OCEANS AND CLIMATE, AND
THEIR EFFECT ON FORESTINSECT INTERACTIONS
Alan Thomson
Natural Resources Canada
Pacific Forestry Centre
Western spruce budworm (Chorisoneura occidentalis Freeman)
Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)
Meet the insect and the host
ƒ
WSB development, emergence, and
establishment on the host
ƒ Emergence from hibernaculum – 116 degree
days (DD) above 5.5°C
ƒ Host bud scales thin enough for penetration (e.g.
just before or at bud flush)
ƒ Optimal 18-day period synchronization between
larval emergence and bud flush. (Thomson et al. 1984)
Why 18 days? Why not emerge
early then wait?
ƒ Host bud scales thin enough for penetration
ƒ Host bud not opened exposing the feeding site
ƒ Life cycle constraint:
ƒ
ƒ
ƒ
ƒ
Fall: adults mate, lay eggs on needles
Eggs develop and hatch
L1 disperse, build hibernacula, moult (L2), overwinter
Spring: emerge, disperse, mine needles or buds
ƒ Don’t feed – can run out of energy!
Douglas-fir: first bud flush
ƒ Sufficient photoperiod – DD accumulation starts
March 12th (southern Vancouver Island and the
Fraser Valley).
ƒ Sufficient heat accumulation: 318 degree days
above 2.78°C (Thomson and Moncrieff 1982)
ƒ First/Average/Last: indicators!
Studying insect-bud flush phenology
ƒ Sets of historical daily weather data covering
outbreak periods
ƒ Adjust for elevation: lapse rates by region, month
ƒ Calculate degree days: start/total DD/threshold
ƒ Budworm: January 1, 116 DD, 5.5°C
ƒ Douglas-fir: March 12, 318 DD, 2.78°C (first bud)
ƒ Compare estimated emergence date with bud
flush indicator
Where and when
Outbreaks:
1909-1910
1916-1920
1923-1930
Since then:
only on the
mainland, moving
eastward
When then, not
now?
Mean January 1 to March 12 maximum & minimum
air temperatures with trend lines
So how is this important?
ƒ The winter maximum and minimum air
temperatures are increasing with time.
ƒ The increase in winter air temperatures allows
the budworm larvae to develop earlier as the
degree days accumulate faster.
ƒ For the Douglas-fir, the temperature is increasing
but the photoperiod is still the same.
Diverging from synchrony
150
Day
125
100
75
O
u
t
b
r
e
a
k
O
u
t
b
r
e
a
k
50
1915
1920
1925
1930
1935
1940
1945
1950
1955
1960
1965
1970
1975
1980
1985
Year
First Bud Flush
Larval Emergence
Flush Trend
Emergence Trend
1990
1995
2000
Days from 18-day optimal phenology
60
O
u
t
b
r
e
a
k
50
40
30
O
u
t
b
r
e
a
k
20
10
0
1956
1989
-10
1915
1920
1925
1930
1935
1940
1945
1950
1955
1960
1965
1970
Year
Days from Optimal Phenology
Trend
1975
1980
1985
1990
1995
2000
Why no outbreaks following 1956 and
1989? Survival and mortality factors
ƒ Outbreaks depend on a range of factors operating
over the whole life cycle
ƒ 100 eggs/female: 98% mortality = stable; >98% =
population decline; 94% = population doubles
ƒ Preceding and following years were well beyond
optimal. There was little opportunity for the
population to develop significantly.
ƒ Eggs -> L1 -> dispersal -> hibernacula –> L2
ƒ Warmer: higher BMR
ƒ Resources used in fall not available in spring
ƒ Caused collapse of later outbreaks on the mainland
Why Oceans?
Winter temperatures
BC: CC Indicators by Ecoregion
ƒ Maximum temperature,
1895-1995 (ºC per
century)
ƒ No winter trend in the
ecoregion containing
southern Vancouver
Island
Mountain effects: valley cross-section
Climate change in mountains
ƒ Valley DDs >> ridge DDS: poor survival
ƒ Ridge DDs: insufficient to complete development?
ƒ Net effect: band of mid-slope defoliation
ƒ Solar heating can raise microclimate by 5-10oC
ƒ Early: more significant than air temperature
ƒ BUT: ~uniform over the slope (unlike lapse)
ƒ Early development more uniform than predicted
ƒ Early year sunshine change key to outbreaks?
Summary
ƒ Earliest budworm outbreaks on S. Vancouver Island
ƒ None there after 1930; occurred on the mainland
ƒ A 90-year winter sea warming trend has increased
air temperatures prior to host photoperiod
ƒ Relative phenology has diverged from optimal, in a
manner that explains the pattern
ƒ Other factors (e.g. fall temperature) also important
ƒ The winter sea warming trend is not evident at the
ecoregion scale
Information, Data, and Image Sources
ƒ Ross Benton, Natural Resources Canada
ƒ Environment Canada, Meteorological Services Canada,
daily climate data archives
ƒ Fisheries and Oceans Canada, lighthouse data archives
ƒ Natural Resources Canada, Canadian Forest Service,
Pacific Forestry Centre
ƒ British Columbia Ministry of Forests and Range, B.C.
Forest Service