About

Glen MacDonald is a distinguished professor in the Department of Ecology and Evolutionary Biology at UCLA. His research focuses on issues of climate change and ecological and societal responses. His lab employs a variety of research tools, including biological, elemental geochemical, and isotopic analysis of lake and wetland sediments, tree-ring analysis, satellite remote sensing, and modeling to develop long-term records of climatic and environmental change and large spatial records of such changes. His studies have included treelines and climate change, drought and its impacts, vegetation and fire, dynamics and carbon stores of wetlands, and sea-level rise and coastal marshes. Field sites for his research have included locations in Canada, the western USA, Russia, Mexico, Egypt, Syria, and India, often involving international teams of academic, government, and NGO researchers.

Research topics

• Geography
• Ecology
• Oceanography
• Physical geography
• Geology
• Environmental science
• Climatology

Selected publications

• Divergent urban vegetation inequality in Northern and Sunbelt United States cities under climate extreme events

  npj Environmental Social Sciences · 2026-04-08

  articleOpen accessSenior author

  Abstract Urban vegetation inequality (UVI) undermines the equitable distribution of ecosystem services such as heat mitigation. However, the role of climate variability in shaping UVI remains unclear. Here we have developed a methodology using satellite, census, and climate data to analyze UVI across 245 major U.S. cities. Our study proposed a vegetation polarization index (VPI), calculated as the normalized difference between the 90th and 10th percentiles of NDVI, to measure UVI. We examined how climate events affect UVI differently in the Sunbelt versus northern cities. Sunbelt cities display exacerbated UVI under drought and warmer climates, while colder and wetter conditions may increase UVI in northern cities. Hot droughts can amplify UVI across almost all cities, with Sunbelt cities showing greater vulnerability. We analyzed UVI trends from 2001 to 2020, revealing that Sunbelt cities exhibit worsening UVI trends, while northern cities show improving trends. These changes are related to climate shifts and socioeconomic factors, underscoring the vulnerability of U.S. cities to fluctuating UVI under climate change. Socioeconomic conditions play a significant role in exacerbating this vulnerability.

  PublisherDOI

• <b>Tidal Wetland Soil Carbon Accumulation Rates for Coastal California</b>

  Figshare · 2026-01-01

  datasetOpen accessSenior author

  Carbon stock and carbon accumulation rate data are vital to multiple aspects of tidal wetland conservation and restoration policy. In California, USA tidal soil data are rare outside of the San Francisco Bay and Sacramento Delta regions, despite the differing conditions experienced by the outer coastline. Here we provide carbon stocks and decadal-to-centennial-scale carbon accumulation rate calculations. This dataset presents 83 soil depth profiles from 15 sites, with 58 cores from 12 tidal wetland sites analyzed for carbon stock, mostly from the outer coastline of California. Mean organic matter content was 11%, and stocks estimated to 1 meter depth ranged from 15.4 to 44.7 kgC m^-2. Organic matter content generally declined asymptotically with depth. Carbon accumulation rates ranged from 39.2 to 130.0 gC m^-2 yr^-1. Neither carbon stock nor carbon accumulation rates were notably different from global average values. Data at this level of reporting are vital for establishing restoration baselines, informing greenhouse gas mitigation planning, and projecting future ecosystem response to sea-level rise.

  PublisherDOI

• <b>Tidal Wetland Soil Carbon Accumulation Rates for Coastal California</b>

  Figshare · 2026-01-01 · 1 citations

  datasetOpen accessSenior author

  Carbon stock and carbon accumulation rate data are vital to multiple aspects of tidal wetland conservation and restoration policy. In California, USA tidal soil data are rare outside of the San Francisco Bay and Sacramento Delta regions, despite the differing conditions experienced by the outer coastline. Here we provide carbon stocks and decadal-to-centennial-scale carbon accumulation rate calculations. This dataset presents 83 soil depth profiles from 15 sites, with 58 cores from 12 tidal wetland sites analyzed for carbon stock, mostly from the outer coastline of California. Mean organic matter content was 11%, and stocks estimated to 1 meter depth ranged from 15.4 to 44.7 kgC m^-2. Organic matter content generally declined asymptotically with depth. Carbon accumulation rates ranged from 39.2 to 130.0 gC m^-2 yr^-1. Neither carbon stock nor carbon accumulation rates were notably different from global average values. Data at this level of reporting are vital for establishing restoration baselines, informing greenhouse gas mitigation planning, and projecting future ecosystem response to sea-level rise.

  PublisherDOI

• Disparities in urban vegetation degradation and heat exposure during drought periods in U.S. cities

  npj Urban Sustainability · 2025-12-15

  articleOpen accessSenior author

  Abstract Policymakers are increasingly recognizing the necessity for the equitable distribution of urban green spaces across sociodemographic groups. Nevertheless, the extant research consistently highlights disparities in this allocation, frequently neglecting the critical implications of extreme droughts on vegetation-related inequalities. Leveraging satellite observations in conjunction with census data, we examine the drought-related disparities in urban vegetation degradation (UVD) and the corresponding heat exposure across sociodemographic groups within major U.S. cities. Our findings reveal that marginalized communities experience more severe UVD during droughts, a trend particularly pronounced in Sunbelt U.S. cities, such as those in Southern California and Texas. Additionally, the unequal UVD during drought exacerbates existing inequalities in heat exposure. These results highlight the urgent need for the implementation of targeted policies, including effective water supply management strategies. Such measures could mitigate thermal environmental injustices and promote equitable vegetation distribution under a warming climate.

  PublisherOA PDFDOI

• Significant challenges to the sustainability of the California coast considering climate change

  Proceedings of the National Academy of Sciences · 2024-07-29 · 12 citations

  articleOpen access

  Climate change is an existential threat to the environmental and socioeconomic sustainability of the coastal zone and impacts will be complex and widespread. Evidence from California and across the United States shows that climate change is impacting coastal communities and challenging managers with a plethora of stressors already present. Widespread action could be taken that would sustain California's coastal ecosystems and communities. In this perspective, we highlight the main threat to coastal sustainability: the compound effects of episodic events amplified with ongoing climate change, which will present unprecedented challenges to the state. We present two key challenges for California's sustainability in the coastal zone: 1) accelerating sea-level rise combined with storm impacts, and 2) continued warming of the oceans and marine heatwaves. Cascading effects from these types of compounding events will occur within the context of an already stressed system that has experienced extensive alterations due to intensive development, resource extraction and harvesting, spatial containment, and other human use pressures. There are critical components that could be used to address these immediate concerns, including comanagement strategies that include diverse groups and organizations, strategic planning integrated across large areas, rapid implementation of solutions, and a cohesive and policy relevant research agenda for the California coast. Much of this has been started in the state, but the scale could be increased, and timelines accelerated. The ideas and information presented here are intended to help expand discussions to sharpen the focus on how to encourage sustainability of California's iconic coastal region.

  PublisherOA PDFDOI

• Climate change and California sustainability—Challenges and solutions

  Proceedings of the National Academy of Sciences · 2024-07-29 · 15 citations

  articleOpen accessSenior authorCorresponding

  Large volumes of liquid water transiently existed on the surface of Mars more than 3 billion years ago. Much of this water is hypothesized to have been sequestered in the subsurface or lost to space. We use rock physics models and Bayesian inversion to ...

  PublisherOA PDFDOI

• Accuracy and Precision of Tidal Wetland Soil Carbon Mapping in the Conterminous United States: Public Soil Carbon Data Release

  Figshare · 2024-01-01

  dataset

  Tidal wetlands produce long-term soil organic carbon (C) stocks. Thus for carbon accounting purposes, we need accurate and precise information on the magnitude and spatial distribution of those stocks. We assembled and analyzed an unprecedented soil core dataset, and tested three strategies for mapping carbon stocks: applying the average value from the synthesis to mapped tidal wetlands, applying models fit using empirical data and applied using soil, vegetation and salinity maps, and relying on independently generated soil carbon maps. Soil carbon stocks were far lower on average and varied less spatially and with depth than stocks calculated from available soils maps. Further, variation in carbon density was not well-predicted based on climate, salinity, vegetation, or soil classes. Instead, the assembled dataset showed that carbon density across the conterminous united states (CONUS) was normally distributed, with a predictable range of observations. We identified the simplest strategy, applying mean carbon density (27.0 kgC m-3), as the best performing strategy, and conservatively estimated that the top meter of CONUS tidal wetland soil contains 0.72 petagrams C. This strategy could provide standardization in CONUS tidal carbon accounting until such a time as modeling and mapping advancements can quantitatively improve accuracy and precision. This data release includes the soil carbon data currently considered public by the data submittors. Additional detail can be found in the publication. Holmquist JR et al. (2018). Accuracy and Precision of Tidal Wetlands Soil Carbon Mapping in the Conterminous United States. Scientific Reports. DOI:10.1038/s41598-018-26948-7

  DOI

• Identification of fossil juniper seeds from Rancho La Brea (California, <scp>USA</scp>): drought and extirpation in the Late Pleistocene

  New Phytologist · 2024-12-10

  articleOpen accessSenior author

  Juniperus spp. are keystone shrubs in western North America and important climatic indicators in paleo-records. However, a lack of taxonomic resolution among fossil species limits our ability to track past environmental changes. Plant macrofossils at Rancho La Brea (RLB) allow for reconstructions of juniper occurrence to species across 60 000 yr. We use microscopy, image analysis, species distribution modeling (SDM), and radiocarbon dating to identify an unknown Juniperus species at RLB and put it into chronological context with fossil Juniperus californica at the site to infer past environmental conditions. We identify the unknown taxon as Juniperus scopulorum Sargent, 1897. The Pleistocene occurrence of this species in California expands its known distribution and documents its extirpation. Temporal ranges of the two fossil junipers alternate, revealing a pattern of differential climatic sensitivity throughout the end of the Pleistocene. Occurrence patterns suggest sensitivity to temperature, moisture availability, and the presence of two mega-droughts at c. 48-44.5 ka and c. 29.3-25.2 ka. Extirpation of both taxa by c. 13 ka is likely driven by climate, megafaunal extinction, and increasing fire. The extirpation of fossil junipers during these past climatic events demonstrates vulnerability of juniper species in the face of global change.

  PublisherDOI

• SIGNIFICANT CHANGES IN HOLOCENE HYDROCLIMATIC VARIABILITY RECORDED IN BARLEY LAKE SEDIMENTS, CALIFORNIA (NORTHERN CALIFORNIA COAST RANGE)

  Abstracts with programs - Geological Society of America · 2024-01-01

  article
  PublisherDOI

• NEOTAPHONOMIC SURVEY OF SMALL TAR SEEPS IN SOUTHERN CALIFORNIA

  Palaios · 2024-11-22

  articleSenior author

  Abstract California’s La Brea Tar Pits is one of the richest Ice Age fossil localities in the world and offers unmatched potential for reconstructing environmental conditions and ecological relationships in the Late Pleistocene. Plant macrofossils are abundant at the site, but their accurate interpretation requires a better understanding of the processes behind their deposition in hydrocarbon seeps and potential spatial resolution, a topic not yet addressed in asphalt pit related research. In this study we monitor temperature, phenology, and seep activity of two hydrocarbon seeps in southern California over the span of a year. For each seep we surveyed surrounding vegetation within 10 meters and sampled seep surfaces for analysis of trapped plant material. We find hydrocarbon seeps to be highly localized with 77–91% of plant material originating from species found within five meters of the seep. Temperature and time-lapse imagery indicate a greater likelihood of transportation of plant material by wind or animal than by water in these particular seeps. Animal transport through fecal matter or entrapment was the most likely candidate for the species Sambucus mexicana to be transported outside the immediate vicinity of the monitored seeps. Variation in observed viscosity of liquid asphalt correlated with seasonal temperature changes, with higher temperatures coinciding with decreased viscosity and increased seep flow. We find observations of seasonal seep flow connected to a warm season bias of plant material, making phenology an important consideration in the interpretation of plant presence and absence in asphaltic fossil contexts.

  PublisherDOI

Recent grants

• Collaborative Research: Identifying Hydroclimatic Regimes of Carbon Stability in Northern Peatlands: Holocene Data Analysis and Process-Based Modeling

  NSF · $627k · 2006–2011

• Collaborative Research: High Resolution Records of Holocene Climate Change, Drought Variability and Monsoon Behavior from the Uinta Mountains of Utah

  NSF · $82k · 2004–2008

• Collaborative Research: A Synthesis of the Last 2000 Years of Climatic Variability from Arctic Lakes

  NSF · $141k · 2005–2009

• Collaborative Research (ETBC): Climate Warming and Northern Peatland Decomposition, Accumulation and Carbon Sequestration Examined Through Molecular and Paleohydrological Analysis

  NSF · $189k · 2009–2013

• Collaborative Research: The California Precipitation Dipole: Spatiotemporal Variability and Forcings Over the Past 3000 Years

  NSF · $193k · 2017–2021

Frequent coauthors

• L. C. Smith

  Providence College

  34 shared

• Yongwei Sheng

  32 shared

• David W. Beilman

  University of Hawaiʻi at Mānoa

  28 shared

• Lauren N. Brown

  27 shared

• James R. Holmquist

  Smithsonian Environmental Research Center

  25 shared

• Katrina A. Moser

  24 shared

• K. V. Kremenetski

  22 shared

• David F. Porinchu

  University of Georgia

  22 shared

Education

• Ph.D., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2005

• M.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2001

• B.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  1999

Awards & honors

• Member of the National Academy of Science