Herbivore and Pathogens on Three Understory Boreal Species: Effects of Environmental Conditions

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Herbivore and Pathogens on Three Understory
Boreal SpeciesEffects of Environmental
Conditions

• Christa Mulder (and Bitty Roy)
• Institute of Arctic Biology
• LTER meeting, December 6 2007

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Climate Change in Interior Alaska
Since 1960s 3C increase in annual temperature
4.5C in winter Growing season 2.6 days /
decade Leaf onset -1.1 day/ decade
Predicted by 2075 0.75 to 2.5C in summer 1.0
to 6.0C in winter
Predicted from historical data Tree-ring data
during previous warm periods ? tree growth and
?drought stress
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Original predictions

• Herbivores should become more numerous in warmer
  sites compared to cooler sites
• Summer warming should affect growth and
  reproduction
• Winter warming should affect survival
• 2) Pathogens should also become more numerous as
  temperatures warm. But pathogen attack may
  decrease in the warmer zones due to drier
  conditions
• 3)Drought stress is expected to increase with
  warming. Stressed plants will have higher attack
  rates, either due to physical damage allowing
  access to pests, or due to physiological
  diversion of resources from defense to
  maintenance
• 4)More rapidly growing plants will have more
  damage because of trade-offs between allocation
  to defense and growth (Coley et al. 1985, Herms
  and Mattson 1992).
• Negative relationship between growth rates and
  damage levels
• 5) Plants will be adapted to their local pest
  environments climate change will result in
  plants facing unfamiliar pest genotypes, which
  will alter attack rates. If there are strong
  genotype by environment interactions, then it
  will not be possible to extrapolate from current
  correlations between climate and pest attack
  rates to future climate scenarios.

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Herbivores
PLANTS
Climate change
Pathogens
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21 Study Sites in Interior Alaska

• Summer warm vs. cold (aspect)
• Winter warm vs. cold (elevation)
• Summer wet vs. dry (slope)

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Environmental variation soil temperature in
August
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Host species 1Alnus viridis var. fruticosa
(green alder)

• Deciduous shrub to small tree
• Found at all but one of our sites
• N-fixing symbionts (Frankia)

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Host species 2Rosa acicularis (prickly rose)

• Deciduous small shrub
• Found only at our warmer sites

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Host species 3Vaccinium vitis-idaea (lowbush
cranberry)

• Evergreen low-growing plant
• Found only at our colder sites

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Methods site environmental variables

• 21 sites each 25 m in diameter
• Slope, aspect, elevation, latitude, longitude
• Soil temperature and moisture, depth of thaw
• Year-round dataloggers above and below snow for
  temperature, relative humidity, and snowmelt

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Methods vegetation descriptions

• Overstory, understory, ground layer
• Canopy cover, moss depth, litter depth
• Host density

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Damage and diversity estimates

• In 2002, 2003, 2004, 2005 and 2006, we.
• Selected multiple leaves per plant (8 alder, 6
  rose, 4 cranberry)
• Estimated of leaf area damaged per damage type
• Surveyed plant for presence of damage types
• Estimated all herbivore damage in 4 feeding mode
  categories
• chewing
• Sucking
• mining
• leaf roller

chewing
rolling
sucking
mining
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Examples of Damage Types on Alder
Rasping
tarspot (Rhytisma salicina)
Edge holes Lophocampa solandriana
Powdery mildewMicrosphaera penicillata
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Damage Types on Roses
big brown spots
Yellow spots Phragmidium c.f fusiforme
Central holes and thrips
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Damage Types on Cranberry
bite edge (Orygia?)
black asco
red-brown dieback (Monilinia?)
central holes (Orygia?)
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Methods Alder transplants

• In 2003, alders grown from seeds from 9 sites
  were transplanted to all 9 sites
• Three of these sites were lost in the 2004 fires
• Remaining 6 sites were surveyed in Aug 2004 and
  Aug 2005
• Remaining plants were harvested in Aug 2005

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Methods cranberry transplants

• Fruits collected from 10 sites in Fall 2004
• Plants outplanted to two common gardens in Spring
  2005
• The two destination sites differed considerably
  in summer conditions

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Can environmental conditions explain variation in
damage levels within or across years?
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Principle Components Analysis on Sites
All three species Alder and rose Alder and
cranberry Rose and cranberry
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Eigenvectors for PCA
PC axis 1summer warm soil PC axis 2winter cold PC axis 3steep, warm air
Thaw (0.36) winter temp (0.42) slope (0.44)
moss cover (-0.36) below snow min temp (0.38) absolute humidity (-0.42)
ground cover (-0.33) elevation (0.34) soil moisture (0.39)
canopy density (0.31) below snow temp (0.33) air temp (0.32)
soil temperature in August (0.31) snowmelt date (0.31) relative humidity (-0.31)
litter depth (0.30) summer air temp (-0.30) below snow temp (0.25)
northness (-0.26) absolute humidity (0.23) litter depth (0.25)
elevation (-0.23) Understory cover (0.21) winter temp (0.21)
snowmelt date (-0.22) northness (0.21) eastness (0.21)
relative humidity (0.22) ground cover (-0.20) below snow min temp (0.20)
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Summer temperature and precipitation, 2002-2006
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Winter temperature and snow depths, 2002-2006
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Approaches

1. Examine relationships with PC scores separately
   for each year.
2. Examine impact of summer (May mean, June-Aug
   mean, RH) and winter (mean temp, min temp, mean
   below snow temp, min below snow temp) variables
   for all years combined
3. Examine relationships between leaf, tree, and
   stand characteristics to develop hypotheses for
   mechanisms (2003 data alder only)
4. Examine impacts of herbivore and pathogen damage
   on reproduction
5. Examine transplant results to evaluate the role
   of plant genotype

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Alder (Alnus viridis var. fruticosa)
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Overall damage patterns alder
Hot summer
Cold Low Snow winter
Low snow winter
High snow winter
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Do environmental conditions explain variation in
alder pathogen damage?
Year R2 PC1 PC2 PC3
2004 0.40
2005 0.51 - -

• Warmer, drier summer conditions may favour
  pathogens
• steep, dry sites with warm air temperatures had
  lower pathogen levels in 2004 (the hot dry year)
  but not 2005 (opposite)
• Across years, higher pathogen levels were
  associated with warmer summer temperatures
• There was little evidence for an impact of
  winter, except possibly a negative effect in 2005
  (low pathogens, following a winter with lots of
  snow)

Variable R2 May temp Summer mean temp RH
pathogens 0.24
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Alder damage by feeding mode
Hot summer
Low snow winter
High snow winter
Cold low snow winter
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Do environmental conditions explain variation in
alder herbivore damage?
Group Year R2 PC1 PC2 PC3
Sucking 2004 0.22 -

• SUCKING
• Within years lower damage levels under warm,
  dry conditions in the warmest year (2004)
• Consistent with lower damage levels on trees that
  are more water stressed (as indicated by d13C) in
  2003
• Across years higher damage following warmer
  minimum winter temperatures

Variable R2 Mean winter temp Min winter temp BS mean BS min
Sucking 0.42
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Do environmental conditions explain variation in
alder herbivore damage?
Group Year R2 PC1 PC2 PC3
Chewing 2003 0.52 -
Chewing 2005 0.34

• CHEWING
• No consistent pattern within years
• Across years analyses suggest lower damage in
  warmer sites
• Consistent with the within-tree analyses (no
  differences between middle and outer leaves)
• Consistent with the within-site analyses only
  LMA consistent correlated with damage
• WINTER higher damage following years with cold
  winters

Variable R2 May temp Summer mean temp RH
chewing 0.21 -
Variable R2 Mean winter temp Min winter temp BS mean BS min
Chewing 0.21 -
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Do herbivore damage levels affect reproduction?
Herbivore damage significant decreases in number
of catkins with increased damage.(Same results
when blocking by site)
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Do pathogen damage levels affect reproduction?
Pathogen damage significant increases. In number
of catkins with increased damage (Same results
when blocking by site)
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Do alder seedlings that grow faster have more
damage?
Herbivory Pathogen pathogens herbivores
Census 1 0.20 ns ns .12
Census 2 ns ns ns ns
Census 3 ns ns ns ns

• Alders showed increased herbivore damage with
  increased growth rate only in the first year
• Overall, little support for a positive
  association between growth rate and damage

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Alder transplant results does genotype matter?

• Using AFLP markers no evidence for clonal growth
  (all our individuals appear to be genets)
• Less herbivore damage on local plants than on
  foreign plants
• Despite this, no evidence for local adaptation
  (plants at home sites do not do better in terms
  of growth and survival than those at away
  sites)
• Also no consistency from year to year in how
  heavily given plants are attacked.
• Lack of local adaptation is consistent with high
  gene flow (monoecious, wind-pollination, seeds
  released in winter)

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Alder transplant results do genotype and
environment matter for damage levels?

• Destination mattered origin and mother did not
• Destination affected survival, growth, and damage
  types
• Higher sucking damage in summer warm sites in
  2003 and 2005
• Lower chewing damage in summer warm sites in 2003
  (consistent with adults)
• Higher pathogen damage at winter-cold sites

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Summary for alders

• High summer temperatures have either a negative
  effect (sucking damage) or no consistent effect
  (chewing, mining, leafrolling) on herbivores
• High summer temperatures have a position effect
  on pathogens
• Warmer winters are followed by higher damage
  levels by the dominant herbivore groups (suckers
  and chewers)
• ?Increases in in WINTER temperature may be most
  problematic for plants because of increased
  herbivory
• ?Increases in SUMMER temperature may be somewhat
  problematic for plants because of increased
  pathogen damage

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Summary for alder contd

• Herbivore damage appears to reduce reproduction
  (as expected)
• Pathogen damage appears to increase reproduction
  (unexpected)

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Cranberry (Vaccinium vitis-idaea)
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Overall damage patterns cranberry
Hot summer
Cold Low Snow winter
Low snow winter
High snow winter
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Do environmental conditions explain variation in
cranberry pathogen or herbivore damage?
Group Year R2 PC1 PC2 PC3
Sucking 2004 0.60
Mining 2005 0.43

• There were no relationships between pathogen
  damage and environmental conditions
• Sucking and mining damage was greater at sites
  with warmer winter temperatures
• Within years (2004)
• Across years

Variable R2 Mean winter temp Min winter temp BS mean BS min
Sucking 0.75
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Alder damage by feeding mode
Hot summer
Hot summer
Low snow winter
Cold Low Snow winter
High snow winter
Cold low snow winter
High snow winter
Low snow winter
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Do cranberry seedlings that grow faster have more
damage?
Herbivory Pathogen pathogens herbivores
Census 1 ns ns -0.25 ns
Census 2 -0.23 ns ns -0.27

• Cranberries showed negative relationships between
  growth rate and damage levels
• Overall, no support for a positive association
  between growth rate and damage quite the opposite

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Cranberry transplant results does genotype
matter for growth and survival?

• Pre-transplant morphology differed by origin
• There were no origin effects post-transplant
• There were strong destination effects on
  morphology
• There were strong destination effects on
  survival.
• These are consistent with the general pattern of
  occurrence of cranberry (not found at summer-warm
  sites)

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Cranberry transplant results do genotype and
environment matter for damage levels?
Source Herbivore Damage Pathogen Damage Pathogen Types Herbivore Types
origin 0.51 0.79 0.51 0.89
destination 0.80 0.45 0.63 lt.0001
destinationorigin 0.68 0.64 0.06 0.22

• Destination mattered origin did not
• Destination affected herbivore diversity but not
  damage levels or pathogen diversity
• There was a marginal destination by origin effect

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Cranberry is there evidence for local adaptation?

• Weak for both origins damage levels were lower
  when planted to the site of origin in only one
  year.

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Summary for cranberry

• Summer temperatures no consistent effect on
  herbivores or pathogens
• Warmer winters are followed by higher damage
  levels by the dominant herbivore group (chewers)
  and by miners
• Strong site effects on both adults and
  transplants, but no evidence for local adaptation
• ?Increases in in WINTER temperature may be most
  problematic for plants because of increased
  herbivory

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Summary for cranberry contd

• Strong site effects in both adults and
  transplants
• Evidence that plants that grow faster are also
  better defended
• No evidence for local adaptation

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Rose (Rosa acicularis)
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Overall damage patterns rose
Hot summer
Low snow winter
High snow winter
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Do environmental conditions explain variation in
rose pathogen or herbivore damage?
Group Year R2 PC1 PC2 PC3
Pathogens 2003 0.26 -
Sucking 2004 0.57 -

• Within years, there was less pathogen damage in
  warmer sites in a cool summer
• Within years, there was less sucking damage at
  sites with a warmer winter temperatures
• Between years, total herbivore damage and sucking
  damage were lower when summer temperatures were
  higher

Variable R2 May temp Summer mean temp RH
herbivores 0.83 -
sucking 0.29 -
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Alder damage by feeding mode
Hot summer
Low snow winter
High snow winter
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General Conclusions

• There is no evidence for a positive effect of
  warmer summers on herbivores
• No positive effects for any species within years
• Lowest levels of damage in 2004 for all three
  hosts
• Sucking insects were particularly sensitive to
  warm temperatures
• There is evidence for positive effects of warmer
  winters on herbivores
• There is evidence that pathogens are favoured by
  conditions that are highly stressful for plants
  (particularly alder
• No evidence for positive relationships between
  damage levels and growth rates
• No evidence for local adaptation to herbivores or
  pathogens

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More conclusions

• 1. Alder reproduction may increase under higher
  pathogen damage mechanisms???
• 2. Cranberry may be directly negatively affected
  by summer-warm conditions.
• 3. None of the host species showed correlations
  between pathogen and herbivore damage at any
  spatial or temporal scale

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Acknowledgements

• Fieldwork Michelle Burrell, Elise Glenn, Sabine
  Güsewell, June Keay, Becky Mueller, Jenny
  Rohrs-Richey, Julie Stewart, Dan Uliassi
• Funding WESTGEC (DOE)
• Caffeine Alaska Coffee Roasting Co.