Hello everyone, The Department of Geography Subterranean Speakers Committee is pleased to announce the next event in our series. FRIDAY FEB. 7 2003 3pm 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 ABSTRACT: 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 conditions. ----- End forwarded message ----- ============================================= ******** *** *** ******** ****** ** *** *** ** ** ** *** *** ** **** ** *** *** ** **** ** ** *** *** ** ** *** ** ********* ******** ****** Toronto Undergraduate Geography Society Sidney Smith (Rm613) 416-978-2057 ------- End of forwarded message ------- ----------- TUGS GENERAL ANOUNCEMENT MAILING LIST - http://tugsonline.cjb.net