[NatureNS] CAPE SPLIT --BLOMIDON NATURALISTS SOCIETY FIELD TRIP --Sat., May 17/08

Date: Tue, 20 May 2008 13:38:46 -0300
From: David & Alison Webster <dwebster@glinx.com>
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black-throated green warb


James W. Wolford wrote:

>   Also the burls on conifer trunks were caused by a rust fungus? (or 
> perhaps a virus or bacterium??).
>
>
> Cheers from Jim in Wolfville, 542-9204
>
Hi Jim & All,            May 20, 2008
    I think the cause of these burls is unknown. In addition to large 
sometimes frequent burls on trunks they also may be abundant on branches 
and especially on roots. Root burls can be at least 20 times the 
diameter of the root on which they develop.

    Early stages of burl development are readily detected on small roots 
& branches (<5 mm diam) as elongated (2-3 times as long as wide) low 
swellings and I have never seen by eye or hand lens any discolored or 
distorted nucleus that might have been a starting point.

    Burls are very rare on fir (I can recall having seen only one small 
one), absent on pine and hemlock (?). Above ground burls are usually on 
white spruce and both white and red spruce have root burls. There seems 
to be a soil effect, burls being most common on poorly drained soils, 
less common on  excessively drained soils and least common or absent (?) 
on well drained soils with ample water holding capacity.

    So I suspect some localized water inbalance that leads to localized 
excessive cambial activity. Once initiated this localized growth 
inbalance would tend to be self perpetuating due to the greater phloem 
tissue area and length. The growth rings of burls, like the rings where 
two trees are growing together to become one trunk, can be ~10 times 
wider than the adjacent normal tissue.

Yt. Dave Webster, Kentville

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