Multi-scale Analysis of Environmental Conditions and Conifer Seedling Distribution Across the Treeline Ecotone of Northern Manitoba, Canada
Mamet, S.D. and G.P. Kershaw. 2013.
Abstract
Treeline represents not only an important physiog-
nomic boundary but also an important transition
between disjunct mesoclimates and environmental
limitations on establishment of tree species. The cir-
cumboreal treeline is controlled by some still to be
understood physiological mechanism dependent on
air temperatures, though younger life stages are
increasingly influenced by numerous other biotic and
abiotic factors at finer spatial and temporal scales. The
goal of this study was to evaluate environmental and
reproductive characteristics across treeline around
Churchill, Manitoba, and to determine which factors
are most important for successful seedling establish-
ment by tamarack, white spruce and black spruce. We
examined mid-winter snowpack, soil characteristics,
seed viability, seedling establishment, and dominant
vegetation at sites within forest and at treeline.
Growing season was longer at treeline due to less snow
accumulation, though soil temperatures were more
variable throughout the year when compared with forest. Conifer seed germination was greater than 88%
for most of the region and total seedling density was
relatively consistent between sites. Seedlings were
negatively associated with other plants within the
forest, but low stature vegetation seemed to facilitate
establishment at treeline. The associations between
seedling establishment and habitat availability obser-
ved at several sites suggest that treeline advance in the
Churchill area could be contingent on the facilitative
effects of plants at and beyond treeline. The results of
this study support the premise that fine-scale biotic
and abiotic patterns and processes such as snowpack
and facilitation by neighboring vegetation certainly
cannot be overlooked in analyses of patterns at tree-
line in a changing Subarctic.
Key Words
treeline; Churchill; Manitoba; habitat index; soil temperature; establishment; snowpack; germination; forest%u2013tundra.
