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

Conceptual Overview Herbivores and Pathogens Plant populations (mortality, growth rates) Community composition Ecosystem Processes Climate Change Dominant or keystone Δ competition or facilitation

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

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

2005 Canker ( Valsa melanodiscus) Survey on A. tenuifolia (Roger Ruess and colleagues)

Effects of canker on whole-stand N inputs are driven by declines in nodule biomass associated with ramet mortality

Also appears to be an effect of canker infection on N fixation rate (at the nodule level)

1)Investigate the susceptibility of green alders (Alnus viridis ssp. fruticosa, synonym =A. crispa) to infection by Valsa melanodiscus under water stress. 2) Monitor the response of the water transport system to infection and colonization. 3) Determine if alders respond to disease by adjusting water use efficiency. 4)Measure the effect of disease development on photosynthesis (light saturation pt., quantum efficiency). An inoculation experiment with Alnus viridis (green alder) and Valsa melanodiscus: Susceptibility to infection and the physiological effects of disease development (Jenny Rohrs-Richey)

Greenhouse Experiment June 1 Aug 23

Two Weeks After Inoculation PycnidiaNecrotic lesion

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)

Non-infected plants fix more carbon than infected plants… but only if they are well-watered.

Stomatal Regulation of Photosynthesis

Spruce bud-worm on white spruce (Picea glauca) Glenn Juday and colleagues

?1975? Deg. C Threshold = 8.0 GDD = 243

BARK spruce budworm damage heat/droughtlimitation

1912 volcanic ash? 1993 & 95 spruce budworm defoliation KILL ZONE 2004 record hot

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

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

Aspen leaf miner infestation of Alaskan forests R. Werner, US Forest Service flyovers

Aspen leaf miner infestation of Bonanza Creek LTER R. Werner, and pers. comm.

Bottom mining reduces photosynthesis L. Defoliart, Wagner et al. in review

Bottom mining reduces photosynthesis J. Schneiderheinze, Wagner et al. in review a a b

Bottom mining disrupts stomatal function Wagner, Defoliart, Doak, Schneiderheinze in review

Top mining affects water balance

Leaf mining leads to early leaf abscission Data: L. Defoliart

Mining reduces aspen growth Wagner, Defoliart, Doak, Schneiderheinze in review.

Summary 1)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 2)Outbreak herbivore on a dominant tree white spruce greatly reduces growth (C fixation) Combined with increased temperature could result in massive die-offs 3)Outbreak herbivore reduces photosynthetic rates (C fixation) and stomatal conductance in a dominant tree species (trembling aspen)

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

Summer temperature and precipitation,

Winter temperature and snow depths,

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

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

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

Woolly alder sawfly, Eriocampa ovata Ruess, R. W., M. D. Anderson, J. S. Mitchell, and J. W. McFarland Effects of defoliation on growth and N2-fixation in Alnus tenuifolia: Consequences for changing disturbance regimes at high latitudes. Ecoscience 13:

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

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 herbivores:higher damage following winters with higher minimum temperatures

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

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.

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

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 (<20%) damage affect photosynthesis, water balance, N fixation? –how do they affect community dynamics (composition)? How in turn does this affect ecosystem processes?

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?

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