THE TREE OF THE MONTH FOR JULY 2016: THE LIME OR LINDEN TREE

Lime flower with visiting bee - image By Ivar Leidus (Own work) via Wikimedia Commons

Limes (or Linden or Pry) make some of the most beautiful of our landscape trees. They were once thought to be a relatively minor component of our prehistoric woodlands due to the relatively low proportion of Lime pollen found in pollen analysis studies. But, being pollinated by bees, they shed far less pollen than wind pollinated species and, factoring this in, we now know that it was the most common tree of lowland England, from the south coast north to the Lake District and the Tyne - with the exception of Cornwall which was predominantly Oak and Hazel - but then some consider Cornwall separate from England anyway. (While on the subject of bee pollination, there has long been concern that Lime is toxic to bees - more below under Silver Limes).

Lime coppice. Image by By Rosser1954 (Own work) via Wikimedia Commons

So where have all these Lime woods gone? They are now uncommon but can be found in localised areas throughout the former 'Lime province'. One reason is that Lime struggles to set fertile seed in mean summer temperatures of less than 20 celsius. This meant that after the warm Atlantic period, when temperatures cooled about 2000 years ago, it effectively became locked in it's existing distribution. But because it can live almost indefinitely if coppiced (in fact it is almost impossible to kill), it might be expected that more would remain. DNA analysis has shown that one ring of coppice growth at Silk Wood near Westonbirt originates from a single coppice stool that has long since rotted away. It measures 48ft in diameter and is estimated to be at least 2000 years old and possibly up to 6500 years as an early colonizer after the last ice age.

Large areas of Lime were cleared by Neolithic and Bronze Age man for conversion to farm land. This was an immense achievement given the tenacity of the species and its ability to re-sprout. The largest remaining Lime wood is Shrawley Wood in Worcestershire (340 acres) and this and another - Lynwode Wood in Lincolnshire - fell into the hands of the unreformed Forestry Commission who immediately set about doing their usual thing, which was clearing the native trees to plant exotic conifers. The trees were felled and poison applied - Ecologist George Peterken described the air as being 'acrid with herbicide' - but Agent Orange had met it's match and the Limes stools gradually recovered 'over-topping the drought bitten Norway Spruce'. 20th Century Forestry Commission had thrown all it's science at the Limes and failed to achieve what our ancestors had managed with hand tools.

We know that Limes woods were still common as late as Anglo-Saxon times partly from its frequency in place names. Lyndhurst and Linwood in the New Forest near us derive from 'Linde', the Anglo-Saxon for Lime. There is also good documentation from the use of coppice poles and from 'bast' - a fibre made from the inner bark and spun into ropes and mats - giving rise to more place names such as Bastwick in Norfolk.

Grazing by deer, goats and sheep has been suggested as another reason for the loss of Lime woods. Oliver Rackham describes it as 'relatively unattractive' to deer, but also notes their absence from the New Forest, Epping Forest and the Forest of Dean (a Forest with a capital 'F' is - or was - a royal deer hunting park). Furthermore, in areas of Oak and Beech such as in South Wales and the Avon Gorge, Limes can be found on inaccessible cliffs - suggesting a sensitivity to grazing.

Climate change, conversion to farmland and grazing have probably all contributed to the decline of Lime woods, but the extent of loss remains something of a mystery.

Large leaf Lime: Image by Stern Porse via Wikimedia Commons

There are two native Limes, the Small leaved Lime (Tilia cordata - Pry) and the Large leaved Lime (T. Platyphyllos). A naturally occurring hybrid of the two is the 'Common Lime' - T. x europaea- which would arise where  the two parent populations grew near each other.

T. platyphyllos can reach 35m and has rounded leaves 10-15cm long.

T. cordata reaches 24m with leaves 3-8cm long.

Common Lime can tower to 45m with leaves 5-10cm long.

T. cordata. Note the erect or horizontal inflorescence which are pendulous in other species. image CC BY-SA 3.0, via wikimedia.org

Basal suckers from Common Lime. image CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=837883

Naturally occurring Common Lime is not at all common and tends to differ slightly from the variety that has been so ubiquitously planted in streets, parks, avenues and churchyards throughout Britain - earning it the 'Common' name. This variety is almost certainly from stock imported from the continent in the mid-seventeenth century. It has a propensity to form suckering shoots at the base and it was learned at an early date that when the tree was felled and the shoots were pegged down, new plants were produced easily and cheaply. However, removal of suckers has also proved to be an onerous maintenance task for municipal authorities where this feature was undesirable.

Another reason Common Lime has been so frequently planted is its speed of growth and tolerance of severe cutting as shown in the photograph. This formal style was once more popular but changing fashions and/or a shortage of war-time manpower led to the regular pollarding cycle being abandoned in many cases and the trees were allowed to regrow large crowns. This has brought another unfortunate characteristic of the species into sharp focus - the fact that it suffers badly from predation by sap sucking aphids. In summer the aphids shower a sticky 'honeydew' which covers anything beneath. This in turn is colonised by sooty mould, coating everything in glutinous black film. Anyone who has parked beneath one in summer will know what I mean! As an ex-council tree officer of many years, I can attest to the number of calls to fell Limes for this reason.

Annually cut Common Limes - Redcotts Recreation Ground, Wimborne

The hybrid Commom Lime is a favoured host of the partial parasite Mistletoe. Image By OrangeDog (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

The golden hue of this Lime is provided by the large yellow flower bracts in July (the photo doesn't do the visual impact justice)

In addition to our native Limes, the genus contains about 30 other species of large or medium sized trees - all with zig-zag young shoots, prominent winter buds and alternately arranged leaves. One of the most characteristic features of the genus is the large yellow membranous bract acting as a wing connected to the flower and seeds. They cannot be missed when at their best in July giving the trees a showy golden shine.

Of the exotic Limes, two very notable species are the Silver Lime and Silver Pendant Lime (T. tomentosa and T. tomentosa 'Petiolaris' which have downy undersides to their leaves giving them a silvery appearance. Silver Lime is native to the Balkans, Hungary and Russia and forms a fine mature tree of 60-100ft. It was introduced in 1767 and is particularly attractive in a light breeze as the white undersides to the leaves flash as they turn.
The graceful pendant variety 'Petiolaris' has drooping branches and makes a stunning specimen tree.

White underside of the leaf of Silver Lime - Canford School Wimborne

Silver Pendant Lime. image By Jean-Pol GRANDMONT (Own work) [CC BY-SA 3.0 creative commons licence via Wikimedia Commons

There has been concern that the nectar from Lime trees is toxic to bees, none more so than Silver Lime and Silver Pendent Lime, beneath which large large numbers of 'drunk' and dead bees have been found. The fear was reinforced by the fact that a tea, tilleul, has long been made from an infusion of the flowers and used to aid sleep - even being recommended as a mild sedative during the war - suggesting narcotic properties. Tea made from the Silver Limes was thought particularly effective. This has led to calls for trees to be removed - or at least not be planted in certain locations. However, research has shown that the phenomenon is a result of bee behaviour rather than toxic nectar. It is bumblebees rather than honey bees that are affected, and the workers only live for a few weeks. Silver Limes flower later than others and the Bumblebee Conservation Trust currently advise: 'There has been a lot of research into the reason why and the current evidence points to the behaviour of bumblebees, and not toxic nectar. For some reason, bumblebees keep feeding upon the flowers, even when nectar runs low. So on hot days, and close to the end of the flowering period, the bumblebees keep feeding, run out of energy, and die. Honeybees, however, seem to realise that there is no nectar left, and will feed upon other flowers instead'.

The Mongolian Lime makes a slow growing  smaller tree of up to 60ft making an ideal tree where there is less space.
The leaves, which are a delightful bronze in spring, are very distinctive and delicately shaped. In winter the red shoots show up very well.
Discovered by Abbe David in 1864 near Peking it was introduced to Kew in 1904. A fine tree all round.

Mongolian Lime (Tilia mongolica) image MPF assumed (based on copyright claims). CC-BY-SA-3.0 via wikimedia Commons

Henry's Lime (Tilia henryana) at Canford School, Wimborne

Henry's Lime (Tilia henryana), like the Mongolian Lime, has very distinct leaves. Henry's Lime has leaf margins set with bristle-like teeth. It is a rare Chinese tree that I only saw for the first time recently at Canford School where there is a young newly planted specimen. It seldom grows to more than 13m and was discovered by Augustine Henry in central China in 1888 - introduced to the west by Ernest Wilson in 1901.
It is a slow grower, but its unique leaves make it worthwhile.

This blog largely produced from works of Oliver Rackham, Richard Mabey and W J Bean.

More Limes to follow...we would love to include your photographs of Lime species too - please send them to us!

Tilia kiusiana (Cambridge Botanical Garden). Very different from most Limes. Good for small gardens

Oliver's Lime (or Chinese White Lime). Leaves up to 14cm have a pure white felt underneath giving a similar effect to the Silver Limes. Discovered by Henry in 1888 and introduced by Wilson in 1900

Henry's Lime seed heads

Top worked Henry's Limes - Cambridge Botanical Garden cafe

Old hollow Lime pollard with aerial roots developing. Lanhydrock, Cornwall