Whilst enjoying our beautiful Autumn out on the common, you cant help but notice that many of the Oaks are very misshapen. There is a reason for this and the answer can be found in an article written in our Common Knowledge Newsletter of December 2009 by Peter Newmark.
Perhaps you have noticed that for the past two years there have been many horribly deformed acorns on the Common’s oak trees – or, to be more specific, the pendunculate oaks. At first, generally in August, greenish protuberances appear on the acorns. They then turn reddish and eventually become brown and woody, by which time they have taken over the whole acorn. The deformation is known as a knopper gall. But what causes the gall?
The answer is a minute gall wasp that lays its eggs in the acorn. When the grubs hatch from the eggs they secrete chemicals that cause the gall to grow. The gall encloses the grub providing food and protection. Eventually the grubs pupate into adult wasps.
Strangely, all these adults are females. They make their way to turkey oak trees, which co-exist in our woodlands with the more frequent pendunculate oaks. In the spring, the females lay their eggs on the catkins of the turkey oaks. Both males and females hatch from these eggs. After mating, the females lay their eggs in the pendunculate oaks’ acorns, and the cycle begins again.
Knopper galls were first found in the UK in the 1960s and became widespread in the 1980s. In some years they are found on almost every acorn, while in other years they are hardly evident. At first there was concern that the result would be decreased fertility of the oak trees, but this seems not to be the case.
How do the squirrels and jays that store very large numbers of acorns for the winter cope with the knopper gall? They avoid acorns with the galls. So in bad years – like this one – most of their acorns come from turkey oaks and other species that do not suffer from galls. As a result there will be more turkey oaks, because the spread of oak trees is largely the result of growth from acorns that have been buried and forgotten. With more turkey oaks there are more possibilities for the gall wasp to successfully continue its life cycle. So, like it or not, knopper galls are here to stay.
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As the Common becomes more popular as a place to rest & play, more work is needed to keep it safe. We cannot do it alone.
As an example – the woods & upper common grasslands need help. These areas support a huge amount of flora & fauna and need continued care. As we are not able to cover it with funding, the Streatham Common Cooperative [SCCOOP] have been organising volunteer days. This happens on a weekly basis, mainly on Tuesday & Thursdays but the odd Saturday too. See what you can offer us. spare hands never go to waste. Its good fun and a great way of meeting people, in addition to directly helping your community.
Mered has been instrumental in raising funding from other areas outside of the public purse…The Bags of Help initiative from Tescos, recently awarded SCcoop [Streatham Common Cooperative – Woodland Wildlife & Water Project] an award of £1,000.00 which will be paid upon satisfactory completion of due diligence. Every penny counts as they say!
If getting your hands dirty isn’t your thing – there are many other ways to support FoSC.
We are always looking for people with bright ideas to help with events, organising and stewarding, and also looking at how we can find funding to sustain the Common into the future. Is there an idea that needs looking at? Are you able to create a plan that can add value to the Common and the community? We need you!!