Ecosystem Ecology of Outbreak

My research focuses on community-to-landscape dynamics of disease and insect outbreak. I'm especially interested in understanding what drives these events, why they become destructive to ecosystems or economic resources, and the consequences to the way ecosystems work. You can follow my occasional posts on twitter: @forestpathogens

Current projects include:

Outbreak-caused changes in ecosystem function

Disease increases woody debris accumulation
Woody debris accumulation in Sudden oak death impacted stands

  • While research has lead to a better understanding of insect outbreak impacts to ecosystem processes such as carbon and nitrogen cycling, we have made less progress understanding the impacts of native and/or exotic pathogens on the same processes
  • This is important because:
    • Pathogen and insect introductions over the last century have resulted in destructive outbreaks and changes in species composition at landscape scales
    • Some studies suggest native pathogens have also become more prevalent and damaging, suggesting these organisms have become more important forces structuring ecosystems and their functions
    • To state the obvious: pathogens are not insects. Put another way, plant pathogens include nematodes, fungi, bacteria, and parasitic plants while insects are relatively large multicellular organisms which sense and respond to the environment in very different ways. Ecosystem ecology has been hampered by 'black boxing' all biological agents which affect functional processes. While this is probably reasonable for some insect and pathogen outbreaks, it is almost certainly unreasonable for others. 

Another example of woody debris accumulation in sudden oak death impacted forests. Accumulation of woody debris is a a fire and carbon sequestration challenge for forest managers.

Community changes following pathogen outbreak

Sudden oak death causes selective mortality within mixed species communities

  • Pathogens cause selective mortality; this can be seen for both host-specific pathogens (and insects) as well has generalist pathogens
  • However, this mortality is selective within as well as among species meaning that pathogens shape not just the composition of forest communities but also vertical structure, biomass, and tree-size distributions. 
  • Understanding community-level pathogen dynamics, and the factors which influence the emergence of disease (mortality and/or health decline) is fundamental to predicting disease impacts and developing management to reduce loss of values resources

Selective tree mortality (Quercus suber) in Phytophthora cinnimomi impacted forests in Southern Portugal. P. cinnamomi has had a major impact on cork production an important local forest resource in the Iberian peninsula. 

Disease management in a multiple objective framework 

Phytophthora ramorum management in Southern Humboldt county (Jay Smith State Park)

  • Basic understanding of disease drivers and the consequences (impacts of disease) provides the foundation to develop actions to address the deleterious impacts of these outbreaks
  • However, managers are almost always working with multiple goals. I work closely with federal, tribal, and private land managers to address disease in the context of these goals which include fuels reduction, biodiversity conservation, timber growth, carbon sequestration, and protection of specific cultural resources 
  • In pursuit of this goal, my work includes field and modeling study designed to assess the efficacy of treatments that reduce host density, alter host community structure, or aim to protect specific resources
  • Study systems include sudden oak death, Heterobasidion root disease, gold spotted oak borer, and polyphagous shot hole borer

Planning tanoak resistance studies with members of Yurok Tribal Forestry and Hoopa Tribal Forestry. Both forestry organizations have been proactive in assessing research needs and preemptive pathogen management.