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Science
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"Urban trees and structure loss in the 2025 Eaton and Palisades fires"
--Kenny, R., Johns, J., Pawlak, C., Fricker, A., Yost, J., Ritter, M., & Maher, A. (2026)
Key Finding: This study found that how closely homes are built together was far more important than where trees were located in predicting whether homes burned. In both the Eaton and Palisades fires structure density was by far the strongest predictor of structure loss.
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"Exploring urban vegetation type and defensible space’s role in building loss
during wildfire-driven events in California"
--Francisco J. Escobedo, Kamini Yadav, Onofrio Cappelluti, Nels Johnson (2025)
https://c3485f4c-a332-43b2-9d06-adbcac8805c1.usrfiles.com/ugd/c3485f_6e86061b5fee4e6c9aa75a107dc2bfd9.pdf
Key Finding: Researchers found that homes surrounded by healthier, more hydrated plants had better survival rates than homes surrounded by dry, drought-stressed plants. The study suggests that the condition of plants—not simply whether plants are present—can influence structure loss. The study also found that building characteristics and neighborhood density are important factors in wildfire losses.
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Dr Travis Longcore, Dr John Harte - Berkeley Public Comment (2025)
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"Wildland-urban fire disasters aren’t actually a wildfire problem"
David E. Calkin, Kimiko Barrett, Jack D. Cohen, Mark A. Finney, Stephen J. Pyne, and Stephen L. Quarles (2023)
https://www.fs.usda.gov/rm/pubs_journals/2023/rmrs_2023_calkin_d001.pdf
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"Protecting the Wildland-Urban Interface in California: Greenbelts vs
Thinning for Wildfire Threats to Homes"
Jon E. Keeley, Greg Rubin, Teressa Brennan, and Bernadette Piffard (2020)
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“Characterisation of Hedge Burning in the Context of Wildland Urban Interface (WUI) Fire Prevention”
Tihay-Felicelli, Meerpoel-Pietri, Santoni et al. (2025)
https://doi.org/10.1002/fam.3266
Key Finding (interpretation per Longcore): This study is cited by others as showing privacy hedges burn intensely enough to threaten adjacent structures. The “hedge” tested wasn’t a live, hydrated hedge but branches dried in the sun for 10–15 days, reaching 8–22% moisture — comparable to hay, far below the 60%+ moisture of live chaparral even in extreme drought. The study “provides absolutely no insight into role of healthy vegetation in a real-world scenario.”
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“Using High-Resolution Land Cover Data to Assess Structure Loss in the 2018 Woolsey Fire in Southern California”
Mockrin, Locke, Syphard & O’Neil-Dunne (2023)
https://www.fs.usda.gov/nrs/pubs/jrnl/2023/nrs_2023_mockrin_003.pdf
Key Finding (interpretation per Longcore): Studying the Woolsey Fire, vegetation around buildings explained very little about probability of structure loss, while proximity of the nearest building was positively correlated with loss. Vegetation immediately surrounding buildings didn’t even pass the first significance screening for further investigation — quoting the study directly: “Despite detailed pre-fire information on vegetation around nearly 11,000 buildings, we did not find a critical role for vegetation in defensible space in relation to building outcomes after the Woolsey Fire.”
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“Fire-Driven Vegetation Type Conversion in Southern California”
Syphard, Brennan, Rustigian-Romsos & Keeley (2022)
https://consbio.org/wp-content/uploads/2022/08/VTC_soCal_Syphard_2022.pdf
Key Finding (interpretation per Longcore): Cited as evidence that removing healthy vegetation opens an “ecological vacuum” rapidly colonized by invasive annual grasses — which Longcore describes as “ubiquitous and aggressive,” and “rapidly expanding” across Southern California landscapes as this study documents.
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“Options for Reducing House-Losses During Wildfires Without Clearing Trees and Shrubs”
Gibbons, Gill, Shore, Moritz, Dovers & Cary (2018)
https://doi.org/10.1016/j.landurbplan.2018.02.010
Key Finding (interpretation per Longcore): One of several studies suggesting the hypothesis that healthy, well-maintained vegetation — especially fire-resistant native species — may serve as buffers by intercepting embers and altering where embers land, rather than simply adding fuel. Longcore groups this alongside Gill (2005), Moritz et al. (2014), and Keeley & Syphard (2019) as part of the “ember buffer” body of evidence.
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“The Importance of Building Construction Materials Relative to Other Factors Affecting Structure Survival During Wildfire”
Syphard, Brennan & Keeley (2017)
Key Finding (interpretation per Longcore): The combined explanatory power of building materials (home hardening) and defensible space — without total vegetation removal — accounted for only 14% of the overall variation in structure loss. Home hardening and defensible space were roughly equally important; structure density, structure age, percent clearance, slope, overhanging vegetation, and distance to a major road all mattered more than any single vegetation factor.
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“The Role of Defensible Space for Residential Structure Protection During Wildfires”
Syphard, Brennan & Keeley (2014)
https://pubs.usgs.gov/publication/70141773
Key Finding (interpretation per Longcore): At the parcel scale, structure loss was reduced by vegetation management — not removal — within 32 ft of structures on gentle slopes and 65 ft on steeper slopes. Defensible space in the study specifically allowed trees to remain; the only increased risk found was from trees overhanging a structure, which Longcore attributes (citing Keeley) to litter accumulating on roofs — “not an intrinsic risk from trees catching fire.” Does not support complete vegetation elimination in Zone 0.
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“Alien Plant Dynamics Following Fire in Mediterranean-Climate California Shrublands”
Keeley, Baer-Keeley & Fotheringham (2005)
https://doi.org/10.1890/04-1222
Key Finding (interpretation per Longcore): Cited alongside Fusco et al. (2022) as evidence that invasive annual grasses — which rapidly colonize cleared ground — are “flashy fuels and highly ignitable for most of the year,” posing a greater risk than the live woody vegetation they replace when an ember lands nearby.
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The UCLA Sustainability Defensible Space Group Collection: scientific papers and expert perspectives related to vegetation management and defensible space:
https://drive.google.com/drive/folders/1-DOF6b-jf6NNyTnUg9K9Mh-l_eD1iLyy?usp=drive_link
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...Under Construction...Science Evolving (Aug 23, 2026)