Several elements to consider from first principles:
i) tree growth: a tree growing at 1 cm diameter per year will have its RPA
increasing in radius by
12 cm per year. If you are interested in that sort of tolerance the report
might become quickly out
of date in a year; for many sites (no planned disturbance of RPAs) and for
many trees (slower growth
than 1 cm) and knowing many sites where if we got the metre distance of the
fence right we would be
celebrating I think a few years (3,4?) would be fine.
Heights, crown size and shading may well change, especially any assessment on
the need for pruning
for access, scaffolding, storage etc; again it's more of a problem for
vigorous trees
ii) tree health: do "B" grade trees develop into "A" grade? Cs into Bs? I
expect not - generally
it's the other way around.
iii) tree failure, loss, death: if trees have disappeared between surveys
your old survey will have
trees recorded which are no longer there; may be an issue in some cases but
not in most.
iv) additional trees; having surveyed a number of sites a second time (using
surveys of other
people) it is surprising how trees can appear from nowhere! I don't know how
this happens but I
guess that judgments have to be made as to what to include and what to
group/exclude.
Going back to a site a second time, especially in a different season, can
lead to very different
experiences - the trees may not have grown but access may change - the mass
of brambles may have
died down for example, lines of sight improved etc.
I think the key thing is, would an updated tree survey make any difference to
the overall assessment
of the site and the trees? That is best considered taking the old survey onto
the site taking into
account that you may be granting planning permission for a two year window
ahead, so if the tree
survey is three years old and the development starts in two years time there
might be 5 years growth
on the trees when excavation starts.
Jon Heuch Tel: +44 (0)1233 713 466 Mob: +44 (0)7810 610 712
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