August 13, 2010

This week in wildlife

In South-West London the horse chestnuts are turning brown. They're one of the earliest trees to come into leaf, way ahead of the oak, ash or even sycamore, and so in some ways it's no surprise to see their leaves begin to colour first.
But things aren't as simple as that: drought can cause leaves to turn prematurely, and this has been one of driest summers on record, so perhaps the early colour is more a sign of summer than autumn. Worse, leaf miner moths (Cameraria ohridella) have hit horse chestnuts in London and the South East hard, turning whole trees brown as the larvae dig into the leaves, which eventually fall. The vigour of the tree is thought not to be affected, as the problem generally occurs too late in the growing season to cause more than cosmetic damage, although repeated infestations could well slow the tree's growth.
The same can't be said about bleeding canker fungus (Pseudomonas syringae), also rife among horse chestnuts in the UK and a threat estimated by some to be as great as Dutch Elm Disease was in the 1960s and 1970s. It's estimated that up to half the UK's horse chestnuts may be affected, with over three-quarters of those in the South East showing signs of infection. Once the bark is breached, the necrotic tissue spreads throughout the tree, with rusty, bleeding wounds on the trunk and branches, weak growth and premature leaf-fall.
Yet according to Pauline Buchanan Black, director general of the charity the Tree Council, the greatest threat to our much-loved conker trees isn't drought, leaf miners or even bleeding canker. It's local councils. "The combination of these diseases over a period of time will see trees being declared dangerous by authorities and being felled. Unfortunately, some councils don't have proactive tree policies and are much more likely to take a knee-jerk reaction to tree care. That will often mean that [when a problem is reported] the response will be 'quick, let's eradicate the problem by eradicating the evidence of it.'"
Don't let your local council cut down the conker trees. They'll only plant 'lollipop trees' in their place - easycare cherries and inoffensive rowans. It's rare to find myself agreeing with Brian Sewell, but a city without big, mature trees is not a city I want to live in.
[with thanks to The Guardian]