• From: "TUGS:Toronto Undergraduate Geography Society" <Tugs@xxxxxxxxxxxxxxxx>
  • To: tugsgeneral@xxxxxxxxxxxxx
  • Date: Mon, 3 Feb 2003 13:38:26 -0500

Hello everyone,

The Department of Geography Subterranean Speakers Committee is pleased to
announce the next event in our series.

FRIDAY FEB. 7 2003
Sid Smith Hall, Room 2125
Dr Katherine McLeod 
Dept. of Geography
York University 

Dr McLeod will present a talk entitled: 
Long-term maintenance of Picea glauca (white spruce) at its Northern Range
Limits, N.W.T., Canada 

Refreshments will be served. We look forward to seeing many of you next
Friday. An extended abstract of Dr McLeod's talk follows.

Sarah Finkelstein, Michael Fox and Mere Meade
Subterranean Committee 2002-2003


Long-term maintenance of Picea glauca (white spruce) at its Northern Range
Limits, N.W.T., Canada

T.K. McLeod
Department of Geography, York University


My research concerns the long-term dynamics of tree species range limits.
The northernmost conifers in North America are white spruce, located in
the Tuktoyaktuk region, which encompasses Tuktoyaktuk Peninsula and the
lower Anderson and Horton River valleys to the east.  White spruce trees
occur as outlying patches located north of treeline within the low arctic
shrub tundra.

These groups of trees, called tree islands, are composed of several short
individuals that may have erect or prostrate growth forms and they are the
focus of the research I will be presenting.  The objectives were (a) to
determine the current sexual reproductive capacity of these northernmost
white spruce (b) to determine the pattern of establishment, by sexual and
vegetative reproduction (layering), (c) to compare the establishment
patterns to instrumental and reconstructed climate records, and (d) to
estimate the age of the tree islands.         

The tree islands produced male and female cones, with very low seed
germination levels.  There was a trend of declining seed germination from
the forest-tundra northward to the low arctic tree islands.  Across the
entire study region, only two seedlings were found.  Initial seedling
transplant experiments indicated that survival over two growth seasons was
not significantly different between the seedlings transplanted inside and
outside the tree islands.  In addition, the level of survival was similar
to reported levels within the boreal forest.

The age of all live and most dead individuals was determined using
dendrochronological techniques.  The reproductive origin of each
individual was determined by excavation of subsurface connections
(establishment from layering) or roots (establishment from seed).
Establishment from layering increased over the period of record, reaching
maximum levels during the mid-20th century, and largely reflecting high
levels recorded from the northernmost tree island sites.  There was a
slightly later peak in establishment at the Anderson River valley area.
For the region as a whole, establishment by sexual reproduction occurred
at low levels, but was continuous over the period of record, for both
areas.  However, for each individual tree island, establishment from seed
occurred infrequently and there was no synchroneity among the tree
islands.  Neither area showed a strong positive response in seedling
establishment to 20th century climate warming.  These results suggest that
layering is the primary reproductive mode maintaining the tree islands,
and that establishment from seed is not a regional response, but appears
to reflect site-specific conditions.  All tree islands were of great age,
dating to the mid to late little climatic optimum.

These findings support the hypothesis that the white spruce tree islands
in northwest Canada are relicts of past more favourable climatic

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Toronto Undergraduate Geography Society
Sidney Smith (Rm613)
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