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Alder is rated fire resistant overall, although an Idaho field trial gives it a fire-resistance score of 4 out of 10.
Four authorities place alder among fire-resistant plants. The extension services of Oregon State, Washington State, and the University of Idaho list it as fire resistant, and the King County Forestry Program includes Alnus species in its fire-resistant trees. The University of Arizona Cooperative Extension in Yavapai County lists alder as resistant when irrigated and maintained. Turkey’s General Directorate of Forestry directs managers to preserve, encourage, or use alder in fire-resistant or slow-burning forest and fire-prevention plantings.
Idaho Firewise supplies the caution. Its field-trial database scores alder 4 of 10 on a scale used to set minimum planting distances. Under the published thresholds applied to that scale, scores from 4 through 7 are mixed, while only scores from 8 through 10 support a recommendation. This finding is less favorable than the four listings, but it measures alder on a different graded scale rather than simply placing it on a recommended list.
The balance still favors calling alder fire resistant. Extension and forestry authorities repeatedly select it for fire-conscious planting, while the Idaho result argues for treating that label as a practical classification, not a claim that the tree cannot burn.
Form
tree
Rated in
OR/WA/ID; Turkey; Yavapai County, Arizona; southern Idaho / Intermountain +1
On this lot
1. Fire evidence and conditions
Fire evidence
Fire-resistant — location does not change the cited classification.
Southern Idaho (ID footprint); partial normalized coverage · 2013-11-08
The official database labels itself "For Southern Idaho" and describes Idaho residents at the urban-rangeland interface. FireApproved publishes 419 existing plant owners that cite its scored rows. This bounded Southern Idaho scope is regional context, not statewide coverage or a conclusion that the score transfers unchanged to every Idaho site.
King County's current wildfire page links this list for the Puget Sound Basin. FireApproved publishes 82 exact source owners as basin context, not statewide Washington guidance or a site-specific recommendation.
The October 2023 joint Pacific Northwest Extension publication explicitly names Oregon, Washington, and Idaho and publishes more than 150 plant profiles. FireApproved has normalized 155 exact plant records from the source; publication scope does not assert that every listed plant suits every site within the three states.
Yavapai County (AZ footprint); partial normalized coverage · 2025-03-14
University of Arizona Cooperative Extension authors Bulletin 34 for Yavapai County. FireApproved publishes 198 exact source owners from its resistant and prone tables and keeps the county boundary visible. County publication scope is regional Arizona context, never statewide scope.
2. Why this plant is relevant here
State distribution
Documented in ID, OR, WA.
Native range
Introduced / established
USDA hardiness
Documented range 5–8.
3. Legal, ecological, and broader status
Legal-list status
Seed-list status
Reported invasive here
Broader regional context
Federal context
How to read this page
The status above is computed from the cited rows below: independent recommendations can support a fire-resistant result, an avoid row can produce keep-away, and disagreement stays visible as conflict. Placement notes preserve each source’s own scheme rather than translating unlike rules into one scale. This is evidence about a plant, not permission to plant it in every part of the defensible space; Zone 0 remains noncombustible.
Plant hardiness evidence
These values describe the plant source. Your ZIP zone comes from the separate 2023 USDA
Plant Hardiness Zone Map. Whole-zone values stay whole-zone, and a single unresolved value
is not treated as a tolerance range. Different source boundaries stay separate: overlapping
statements are compared independently, while only ranges with no shared zone are called a conflict.
5–8 explicit range · whole zone precision · source stated
Source taxon: Alnus · exact match.
Source location: Plant profile USDA hardiness zones field.
Where its sources say to plant it
Placement rules below use each source's own distances or named zones, tied to its rating.
They are not interchangeable with the directory's current Zone 0 guidance.
Fire Resistance of Plants Master Database: plantable at 70' from home [Idaho minimum planting distance] (mid-scale rating)
Yanan Orman Alanlarının Rehabilitasyonu ve Yangına Direnç…: Dere vejetasyonlarının korunması [yardop-6976-operational-fire-resistant-planting] (with its recommendation)
The evidence
Grouped by what each source concluded. Primary evidence rated the plant itself
(a lab, field program, or original curation); corroboration compiled or
republished another source's rating and resolves to its root lineage.
Listed as Alder — Alnus sp.. The bulletin says fire-resistant plants tend to resist ignition when irrigated and maintained, while fire-prone plants may ignite readily and burn intensely.
The YARDOP circular directs managers to preserve, encourage, or use this named taxon in fire-resistant or slow-burning forest and fire-prevention plantings.
