In his noon-hour « Midi de la foresterie » lecture on March 20th, Dr. E.H.(Ted) Hogg, research scientist at the Canadian Forest Service’s Northern Forestry Centre in Edmonton, described how climate change is influencing biomass production and the health of trembling aspen (Populus tremuloides) forests in western Canada. When evidence of aspen dieback events occurred in the early 1990s, presumably as a result of drought, Canadian scientists initiated the CIPHA (Climate Impacts on Productivity and Health of Aspen) program to assess whether global warming was effectively responsible for dieback. The main objective of this research is to monitor changes in climate and forest conditions in order to better forecast future conditions and impacts. The CIPHA program established plots in western and eastern parts of the aspen forests to monitor carbon, water and energy fluxes. Sampling includes tree coring to evaluate past climate conditions from growth rings and other forest inventory (height, dbh, regeneration, etc.). Researchers also monitor forest health indicators such as defoliation, dieback, mortality, insect presence and diseases. For example, white tree rings indicate years of defoliation by forest tent caterpillar. Leaf area index are determined and soil analyses are also conducted. Stand biomass has been estimated by tree measurements and national biomass equations.
Presence of white ring
Tree-ring analyses show that aspen growth has generally declined since 1951, due to drought and insect defoliation, and that droughts in 2001 and 2002 caused severe dieback of aspen forests. Overall, productivity of aspen forests has been reduced by 30% in all CIPHA plots largely due to drought, although other factors such as insect defoliation, wood boring insects, pathogens, fungus and disease exacerbate drought effects. Using aerial survey mapping and LANDSAT imagery, coupled with ground measurements, live aspen biomass loss in drought-affected areas has been estimated at 20% of total aspen biomass in surveyed area.
Changing climate effects have obviously not been limited to Canada’s aspen forests. Citing a 2010 article* in Forest Ecology and Management that he co-authored with 19 other scientists from around the globe, Dr. Hogg provided compelling evidence of similar impacts occurring since the 1980s in other forests on all continents. While periods of drought may increase in many regions as a result of a changing climate, other factors, including effects on disturbance regimes, growing seasons, regeneration success, changing competition effects among species, etc. will combine to push forest ecosystems into unprecedented conditions. Not a pretty thought….
Drought-induced forest decline :
An emerging global change issue (Allen et al. 2010*)
*Allen, G.D. et al. 2010. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. For. Ecol, Manag. 259: 660-684.
Résumé de la présentation : Nyambayar Suran, étudiant en Sciences de l'environnement, UQAT.
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