MPB & Climate

MPB & Climate
- MPB Basic Facts
  - Hosts - pines (mainly lodgepole, ponderosa, sugar & white, but maybe jacl as well)
  - Range - w. NA (Mexico to central BC)
  - MPB biology
    - virtually entire life under the bark
    - adults emerge in summer to find host tree
    - cannot overcome tree resistance on its own
    - bark provides food, protection from elements & predators
    - beetles produce glycerol (antifreeze) in winter
    - beetles are cold-blooded
      - sufficient heat for development (egg > larva > pupa > adult)
      - temperature regulates activity (emergence & flight)
  - Timing is everything
    - phenology
      - in sync with seasons
      - egg - larva - pupa - adult
      - best to OW in most hardy state (L3/4)
    - synchrony
      - in sync with each other
      - i.e. pop'n acting at the same time
      - ... flight temp. threshold (25°C)
      - ... result is a mass, synchronized flight
- Current Outbreak
  - started in ~2000, now declining
  - 17.5 million ha affected
    - BC total = 95 million ha
    - BC forests = 60 million ha
    - = 5 x's Vancouver Island
    - projected 60% of mature lodgepole pine in BC will be killed
    - we harvest ~315,000 ha per year vs. 17.5 million ha (435 million m3) of MPB outbreak
  - 2 key factors for outbreak
    - abundant food supply, fire ...
      - historically 500,000ha / yr burned
      - now ~30,000ha
      - now have 3x's the amount of mature pine
    - climate
      - winter
        
        takes -35° / -40°C to kill in mid winter
        
        takes -20° / -25°C in "shoulder season"
      - summer
        
        flight (dispersal) to find new hosts
        
        cold-blooded, warm temperatures better ...
        
        ... 25°C optimal
        
        dry conditions better ...
        
        ... weak flyers
        
        ... rain "dampens" kairomones
        
        ... drought stresses tree
- Climate ==> MPB
  - current range of MPB limited by range, not host
  - critical climate factors
    - winter cold - survival
    - summer warmth - dispersal (mass flight)
    - summer drought - stresses trees
  - thus if climate change favours MPB, it can expand
  - 3 "climate categories"
    - 1) climate inhospitable
      - insufficient heat to complete life cycle
      - too cool in summer (dispersal flight prolonged or delayed)
      - too cold in winter (survival)
      - beetles may inhabit but easily "wiped out"
    - 2) climate benign
      - conditions are sufficient for continued survival
      - outbreaks few and far btwn, last only a few years, over small areas
    - 3) climate favourable
      - conditions favour the MPB
      - periodic outbreaks ...
      - ... large in size
      - ... can last many years (up to 20 yrs)
    - #1 decreasing, #2 & 3 increasing
  - concern for boreal forest (Jack Pine forests across the Rockies)
- MPB ==> Climate
  - new area of study, not much empirical data
  - boreal forests act as a small carbon sink
    - 3 factors at play
      - photosynthesis
      - decay
      - fire
      - ... balance of the 3 factors
  - forests killed by MPB act as a carbon source
    - for last 5 years MPB is the single largest source of CO2 in Canada
    - 270-320 megatonnes of carbon released btwn 2000-2020
    - equivalent to 990 megatonnes of CO2
    - trees killed by MPB susceptible to fire & decay
  - recovery ... new forest will grow and sequester some of the carbon
  - but ...
    - climate change will ... favour other insects as well
      - spruce beetle
      - western (spruce) budworm
      - forest tent caterpillar
    - climate change will ... stress trees at the margins of their range
  - to date the impact of insects has not been incorporated into large scale carbon budget models
  - need for more studies