Research

A grand challenge for humanity is predicting how climate change will alter the functioning of the biosphere and the services it provides. Current predictive models suffer from two main limitations. First, most models assume that plant physiology is driven by ambient macroclimate, but this is almost never accurate. Instead, plant traits operate via energy budgets to decouple macroclimate from the microclimates at which physiological processes occur. For example, plant leaves and forest canopies buffer variation in ambient temperature, which promotes maintenance of plant temperatures near metabolic optima and provides thermal refugia in variable climates. Second, most models are based on tissue, organ, or organismal physiology, so their predictions do not easily map to higher levels of organization (such as communities and ecosystems) that experience spatial variation in microclimate and physiological traits. For example, while climate has a well-established influence on rates of leaf-level carbon assimilation, it has a much weaker influence on rates of ecosystem-level carbon assimilation.

Predicting how spatially and biologically complex natural communities will respond to climate change requires a mechanistic mathematical framework for scaling plant-environment interactions across levels of organization, linking small scale climate and physiology with large scale ecosystem dynamics. We are synthetizing approaches from meteorology and scaling to develop novel integrative theory for predicting plant microclimates from macroclimate and forest structure. Microclimatic variation then drives variation in plant physiological rates, which “scale up” to control higher level processes such as primary productivity and evapotranspiration.

The Forest MacroSystems (FMS) network is a set of long-term forest monitoring plots that provide data for analyzing and understanding drivers of global variation in forest diversity, demographics, and dynamics. It was established in 2011 in collaboration with the Enquist Macroecology Lab and several others. The FMS network currently comprises nine sites arrayed across a latitudinal climate gradient, from tropical seasonal forest in Panama (9° N) to temperate rainforest in British Columbia (50° N). The network is expanding; please contact Sean Michaletz if you are interested in installing a site!

We are currently working on several projects based on FMS network data. One project synthesizes radiative transfer theory and metabolic scaling theory to quantitatively predict energy non-equivalence in forest communities, and test this using FMS data. Another project is examining the influences of plant size, plant functional traits, and climate on global variation in forest mortality rates.

We have helped develop, organize, deliver and teach a series of international Plant Functional Traits Courses (PFTC) since the very beginning. The PFTC unite scientists of all career stages from around the world to collect, analyze, and publish functional ecology data. We have held five courses since 2015, in China, Peru, and Svalbard. The next two courses will be held in Norway and South Africa.

During the PFTCs, our lab has focused on the role of leaf traits and temperature in leaf metabolism. Specifically, we have collected data on leaf energy balance traits and photosynthesis temperature response from diverse taxa spanning large elevational climate gradients at each site. These data characterize the kinetics of leaf metabolism, and are being used to understand how climate effects on leaf metabolism “scale up” to control higher level processes such as plant growth and ecosystem production.

A central challenge facing science is understanding how the environment influences plant physiology across scales. While it’s been known for more than a century that physiological rates are influenced by temperature, predicting emergent outcomes at higher levels of organization is more complex. Indeed, understanding how climate influences metabolism and how this ‘scales up’ to higher levels is a realm of intense research.

Temperature influences plant growth via kinetic effects on metabolism and has been proposed to obey a general Arrhenius relationship. However, this is complicated by adaptive responses of biochemistry that compensate for climate variation. Further, local adaptation of plant traits acts via energy budgets, ensuring that plant microclimates remain relatively close to photosynthetic optima. While we have known that plant microclimates are decoupled from macroclimate, recent work by us and others has documented a general homeostasis of plant microclimates.

It is often thought that a wildfire will consume and kill all of the vegetation within its perimeter, but this is more an exception than a rule. Indeed, heterogeneity of fuels and microclimate leads to heterogeneity of fire behavior and effects, so that injured but surviving plants often remain after a wildfire. This has important emergent outcomes spanning levels of biological organization, from cellular photosynthesis and respiration to ecosystem production and evapotranspiration. However, despite more than half a century of research, the mechanisms by which fire injuries occur and interact are not well understood.

For more than two decades, we have been studying the effects of wildfires on plants. Our work focuses on the physical mechanisms linking wildfire behavior to plant physiology, and how fire effects “scale up” across levels of biological organization, from cells to ecosystems. We use a variety of approaches, including field and laboratory experiments, mathematical modelling, and highly parallelized High Performance Computing simulations.