1. Assessment of factors affecting aspen growth, health & dieback in western Canada:
An overview of insights & challenges from the CIPHA study
Presented by E.H. (Ted) Hogg,
Research Scientist, Forests & Climate Change
Northern Forestry Centre, Edmonton, Alberta
Natural Resources Canada, Canadian Forest Service
WBEA-TEEM Forest Ecosystem Health Workshop
Calgary, Alberta
4-5 May 2010

2. Monitoring experience & activities
Participated in large-scale field experiments involving tower-based
monitoring of forest-atmosphere fluxes of carbon, water & energy
Leading a CFS study (CIPHA) focusing on impacts of
recent drought & insects on aspen growth & dieback
BOREAS/BERMS
Old Aspen flux tower
Prince Albert National Park
CIPHA (Climate Impacts on Productivity & Health of Aspen)
Initiated in 2000
Annual monitoring at 180 plots
Aspen
tree-rings
20 m
25-30 trees
per plot
2 plots per stand
3 stands per site
CIPHA study region

3. CIPHA study Tree-ring analysis of factors
affecting past growth of aspen
Aspen tree-rings
Regional growth was positively related
to moisture (CMI) and negatively
related to insect defoliation (D)
Note the 50% collapse in regional
growth during , caused by
drought & multi-year defoliation
Average detrended aspen growth at
CIPHA sites in western Canada (150 plots)
Severe drought years
Detrended growth (BAI’)
Severe defoliation years
Aspen forests
defoliated by
forest tent caterpillar
Photo taken NW of
Fort McMurray
26 June 2008
Regression equation:
BAI’ = CMI CMI CMI-2
CMI CMI-4 – D, r2 =0.697
From Hogg et al Can. J. For. Res. 35:
(results updated to 2004)

4. CIPHA study Impact of the severe regional drought of 2001-2002
The drought led to a 30% decrease in regional aspen growth & was
the main cause of a widespread increase in dieback & mortality
(Hogg et al. 2008, Can. J. For. Res.)
Annual health assessments showed an increase
in wood-boring insects which may have
amplified & prolonged the drought’s impact
2003
2008
Average aspen mortality at
25 CIPHA sites (150 plots)
Repeat photography of CIPHA plot
(BAT 1-2) showing drought impact
Sites included in the analysis of mortality

5. Drought-induced forest dieback & decline
An emerging global concern
Recent publication: (Forest Ecology & Management):
“A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests”
By Craig Allen (US Geol. Survey) and 19 co-authors
from the US, Canada, Algeria, Argentina, Australia, China, France, Italy, Korea, Russia, Spain, Switzerland, & Turkey
The paper highlights a recent increase in published reports of climate-
related forest mortality from all of the world’s forested continents
Drought-induced aspen
mortality in western Canada
photo by M. Michaelian, 2004
Increase in % papers on forests reporting on drought & mortality
An imperfect indicator in the absence
of a global monitoring system for forests!

6. An overview of insights and challenges
Some key messages from CIPHA and related research
1. Climatically-related variation in moisture regimes has a major influence on the growth, health & dieback of forests across the western Canadian interior
e.g., Hogg (1994 CJFR), Hogg & Hurdle (1995 WASP), Hogg & Bernier (2005 For Chron), Hogg et al. (2008 CJFR)
2. Need to consider the potential impacts of insects & diseases in the assessment of factors affecting tree growth & mortality
e.g., Hogg (1999 Ecol Modell), Hogg et al (2002 CJFR), Hogg et al (2005, CJFR)
3. Changes in tree mortality can provide an important indicator of change but are challenging to quantify across large areas (high degree of patchiness)
e.g., Hogg et al.(2008, CJFR), van Mantgem et al. (2009, Science), Michaelian, Hogg, Hall & Arsenault (in prep.)
4. A multi-scale, interdisciplinary approach to monitoring is needed to reliably
quantify and understand the causes of change in forests across large areas
e.g., Sellers et al. (1997 JGR, BOREAS special issue), Michaelian, Hogg, Hall & Arsenault (in prep.)
5. Long-term monitoring & use of historical (or paleo) data provides value in understanding the role of natural variation versus human-related effects on ecosystem indicators

7. Example: Aspen-spruce mixedwood forests near Fort McMurray
Photos taken during June 2008 flight by CFS (Arsenault & Michaelian)
confirmed Alberta SRD records showing extensive defoliation of both
aspen (forest tent caterpillar) and white spruce (spruce budworm)
Climate records showed evidence of severe drought during
Such events pose a risk for multi-species forest decline in coming years
including mortality of drought-sensitive species such as balsam fir & birch
Drought
( )
Mixedwood forest east of Fort McMurray
showing impacts on both aspen & white spruce
(Photo by M. Michaelian, 26 June 2008)
Climate Moisture Index calculated using
method of Hogg (1997, Agric. For. Meteorol.)