Birches
What are they?
Birches are deciduous trees in the birch family (Betulaceae). Their male flowers form catkins, which are purplish as they begin to elongate, becoming yellow as they mature in spring; they typically hang in clusters of three to six. The female flowers form upright catkins and can usually be found just a little further back along the branch. After fertilisation, the female catkins swell and becoming pendant. As the seeds mature, the cones break up on the tree, with the seeds and bracts falling and being dispersed by the wind. Birches produce vast quantities of seed and many species are early colonisers of disturbed, open or abandoned ground. They form early successional habitats before later being replaced by climax woodland species such as ash and oak.
Where are they found?
Our native birches are very common in natural and semi-natural habitats, especially on heathland on acid soils and in wetlands. They are also widely planted (along with introduced species) in parks, roadsides and amenity areas.
Identification
As a group, birches are rather distinctive in typically having very pale, often peeling, bark and thin and wiry yung twigs. Identifying individual species can at times be rather difficult,especially when concerning introduced trees which may be from a wide range of species and horticultural cultivars. Close attention to twig and leaf features as well as to bark and - often - fruiting catkins is needed and may sometimes require more than one visit to the tree at different times of the year.
Silver Birch Betula pendula
Widespread and common throughout the region. Native on drier acid soils but also widely planted elsewhere. Flowers April to May. Leaves very variable and essentially not distinguishable from those of Downy Birch, though they tend to have a longer, more tapered tip. Mature trees are best distinguished from Downy Birch by the twigs, which in this species are hairless and rather rough to the touch, due to the presence of whitish warts.
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Downy Birch Betula pubescens
Widespread and common throughout the region, though less so than Silver Birch. Native on acid soils and more tolerant of wet ground than Silver Birch but also widely planted elsewhere. Flowers April to May. Leaves very variable and essentially not distinguishable from those of Downy Birch, though they tend to have a less tapered tip. Mature trees are best distinguished from Silver Birch by the twigs, which in this species are downy and not rough to the touch.
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Hybrid Birch Betula x aurata
Downy and Silver Birches commonly occur together and are known to hybridise, producing this hybrid. However, the two parents are so variable that confirming hybrids is extremely difficult and it is unclear how common or widespread they might be. Most often, plants show young twigs with both rough lenticels and downy pubescence, while the female catkins have rather broad-shouldered scales. It seems that hybrids are best resolved using laboratory techniques and therefore beyond the scope of most of us!
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Himalayan Birch Betula utilis
Introduced from Asia as an ornamental and widely planted in recent years in urban areas as an amenity tree. Flowers April to May. Leaves similar to our native birches but usually a little larger and relatively broader; shiny on upperside, with 7-12 pairs of veins. Female catkin bracts with side lobes directed forwards. One-year-old twigs hairy. Most trees planted recently have been of the subspecies jacquemontii which is favoured for its chalky white bark.
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Paper Birch Betula papyrifera
Introduced from North America as an ornamental and occasionally planted as an amenity tree, but largely replaced by the more popular Himalayan Birch in recent years. Flowers April to May. Leaves similar to our native birches but usually a little larger and relatively broader; dull on upperside, with 5-8 pairs of veins. Female catkin bracts with side lobes directed outwards or slightly forwards. One-year-old twigs hairless.
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