This autumn our trees have donned the most spectacular garments of reds, oranges and richest gold, enriching the turn of the season with vibrant colour. Yet that is by no means their only gift. Trees, woodlands and forests provide microsystems essential for the survival of thousands of different species. They provide birds with a rich harvest of seeds, berries and invertebrates as well as nesting sites offering protection and concealment. They provide song posts and snags for raptors to use as lookout posts and food-handling sites. Many of our bat species make use of tree holes for summer and winter roosts. Branches and hollows also provide ideal environments for a large variety of spiders to locate their webs. Bees and wasps will often site their nests in tree hollows, and many species of beetle feed on tree foliage, bark, roots, buds, flowers and seeds. Adult butterflies and moths frequently use stubs of broken branches or bark fissures as egglaying sites, their larvae emerging to feed on the leaves. Even slugs and snails can scale the heights, grazing on leaves and algae growing on the bark. Squirrels rely on trees for shelter, food and as corridors in which to move around. Trees also shade streams and rivers, keeping them cool in summer, important for the survival of fish and aquatic insects, while fallen leaves provide a further source of food and shelter.
The true value of any individual tree is not necessarily related to the number of different species directly associated with it. Colonisation of single trees of the same species in different geographical locations lead to differences in associated wildlife -a particular tree species might have relatively few insect species associated with it, but if those insects happen to be prolific in number, then the tree may harbour a significant food source for local wildlife. An individual tree may be an important roost, nesting site or food source for a particular wildlife species, or it may be situated in a site where it provides vital shade for local plants or animals. Certain trees or groups of trees may also have an especially high ecological value due to size, species or condition, for example, ‘veteran trees,’ typically in the second or mature stage of their lives have distinctive features such as hollowing or associated decay fungi, holes, wounds and large dead branches which provide important habitats for wildlife.
It would be almost impossible to imagine a world without trees, but with growing concern about climate change it is vital to know what effect will it have on them and on the plants, animals and insects that depend upon them for survival. The severity of the impact of climate change on our trees and woodlands is difficult to evaluate because possible levels of impact tend to vary according to which consultation authority or report is examined. However, according to a Climate Change Risk Assessment prepared by the Forestry Commission England, there is cause for concern. Drier, warmer summers are likely to have a serious impact on drought sensitive tree species in areas of shallow or sandy soil, particularly affecting those in southern and eastern England. Weakened trees will be susceptible to greater incidence and severity of tree diseases and pest outbreaks. Drier conditions will also increase the risk of forest fires. Warmer, wetter winters and severe winter gales will lead to increased levels of storm damage.
In discussing the impact of climate change on woodland fauna, the Forestry Commission report notes that there is already clear evidence of changes to emergence and first flight times for a range of butterflies and moths and hoverfly species, and that there have also been changes in the arrival times of migrant bird species. The abundance of moth species has also shown a significant decline, with an average loss of about two species per year. A relationship between summer temperature and winter precipitation may help to explain the 60% decline in macrolepidoptera (the larger butterflies and moths) since the 1930s. The effects of increasing CO2 concentrations are likely to include possible changes in timber quality and changes to the nutritional quality of foliage for insect herbivores.
Populations of deer have a significant impact on the establishment and regeneration of both plantation forests and semi-natural woodlands and can be expected to increase in response to climate change. In fact, deer cull data for Scotland confirm anecdotal evidence that this already happening. On a cautionary note, although this particular trend is consistent with current understanding of the likely effects of climate change, a causal relationship cannot be unequivocally demonstrated. In short, changes in the distribution of many species are difficult to interpret because of the complexity of the underlying drivers, with land use, land management and other factors also implicated.
What seems to be certain is that climate change is inevitable, but how severe its impact it will be rather depends on what can be done now to mitigate its effects on trees, woodlands and associated wildlife. Some of the measures suggested include protecting the trees and woodland we already have, reducing deforestation and restoring forest cover where possible. It means planting a wider range tree species with a wider range of origin, with tree species selection being based on the predicted future climatic conditions rather than those current, thus reducing risk through diversification. As mentioned, woodlands that link with each other and with other habitats facilitate the movement of species through the landscape, but this is particularly important in the context of climate change, as it can increase the ability of species and ecosystems to adapt to new conditions. More extensive woodlands comprising a diverse range of habitats and sites will help enhance the ability of individual species to endure as climate change progresses.
Finally, it’s not only up to large bodies like the Forestry Commission to take action. Individuals can also make a difference. Consider carefully before you decide to remove a tree situated on your property, even if it does not have a preservation order on it. Instead, consider where you may be able to plant a tree or trees, either on your own land, as part of a community group project, or even at your place of work. Always take care when selecting which species to plant, considering the impact its full size is likely to have on the local environment and its associated wildlife. Take care when walking through the countryside and in its woodlands and forests. I’ll leave the last words to the Countryside Code.
We all have a responsibility to protect the countryside now and for future generations, so make sure you don’t harm animals, birds, plants or trees and try to leave no trace of your visit.
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