PARENT SESSION
Oral Session # 93: Vegetation Change and Response.
Presiding: B Parry Hecht
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 105.
Population, community, and ecosystem-level constraints on Picea mariana establishment in boreal peatlands following permafrost thaw.
Camill, Phil*,1, Adams, Julian2, Limmer, Jacob1, Kalim, Sahir1, Rafert, Greg1, Middleman, Rosali1, Andreassi, Chris1, 1 Carleton College, Northfield, MN2 University of Virginia, Charlottesville, VA
ABSTRACT- Because Picea mariana (black spruce) is often the sole canopy dominant in boreal permafrost peatlands, it significantly impacts ecosystem processes, including rates of carbon cycling and permafrost formation. Classic models of cyclic succession suggest that thawed, Sphagnum-dominated collapse-scar bogs are colonized by P. mariana from surrounding permafrost plateaus, leading to the eventual reformation of permafrost and attendant shifts in C accumulation. However, little is known about the processes controlling P. mariana establishment in boreal peatlands. Our goal was to describe demographic transitions of seed arrival, germination, and survival as mediated by community and ecosystem-level factors for 18 thawed bog sites in Manitoba, Canada. We collected 5-6 years of data on seed rain and seedling germination and survival using a combination of seed traps, artificial seed additions, and seedling transplants (n = 2160) into three treatments: water table depth (high/med/low), NPK fertilization (+/-), and vascular plant competition (+/-). Results indicate strong limitations on recruitment by population, community, and ecosystem-level processes. Seed dispersal declined with distance from permafrost plateaus, and collapse scars received an average of 3x fewer seeds than plateaus. At the community level, germination was severely inhibited (<0.1% after five years) by growing Sphagnum surfaces that overtopped germinants, but it was increased to 10-40% by artificially killing the moss substrate. At the ecosystem level, seedling survival and germination were strongly controlled by water table depth. Seedling survival after five years was limited to S. angustifolium lawns (91% survival) and S. fuscum hummocks (96% survival) where mean water table depth was > 10cm. Almost no seeds germinated in wet S. riparium communities, where survival of seedling transplants was 5%. These results suggest that P. mariana establishment is strongly controlled by water table changes associated with peat accumulation and bryophyte succession as well as factors that control mortality of the moss substrate.
Key words: Picea mariana, peatland, boreal, recruitment