Wednesday, 6 February 2013

Lime Trees

A flurry of snow yesterday evening reminded us that Winter has not yet relinquished its grip. In medieval times these February days must have been desperate: food stocks running low; soil too wet for sowing or planting; thin bodies finding the cold increasingly numbing. A couple of lines in a poem (14th century?) leave me puzzled:

                        The boneless fish close quaking lies
                        And eats for cold his aching feet.

I've no idea what the "boneless fish" could be and yet the reader can feel the biting chill.

So, in these dark days, what can the wildlife enthusiast enthuse about?  

Some fairly large hybrid limes (Tilia x cordata) stand adjacent to our house and yesterday morning, in the bright sunshine, the twigs took on a pinkish glow. The buds are enclosed in cherry-red scales and, as the sap begins to rise, these buds are swelling; the twigs are also red and I suspect these were the cause of the glow. We have two native species of Lime, The Large-leaved and the Small-leaved; Tilia x cordata is the hybrid formed by these two. Our native limes are unusual as, along with the (unrelated) Maples, they are insect pollinated. 
Pink twigs and buds of Hybrid Lime, Byfield, 6 February, 2013

Oak, willow, birch, poplar and so on are wind pollinated. As this is such an inefficient system they need to produce vast quantities of pollen and in suitable conditions such as wet, acid soil, these pollen grains - which are very resistant to decay - will remain for thousands of years. The pollen of Limes is rarely found in these ancient deposits and for a long time palaeobotanists, analyzing these grains, believed it was a scarce tree in Britain's prehistoric woodlands. In fact the reason why Lime pollen is infrequently found is simply that these insect-pollinated trees only need to produce pollen in small quantities. We now know that the Small-leaved Lime (Tilia cordata) was extremely common some four thousand years ago, dominating quite large areas of woodland.

In terms of wildlife, Lime trees are of considerable importance, not least because their leaves are highly nutritious. Aphids abound on them, especially Eucallipterus tiliae, and it is the main pabulum of the Lime Hawk-moth. Common too are many galls, the one illustrated being that caused by the mite Eriophyes tiliae, but there are at least another dozen of these gall-forming organisms to be found on Lime

Galls of the mite Eriophyes tiliae, 
Byfield Pocket Park, Summer, 2012

One day someone will explain to be why Limes are so often planted as street trees, because I regard them as a really unfortunate choice: the leaves get covered in aphids, which drip sticky honeydew on to any cars parked beneath; the trunks constantly produce suckers and, in Northamptonshire alone, hundreds (thousands?) of hours must be spent annually removing them; the falling leaves decay at the roadside producing a particularly wet and slippery mush. As I say, a strange choice. Rant over!


A thicket of suckers on Hybrid Lime, Tilia x europaea
Byfield, 6 February, 2013

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