Research
Header Image: Looking East from Friday Harbor Laboratories, San Juan Island, Washington
I use integrative and comparative approaches to elucidate the importance of leaves for plant evolutionary ecology. The main questions of my research focus on establishing links between different processes across species: 1) How and why does the conservation of developmental programs constrain the evolution of leaf structure and function? 2) How does variation in developmental processes determine variation in leaf structure? 3) How does variation in leaf structure determine variation in leaf function? 4) How does resulting variation in structure and function drive differences in plant growth and adaptive diversification? and 5) ​How does variation in adaptive capacity, as driven by structure-function mechanisms, drive ecological and biogeographical patterns?​ Much of this work focuses on the fundamental role of leaf hydraulic anatomy and physiology on drought tolerance or avoidance.

​See below for more some answers to these questions, and for some other related questions!
How does developmental-based plasticity mediate species adaptation to environmental stress?

Leaf development is remarkably plastic. Such plasticity contributes to whole plant acclimation via physiological changes that scale to influence whole plant performance. The coordination in morphological, anatomical, and functional changes associated with this plasticity can reveal insight into 1) how anatomical traits change by development, 2) dynamics of variability in carbon allocation, and 3) how traits constrain physiological function. Addressing these links is important for understanding how traits influence species responses to climate change stressors by exerting physiological constraints on species distributions. 
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Within species, I am interested in investigating the developmental (see below), compositional, and structural changes that occur when leaves develop as a result of a given environmental stress (e.g. drought). Specifically, I focus on determining the mechanistic links between development -> structure and composition -> physiological function.

Selected publications:
  • Baird AS, Anderegg LDL, Lacey ME, HilleRisLambers J , Van Volkenburgh, E. (2017) Comparative leaf growth strategies in response to low-water versus low-light availability: variation in leaf physiology underlies variation in leaf mass per area (LMA) in Populus tremuloides. Tree Physiology​
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Synthetic model for grass leaf ontogeny that predicts developmentally based scaling of vein traits with final leaf size across species.
Diversity in leaf trichome structure and density, from species distributed across California
How does variation in developmental processes determine leaf structure, allometry and function across species?

Developmental processes link organismal genotype and phenotype. While most developmental processes distinguish species form and function, some developmental programs are highly conserved across species. The conservation of such processes can result in further constraints on evolutionary trait diversification, whereby changes in the specific trait value occur (i.e. size/ dimensions) but not compositional changes in the trait. This leads to predictable relationships among the sizes of organs and certain traits, i.e. developmental scaling. Development-based scaling can be extremely powerful because this framework can more clearly elucidate how traits are mechanistically coordinated and how variability during development determines the resulting traits that lead to and/or constrain adaptation.

I am interested in 1) identifying and characterizing developmental algorithms that may influence allometric trait scaling 2) determining patterns in allometric scaling of traits, and whether or not such linkages arise from developmental constraints and 3) investigating the role of trait linkages for climate adaptation.

Selected publications:
  • Baird AS, Taylor SH, Pasquet-Kok J, Vuong C, Zhang Y, Watcharamongkol T, Scoffoni C, Edwards EJ, Christin P-A, Osborne C, Sack L. (2021) Developmental and biophysical determinants of grass leaf size worldwide. Nature ​
  • Baird AS, Reddi S, Pasquet-Kok J, Vuong C, Zhang Y, Watcharamongkol T, John GP, Scoffoni C, Osborne C, Sack L. (2021) Allometry of cells and tissues across C3 and C4 grasses. Submitted
  • Baird AS, Medeiros CD, Buckley T, Sack L. Developmental basis of leaf trichome density. In Preparation
How does diverse leaf anatomy influence species hydraulic function and what are the evolutionary, ecological, and functional consequences of this linkage?

Diversity in the hydraulic transport system of leaves is a major determinant of organismal productivity and species adaptation. Stomatal opening for gas exchange results in major transpirational water loss, and if not continually replaced by an efficient hydraulic system would result in desiccation of cells and loss of function. The diversity in this efficiency (Kleaf) arises from both structural and compositional changes in leaf anatomy that influence the conductance pathways for water flow to the sites of evaporation. Both inside- (Kx) and outside-xylem (Kox) pathways influence Kleaf because both inside- and outside-xylem pathways can contribute a substantial portion of resistance to water flow. Greater variability in a trait that influences one or the other (Kx or Kox) and has significant impact on Kleaf will thus reduce the impact of the other pathways on Kleaf. Yet, our understanding of the specific structural and compositional properties of leaves that determine Kx or Kox, and their relative impacts on Kleaf is unclear. I aim to determine how diversity in leaf properties determine Kx or Kox and their resulting impacts on Kleaf at varying taxonomic scales (across families -> within families -> within genera) and in relation to adaptation to climate, while incorporating a comparative phylogenetic framework.
​Current projects:
Major: Large, and Minor: Small and intermediate vascular bundles in the grass blade of C4 species Cenchrus setaceus




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Grasses are incredibly important for ecosystem function, agricultural production and much more. Shown here: lawn grass (top left), corn grown for feed (top right), grass sp. occurring in both open areas and understoreys (bottom left) and grass sp. co-existing with other species (bottom right)
How does diverse leaf surface anatomy influence leaf surface physiology? What is the role of development in driving or constraining such variation?

Across species, leaf surfaces display remarkable diversity in anatomical characteristics, including differences in cell size, number, trichome diversity, and also in morphological size (i.e. whole leaf area). Some of my work aims to elucidate how such variation scales to mechanistically influence leaf fluxes. I also aim to provide a developmental insight into how this vast variation arises.

Selected publications:
  • Baird AS, Taylor SH, Pasquet-Kok J, Vuong C, Zhang Y, Watcharamongkol T, Scoffoni C, Edwards EJ, Christin P-A, Osborne C, Sack L. (2021) Developmental and biophysical determinants of grass leaf size worldwide. Nature 
  • Henry C, Buckley T, Browne M, Ochoa M, Baird AS, Brodersen C, Sack L. Foliar water uptake: relationship to leaf structure in native California species. In Preparation
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How do abiotic, biotic and phylogenetic factors determine leaf size across species?
How does diverse venation architecture evolve and what are the ecological consequences of this diversity?

The venation architecture of angiosperms is remarkably diverse, ranging from the parallel venation of most monocotyledons to the hierarchical venation network of eudicotyledons. Indeed, such groups of plants are quite evolutionarily distinct, and differences in their venation architecture may be expected.

​Current projects
  • I am interested in using species of the Orchidaceae as a model lineage for understanding the evolution of diverse venation architecture and the resulting influence on species ecologies. Species from this lineage have venation architecture ranging from leaves with highly parallel veins and an elongated lamina to leaves with reticulate veins and also an elongated lamina (and sometimes not highly elongated).
Research assistants (past and present)​
  • Julia Bowers (UCLA, 2022-present), project: "Associations of leaf trichome and stomatal traits"
  • John Liang (UCLA, 2022-present), project: "Climatic drivers of leaf trichome traits across California plant communities"
  • Michelle Hii (UCLA, 2022-present), project: "Is trichome density decoupled from leaf size?"
  • Josh Matsuda (UCLA, 2022-present)
  • Kirthana Pisipati (UCLA, 2022-present), project: "Climatic drivers of leaf trichome traits across California plant species"
  • ​Benjamin Simon (UCLA, 2022-present), project: "Scaling of leaf trichome density and size with irradiance"​
  • Caroline Pohl (UCLA, 2022)
  • Silva Tagaryen (UCLA, 2022)
  • Sachin Reddi (UCLA, 2019-2021), projects: "Allometries underlying grass leaf size" & "Modeling the energy balance of angiosperm leaves"
  • Jason Zhao (UCLA, 2018-2019), project: "Hydraulic and photosynthetic coordination in Tomato"
  • Thomas Condon (UCLA, 2018-2019)


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Collaborations (past and present)

I welcome collaborations with scientists across fields. Please reach out if you would want to work together to tackle fundamental questions in plant science!

Current collaborators: