Peer Reviewed Studies

What does Science say

Even the best science is provisional: each study has limits—sampling bias, regional context, model assumptions, and confidence bounds—that make findings evolving rather than absolute. The safest communities treat wildfire policy as iterative: publish assumptions, invite public comment, pilot changes, measure outcomes, and adjust. The state’s ember-zone framework was designed to evolve with stakeholder input; by contrast, many residents experienced Berkeley’s process as closed-door and hard to engage. To keep people genuinely safe, we need transparent communication, routine listening sessions, and data-driven revisions—not one-and-done rules.

    • Syphard & Keeley (2019) – statewide CA, 40k+ structures.
      Finding: Across 2013–2018 fires, building characteristics explained more of the survival vs. loss difference than defensible-space distance. This supports focusing policy on materials/retrofits, not a categorical live-plant ban at 0–5 ft.
      Authors/background: Alexandra D. Syphard (Conservation Biology Institute), Jon E. Keeley (USGS/WERC). Journal: Fire (peer-reviewed).
      Link: https://www.mdpi.com/2571-6255/2/3/49. MDPIU.S. Geological Survey

    • Syphard, Brennan & Keeley (2014) – defensible-space distances.
      Finding: Benefits are strongest nearest the home (≈5–20 m; slope-dependent) and mixed/weak beyond ~30 m, implying nuanced vegetation management beats blanket removals. This weakens the case for across-the-board bansinside 5 ft when materials/upkeep are addressed.
      Authors/background: CBI + USGS/WERC. Journal: International Journal of Wildland Fire.
      Link (publisher PDF): https://consbio.org/wp-content/uploads/2022/05/Syphard_defensibleSpace.pdf. Conservation Biology InstituteCSIRO Publishing

    • Syphard, Brennan & Keeley (2017) – materials vs. vegetation.
      Finding: Construction materials/age/arrangement outperform broad vegetation metrics at predicting survival; defensible space helps but is secondary. This argues for vent/window/eave upgrades over a universal near-house plant ban.
      Authors/background: CBI + USGS/WERC. Journal: International Journal of Disaster Risk Reduction.
      Link (OA PDF): https://forestwatch.org/wp-content/uploads/2019/02/2017_Syphard-et-al_Importance-of-building-construction-materials-during-wildfire.pdf. Los Padres ForestWatchU.S. Geological Survey

    • Knapp, Valachovic, Quarles & Johnson (2021) – Camp Fire (Paradise).
      Finding: Nearest destroyed structure and # of destroyed structures within 100 m were the strongest survival predictors; vegetation 30–100 m mattered, while 0–30 m canopy had no clear effect in pre-fire planning models. The paper urges eliminating near-home combustibles (0–1.5 m) and improving windows/siding, not banning irrigated live plants wholesale.
      Authors/background: USFS, UC ANR, IBHS; Journal: Fire Ecology.
      Link: https://fireecology.springeropen.com/articles/10.1186/s42408-021-00117-0. SpringerOpen

    • Mockrin, Locke, Syphard & O’Neil-Dunne (2023) – Woolsey Fire, ~11k bldgs.
      Finding: Vegetation immediately around buildings was not a strong predictor of loss compared with building materials (multi-pane windows, enclosed eaves) and landscape context. That result supports hardening + context-specific management rather than a categorical plant ban.
      Authors/background: USFS NRS + collaborators; Journal: Journal of Environmental Management.
      Link (USFS page + PDF): https://research.fs.usda.gov/treesearch/67085. USFS Research & Development

    • Gibbons et al. (2018, Australia) – “options without clearing trees & shrubs.”
      Finding: Greener vegetation (higher NDVI) near homes reduced losses, and retaining trees/shrubs as discrete patches reduced risk vs. broad clearing. Context differs (AU), but it demonstrates viable alternatives to blanket removals.
      Authors/background: Australian National University + colleagues; Journal: Landscape and Urban Planning.
      Link (OA): https://moritzfirelab.org/wp-content/uploads/2018/11/gibbons_etal_landscapeurbanplanning_2018.pdf. 

    • Cohen (2004) – radiant heat limits; embers/near fuels dominate.
      Finding: Modeling + experimental crown fires show radiant heat ignition distances are limited; most WUI home destruction requires ember entry or ignition of adjacent combustibles. That supports banning wood mulch/wood fences/debris near walls, not all living plants.
      Author/background: Jack D. Cohen (USFS researcher). Journal: Canadian Journal of Forest Research.
      Link (OA PDF): https://www.frames.gov/documents/catalog/spa/cohen_2004.pdf. Fire Research ExchangeCanadian Science Publishing

    • IBHS (2019) – deck ember tests.
      Finding: Embers accumulate at deck–wall joints and readily ignite combustible decking/debris; spread can move toward the structure. Policy should target deck retrofits/cleanlines over plant bans.
      Background: Insurance Institute for Business & Home Safety, full-scale lab testing.
      Link (PDF): https://ibhs.org/wp-content/uploads/Ignition-Potential-of-Decks-Subjected-to-an-Ember-Exposure.pdf. Institute for Business Safety

    • IBHS (2019) & NIST (2013/2022) – vent & neighborhood exposure.
      Finding: Wind-blown embers enter vents, causing attic fires; NIST identifies many ignition pathways and community-scale exposures. This backs ember-resistant vents & community hardening, not plant prohibitions as a stand-alone fix.
      Background: IBHS technical briefs; NIST Technical Notes 1748 & 2205.
      Links: IBHS vents; NIST TN1748; NIST TN2205. Institute for Business SafetyNIST Publications+1

    • UC ANR/IBHS guidance syntheses (2010–2021).
      Finding: Home-hardening features (Class-A roofs, ember-resistant vents, tempered multi-pane glazing, boxed eaves) are decisive; organic mulches and wood features next to walls are high-risk. Guidance favors “lean, clean, green” near walls—not a universal living-plant ban.
      Background: UC ANR Publications 8393 & 8695; IBHS primers.
      Links: UC ANR 8393 PDF; UC ANR 8695 page. 

    • Bethke et al. (2016) – review of “fire-resistant” plant lists.
      Finding: Most lists lack standardized testing or consistent criteria; many recommendations are anecdotal. Science supports maintenance/placement and moisture, not blanket species bans.
      Authors/background: UC Cooperative Extension & UC Davis CCUH. University report.
      Link (PDF): https://ccuh.ucdavis.edu/sites/g/files/dgvnsk1376/files/inline-files/Bethke_final_report_2014-2015.pdf. ccuh.ucdavis.edu

    • UC ANR “Fire-resilient plants” portal (evidence summary).
      Finding: Reiterates Bethke et al.; frames “fire-resilient” as care and arrangement, not immutable species traits—contradicts one-size plant bans.
      Background: University of California Agriculture & Natural Resources.
      Link: https://ucanr.edu/program/uc-anr-fire-network/fire-resistant-plants. UC Agriculture and Natural Resources

    • Mulch combustibility (Quarles & Smith; UNR/UCANR, 2011).
      Finding: All organic mulches tested are combustible; wood chips/needles near walls are a known ember hazard. This supports targeting mulch/wood features rather than living plants broadly.
      Background: University of Nevada & UC ANR extension testing.
      Link (PDF): https://ucanr.edu/sites/default/files/2020-07/329978.pdf. 

    • USGS Landslide Handbook (Circular 1325).
      Finding: Roots add soil cohesion and vegetation reduces surface erosion; poor drainage near slope crests increases failure risk. A blanket plant removal/compacted hardscape can increase localized erosion/instability unless drainage/infiltration are designed.
      Background: USGS federal technical handbook.
      Link (PDF): https://pubs.usgs.gov/circ/1325/pdf/C1325_508.pdf. U.S. Geological Survey

    • FEMA P-2181 fact sheets (2022).
      Finding: Slope stabilization and drainage design are critical to avoid erosion/failures; policy should direct water away from slopes and maintain protective cover. If Zone 0 forces bare or compacted strips, runoff can worsen.
      Background: FEMA Hurricane & Flood Mitigation Handbook.
      Links: Drainage; Slope stabilization. FEMA+1

    • Global meta-analyses: mulching sharply cuts runoff/erosion.
      Finding: Runoff ↓ ~47% and soil loss ↓ ~76% on average with mulches; removing organic cover near homes without equivalent protection raises erosion risk on slopes.
      Background: Fan et al., 2023 (Geomorphology); Prosdocimi et al., 2016 (Earth-Science Reviews).
      Links: Fan 2023; Prosdocimi 2016. ScienceDirect+1

    • Compacted decomposed-granite (DG) & infiltration.
      Finding: Lab studies show higher compaction → lower saturated hydraulic conductivity in decomposed granite soils, meaning more surface runoff unless a true permeable system is installed.
      Background: Yin/Hossain, Canadian Geotechnical Journal.
      Link (abstract): https://cdnsciencepub.com/doi/abs/10.1139/T10-015. Canadian Science Publishing

    • Permeable pavements perform when designed/maintained.
      Finding: Permeable pavers/porous concrete attenuate peaks and infiltrate if built to spec—this is the right non-combustible Zone 0 treatment on slopes, not sealed or compacted surfaces.
      Background: U.S. EPA BMP fact sheet; Minnesota DOT/LRRB review.
      Links: EPA BMP; LRRB review. Environmental Protection Agency