Understanding and predicting the consequences of climate change on ecosystems is emerging as one of the greatest scientific challenges of our time, and examining how trees and forests respond to environmental change is of particular importance due to the central role they play in supporting biodiversity, regulating global carbon, water, and nutrient cycles, and providing a multitude of vital ecosystem and social services.
Climate-related impacts have already been observed in diverse forests around the world, and are expected to become more widespread and intense in the coming decades. Projected future climate changes, including higher temperatures and atmospheric carbon dioxide, altered precipitation patterns, greater frequency of extreme events such as heat waves and drought, and shifts in growing seasons, will have profound physical and biological effects on trees and associated forest ecosystems globally.
The overarching goal of my research is to advance our knowledge of the physiological mechanisms controlling tree performance and forest ecosystem responses to climate change. I study how uptake, transport and usage of water and carbon by trees are coordinated, and how they are affected by tree structural properties and by variability in soil and atmospheric conditions. Some questions I seek to help answer include:
- How does physiological performance vary within and among trees of different size and age?
- What functional traits determine the sensitivity of different tree species to climate changes and how do these traits influence tree distributions?
- How do tree physiological processes scale from leaf to landscape scales?
- What are the ecosystem consequences of climate impacts and how can management actions mitigate these impacts and improve tree and forest health?
My research in collaboration with other scientists combines diverse methods and tools from the fields of plant physiology, forest ecosystem ecology, stable isotope biogeochemistry, dendrochronology, remote sensing, and micrometeorology. I also utilize advanced rope-based climbing techniques in order to directly study tree and forest canopy structure, function, and biological diversity.
Here are some of my current projects:
Giant sequoia (Sequoiadendron giganteum) is one of the most iconic species on Earth. However, the sequoias' continued health may be threatened by climate change, particularly severe drought. Since 2015 I have been working with an interdisciplinary team from UC Berkeley, National Park Service, US Geological Survey, and Carnegie Airborne Observatory to understand the physiological mechanisms and spatial patterns of giant sequoia tree and forest drought response from leaf to landscape scales.
Tree water use dynamics
All plants need an adequate supply of water to sustain their metabolism, growth and survival, and plant water and carbon relations are fundamentally linked. I have been involved in several projects examining tree water use dynamics to gain a better understanding of these linkages, and am currently working with researchers from UC and Northern Arizona University to quantify environmental controls on water status and water use of several conifer and angiosperm trees in California and Arizona.
Increasingly hotter droughts and severe wildfires associated with climate change has led to widespread tree mortality resulting in significant impacts on forest ecosystem biodiversity and function throughout California and western US. I am currently working with an interdisciplinary team from the California Academy of Sciences and the US Forest Service's Pacific Southwest Research Station on a project aimed at improving our ability to increase the resilience of western forests to these impacts using prescribed fire.
The rainforests of southeast Asia are one of the most globally significant biological hotspots, yet are continually threatened by deforestation and developmental pressures and now face new risks from global climate change. In 2016 I joined an international team of researchers and conservationists from the California Academy of Sciences and other institutions to document the biodiversity of an ancient Dipterocarp rainforest on Penang Hill, Malaysia in support of its' proposed designation as a UNESCO Biosphere Reserve.
Limits on the capacity of trees to transport water from roots to treetop leaves strongly constrains tree physiological performance and ultimately maximum height. I have been involved in several projects examining how biophysical factors control the physiology and growth of coast redwood (Sequoia sempervirens) and giant sequoia (Sequoiadendron giganteum) trees. I continue to be interested in examining how height - both within and among trees - influences physiological performance and climate response.