[NatureNS] Tree decline; tedious unless you like trees

From: David & Alison Webster <dwebster@glinx.com>
To: NatureNS@chebucto.ns.ca
Date: Thu, 26 Apr 2012 17:10:49 -0300
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Dear All,                    Apr 26, 2012
    The pattern of growth ring width in a Red Spruce that went over in the
wind of Dec 13, 2010 caught my eye last winter so I took measurements; it 
tallied with other unusual features of the tree and recent weather. Unlike 
annual plants, perennials have to cope with sometimes cumulative adverse 
effects of past years. This is a speculative reconstruction of the slow 
death of a tree.

    The tree was growing on a shallow soil over bedrock where trees were 
widely spaced and the measurements of ring growth were at a height of about 
5 dm above soil surface. Appreciably below this the outer rings (outer 10-15 
cm) were obscured by wood rot that had invaded from below; the wood above 
~40 cm being entirely sound. The crown was all live but increasingly short 
terminal growth evidenced decline.

    Usually when a tree on shallow soil is uprooted by wind, a root plate of 
large diameter is tilted up. Consistent with rot only in the outer wood, the 
root plate was small and partially rotten roots up to 1 dm across had broken 
off near the trunk.

    For ease of measurement, and because there were successive years of 
essentially similar width, I measured the total width over groups of years. 
Over the last 9 years (2002-2010 inclusive) only 12 mm of wood was added to 
the radius. [A few hundred paces NE of this, closely spaced conifers in good 
soil shed most needles early in the summer of 2000, under very dry 
conditions, and were cut. Trees with similar symptoms that were not cut were 
dead by fall.]

    Working back through time, the preceeding year, number of growth years, 
mm growth increment and mm/year increment were as follows:
2001, 9, 12 mm, 1.3 mm/yr,
1997, 4, 8 mm,  2.0 mm/yr,
1992, 5, 24 mm, 4.8 mm/yr,
1987, 5, 27 mm, 5.4 mm/yr,
1982, 5, 24 mm,4.8 mm/yr,
1978, 4, 10 mm, 2.5 mm/yr.
          32, 105 mm, 3.28 mm/yr.

    Working forward through time we see that growth rates up to and 
including the 5-yr period 1993-1997 were normal, decreased by about 60% over 
the 4-yr period 1998-2001 and decreased [relative to1993-1997 rates] by 
nearly 75% over the 9-yr period 2002-2010.

    So it appears that conditions were dry enough to slow growth from 1998 
to 2001 inclusive and near the end of this period (probably 2000 to judge 
from the nearby site) dry enough to induce appreciable death of roots and 
invasion by wood rot fungi which by about 2010 had reached the base of the 

    It is no coincidence that BSLB got a bad reputation and this tree ran 
into trouble at about the same time; North Alton and Halifax had somewhat 
similar dry weather for several years apparently.

    The story of this tree is by no means unique to Red Spruce. In fact, 
while discarding some old magazines recently, so I could find the floor, I 
came across an interesting article about a disease of coconut palms [The 
curse of Cadang-cadang, Karl Maramorosch, Natural History 96(7):20-22, 
1987]. Affected trees take on average 10 years to die and can take as much 
as 20 years.
\YT, Dave Webster, Kentville

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