Sunday, 9 November 2014

Lime Trees

Every so often I have a rant about lime trees. This is one of those occasions.

Two species of lime are found wild in Northamptonshire. One is the Large-leaved Lime, Tilia platyphyllos and the second is Small-leaved Lime, Tilia cordata. The former is native in some parts of Britain, but in Northants it is probably an introduction. The latter is a far more interesting plant as, though quite uncommon, it is undoubtedly a native.

Most of our native trees such as oak, birch, alder, beech, willow and pine are wind pollinated and produce vast quantities of pollen grains to allow for the huge odds against them reaching the stigma of the female flower. The outer 'casing' of these grains is tough and very resistant to decay and, as a consequence, the pollen is found in copious amounts in ancient deposits. We therefore know these trees were native and widespread. Lime trees are insect pollinated. They produce pollen in far more limited amounts and the grains are sticky in order better to cling to insects. This pollen is much less common in these ancient deposits, and for a long time it seems to have been thought that limes were relatively uncommon. We now know that the Small-leaved Lime was a major component of woodland at around 5000 years B.P. (before present) but declined through a complex set of circumstances involving human activity and climate change.

Common Lime, Tilia x vulgaris, still in leaf
on Byfield's playing fields. 9 November, 2014

Of course, the lime with which most of us are familiar is Tilia x vulgaristhe Common Lime, planted on a huge scale in streets and parks the length and breadth of Britain. It is a hybrid between our two native species and occasionally occurs in the wild. The Common Lime will sometimes produce viable seed but, like most hybrids, it is generally sterile. The flowers are fragrant, with the perfume being stronger in some years than others, but beyond this limes have, imo, little to be said for them.

Leaf of Common Lime bearing three galls of the mite,
Eriophyes tiliae. Byfield, 9 November, 2014
All three limes (which incidentally are not at all related to the citrus fruit) are valuable for wildlife, with the Lime Hawkmoth (Orthops cervinus), the bugs Orthotylus nassatus, Lygocoris viridis and Phytocoris tiliae and many mites, being particularly associated with these trees. In Northampton and elsewhere limes are frequently a host to Mistletoe, Viscum album. As a wildlife enthusiast I always approach a lime tree with anticipation.

So, what is my rant? 

Of all the trees available for planting in our streets, the Common Lime must be one of the worst choices, with one of the problems being directly related to its attractiveness to wildlife.

Problem 1

Lime trees are often infested with aphids. The aphid I most frequently take is Patchiella reaumuri but perhaps Eucallipterus tiliae is the more problematic. Both secrete honeydew but Eucallipterus produces such copious amounts that it will fall as a steady and sticky rain on any cars parked beneath. The honeydew also covers the leaves and nourishes sooty moulds, blackening the surfaces. Lewis Carroll would have called it a process of uglification.

Problem 2

Being deciduous, limes lose their leaves in late autumn. Perhaps I am wrong but these leaves, when wet, seem to form a particularly messy and slippery layer on pavements and roads. How often these have been a factor in accidents I don't know, but I suspect they are frequently culpable.

Problem 3  
Suckers around a Common Lime.
Byfield, 9 November, 2014

Here is the most serious issue. Limes, especially the Common Lime, have a propensity to produce a thicket of suckers from the base of the trunk. 

In open countryside this is not particularly a problem, but on street trees they are a real nuisance. In the autumn there must be a small army of local authority workers out and about dealing with these suckers and the overall cost must be enormous.

Base of Common Lime with chopped off suckers.
Daventry, 9 November, 2014

The results are tidy but ugly - and in twelve months time the whole wasteful process must be repeated!

How long will it be before town planners see sense? Rowans and whitebeams. hornbeams, alders, birches and even oaks are all native trees, largely without the problems associated with limes. A few heads need knocking together!


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