Springfield Park #2: Yew with a View
The cache, a small screw-capped sample tube, is tucked inside the roots of this toxic, mysterious and most useful tree on a mound up towards the western corner of this lovely north London park which is open daily from 08:00 to dusk. From the mound there is a fine view east down and across the park toward the River Lee and beyond.
The (English or European) yew (Taxus baccata) is a conifer native to western, central and southern Europe, northwest Africa, northern Iran and southwest Asia. The word yew is from ProtoGermanic *īwa and probably means brown. Baccata is Latin for 'bearing red berries'.
It is a small-medium sized tree usually growing 10-20m tall - but exceptionally up to 28m. The trunk diameter is typically up to 2m but may grow up to 4m or more. See here for a full description of the tree which often forms the understorey in beech woods.
It is one of the longest lived tree and typically can reach 4-600 years. Some specimens live longer but the age of yews is often overestimated. 10 yews in Britain are believed to predate the 10th century. Their age is impossible to find accurately as there is rarely any wood as old as the entire tree, and the boughs themselves often become hollow with age, making ring counts impossible.
Evidence based on growth rates and archaeological work of surrounding structures suggests the oldest 
yews, such as the Fortingall Yew in Perthshire, Scotland (see photo here), may be in the range of 2,000 years placing them among the oldest plants in Europe. One characteristic contributing to yew's longevity is that it is able to split under the weight of advanced growth without succumbing to disease in the fracture, as do most other trees. Another is its ability to give rise to new epicormic and basal shoots from cut surfaces and low on its trunk, even at an old age.
Toxicity: All parts of a yew are toxic to humans and most animals, due to taxine alkaloids except the berries (however, their seeds are toxic). Additionally, male and monoecious yews in this genus release cytotoxic pollen, which can cause headaches, lethargy, aching joints, itching, and skin rashes; it is also a trigger for asthma. These pollen grains are only 15 microns in size, and can easily pass through most window screens.
The foliage itself remains toxic even when wilted, and toxicity increases in potency when dried. Ingestion and subsequent excretion by birds whose beaks and digestive systems do not break down the seed's coating are the primary means of yew dispersal. Horses have a relatively low tolerance to taxine; cattle, pigs, and other livestock are only slightly less vulnerable.
Symptoms of poisoning include: increased heart rate, muscle tremors, convulsions, collapse, difficulty breathing, circulation impairment and eventually cardiac arrest. However, there may be no symptoms, and if poisoning remains undetected death may occur within hours! Fatal poisoning in humans is very rare, usually occurring after consuming yew foliage which is more toxic than the seed.
Uses and traditions: In the ancient Celtic world, the yew tree (eburos) had huge importance. A passage by Caesar narrates that Cativolcus, chief of the Eburones poisoned himself with yew rather than submit to Rome. There are several similar instances. One explanation for the Irish name Eóġan / Eoghan is that it derives from the yew's importance in ancient Ireland and means 'born of the yew'.
Religion: The yew is traditionally and regularly found near chapels, churches and cemeteries as a ancient 
symbol of the transcendence of death. It has also been suggested that yews were planted at religious sites as their long life was suggestive of eternity, or because being toxic they were seen as trees of death.
Another suggested explanation is that yews were planted to discourage farmers and drovers from letting animals wander onto the burial grounds, the poisonous foliage being the disincentive. Fronds and branches of yew were often used as a substitute for palms on Palm Sunday. See a short video on the 'Yew - the Sacred Tree here.
Medical: Substances found in the bark of yew are anti-cancer agents. The precursors of the chemotherapy drug paclitaxel (Taxol) can be synthesized easily from extracts of the leaves of European yew.
Woodworking: Yew is the wood of choice for longbow making; the heartwood is always on the inside of the bow with the sapwood on the outside. This makes most efficient use of their properties as heartwood is best in compression whilst sapwood is superior in tension. However, much English yew is knotty and twisted, and therefore unsuitable for bowmaking; most trunks do not give good staves and even in a good trunk much wood has to be discarded.
Many yew trees were planted throughout Britain and Ireland, among other reasons, as a resource for bows. Also the import of yew wood to England for longbows was so extensive that it depleted the stocks of good-quality, mature yew over a vast area of Europe. Measures were subsequently taken to protect further stocks.
Horticulture: Today it is widely used in landscaping and ornamental horticulture. Due to its dense, dark green, mature foliage, and its tolerance of even very severe pruning, it is used especially for formal hedges and topiary. Its relatively slow growth rate means that it needs to be clipped only once per year (in late summer). Over 200 cultivars have been named.
It is a popular bonsai and makes a fine small- to large-sized plant - see here for some great examples.
Value to wildlife: Yew hedges are very dense, offering protection and nesting sites for many birds. The fruit is eaten by the blackbird, mistle thrush, song thrush and fieldfare, and also by small mammals such as squirrels and dormice. The leaves are eaten by caterpillars of the satin beauty moth.
Conservation: Clippings from ancient UK specimens were taken to the Royal Botanic Gardens in Edinburgh to form a mile-long hedge in order to maintain its DNA, as it is threatened by felling, partly due to rising demand from pharmaceutical companies, and disease.
See here for more information on this fascinating tree and here for a blog spotlighting the yew. See here for a detailed Ogham Tree page featuring the yew and see here and herefor short ID videos.
Notable British Yew Trees:
Largest girth: 11.91m @ Breamore Parish Churchyard, Hampshire (in 2014) - see photo left.
Oldest: 23,000 years The Fortinghall Yew, Perthshire