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Index of Subjects Dear Dave, Paul other slipperers: What's the situation here in regard of soil temperature, on rocky ground as opposed to deep soil? As I understand it, heat conducts out from within the Earth largely as a result of intrinsic radioactive decay in the centre, maybe plus molten core friction, so there's a gradient of temperature from the middle out to the surface -- well known. As some soils are full of isolated, insulating air holes (like styrofoam), I'd guess that in these soils, the conductive re-supply of heat from within in response to winter surface cooling from without would be relatively poor. By contrast, the thermal conductivity of solid rock (with no holes) would be higher, so heat re-supply from within, out to the surface, should be greater in big deeply embedded granite boulders or complete rock outcrops. So if this is correct, your shallow roots could actually remain a bit warmer over an apparently barren, forbidding granite outcrop than over a seemingly more welcoming, nice aerated soil in a field or wood. I'm not sure of all this, but got puzzled in general because 10 mm bristletails (insects, Archaeognatha) here hibernate in rock crevices on rotten volcanic cliffs on the Bay of Fundy from late September for ~6 months, in the face of harsh winds and -20°C outside temperatures in Jan-Feb. I never did this properly, but when I took out a meter and a thin thermocouple and poked the end under even small rocks and down cracks, I got temperatures in the range of 2-3°C. This range is very survivable provided that heat is not removed from the sites by convection (penetration by cold winds). Likewise, Dave's thick ice cover at 0°C will actually protect from convective losses that would otherwise take the insect or root down to the ambient -20°C, or whatever it is. It would be interesting to know what range of temperatures have been measured in what types of soil and rocks in winter at what depth, presumably a huge field of knowledge. I'll guess that not everything freezes to 12 inches down in this latitude. This is probably another one for you, D.W. Does any of it hold up? Steve (Halifax) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Quoting Paul MacDonald <paulrita2001@yahoo.com>: > An interesting account Dave. > I got some growing from stock from a test tube operation - they hold > on but not much more. > Their tolerance for cold seem variable. Along the Shelburne River > there is a large stand - covers several hectares I would surmise. > Very lovely. > The interesting thing is many plants are growing on top of granite > boulders with the > only soil from decaying hardwood leaves - the temp of the soil must > drop quite low > there in the winter - so their roots must be hardy. > On the other hand they have a good supply of water during the > growing season but no standing or very little > at least in the winter to make ice. Oxygen does not look to be a problem. > Unfortunately or perhaps fortunately it is not an easy spot to > visit but well worth the trip > for me at least. Half the fun is getting there - lol > Hope we can get the snowshoes out soon > Paul > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > ________________________________ > From: David & Alison Webster <dwebster@glinx.com> > To: NatureNS@chebucto.ns.ca > Sent: Sunday, January 15, 2012 10:31:30 PM > Subject: [NatureNS] The rise and fall of Common Lady's Slippers (long) > > 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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