in a forest environment, some increase in productivity is likely and the forestry sector may benefit from this. Large leaved species such as the non-native sycamore may also out-compete native species that have a higher biodiversity value. Other effects of increasing CO2 concentrations are likely to include reduced leaf area water use, an increase in leaf area, possible changes in timber quality and changes to the nutritional quality of foliage for insect herbivores. As discussed previously, increased temperatures are likely to lead to earlier bud growth in the year. This has already been shown to affect some species. For example, oaks in Britain are now experiencing budburst up to two weeks earlier than in the 1950s. Sycamore, hawthorn and hornbeam are also budding earlier in the year. Although the growing season is therefore expected to extend for many species, this earlier budburst could also increase the risk of frost damage early in the year. Warmer temperatures later in the year may also cause delayed or incomplete winter hardening and therefore increased susceptibility to frost damage. Additionally, warmer winters may not fulfil the winter chilling requirements for flower and seed germination, thereby affecting natural regeneration. Long-lived woodland species may be less able to adapt to such changing conditions as those with a shorter life cycle. Woodland flora are also expected to respond to earlier springs, with temperature sensitive species like garlic mustard and cow parsley leafing earlier and dominating over snowdrops and bluebells. As a result of higher peak temperatures the top-dying of Norway spruce is likely to increase in England and eastern Scotland and Norway spruce could cease to be a productive species over much of England.
Increasing heat and drought in the south and east are also likely to
increase tree loss, particularly among newly established trees and
mature trees in hedgerows and urban environments. Coniferous species
may also In south-east England, reduced summer rainfall and an increased evaporative demand are likely to lead to longer periods of drought stress on trees. This is already known to affect beech trees in south-east England. Conversely, increased winter rainfall could increase the risk of water-logging, thereby reducing tree stability. Water-logging could also cause fine root death and thus indirectly affect the ability of trees to take up water, which in turn could affect their ability to withstand summer droughts. The final direct impact is likely to come from changing wind speeds. The UKCP09 report on recent climate trends shows that storms have become more intense in recent decades. If this trend continues woodland will likely become more vulnerable to wind damage.
Outbreaks of bleeding cankers, green spruce aphid and pine weevils are also likely to increase as the climate warms. Fungal pathogens such as Phytophthora ramorum, responsible for the condition known as ‘sudden oak death’ may also thrive. Up to early December 2006 a range of tree species in Cornwall including beech, southern beech, horse chestnut, sweet chestnut, sessile oak, Turkey oak and sycamore have all been found with potentially lethal infections of this fungus. Red band needle blight is another fungal disease that could become more widespread in the UK. It was first spotted in the UK in the 1950s but has only become a serious problem recently. The disease, recognisable by a distinctive red band around each needle, can kill trees, affect their rate of growth and reduce the quality of their timber. It thrives on Corsican pine, but has also attacked indigenous species such as Scots pine. Mammalian tree pests such as the grey squirrel and various deer species may also be more likely to survive the winter under warmer conditions, with deer additionally benefiting from earlier spring growth of ground vegetation. Forest fires pose a considerable threat to woodland worldwide. Although the risk may be higher in warmer and drier countries, parts of the UK are certainly vulnerable. Although the earlier growth of ground vegetation could reduce the risk of forest fires in spring and early summer, extended summer droughts, such as those of 1976 and 1995, result in a build up of dry, dead and highly flammable vegetation. Flooding associated with sea level rise or fluvial inundation may also pose a significant threat to trees in coastal areas or river floodplains, either directly or gradually and indirectly through habitat change. In some cases wet woodland species may benefit from increased fluvial inundation. Mitigation and adaptation Woods and forests of the world have an important role to play as carbon ‘sinks’, essentially absorbing atmospheric carbon dioxide that would otherwise contribute to climate change. Woodland is also important in that it provides biomass, an alternative to burning fossil fuels and the use of short rotation forestry can provide timber that often provides a practical alternative to using fossil fuel intensive materials. In order to manage the response to climate change there are several ways in which the forestry sector and landscape managers can adapt to the changing circumstances. For example, climate change predictions should be taken into account when choosing stock. Species already at the edge of their range or with poor capacity to reproduce may need to be discounted. The introduction of more southerly or drought resistant species could help revitalise existing woodlands and establish more robust new woodland. Increasing the species mix of the woodland can also enhance its adaptive capacity and help to alleviate the threat from pests and diseases that target specific species. Areas of land vulnerable to sea level rise or changed hydrological conditions may also need to be discounted from new planting schemes. On a landscape level, larger, better connected woodland will enhance the ability of woodland and individual tree species to adapt to a changing climate, for example through migration within the woodland area. This may include managing, protecting and connecting woodlands to increase resilience and reduce the impacts from other external pressures that might have a cumulative or synergistic impact with climate change. The risk of
fire can also be reduced through management of fuel loads, managing
for appropriate age and species structures of woodlands, and the use
of fire breaks. There is potential to increase the biodiversity value and climate change resilience of commercial forestry and non-commercial woodland by utilising the latest climate change research and promoting effective co-ordination between planners and the wider public. Research into the effects of environmental and
climate change on forestry and how the forestry sector can adapt to
and mitigate climate change is now being actively progressed through
bodies such as Forest Research, an agency of the Forestry Commission
which has recently developed a "Centre for Climate Change." By understanding the climate challenges
ahead we can better inform our responses to it and give
wildlife-rich British woodland a fighting chance of survival. Article written by Stephen Isaac AIEMA |
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