Synergistic responses to climate change: Are they evident for green alder at treeline in the Mackenzie Delta, NWT?
Lantz, Trevor*,1, Gergel, Sarah*,1, Henry, Greg*,1, 1 University of British Columbia, Vancouver, BC, Canada
ABSTRACT- In the western arctic, temperatures have increased at more than twice the rate as other parts of the world, likely due to anthropogenic climate change. There is growing evidence that tall shrubs are proliferating and replacing dwarf shrub communities in these areas, possibly as a result of temperature changes. Disturbances such as fire may also facilitate colonization by tall shrubs through exposing new substrates and increasing the depth of the active soil layer. To examine population dynamics in green alder (Alnus viridis ssp. crispa) we sampled at forest-tundra and tundra sites in the Mackenzie Delta, NWT. At all sites vegetative reproduction appears to be of secondary importance to recruitment via seed, as only 5% of individuals in patches at all site types consisted of more than one ramet. Average age of alder clones was significantly lower (<12 years old) on tundra compared to forest-tundra sites, indicative of recent recruitment. In contrast, a relatively uniform age distribution on forest-tundra suggests that in these populations recruitment has remained constant. Alder at burned forest-tundra sites also showed increased growth and catkin production. Together, these results suggest that the direct effect of increasing temperature on green alder could act synergistically with the increasing frequency of fires to facilitate alder spread throughout the tundra.
Key words: shrub proliferation, green alder, climate change, disturbance
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