Synergies, feedbacks and tipping points: mountain pine beetle s rapid range expansion threatens invasion of North American boreal pine forests Allan L. Carroll The University of British Columbia Department of Forest & Conservation Sciences Vancouver, Canada
Overview Climate change versus insects Relevance to forest disturbance Climate change, forest management and disturbance: the potential for synergies, feedbacks and tipping points The mountain pine beetle: o o o o o Biology and dynamics Influence of climate change and forest management Synergies and an unprecedented outbreak Feedbacks on a global scale Tipping point: breach of the Rocky Mountains The future? Conclusions
Climate change and insects Climate change effects have been documented on all continents and for all taxa Taxa most affected to date - insects Insects as ectotherms: o All aspects of life histories determined by temperature o Rapid responses (positive and negative) to changing climate o Evidence to date: Behavioral shifts Genetic expression Range expansion/contraction
Evidence from the past: climate change versus historic insect herbivory Non-Betulaceae Betulaceae All Eocene (warm) Paleocene (cool) 0 10 20 30 40 50 Fossil leaf specimens with insect herbivory (%) Significant increase in insect herbivory during late Paleocene early Eocene global warming interval (Wyoming) Assume similar pattern (greater magnitude) with current/future warming Adapted from Wilf et al. 1999; Science 284: 2153-2156
Herbivory: relevance to forestry Timber volume (m 3 10 6 ) lost per year 100 75 50 25 0 Canada 1982-1987 Wildfire Insects Disturbance annually affects millions of hectares of forests In boreal and sub-boreal regions, insects have much greater impacts than wildfire Increased disturbance by herbivorous forest insects may threaten sustainable forestry Source: National Forestry Database, Canada, 1995
Given the sensitivity of insects to climate, and historic evidence of increased herbivory in a warming environment, climate change is expected to alter the dynamics, and impacts of eruptive insect herbivores.
Major bark beetle outbreaks 1980-2005 47 million ha affected Identified climate change signals: o o o Spruce beetle warmer summers = voltinism shift (Berg et al. 2006) Pinyon ips beetle warmer summers = temperatureexacerbated drought, altered host susceptibility (Breshears et al. 2005) Mountain pine beetle milder winters/warmer summers = range expansion (Carroll et al. 2004) Spruce beetle Mountain pine beetle Pinyon ips beetle Adapted from Raffa et al. 2008
A landscape-scale outbreak by an eruptive insect herbivore requires i) A climate that favours insect survival ii) An abundance of susceptible host trees Anthropogenic activities directly/indirectly affect both requirements Anthropogenic inputs The mountain pine beetle example: Favorable climate Abundant hosts Synergy Feedback Tipping point Photo: L. Maclauchlan
The mountain pine beetle Dendroctonus ponderosae 1 mm Historic range: western North America Periodic outbreaks Hosts: virtually all pines Tissues consumed: phloem Successful reproduction º tree death
Biology basics the tree Beetles prefer large trees: o higher quality food and larval habitat o protection from natural enemies and weather extremes However, large trees tend to be more resistant o constitutive resin ducts o induced resin production
Biology basics the beetle Colonizing beetles emit aggregation pheromones Resultant mass attack overwhelms tree defenses Beetles also introduce bluestain fungi o o o Pathogenic to most trees Block vascular tissue, stop resin production Provide nutrients for maturing beetles
MPB Occasionally normally exists as a member of the boleinfesting bark beetle assemblage responsible for maintenance of stand health. The dynamics of eruption and outbreak
Endemic populations Insufficient beetles to colonize healthy trees Normally found in trees attacked by other beetle species Rate of change in population 13 11 Attacked trees are rare and scattered throughout the forest 7 Average no. Mortality and offspring production 5 of eggs per in balance female = 60 97.5% 9 3 1 70 80 90 100 Generation mortality (%) Adapted from Safranyik and Carroll 2006
Natural mortality factors Competition Weather Woodpeckers Host resistance Invertebrates Pathogens
Incipient populations Infestations are scattered 13 Number of infested trees increases annually Clumps of infested trees grow in size and number over time Most attacked trees in larger diameter classes Rate of change in population 11 9 7 5 3 2 1 Population doubles 95.0% 70 80 90 100 Generation mortality (%) Adapted from Safranyik and Carroll 2006
The endemic-incipient transition: consequences 45 42 40 Relative beetle production 35 30 25 20 15 10 5 0 0 10 20 30 40 Tree diameter (cm) Adapted from Safranyik and Carroll 2006
The endemic-incipient transition: consequences ³5 yr 2-3 yr From stand to landscape in 2 3 years
Epidemic populations 13 Widespread Large annual increases in infested areas Extremely resilient to losses through normal mortality Rate of change in population 11 9 8 7 5 3 2 1 80-95% mortality 70 80 90 100 Generation mortality (%) Adapted from Safranyik and Carroll 2006
2.0 The mountain pine beetle: past recorded outbreaks Annual area (ha 10 6 ) affected 1.5 1.0 0.5 0 1910 1930 1950 1970 1990 2010 Year 1999 Mountain pine beetle Lodgepole pine Jack pine Approx. 1.5 million ha affected during the 1980 s
Anthropogenic inputs The mountain pine beetle example: Favorable climate Abundant hosts Synergy Feedback Tipping point Photo: L. Maclauchlan
Anthropogenic exacerbation of outbreak requirements 1) Favorable climate Very low Low Moderate High Extreme Climatic suitability 1 2 C increase in mean annual temperature since 1950 o Increased beetle survival o 75% increase in area of extreme climatic suitability o Rapid range expansion into newly available habitats 2) Abundant hosts Area (ha 10 6 ) 4 3 2 1 0 40 80 Adapted from Carroll et al. 2004 Susceptible pine 5 1910 1990 120 160 200 240 40 80 Forest age (years) Adapted from Taylor and Carroll 2004 120 160 200 240 > 3x increase in susceptible pine during the previous century o Fire suppression (wildfires reduced to <1% of past impacts) o Selective harvesting
10.0 2007 9.0 8.0 2006 2005 2008 2009 The synergy: Favorable climate x abundant hosts Annual area (ha 10 6 ) affected 7.0 6.0 5.0 4.0 3.0 2004 2003 2010 2011 2012 1999 2012 2.0 2002 Mountain pine beetle Lodgepole pine Jack pine 1.0 Year 2001 2000 1999 0 1910 1930 1950 1970 1990 2010 18 million ha affected 60% mortality of all pines by 2020 Unprecedented outbreak
The feedback: Increased carbon emissions to the atmosphere Ecosystem carbon stock change (Mt C yr -1 ) 10 5 0-5 -10-15 -20-25 -30 Sink Source -35 2000 2005 2010 2015 2020 Year Control scenario (fire and normal harvest) Control + beetle 270 Mt C to atmosphere Equivalent to 5yrs of emissions from Canadian transportation sector Potential feedback to global climate system Disturbance Atmospheric C Warming From Kurz et al. 2008
The tipping point: breach of the Rocky Mountains Rocky Mountains Long-distance dispersal events in 2002, 2006 Beetles travelled 300 400km east across northern Rockies Invasion of the Alberta plateau Persistence due to a warming environment A novel disturbance agent in naïve habitat
The tipping point: expansion corridor Lodgepole pine Mountain pine beetle Jack pine Lodgepole/jack hybrids Lodgepole/jack pine hybrid zone invasion corridor to the boreal forest 2010 beetles reached the jack pine
Mean ( SE) concentration (ppm) Mean ( SE) brood per female The tipping point: evolutionarily naïve host trees 70,000 Total terpenes 60,000 50,000 40,000 30,000 20,000 10,000 0 16 12 8 4 0 Lodgepole (experienced) Lodgepole (naïve) Jack pine 0 2 14 Days after wounding Historic climatic suitability From Clark et al. 2014 Very low Low Moderate High From Cudmore et al. 2010 Experienced trees respond rapidly and aggressively to wounding; minor response by naïve lodgepole and jack pines Higher offspring production in habitats with shorter association with mountain pine beetle Insufficiently evolved defenses may exacerbate spread and impacts in novel habitats
The future: favorable climate Lack of consensus among models Either presently suitable and declining, or unsuitable and improving Research ongoing From Safranyik et al. 2010
The future: susceptible hosts Pine volume declines in central Canada Reduced probability of sustained epidemic Lower rate of spread Pine (lodgepole and jack) volume (m 3 /ha) <0.1 21-40 0.1-2 41-80 3-5 81-120 6-10 121-250 11-20 251-500 Little's distribution range From Lempriere et al. 2008
Conclusions - specific The recent mountain pine beetle outbreak is a direct result of synergy between a warming environment and wildfire suppression Synergy has facilitated: o Altered C dynamics, potential feedback to CC o Rapid range expansion and invasion of naïve forest types Eastward spread ongoing, boreal jack pine colonized, eastern pines at significant risk
Conclusions - general Climate change will facilitate a general increase in insect herbivory and forest disturbance Climate change may synergize with forest management legacies to produce catastrophic outcomes Landscape-scale outbreaks can feedback to the global climate system when unprecedented, and facilitate future disturbance Synergistic effects of climate change and forest management can lead to tipping points and permanently altered ecosystems (regime shifts)