Friday, 14 June 2013

Urban Trees of Sheffield -- An interactive tour

"But let it be remembered, that the principles of a science are to be taught as truly with
 reference to the commonest forms as to the rarest.  And have we not the fields and the rivers?
But besides this, is not the whole suburb of this metropolis one magnificient botanic garden?"

 John Lindley, in his Inaugural Address as Professor of Botany in London University, 1827
(Quoted in Walters, 1993, Wild & Garden Plants)

View The Trees of Sheffield -- An Interactive Map in a larger map

This is something that I have had at the back of my mind for a few years, and have been, very slowly, mentally collecting notes on. I've finally decided to get on with it and put it out there. The idea was basically to provide a guide to the more interesting or unusual of Sheffield's urban trees, perhaps for a walking tour, or for those who would like to see a certain species.

Google Maps also allows collaborations on these types of maps, so, if you would like to get involved, and edit the map in some way, please let me know. I know there are lots of relatively common, interesting trees, in Sheffield's streets and gardens that are not on here. So, if you know of one that is easily viewable, and is not too far from the city centre, please let me know. I particularly need to add the trees of Weston Park; outside of the botanic garden, this probably has the best collection of trees in a location near to the city centre. 

The other place close to the city centre with a great collection of trees would be Tapton Experimental Gardens; unfortunately this is still closed as the University of Sheffield decides its fate. If I am not mistaken, Weston Park has, amongst others, Hungarian Oak, two varieties of Tulip Tree, the Tree-of-heaven, and Cappadocian Maple. The only tree I can remember seeing in Tapton is Bronvaux Medlar (+Craetaegomespilus dardarii), one of the very few trees that is a chimera of two species, rather than a hybrid; however, I am sure there are many more interesting species in there!

Another nice thing about Google Maps is that it allows data layers such as the one above to be exported as KML files. This should allow one to generate the corresponding biological records of the trees by opening the file in a GIS software like QGIS, reprojecting the layer to the OS National Grid, and exporting the points. Another exciting software for analysing the environmental importance of trees is the USDA Forest Service's application iTree. If one has enough information on the locations and sizes of trees in an area, this free piece of software will calculate all sorts of interesting metrics: the trees' cooling effects; their contribution to the reduction of urban pollution; and carbon storage to name a few! These 'urban ecosystem services' are discussed in many places, but I have found the relatively short, but very readable book, by William G. Wilson called 'Constructed Climates' to be a great introduction to this fascinating topic.

Saturday, 1 June 2013

Coppiced Hornbeam in Hedges

I was out surveying around Watton in Norfolk recently, and found these wonderful coppice Hornbeams in a field hedge.

According to Edward Milner's Trees of Britain and Ireland (2011), the prime use of Hornbeam was as firewood, and he cites the 17th century arborist and gardener John Evelyn as reporting that it burns "like a candle". I don't know if the poles resulting from cutting these specimens would have been used in such a way. The coppice effect may just be the outcome of the hedge having been laid many times in its past, and then being neglected at some point; presumably if the main function of a hedge is to be stockproof, the poles would have been laid rather than harvested. Alternatively, some hedges were managed by coppicing, especially if their primary function was not for containing animals; so perhaps this hedge was essentially only a boundary marker, and so has been managed by coppicing for a long time.

It seems from Oliver Rackham's Ancient Woodland (2003, 2nd Ed.) that Hornbeam is relatively rare in hedges. He states in Chapter 14 that "in a few places hornbeam grows in ancient hedges, particularly in the Harleston [Norfolk] hornbeam area". Interestingly, in the recent Flora of Suffolk (Sanford & Fisk, 2010), the authors suggest that in that county, hedges with Hornbeam are often the remaining "ghostly" edges of long grubbed out woods. Suggestively, this hedge was accompanied by a ditch, a common boundary marker of ancient woodlands.

Hornbeam was only occasional to rare in the hedges of this site near Watton, but the glorious, fresh, colours of the leaves, coupled with the twisted, degrading bases, was a real treat.