About

Lawren Sack is a professor in the Department of Ecology and Evolutionary Biology at UCLA. His research broadly focuses on the mechanisms underlying the function and co-existence of plant species, including responses to resources, tolerance of environmental challenges, and competition. His work explores the evolution and functional consequences of diversity in plant traits, examining processes across scales from molecules to ecosystems. Current research areas include the hydraulics of leaves and whole plants, the evolution and diversity of leaf designs, plant responses to resource supply combinations, scaling laws of plant design during evolution and ontogeny, and ecohydrology of native versus invasive forests.

Research topics

• Biology
• Computer Science
• Ecology
• Geography
• Environmental science
• Botany
• Artificial Intelligence
• Neuroscience
• Geology
• Atmospheric sciences
• Genetics
• Database
• Environmental resource management
• Meteorology
• Agronomy

Selected publications

• Cell wall pectin reshapes leaf drought tolerance in dry forests

  Nature Communications · 2026-01-07 · 1 citations

  articleOpen access

  Cellular and leaf structural traits influence the regulation of leaf water balance, which in turn impacts leaf gas exchange, plant productivity and drought tolerance. Yet, the role of cell wall composition, and especially that of components that render cell walls flexible—such as pectin—in leaf water relations remains elusive. Here, we investigate the linkages among 26 traits, including cell wall composition, anatomy, and drought tolerance (described by pressure-volume curves) across 69 woody species from sub-tropical dry and wet forests. We find that the lower wilting point of species of dry forests relative to wet forests is associated with contrasting anatomy and wall composition. Pressure-volume traits correlate more strongly with wall composition, and particularly pectin concentration, in dry forests, and with anatomy in wet forests. Thus, pectin-enriched cell walls contribute to the ecological specialization of woody plants in dry versus wet forests. Our findings indicate that leaf hydraulic designs diverge according to two strategies: dry forest species vary in elastic and osmotic function via contrasting pectin concentration (“flexible cell wall” strategy), whereas wet forest species do so via contrasting palisade tissue investment (“stable leaf tissue” strategy). Overall, diversity in cell wall properties across species are strongly linked with drought tolerance. This research integrates leaf physiology, anatomy, and cell wall composition to understand species habitat specialization. The findings suggest that wet forest species vary in hydraulic function via contrasting palisade tissue investment, whereas dry forest species do so via contrasting pectin concentration.

  PublisherOA PDFDOI

• Priorities of woody species trait-climate associations at continental scale

  Research Square · 2026-04-20

  preprintOpen accessSenior author
  PublisherOA PDFDOI

• Plant elemental diversity increases ecosystem productivity and temporal stability

  Ecological Monographs · 2026-02-01

  article

  Abstract The elemental composition of organisms (i.e., the elementome) directly constrains metabolic machinery and aligns with functional traits, linking organismal performance to nutrient cycling and energy flow at the ecosystem level. In theory, elemental diversity captures the community functional heterogeneity by quantifying variation in the multidimensional elementomes of co‐occurring species within a community. However, empirical evidence connecting organismal elemental diversity to ecosystem functioning and identifying its environmental controls remains scarce. We compiled an unprecedented dataset on plant elemental concentrations, encompassing more than 2500 species and 14 analyzed elements (including macronutrients, micronutrients, and trace elements) sampled from leaves, stems, trunks, and fine roots across 8 biomes and 72 sites, covering multiple ecosystem types including forests and grasslands. Using these data, we investigated the spatial patterns and drivers of plant elemental diversity and evaluated its relationship with ecosystem productivity and stability. Our results indicate that plant elemental diversity decreased with latitude, with interannual variability in temperature and mean annual precipitation as the primary controls on its spatial distribution. Moreover, ecosystems with higher plant elemental diversity exhibit greater efficiency in the use of carbon, water, and light, thereby translating into higher productivity and greater temporal stability across and within forests and grasslands, and these effects persisted even after accounting for climate and soil factors. Taken together, our results support the influence of plant elemental diversity as a distinct dimension of biodiversity with functional implications. Complementing trait‐ and taxonomy‐based measures, plant elemental diversity improves predictions of ecosystem productivity and temporal stability under ongoing climatic variability, and can substantially advance research on biodiversity and ecosystem functioning.

  PublisherDOI

• Plant elemental diversity increases ecosystem productivity and temporal stability

  Open MIND · 2026-01-16

  dataset

  The elemental composition of organisms (i.e., the elementome) directly constrains metabolic machinery and aligns with functional traits, linking organismal performance to nutrient cycling and energy flow at the ecosystem level. In theory, elemental diversity captures the community functional heterogeneity by quantifying variation in the multidimensional elementomes of co-occurring species within a community. However, empirical evidence connecting organismal elemental diversity to ecosystem functioning and identifying its environmental controls remains scarce. We compiled an unprecedented dataset on plant elemental concentrations, encompassing more than 2,500 species and 14 analyzed elements (including macronutrients, micronutrients, and trace elements) sampled from leaves, stems, trunks, and fine roots across eight biomes and 72 sites, covering multiple ecosystem types including forests and grasslands. Using these data, we investigated the spatial patterns and drivers of plant elemental diversity and evaluated its relationship with ecosystem productivity and stability. Our results indicate that plant elemental diversity decreased with latitude, with interannual variability in temperature and mean annual precipitation as the primary controls on its spatial distribution. Moreover, ecosystems with higher plant elemental diversity exhibit greater efficiency in the use of carbon, water, and light, thereby translating into higher productivity and greater temporal stability across and within forests and grasslands, and these effects persisted even after accounting for climate and soil factors. Taken together, our results support the influence of plant elemental diversity as a distinct dimension of biodiversity with functional implications. Complementing trait- and taxonomy-based measures, plant elemental diversity improves predictions of ecosystem productivity and temporal stability under ongoing climatic variability, and can substantially advance research on biodiversity and ecosystem functioning.

  DOI

• Cell wall pectin reshapes leaf drought tolerance in dry forests.

  Open Access CRIS of the University of Bern · 2026-01-07

  articleOpen access

  Cellular and leaf structural traits influence the regulation of leaf water balance, which in turn impacts leaf gas exchange, plant productivity and drought tolerance. Yet, the role of cell wall composition, and especially that of components that render cell walls flexible-such as pectin-in leaf water relations remains elusive. Here, we investigate the linkages among 26 traits, including cell wall composition, anatomy, and drought tolerance (described by pressure-volume curves) across 69 woody species from sub-tropical dry and wet forests. We find that the lower wilting point of species of dry forests relative to wet forests is associated with contrasting anatomy and wall composition. Pressure-volume traits correlate more strongly with wall composition, and particularly pectin concentration, in dry forests, and with anatomy in wet forests. Thus, pectin-enriched cell walls contribute to the ecological specialization of woody plants in dry versus wet forests. Our findings indicate that leaf hydraulic designs diverge according to two strategies: dry forest species vary in elastic and osmotic function via contrasting pectin concentration ("flexible cell wall" strategy), whereas wet forest species do so via contrasting palisade tissue investment ("stable leaf tissue" strategy). Overall, diversity in cell wall properties across species are strongly linked with drought tolerance.

  PublisherDOI

• Root quantity traits: a leading dimension in root trait space

  New Phytologist · 2026-03-11 · 1 citations

  article

  Plant resource uptake depends on the interplay between the quantity and quality of roots, yet their coordination at the community level remains poorly understood. Using standardized root cores across 20 diverse grassland sites on the Inner Mongolian Plateau and the Tibetan Plateau, we quantified community-level root quantity traits (mass, length, and nitrogen density per soil volume) and quality traits (specific root length (SRL), nitrogen concentration, and root tissue density (RTD)). The two regions differ markedly in soil, climate, and species composition. Community-level root traits clustered into three orthogonal dimensions. The root quantity dimension, reflecting carbon investment in roots for soil exploration, was correlated with soil nitrate concentration. Two root quality dimensions captured contrasting strategies: a foraging-efficiency dimension represented by a negative correlation between RTD and SRL, and an uptake-efficiency dimension related to root nitrogen concentration. Different from the quantity dimension, the efficiency dimensions were regulated by distinct environmental factors within each region, highlighting the context-dependency of root trait-environment interactions. Collectively, our findings show that community-level root strategies can be captured by a tri-dimensional root quantity-quality trait matrix, which represents a novel understanding of the community-level plant assemblies and their responses and adaptation to climate change.

  PublisherDOI

• Environmental influences and coordination of Rhododendron carbon and water economics at leaf and species scales

  Functional Plant Biology · 2026-03-29

  article

  The ratio of leaf surface area to dry mass, specific leaf area (SLA), relates function to carbon investment, but how the environment impacts SLA and whether SLA represents whole-plant resource acquisition remains debated. We tested two hypotheses using 12 Rhododendron species from four taxonomic sections with different leaf habits: (1) for leaves, we hypothesized that species, leaf position and light interception impact SLA, but higher SLA would be accompanied by higher net photosynthesis (A), stomatal conductance (gs), and maximum leaf hydraulic conductance (Kleaf), maintaining A/gs and Kleaf/gs across the canopy, and (2) for species, we hypothesized those from stressful climates would have lower SLA, higher Kleaf, higher stomatal density, and smaller stomata. At the leaf-scale, Kleaf was higher for species with lower SLA, contrary to predictions. We observed strong coordination of SLA and carbon to nitrogen ratio, but the relationship of Kleaf/gs to SLA was characterized by species replacement along the leaf economic spectrum, suggesting weak leaf-level trait coordination as a mechanism for low drought tolerance. Across species, lower SLA was associated with lower summer precipitation, lower precipitation seasonality, and larger guard cells. We show that leaf habit and habitat associations shape the functional significance of SLA, determining resource acquisition at leaf and species scales.

  PublisherDOI

• Resolving the contrasting leaf hydraulic adaptation of <scp>C₃</scp> and <scp>C₄</scp> grasses

  New Phytologist · 2025-01-05 · 8 citations

  articleOpen accessSenior author

  Summary Grasses are exceptionally productive, yet their hydraulic adaptation is paradoxical. Among C 3 grasses, a high photosynthetic rate ( A area ) may depend on higher vein density ( D v ) and hydraulic conductance ( K leaf ). However, the higher D v of C 4 grasses suggests a hydraulic surplus, given their reduced need for high K leaf resulting from lower stomatal conductance ( g s ). Combining hydraulic and photosynthetic physiological data for diverse common garden C 3 and C 4 species with data for 332 species from the published literature, and mechanistic modeling, we validated a framework for linkages of photosynthesis with hydraulic transport, anatomy, and adaptation to aridity. C 3 and C 4 grasses had similar K leaf in our common garden, but C 4 grasses had higher K leaf than C 3 species in our meta‐analysis. Variation in K leaf depended on outside‐xylem pathways. C 4 grasses have high K leaf : g s , which modeling shows is essential to achieve their photosynthetic advantage. Across C 3 grasses, higher A area was associated with higher K leaf , and adaptation to aridity, whereas for C 4 species, adaptation to aridity was associated with higher K leaf : g s . These associations are consistent with adaptation for stress avoidance. Hydraulic traits are a critical element of evolutionary and ecological success in C 3 and C 4 grasses and are crucial avenues for crop design and ecological forecasting.

  PublisherOA PDFDOI

• Bounds on stomatal size can explain scaling with stomatal density in forest plants

  New Phytologist · 2025-10-06 · 1 citations

  article

  Summary A prevailing hypothesis posits that achieving higher maximum rates of leaf carbon gain and water loss is constrained by geometry and/or selection to limit the allocation of epidermal area to stomata ( f S ). Under this ‘stomatal‐area minimization hypothesis’, higher g s,max is associated with greater numbers of smaller stomata because this trait combination increases g s,max with minimal increase in f S , leading to relative conservation of f S semi‐independent of g s,max due to coordination in stomatal size, density, and pore depth. An alternative hypothesis is that the evolution of higher g s,max can be enabled by a greater epidermal area allocated to stomata, leading to positive covariation between f S and g s,max ; we call this the ‘stomatal‐area adaptation hypothesis’. Under this hypothesis, the interspecific scaling between g s,max , stomatal density, and stomatal size is a by‐product of selection on a moving optimal g s,max . We integrated biophysical and evolutionary quantitative genetic modeling with phylogenetic comparative analyses of a global data set of stomatal density and size from 2408 vascular forest species. The models present specific assumptions of both hypotheses and deduce predictions that can be evaluated with our empirical analyses of forest plants. There are three main results. First, neither the stomatal‐area minimization nor adaptation hypothesis is sufficient to be supported. Second, estimates of interspecific scaling from common regression methods cannot reliably distinguish between hypotheses when stomatal size is bounded. Third, we reconcile both hypotheses with the data by including an additional assumption that stomatal size is bounded by a wide range and under selection; we refer to this synthetic hypothesis as the ‘stomatal adaptation + bounded size’ hypothesis. This study advances our understanding of scaling between stomatal size and density by mathematically describing specific assumptions of competing hypotheses, demonstrating that existing hypotheses are inconsistent with observations, and reconciling these hypotheses with phylogenetic comparative analyses by postulating a synthetic model of selection on g s,max , f S , and stomatal size.

  PublisherDOI

• The determination of leaf size on the basis of developmental traits

  New Phytologist · 2025-02-24 · 6 citations

  articleSenior authorCorresponding

  Mature leaf area (LA) is a showcase of diversity - varying enormously within and across species, and associated with the productivity and distribution of plants and ecosystems. Yet, it remains unclear how developmental processes determine variation in LA. We introduce a mathematical framework pinpointing the origin of variation in LA by quantifying six epidermal 'developmental traits': initial mean cell size and number (approximating values within the leaf primordium), and the maximum relative rates and durations of cell proliferation and expansion until leaf maturity. We analyzed a novel database of developmental trajectories of LA and epidermal anatomy, representing 12 eudicotyledonous species and 52 Arabidopsis experiments. Within and across species, mean primordium cell number and maximum relative cell proliferation rate were the strongest developmental determinants of LA. Trade-offs between developmental traits, consistent with evolutionary and metabolic scaling theory, strongly constrain LA variation. These include trade-offs between primordium cell number vs cell proliferation, primordium mean cell size vs cell expansion, and the durations vs maximum relative rates of cell proliferation and expansion. Mutant and wild-type comparisons showed these trade-offs have a genetic basis in Arabidopsis. Analyses of developmental traits underlying LA and its diversification highlight mechanisms for leaf evolution, and opportunities for breeding trait shifts.

  PublisherDOI

Recent grants

• Collaborative Research: The Evolution of Leaf Form in Viburnum (Adoxaceae)

  NSF · $120k · 2009–2013

• CAREER: The coordination of leaf hydraulics, structure and gas exchange

  NSF · $888k · 2006–2007

• Collaborative Research: MRA: Scaling from Traits to Forest Ecosystem Fluxes and Responses to Climate Change, from Stand to Continent

  NSF · $874k · 2020–2025

• COLLABORATIVE RESEARCH: Mechanisms for the decline of leaf hydraulic conductance with dehydration, and plant and environment level impacts

  NSF · $574k · 2012–2016

• Collaborative Research: Meeting: Vascular Transport in Plants - Research Frontiers and Priorities (Washington, DC March 2015)

  NSF · $36k · 2014–2016

Frequent coauthors

• Christine Scoffoni

  California State University Los Angeles

  72 shared

• Jérôme Chave

  Institut de Recherche pour le Développement

  43 shared

• Thomas N. Buckley

  Plant (United States)

  37 shared

• Megan K. Bartlett

  University of California, Davis

  37 shared

• Isabelle Maréchaux

  Centre de Coopération Internationale en Recherche Agronomique pour le Développement

  31 shared

• Kristina J. Anderson‐Teixeira

  ForestGEO

  31 shared

• Nianpeng He

  Northeast Forestry University

  31 shared

• Peter B. Reich

  University of Minnesota

  30 shared

Education

• Ph.D., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2000

• M.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  1996

• B.A., Biology

  University of California, Los Angeles

  1994