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Trees transformed in autumn and winter

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Posted: Thursday 25th October 2018 by WildBlog

(c) David Tipling/2020VISION

By Louise Treneman, Avon Wildlife Trust Living Landscape Assistant and Jenny Greenwood, Avon Wildlife Trust Monitoring Officer

Few of our native trees are evergreen, meaning that, come winter, most trees will have shed their foliage. Whilst a tree may look a little bare without its leaves, this transformation can reveal other features that were previously obscured. As the general character and growth form of a tree becomes apparent, so too does the diversity of other organisms which call the tree home.

Trees are an important habitat for many species, providing a range of services which may or may not benefit the tree itself. Many mammal and bird species nest or hibernate in cracks or hollows, and insects breed in the water that collects in small pools on the trunk. The bark surface can provide ideal growing conditions for epiphytic species, which gain their nutrients from water and air, while for many parasites, the tree itself provides (albeit reluctantly) a source of nutrition. In general, suitability as habitat for other wildlife increases with tree age; cracks and fissures in the bark, decaying wood forming hollows and pools, all provide important niches which can be exploited by a variety of organisms, and successful colonisation by one species may open up a host of opportunities for others.

Here we highlight some of the epiphytes and parasites common in native UK woodlands that are most easily spotted on trees during the winter months.

Mistletoe
Mistletoe can be spotted from long distances as dense, round clumps in the branches of trees, particularly apple and poplar. A spindly, much-forked evergreen, the plant produces tiny yellow flowers in February to April and sticky, white berries in November and December. Mistletoe is a hemi-parasite, capable of photosynthesis, but also taking water and nutrients from the tree. The species is important for a range of insects and birds, including mistle thrush.

String-of-sausages lichen
This easily-identifiable grey-green beard lichen drapes itself over branches and trunks of trees. Its straggly tangled stems form a sausage-like structure that swells at intervals. The stems are roughly 3mm in diameter and can be up to a metre long. Formerly widespread in southern and western Britain, this lichen is now only found in the south west of England, due to a high sensitivity to sulphur dioxide pollution.

Turkey tail fungus
This common bracket fungus is found on almost any kind of dead wood. It has distinctive concentric coloured rings, coming in varied colours, from browns and reds to blues, greys and greens. Whatever variant of colour palette you find, the wavy edge will always be creamy white, distinguishing it from other Trametes species. This fungus can be found all year round on deciduous wood.

Polypody fern
Look up high into the branches of a large tree in winter and you may spot the still-green fronds of a polypody. A shade-loving group, they are also found growing at the base of trees and on rocks. Distinguished by two rows of simple, finger-like leafy projections (pinnae) along the main stem, bearing circular clusters of spores, our three native species can be difficult to distinguish as they regularly interbreed.

Photos: Mistletoe (c) Gill Hambleton, String of Sausage Lichen (c) Jymm GNU Free Documentation License.

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