[Tagging] knotted willows

Jerry Clough - OSM sk53_osm at yahoo.co.uk
Mon Feb 20 14:04:06 UTC 2017


There are problems with this approach.
Many trees are pollarded once in their lifetimes: I'm currently looking out at some Beech trees which were probably pollarded 70 years ago, and there's a Birch which was pollarded rather crudely 50 years ago in the neighbours garden. Ancient pollards can be 500 years old. Re-pollarding a tree which has not been managed in this way for a long time is a rather hazardous operation for the tree. 
  
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Pollarding - Wikipedia
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If a macrophanerophyte is regularly pollarded then it's probably wrong to call it a tree. Most coppiced plants will only be allowed to grow to 5-8 m high and the individual stems will rarely be more than 10cm diameter. In Britain Hazel, Sallows, and Ash are certainly still coppiced. Oak has been coppiced in the past as a source of charcoal. However, like pollarded trees neglected coppice stools can grow into large multi-stemmed trees. A typical scenario is a wetland site where seedlings of any trees are cut close to ground-level ('coppiced') to maintain the wetland habitat: this is a relatively easy intervention and can be repeated. However, once tree cover can no longer be halted, or when the ground dries out, then the coppice stools will be left to grow of their own accord. In most former gravel pits in Britain there are numerous examples of 15m high mutli-stemmed Crack Willows which originated in this way.
In general I don't think coppicing is a useful thing to apply to an individual tree. Coppicing is more usually a woodland management technique and therefore belongs to natural=wood and landuse=forest. A typical woodland form in Britain is a wood which is coppice with standards. The understorey (most usually Hazel, but in Bradfield Woods it's Ash) is coppiced on a cycle which may be from 5-20 years. Some trees are always retained and form the canopy. Historically the understorey produced firewood, and poles, the standard trees were felled for timber. 
For individual trees we might recognise the following properties:
   
   - The tree is a pollard (i.e., has been pollarded at least once fairly early in its life)
   - The tree is currently managed by repetitive pollarding
   - The tree is multi-stemmed as a result of growing from a coppice stool
   - The tree is multi-stemmed as a result of growing from the planting of 2 or more saplings in a bundle (bundle planting)

Tall Common Limes (Tilia x europea) are often managed by a pollarding-like process: side branches are removed, the crown is severely reduced, and the trunk is cut short at the top. I'm not sure if this qualifies as a pollard.
Additionally there are other styles of regular pruning. For instance fruit trees in the Swiss Mittelland are pruned in a way which is very recognisable, so that it is quite easy to identify former orchards where the pruning ceased decades ago. The tree is usually pruned to have a leader and four principle branches. I suspect this Wikipedia article describes the technique in depth. Oaks growing in Dehesa (Cork, Holm and Pyrenean) are pruned in a not dissimilar manner, perhaps with 3 main branches, but the centre of the crown is kept fairly open. You can see examples here. However I would not choose to add this information to OSM: it is safe to assume that trees in Spanish Dehesa and Swiss Orchards will generally be manage this way. Quite beside which there are something like 37 million oaks in the dehesas of Extremadura.
Jerry


  
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Oeschbergschnitt – Wikipedia
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      From: joost schouppe <joost.schouppe at gmail.com>
 To: "Tag discussion, strategy and related tools" <tagging at openstreetmap.org> 
 Sent: Friday, 17 February 2017, 16:26
 Subject: Re: [Tagging] knotted willows
   
Considering that there are several management styles for individual trees, we could have something like
tree:managament=pollard
Other values might be none (allowed to grow free), copicce (pruned almost to the ground), espalier (pruned into a flat vertical surface), etc.
tree:management:operator=* could then be used to indicate who is keeping the tree pruned. 

Maybe tree:pruning_style would be more logical?
2017-02-11 13:34 GMT+01:00 Wolfgang Zenker <wolfgang at lyxys.ka.sub.org>:

Hi,

* joost schouppe <joost.schouppe at gmail.com> [170211 09:43]:
> One of the defining small landscape elements in Flanders (and probably many
> rural areas in Europe) is the "knotted willow". I'm not sure if this is the
> right term in English, in Dutch "knotwilg" really is a thing.

> How would you tag such a thing? (I could not find any previous discussions
> anywhere)

> natural=tree
> genus=Salix
> +
> management_style=knotted

> Or something like that?

> Apparently there's two words in Dutch:
> - knotwilg: knotted at about 2 meters high
> - grienden: knotted at a hight of maximum 50 cm

apparently english has words for these managements styles:
- "knotwilg" would be called "Pollarding"
- "grienden" would be called "Coppicing"

Wikipedia has pages on both.

Wolfgang

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