Disease and Insect Effects on Ecosystem Processes in the context of Climate Change

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Disease and Insect Effects on Ecosystem
Processesin the context of Climate Change

• Christa Mulder
• UAF

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Conceptual Overview
Community composition
? competition or facilitation
Herbivores and Pathogens
Plant populations (mortality, growth rates)
Ecosystem Processes
Dominant or keystone
Climate Change
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OUTBREAK SPECIES
Community composition
Plant populations (mortality, growth rates)
Herbivores and Pathogens
Ecosystem Processes
Dominant or keystone
NON-OUTBREAK SPECIES
Community composition
? competition or facilitation
? abundance dominant or keystone
Plant populations (mortality, growth rates)
Herbivores and Pathogens
Ecosystem Processes
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Overview

• Outbreak species
• Alder (Alnus tenuifolia) and canker
• Spruce and spruce budworm
• Aspen and leafminer
• Non-outbreak species parasite communities on
• 1) Alder (Alnus viridis)
• 2) Cranberry (Vaccinium vitis-idaea)
• 3) Rose (Rosa acicularis)

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• Canker (Valsa melanodiscus) Survey on A.
  tenuifolia
• (Roger Ruess and colleagues)

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Effects of canker on whole-stand N inputs are
driven by declines in nodule biomass associated
with ramet mortality
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Also appears to be an effect of canker infection
on N fixation rate (at the nodule level)
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An inoculation experiment with Alnus viridis
(green alder) and Valsa melanodiscus Susceptibili
ty to infection and the physiological effects of
disease development (Jenny Rohrs-Richey)

• Investigate the susceptibility of green alders
  (Alnus viridis ssp. fruticosa, synonym A.
  crispa) to infection by Valsa melanodiscus
  under water stress.
• Monitor the response of the water transport
  system to infection and colonization.
• Determine if alders respond to disease by
  adjusting water use efficiency.
• Measure the effect of disease development on
  photosynthesis (light saturation pt., quantum
  efficiency).

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Greenhouse Experiment
June 1
Aug 23
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Two Weeks After Inoculation
Pycnidia
Necrotic lesion
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Water Availability
and Disease Incidence

Infected Alders
Well-watered plants are less likely to become
infected than water-limited plants (early in the
growth season)
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Non-infected plants fix more carbon than
infected plants but only if they are
well-watered.
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Stomatal Regulation of Photosynthesis
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(No Transcript)
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Spruce bud-worm on white spruce (Picea glauca)
Glenn Juday and colleagues
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Deg. C Threshold 8.0 GDD 243
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spruce budworm damage
heat/drought limitation
BARK
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(No Transcript)
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(No Transcript)
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Aspen leaf miner moth(Phyllocnistis
populiella)(Diane Wagner, Pat Doak, Linda
DeFoliart, Jenny Schneiderheinze)

• Univoltine
• Adults emerge in May before leaf-out, mate
• Lay eggs on both sides of new leaves
• Eggs digest cuticle, sink into leaf

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Aspen leaf miner moth (Phyllocnistis populiella)

• Larvae restricted to one side of leaf
• cannot switch sides
• cannot exit and reenter
• Consume epidermal cells as move during instars I
  III
• Separation of cuticle from mesophyll causes
  white appearance of mines

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Aspen leaf miner infestation of Alaskan forests
R. Werner, US Forest Service flyovers
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Aspen leaf miner infestation of Bonanza Creek
LTER
R. Werner, www.lter.uaf.edu and pers. comm.
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Bottom mining reduces photosynthesis
L. Defoliart, Wagner et al. in review
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Bottom mining reduces photosynthesis
a
a
b
J. Schneiderheinze, Wagner et al. in review
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Bottom mining disrupts stomatal function
Wagner, Defoliart, Doak, Schneiderheinze in review
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Top mining affects water balance
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Leaf mining leads to early leaf abscission
Data L. Defoliart
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Mining reduces aspen growth
Wagner, Defoliart, Doak, Schneiderheinze in
review.
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Summary

• Outbreak pathogen (canker) on a keystone shrub
  species (alder)
• reduces fixation rates of nodules on infected
  trees
• reduces carbon fixation rates via reduced
  stomatal conductance
• climate change reduced water availability may
  increase susceptibility to this disease
• Outbreak herbivore on a dominant tree white
  spruce greatly reduces growth (C fixation)
• Combined with increased temperature could result
  in massive die-offs
• Outbreak herbivore reduces photosynthetic rates
  (C fixation) and stomatal conductance in a
  dominant tree species (trembling aspen)

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Non-outbreak species on leaves(Christa Mulder
Bitty Roy)
Alnus viridis (alder) 13 herbivores 9 pathogens
Rosa acicularis (rose) 11 herbivores 13
pathogens
Vaccinium vitis-idaea (cranberry) 5 herbivores 7
pathogens
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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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Total damage patterns 2002-2006

• Fairly constant total biological damage
• Relative contribution of herbivores vs.
• pathogens varies

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Herbivory patterns by feeding mode

• Fairly low damage in record hot year for all
• three species
• Lowest sucking damage in record hot year
• for all three species
• Highly variable relative contributions by
• different guilds

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Impacts of herbivores and pathogens on
reproduction in alder
Herbivore damage is negatively related to catkin
production Pathogen damage is positively related
to catkin production
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Woolly alder sawfly, Eriocampa ovata
Ruess, R. W., M. D. Anderson, J. S. Mitchell, and
J. W. McFarland. 2006. Effects of defoliation on
growth and N2-fixation in Alnus tenuifolia
Consequences for changing disturbance regimes at
high latitudes. Ecoscience 13402-412.
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Mortality in cranberry

• Cranberry ramet mortality rates are high (15-75
  over the course of 4-5 years, or 3-15 per year)
• Winter-warm sites had higher rates of mortality
  and high rates of red-brown dieback
• Cause and effect are unclear
• Could be physical damage
• Could be a disease attacking already dying leaves
• Could be caused by a disease

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Climate change and herbivores / pathogens Alder

• Warmer, drier summer conditions may favour
  pathogens
• Higher pathogen levels in warmer years, and at
  warmer sites in 2004 (record hot dry year)
• BUT sucking insects were lower at warm sites or
  in warm years
• Cold winters may favour herbivoreshigher damage
  following winters with higher minimum
  temperatures

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Climate change and herbivores / pathogens
cranberry and rose

• Cranberry
• Sucking and mining damage were greater at sites
  with warmer winter temperatures (in 2004) and in
  warmer years
• Rose
• Between years, total herbivore damage and sucking
  damage were lower when summer temperatures were
  higher

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Summary

• TOTAL damage levels are fairly constant across
  years for all three species
• COMPOSITION of the parasite communities varies
  greatly between years
• Relationships with environmental characteristics
  depend on the feeding mode
• For alder, these damage levels may be high enough
  to substantially reduce N fixation rates
• Cranberry ramet mortality rates are high but
  cause is unclear.

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OUTBREAK SPECIES
Community composition
?
?
Plant populations (mortality, growth rates)
Herbivores and Pathogens
Ecosystem Processes
Dominant or keystone
N fixation, C fixation, transpiration
NON-OUTBREAK SPECIES
Community composition
? competition or facilitation
? abundance dominant or keystone
Plant populations (mortality, growth rates)
Herbivores and Pathogens
Ecosystem Processes
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Gaps

• Are the outbreak species fundamentally different
  from non-outbreak species, or can many of the
  numerous non-outbreak species become outbreak
  species with major impacts?
• Loss of dominant species will change species
  composition how will that affect ecosystem
  processes?
• Non-outbreak species
• How does low-level (lt20) damage affect
  photosynthesis, water balance, N fixation?
• how do they affect community dynamics
  (composition)? How in turn does this affect
  ecosystem processes?

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Links to thresholds and regime changes

• Spruce bud-worm may reduce the temperatures at
  which massive tree die-offs occur
• Alder and canker could hot, dry conditions
  (have) increase(d) susceptibility to the point
  where outbreaks are possible?
• Could warm winters increase overwintering
  survival of herbivore species on alder to the
  point where they become outbreak species?

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Links to Invasive Plants

• Future research (Mulder lab) how do biotic
  factors, including herbivores and pathogens,
  accelerate or retard the advance of invasives in
  burned habitat?
• Potential for acceleration
• Enemy release from soil pathogens
• Introduction of new plant pathogens to natives
• Potential for deceleration
• Herbivory
• Pathogens on invasives