Effects of simulated climate change on post-disturbance Populus tremuloides - Picea mariana ecosystems in northwestern Quebec
Dabros, A.. 2008. McGill University, PhD
Abstract
In the mixedwood-boreal transitional forest of northwestern Quebec, the establishment of
trembling aspen (Populus tremuloides Michx.) has been observed at the extremes of their
regional distribution, in areas previously dominated by black spruce ( Picea mariana
(Miller) BSP). Our main objective was to explore how climate change could affect the
growth and performance of aspen and black spruce. Climate change simulation was
provided by the installation of twenty open-top chambers (OTCs) and twenty control
plots in the summer of 2005 at three disturbed sites (post-fire, logging road and logging).
Each plot enclosed a pair of aspen and spruce seedlings. In comparison to control plots,
the conditions in the OTCs were marked by higher air temperatures (2-3oC), drier soil (up
to 10% volumetric moisture content) and cooler soil (up to 2.6oC), lower supply rates of
Ca and Mg, and slower decomposition of aspen litter. Warm weather and high rainfall
were likely responsible for increased height growth and advanced spring bud burst of
aspen growing in the OTCs during the 2006 growing season, but not during the cooler
and drier season of 2007. Leaf calcium concentration was higher, and beetle leaf
herbivory was lower for OTC aspen in comparison to control plot aspen. Spruce was not
affected by OTC treatment in terms of height growth, but its final dry biomass was
higher, and spring bud burst was advanced by 2-3 days in the OTCs compared to control
plots. Both species showed trends of higher root tip number and lower % ectomycorrhizae
(ECM) colonization in the OTCs, and vice versa in the control plots. Aspen appeared to
be more dependent on ECM colonization; therefore, potential effects of climatic changes
on ECM would have a larger impact on aspen than spruce. Overall, aspen may be more
responsive (positively and negatively) than spruce to erratic inter-seasonal weather
conditions often associated with climate change. A less sensitive, more stable response to
weather variations may give spruce an advantage over aspen in the long term, as the years
in which the conditions are less favourable towards the physiological requirements of
aspen may be detrimental to their regional populations.
