Landscape and defensible space

 

A sketch of the Defensible Zones. From Fire Safe Marin

 After the deadly wildfires of January 2025, the high fire risk zones in California will be subjected to a new requirement which bans all combustible materials within 5 ft of residences, in a “Zone 0” . The goal is to create a defensible space around homes that slows the fast path of the wildfires.

The City Council of San Francisco Bay Area has already voted for it, and next year one thousand homes in Berkeley Hills will be under this regulation.

Though it will be difficult for residents to comply with it, California is in the process of adopting the Zone Zero requirements.

The executive order issued by CA Governor Newsom, published on February 6th 2025, does the following:

. Directs the State Board of Forestry to accelerate its work to adopt regulations known as “Zone 0”, which will require an ember-resistant zone within 5 feet of structures located in the highest fire severity zones in the state.

. Tasks the Office of the State Fire Marshal with releasing updated Fire Hazard Severity Zone maps for areas under local government responsibility, adding 1.4 million new acres of land into the two higher tiers of fire severity, which will update building and local planning requirements for these communities statewide. *

. Requires the Department of Forestry and Fire Protection (CAL FIRE) and the Governor’s Office of Emergency Services (CAl OES) to work with local, federal and tribal partners on improvements to the Federal resource ordering system for wildfire response.

 Special attention deserves the inclusion of tribal partners, since there is a historical record for disagreeing  with the Forest Service fire suppression policies and the indigenous people’s fire practices, since they have always relied on the use of fire to manage the landscape for food and cultural material needs. “Like the Spanish before them, federal foresters had determined that because fire was the enemy of productive and profitable forest management, those who advocated its use -like fire itself- must be suppressed. As Karl Marie Norgaard notes, “The exclusion of fire from the landscape has led to a dramatic reduction in the quality and quantity of traditional foods, negatively affected spiritual practices, threatened cultural identity, and infringed upon political sovereignty.” (Miller, 2024)

 Landscape architects have proved that the Zone 0 policy is not totally correct. On April 9th 2025, I have assisted to a Webinar about Landscape - Defensible Space where architect Clark Stevens (sustainable land use planner) has shown that many houses in green corridors of Los Angeles were saved:

Christmas Tree lane is the diagonal in the second map. The conifers corridor did not transmit fire. Basically, per his explanation, more gardens mean less houses burnt.

 

The defensible space focuses on how to reduce direct flame contact. But there are different approaches that we should consider as well, like planting high moisture plants, using fire rated mulch or non combustible ground cover.

The Home Protection Zone should be designed to promote fire-wise landscaping and water conservation. The landscape professionals’ recommendation is to begin with a minimum planting zone of native species to medium density as we move outward the house.

Use more irrigation on Zones 0 and 1. Decrease the irrigation when the distance increases. It is  not about the use of water but the retention, like planting cactus or having swimming pools.

The following sketch, from the Webinar, exemplifies the best transition between defensible zones:

References:

Cut back your roses? Berkeley sets new rules for its most wildfire-prone areas. April 16th, 2025.

Miller, Char (editor). Burn Scars. A Documentary History of Fire Suppression, from Colonial Origins to the Resurgence of Cultural Burning. Oregon State University Press. 2024.

*An interactive map can be seen on pyrecast.org where we can select fuels, weather, risk and active fires. It allows all users, including homeowners and developers, to evaluate the fire hazard conditions of every lot in the USA.

NOTE: this post is also published on AIA Los Angeles blog:

https://www.aialosangeles.org/news/news-and-blogs/