Species in hedges

Yesterday I went on a field trip to a Old Sneed / Sneyd Park, a bit of land in Bristol that's somehow managed to escape being built on, despite being surrounded by houses. It looked like this - except you have to imagine it raining. Relentlessly. All afternoon (until the exact moment we decided to leave).

CC image by George Evans

It was an interesting spot, having a strange combination of species. There were superb and massive old oak trees which must surely support all sorts of creatures - many invertebrates, birds and bats. But now and then you'd come across some invasive interloper: there was a huge stand of bamboo which made you feel like you'd wandered onto the set of 'Crouching Tiger Hidden Dragon'.

So the thought of native and non-native species was uppermost in my mind. There are a number of hedges on the site and Jim explained that a hedge in 'favourable condition' should have less than 10% non-native species in it. This among various other criteria of course, and you can download Defra's Hedgerow Survey Handbook for all the details.

The Handbook also requires surveyors to count the number of woody species growing in a hedge, along a 30m stretch. This allows you to make a stab at its age, which is pretty neat. This idea was developed by Max Hooper.  Using aerial photos he discovered (in the 1960s) that the country was losing 10,000 miles of hedgerow a year! and started to look at what effect this would have on wildlife. He worked out that 70% of the variation in trees and shrubs in a hedge was explained by its age, and that a hundred years for every species present was a good rule of thumb (i.e. five species in 30m would indicate 500 years, and so on).

Autumn hedgerow (CC image by David Anstiss). The colours of the leaves and twigs can help guide you to different species.

So if you are out collecting winter twigs for your collection, it's an interesting thing to bear in mind. You might not want to get out a tape measure, but if you notice a good variety of native trees and shrubs in wandering along a hedge, that probably indicates it's quite ancient. Having said that I know my landlord has recently planted an excellent hedge brimming with native species. But the plastic tree guards probably give that away.

Another thing I found interesting in the Hedgerow Survey Handbook is in appendix 10, which shows you how to estimate the age of different trees and shrubs according to the diameter of their trunks. It's easy to spot a veteran oak as it's noticeably enormous - but if you're looking at something that never gets so fat (a field maple for example) then it doesn't have to be so big to get into their 'potentially interesting' category. There's much fascinating information about veteran trees in Helen Read's English Nature publication  (and there are other free downloads from the Ancient Tree Forum also). They're fascinating in themselves but are also very valuable to other species: lichens, fungi, insects...

CC image by Stefan Czapski.(This field maple has been pollarded, which might alter its growth rate
 - it could be even older than its fatness suggests.)

Another interesting thing you can do is check an area on the historic maps at Edina Digimap (they thought it was hilarious to title them 'Ancient Roam'). They don't go back hugely far of course, but sometimes you can see the 1860s, which gives you an idea of how built up areas looked before houses appeared. (There's a huge trunk of an ash tree just near my house - it manages to cling on despite having no big branches - and it seems to get its very own tree symbol on the large scale 1880s map, which is nice.) Looking at the maps for the Sneyd Park area it's interesting to see that the pond was already there in the 1880s, and was extended around the turn of the century.

Anyway. I'm getting sidetracked. Winter is definitely coming and if you want to make a winter tree collection (with leafy clues still available to help you), your moment has surely arrived.

Pieter Bruegel the Elder's 'Hunters in the Snow' (from the Famous Paintings with Winter Trees series. These have alternate branching... that must narrow it down)