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Dear All, Jan 15, 2012
SUMMARY:
A stand of Cypripedium acaule (Common Lady's Slipper) that became
established (probably early to mid 1990s) along a section of pick and shovel
woods road that I built about 1984 gradually increased in abundance until at
least 2006. Sometime after this, drawing on memory between June 2009 and
summer 2010, abundance decreased abruptly throughout a mapped area of 113
m^2. This abrupt decrease may have been triggered by an unusual buildup of
ice at the soil/snow interface caused by unusually cold soil and observed
about 500 paces NW of this area, or the associated unusually deep or
prolonged penetration of frost.
BACKGROUND:
In the years 2003 to 2006 inclusive I made rough maps of plant location
in a small area of the North Alton woodlot and recorded state (flowering,
fruiting, not flowering, browsed, damaged etc.) The total number of plants
within the mapped area increased each year; 90, 103, 114 and 120 for the
years 2003 to 2006 respectively.
In theory one could follow the state of individual plants over years and
initially this worked fairly well. But as plants in some groups became
increasingly crowded the identity of some plants over years became
uncertain. So I discontinued both mapping and counting in 2006.
Softwoods in this area had been cut about 1950, the woods were still
fairly open until about 2000 but had started to close in south and west of
one portion of the mapped area by 2006 so I did some thinning in late
winter ( probably March of 2007 & 2008).
When I hand-pollinated some flowers in 2007, 2008 and 2009, in the
previously mapped area, I noticed no change in stand density but by summer
2010 there were very few plants in this area.
The mapped area is not large, about 113 m^2, but is spread along aboout
100 paces of road as four relatively distinct patches. Because all patches
were affected it seems unlikely that either disease or tree thinning was the
cause.
When cutting wood to the NW of this Lady's Slipper stand, in late winter
of 2009, when there were still scattered patches of snow, I noticed a very
unusual condition. Temperature at the soil/snow interface is usually close
to 0o C with soil heat gradually melting snow at this interface but ice was
nearly always present at this interface and up to about 10 cm thick. Ice at
that interface would suggest melting from above and subsequent freezing of
percolated water when it reached cold soil. It seems possible that stand
loss was caused either by cold injury or by direct or indirect effects of
low soil oxygen.
This is of course conjectural but it is something to watch for.
Yours truly, Dave Webster, Kentville
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