Assessment of factors affecting aspen growth, health & dieback in western Canada:

1. Assessment of factors affecting aspen growth, health & dieback in western Canada: Presented by E.H. (Ted) Hogg, Research Scientist, Forests & Climate Change Northern Forestry Centre, Edmonton, Alberta Natural Resources Canada, Canadian Forest Service E-mail: ted.hogg@nrcan.gc.ca An overview of insights & challenges from the CIPHA study 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 1977-1982, 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’ = 1.169 + 0.0111 CMI + 0.0099 CMI-1 + 0.0071 CMI-2 + 0.0058 CMI-3 + 0.0055 CMI-4 – 0.0119 D, r2 =0.697 From Hogg et al. 2005. Can. J. For. Res. 35: 610-622 (results updated to 2004)

4. 2003 2008 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 Average aspen mortality at 25 CIPHA sites (150 plots) Sites included in the analysis of mortality Repeat photography of CIPHA plot (BAT 1-2) showing drought impact

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 2006-2008 • 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 (2006-2008) 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.)