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On 14/05/2011 18:28, TimSC wrote:
<blockquote cite="mid:4DCEBBB2.3000509@sheerman-chase.org.uk"
type="cite">On 14/05/11 17:39, Andy Mabbett wrote:
<br>
<blockquote type="cite">
<br>
The Woodland Trust do something similar (no URL, sorry, as I'm
mobile).
<br>
<br>
<br>
</blockquote>
Do you mean <a class="moz-txt-link-freetext" href="http://www.woodlandtrust.org.uk/en/visit-woods/">http://www.woodlandtrust.org.uk/en/visit-woods/</a> ? I
already asked for their data set but they were not very
communicative... It would be cool to have though. (A fairly
comprehensive list of public and permissive access woods for the
UK and their operator.)
<br>
<br>
TimSC
<br>
<br>
<br>
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<br>
</blockquote>
I'm sure Andy means this <a
href="http://www.ancient-tree-hunt.org.uk/discoveries/interactivemap/">http://www.ancient-tree-hunt.org.uk/discoveries/interactivemap/</a>
which I think is backed by the Woodland Trust. <br>
<br>
My own experience & discussions with local tree experts suggest
that the data collected by this survey is fairly unreliable. There
are too many 'citizen science' programmes of this kind which don't
produce really useful data because they lack any quality thresholds.
It's best to see them as designed to get people involved:
essentially they are marketing exercises. I've got a blog entry on
the stocks about a similar issue: I'll probably end up doing
several.<br>
<br>
To put a bit of context on the 10,000 trees in the Kent programme:
the Girona tree import was 28,000 trees and I think Tom Chance's
Lambeth set is of a similar size. The figure I have at the back of
my mind for Nottingham street trees is 8000, but I suspect that this
is too low. I know that Nottingham University Campus & the
adjacent Wollaton Park have over 3000 significant trees (probably
excluding ones in woodland): these are in our local tree expert's
patch. With his guidance the council have produced some excellent
leaflets on trees in local parks, such as <a
href="http://www.nottinghamcity.gov.uk/index.aspx?articleid=3383">The
Arboretum</a>. I presume the BCTV Kent project is therefore
restricted to large trees: one of the problems with the Ancient
Trees survey is that it has tended to be affected by wild
overestimates of trees size and age. Another is that prominent and
fast growing trees (think Poplars, which are short-lived) tend to be
over-represented<br>
<br>
I've got a limited experience of a systematic tree survey: I
attempted to locate all the Oaks in Attenborough Nature Reserve, <a
href="http://www.flickr.com/photos/sk53_osm/5492103506">mapped
them</a> with GPS & measured BHG (Breast Height Girth). In an
area of around 250 ha this took me 5 1.5 hour visits for around 100
trees from small saplings to ones upto 3 m BHG. I did this for the
following reasons: a) because the ability to say I found insect x on
tree y was useful; b) to see how much work was required; c) oaks are
relatively rare at Attenborough so it was an achievable set of data
to collect. The data set is now very out-of-date: I have not
resurveyed to see which trees have survived the new flood defense
work (most by the railway line will have gone for good), and I'm
continually noticing trees I missed. <br>
<br>
Tree identification is often non-trivial: a professional botantist I
know was hired to re-survey the Brithdir Arboretum within
Coed-y-Brenin because the orginal planting plan had either not
survived, or which trees had survived was not known. He told me that
identifying some individual trees took him hours. Certain heritage
trees have been surveyed on a national level for decades: notably
ancient Yews, and the native <a
href="http://sppaccounts.bsbi.org.uk/content/populus-nigra-1">Black
Poplar</a> (<i>Populus nigra betulifolia</i>). In the latter case
<a
href="http://www.amazon.co.uk/Black-Poplar-Ecology-History-Conservation/dp/1905119054">a
book</a> was published by the Botanical Society's Black Poplar
referee Fiona Cooper. However, the map was selective as landlords
have been known to fell trees to prevent visits by Poplar geeks.
Many counties include native Black Poplar in their BAP (Biodiversity
Action Plans). Richard Mabey has good accounts of both these trees
in <i>Flora Britannica</i>.<br>
<br>
So to summarise: its important to have a clear objective before
mapping trees. So far on OSM most mapping of trees has been casual,
and therefore implicitly is for the renderer. I can think of several
areas where clear objectives can be formulated:<br>
<ul>
<li>In many urban contexts - parkland, amenity grassland,
churchyards - mapping isolated trees or groups of trees seems
both achievable and potentially useful. </li>
<li>Tom Chance (and others) are interested in locating fruit
trees: again achievable. </li>
<li>I'm probably more interested in rare or unusual trees which
are usually specimen trees in parks and larger gardens, and I'm
keen that they be accurately identified. Having a known location
of a given tree means that one can visit that tree and
familiarise oneself with its appearance. It's then a lot easier
to spot other specimens.This, though, is really a complete
activity in itself.</li>
</ul>
A reasonably accurate identification is what really adds value, and
that's the hard bit.<br>
<br>
Jerry<br>
<br>
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