Research area

Plant–microbe interactions

How fungi shape the future of forests

We study how beneficial and harmful fungi influence tree survival, forest diversity and resilience as environments become hotter, drier and less fertile.

Collaborative research: This work is conducted in collaboration with Joe LaManna at Marquette University and Posy Busby at Oregon State University with support from the National Science Foundation.

The H.J. Andrews Experimental Forest provides a natural laboratory for studying how trees and fungal communities respond to environmental stress.

Central question

When do fungi help trees—and when do they hold them back?

Fungi can act as mutualists that help trees acquire water and nutrients, or as pathogens that reduce survival. We ask how drought and nutrient stress change the balance between these opposing effects.

Plant–fungal interactions across stress gradients

Conceptual diagram showing how competitive, facilitative, and host-specific plant–microbe interactions change with abiotic stress — **Figure 1.** The Stress Gradient Hypothesis and its extension to host-specific antagonistic and facilitative plant–microbe interactions. Doolittle et al. (2026), *Ecology*. View publication →

Graphs relating climate to fungal diversity, relative abundance, and host specificity across three fungal guilds — **Figure 4.** Climate relationships with fungal diversity, relative abundance and host specificity across soil pathogens, ectomycorrhizal fungi and foliar pathogens. Neat et al. (2026), *Ecology*. View publication →

Stress changes the relationship

In favorable conditions

Competition and host-specific pathogens may create negative feedback, preventing common tree species from dominating and helping maintain diversity.

Under greater stress

Mycorrhizal fungi and leaf endophytes may become more important allies, helping trees withstand drought and nutrient limitation and shifting feedback in a positive direction.

Environmental gradients across the H.J. Andrews landscape help us connect seedling responses to long-term forest change.

From seedlings to forest futures

At the H.J. Andrews Experimental Forest, field observations, reciprocal transplants and greenhouse experiments reveal how trees and fungal communities respond to moisture and nutrient gradients. Long-term forest data then help us ask how these interactions may alter tree abundance and diversity across the Pacific Northwest.

Why it matters

Understanding when microbes affect tree growth and survival can improve forecasts of forest change and inform restoration and reforestation as climate stress intensifies.

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