Wednesday, 8 January 2014

Snippets about evergreen trees

For rather obvious reasons there is a tendency to pay more attention to evergreen trees in the winter months. Passing through Byfield churchyard I plucked a twig from a Yew tree, Taxus baccata, recognising the  bud-like structure formed by a tight cluster of leaves

Gall on a Yew twig caused by the fly Taxomyia taxi.
Byfield churchyard. 2 January, 2013

It was the gall of Taxomyia taxi, a small fly belonging to a specialist family of gall-inducing flies called the Cecidomyidae. It is widespread and rather common but is a new record from this area of the county.

Am I allowed to mention Privet? Privets are not fully evergreen, being semi-deciduous, but our native species, Ligustrum vulgare, manages to retain most of its leaves through the winter months. It too is sometimes attacked by a cecidomyid fly, in this case Plagochila nigripes. I have searched for it in vain yet remain optimistic, but will have to wait until late summer for clues to its presence. 

Wild Privet in fruit. Byfield, 5 January, 2014

The main winter feature of Wild Privet are the black berries. If they resemble small back olives it is hardly surprising as the shrub is a member of the Olive family, Oleaceae. It is quite a good indicator of limy soil and its distribution in the county reflects this, being absent from areas of acid soil.

We have a small group of the evergreen Holm Oak in our pocket park as well as several holly bushes. The Latin name of the former is Quercus ilex, whilst Holly is Ilex aquifolium. The reason for the shared word 'ilex' is not immediately obvious until the juvenile shoots of the Holm Oak are examined. It will be seen that the leaves have sharply saw-like edges, not unlike the leaves of Holly. 

few weeks ago a Holly leaf with a curious structure growing from its surface caught my eye. It appeared from a distance to be the larval case of a coleophorid moth but I was fairly certain that none of these moths were associated with Holly. A closer examination left me feeling rather silly for the "larval case" was simply a thorn penetrating the leaf, although how this had happened was unclear.

The leaves of Holm Oaks are attacked by several gall-forming insects, mostly tiny Cynipid wasps, related to those which cause oak apples to form. However, some moths rise to the challenge of feeding on these tough leaves and the next photograph shows the mines created by Zeller's Midget, Phyllonorycter messaniella

These blotches are the  mines of the micro moth
Phyllonorycter messaniella, aka Zeller's Midget
Byfield Pocket Park, 6 January, 2014

It is a rather dull little moth and in my experience its presence is more often to be established by finding these blotched leaves than finding the adult insect. It is found on several oak species and also Beech, Hornbeam and Sweet Chestnut. Not surprisingly it is a widespread insect. The attentions of this moth are unlikely to harm the trees.

Whereas oaks are a pabulum for many insects our native Holly is relatively free of these nibblers, chewers and borers. But one insect likely to be found feeding on the leaves is the Holly Leaf Miner, Phytomyza ilicis. It is abundant and very few Holly bushes are free of its attentions.

The Holly Leaf Miner is a two-winged fly of the Agromyzidae family. Like Keller's Midget, the adult insect is not often caught - at least I never seem to find it in my net - but its blotch mines, with their yellow borders, are unmistakable. Incidentally the caterpillars of the Holly Blue butterfly also feed on Holly, choosing the tender young leaves through June and July, but I have yet to find this species in our pocket park.

The caterpillars of the Holly Blue will also feed on Ivy. Any found on this plant will belong to the second brood of the year and will feed on the flowers in late summer. In fact Ivy is largely untroubled by insects; I know of no insect which mines the leaves. Occasionally a swollen, purple-tinted flower bud will be found, this gall showing the presence of a cecidomyid fly, Dasineura kiefferi. I have yet to find it.

The swelling fruit of Ivy in Byfield Pocket Park
6 January, 2014

The autumn of 2013 was a very good one for berries and those of Ivy are now plumping up nicely and will help to sustain thrushes and Wood Pigeons through the late winter. There are several poisons found in the tissues of Ivy but seem not to bother birds. As for humans, large quantities of the berries would need to be consumed for harm to result. Incidentally our native Ivy is completely unrelated to the North American Poison Ivy, which belongs to the Cashew Nut family, Anacardiaceae. 

Finally, a word about pines. Three conifers are native to Britain: Scots Pine (Pinus sylvestris), Yew (Taxus baccata) and Juniper (Juniperus communis). Only Juniper is native to Northamptonshire but is now extinct here as a wild plant; it once grew on Juniper Hill, near Brackley (SP587325), apparently close to the supposed site of Larkrise. Yew is widely naturalised, as is Scots Pine.

Pines alongside Byfield railway station, taken from
"A History of the Stratford-upon-Avon and Midland
 Junction Railway" by Richard Riley and Bill Simpson 

A few pine trees have been present in the vicinity of the Byfield's former railway station for many years, as shown in this old photograph. (This photograph is not viewable on some laptops.)  The clump still exists but it is now impossible to photograph the group from the same position. Nevertheless as the next photograph shows they are now substantial trees although, growing in rather poor soil they are, some forty years on, not enormous.


The same pines, now on the periphery
of the pocket park. 8 January, 2014

In this later view the cutting, on the top of which the trees stand, is behind the  clump. As the trees have aged the lower branches have died off, giving the trees their typical mop-headed appearance.

Scot's Pine. Byfield Pocket Park
8 January, 2014

This final picture of pines shows what is probably the pocket park's largest specimen. It stands in the corner of a piece of meadow grazed from time to time by sheep.

I have not spent much time investigating the wildlife associated with these trees and this is very remiss of me as Scot's Pine can support a wide range of invertebrates...clearly a job for 2014.

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