Landscaping Plants and Wildfire: Research and Notes
FIRESafe MARIN publishes lists of common residential landscaping plants that we consider to be either "fire-smart" or "fire-hazardous." These labels can sometimes be confusing, and are not universally true. ALL PLANTS CAN BURN, even those listed in our "fire-smart" recommendations, and some plants we consider fire-hazardous can be maintained in a way that limits their hazards. Homeowners have a responsibility to maintain all plants with proper soil health, regular pruning, and appropriate irrigation.
The lists published here are based on the field experience of FIRESafe MARIN's staff and fire experts, and on the characteristics of the plants themselves, based on guidelines and research published in many sources (see below). These lists are not exhaustive or comprehensive. Many suitable plants are not listed, and many fire-hazardous plants are not here, either. Some plants may have ecological benefits, or drawbacks, that outweigh their relative fire hazard. These lists are intended to serve as examples for homeowners, and we strongly recommend that everyone seek the guidance of licensed arborists (for tree selection and maintenance) and experts like the UCCE Marin Master Gardeners for more detailed advice on maintenance and plant selection.
Fire-Prone vs Fire-Hazardous | Fire-Safe vs Fire-Smart
FIRESafe MARIN no longer uses the terminology "fire-prone" or "pyrophytic" to describe plants. "Fire-Hazardous" better describes the subjective conditions that may contribute to fire hazard, related to a particular site, plant, or grouping of plants. In our collective experience, some plants tend to present more, or less hazard in a given environment. Fire-Smart plants are representative of plants that tend to be easier to maintain, possess characteristics similar to those recommended by research institutions like the UCCE, and are less likely to contribute to wildfire hazard when properly maintained.
FIRESafe MARIN's list of recommended plants for residential landscaping was first published in 1995, in cooperation with local experts, including biologists, botanists, fire ecologists, urban foresters, and firefighters. The list was updated and published again in 1996 in cooperation with the University of California Cooperative Extension (Moritz, R. and S. Pavel. 1996. Pyrophytic vs. Fire Resistant Plants University of California Cooperative Extension HortScript February No. 18.). The 1997 report "Defensible Space Landscaping in the Urban/Wildland Interface: A Compilation of Fire Performance Ratings of Residential Landscape Plants" by the University of California Forest Products Laboratory served as a basis to further update the FIRESafe MARIN list, for a final print publication in 1998 - a format which served until 2017.
The UCCE no longer publishes or teaches from plant "lists," instead adopting a curriculum that teaches maintenance and characteristics of plants for use in each site's particular environment. Because FIRESafe MARIN is not a teaching institution, and we can draw from the collective experience of a wide variety of experts and observers, we continue to see a value in providing a list of representative species that share these characteristics.
Our list of plants is not intended to be comprehensive - many plants that we consider to be either fire-hazardous or fire-smart do not appear on the list. We've attempted to list some of the most common varieties in Marin's complex landscaped wildland urban interface environment. Our list is based primarily on three factors: characteristics, chemistry, form, and structure of the plant itself; real world observations in a fire environment; and references or inclusion in other lists and categories. Other considerations, such as water requirements, invasive vs native status, and suitability for Marin's climate zones, play a role in the inclusion of particular species.
It is imperative to understand that ALL PLANTS CAN BURN, especially if in poor health, poorly maintained, drought stressed, improperly irrigated, or if other factors exist in the local environment. Proper maintenance is critical to maintain the fire-resistant properties of listed plants. FIRESafe MARIN makes no guarantees about the hazard or safety of any plant on these lists. The relative wildfire resistance of a home depends on numerous factors, including construction methods and materials, site location, aspect, slope, neighboring properties, defensible space, and the presence of dead vegetation and other nearby combustibles. Species and health of live plants in landscaping is only one factor of many.
This list is routinely reviewed and updated as new information and evidence becomes available. A 2017 review altered the list substantially, primarily removing plants now understood to be invasive, and providing a new online viewing tool and references.
Research Literature Review
Plant Flammability Testing, Fire-Resistant Plant Lists and Relevance of a Plant Flammability Key for Ornamental Landscape Plants in the Western States
The 2016 "Research Literature Review of Plant Flammability Testing, Fire-Resistant Plant Lists and Relevance of a Plant Flammability Key for Ornamental Landscape Plants in the Western States" published by the Farm and Home Advisor’s Office of the University of California Cooperative Extension provided an opportunity to review and update FIRESafe MARIN's list. This report states:
Plant flammability and testing protocols to support fire resistant landscaping recommendations has been ongoing in California since the 1950’s (Weise, White, Beall, & Etlinger, 2005, Ching & Stewart, 1962). The literature on these topics was thoroughly examined and discussed by White and Zipperer (2010). Within the last 20 years, only three scientific studies were found that examine flammability relating specifically to ornamental landscape plants in California. The University of California Forest Products Lab (UCFPL) (1997) prepared an internal report for the California Department of Forestry and Fire Protection that also addresses ornamental horticulture flammability and plant list issues. This report included a curated list of ornamental landscape plants for fire-resistant landscaping in California based on their review. In their study to develop a plant flammability testing protocol, Etlinger and Beall (2004) discuss prior research on plant flammability, plant rankings and plant lists for fire-resistant landscaping. Weise et al. (2005) provide a review of literature as an introduction to their research conducted on seasonal plant flammability of selected ornamental landscape specimen in California using a particular testing method, the cone calorimeter.
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