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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.
1978-2010
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
trunk.
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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