Defensible Space Zone Zero: Balancing Fire Safety with Shade and Climate Concerns

In the wildfire-urban interface (WUI) areas of California and the Verdugo Hills, fire preparation is of immense importance. But for those who live in any foothill community in California, drastic fuel modification changes are coming their way with the intent of creating defensible space … and the public notification has been zilch.

Zone Zero is a proposed regulation aimed at reducing the likelihood of a home igniting from embers by creating a defensible space. Zone Zero is the first five feet immediately surrounding a structure. The proposed regulation requires that all vegetation and combustible materials be removed: eliminating mulch, wood fencing, plants and trees in this five-foot zone. Any tree or part of the tree’s canopy in this five foot zone is proposed to be removed. 

While the intent is clear – protect life and property – is total removal of all vegetation in Zone Zero the right move? Fire scientists feel this is a drastic solution.

Especially removing trees adjacent to urban homes, what are the unintended consequences, particularly for habitat, shade and the urban heat island effect?

Recent fire science supports keeping well-maintained, moisture retaining trees and vegetation which can slow or stop embers. In the Palisades and Eaton fires, mature trees and hedges functioned as ember catchers and saved homes. The Eaton Fire found that trees protected complete streets and that structures burned trees, not visa-versa. These urban fires were structure to structure fires not vegetation fires.

Zone Zero in a nutshell is to create defensible space:

* No combustible mulch, wood chips, rubber mulch, etc.

* No sheds, trellises, wood fences, wood piles or storage of materials

* No plants or trees in Zone Zero

* Includes all residential, industrial, multifamily and institutional structures in certain very high fire hazard severity zones.

The regulation does not explicitly require removing all trees near structures but, when combined with fire agency and insurance interpretations, it will lead to the removal of canopy trees if trunks or branches overhang within the five-foot zone. A big concern is for trees that are next to multistory buildings.

In Southern California, large shade trees near homes provide cooling and aesthetic value. Mature trees provide critical ecosystem services: filtering air, supporting wildlife, stabilizing soil, and – most crucially – reducing heat. Urban heat island effect refers to buildings, roads and other human-built structures that absorb the sun’s heat more than natural surfaces such as grass, soil and trees, raising the surrounding air temperature sometimes by 15 degrees. Shade trees reduce this effect by cooling the air and reducing surface heat. Trees help cool neighborhoods, cutting energy use for air conditioning and supporting public health.

With Zone Zero proposing widespread canopy loss near homes, neighborhoods will see an increase in energy bills, especially during summer months. Vulnerable communities, which face higher heat-related health risks and deaths, make canopy loss even more concerning.

Integrating current fire science with urban forestry best practices, defensible space can exist along with mature, maintained trees. Trees and plants should be permitted for their cooling and shading benefits. Zone Zero must holistically balance the need for ignition-resistant zones and the equally urgent need for shaded, healthy, climate-resilient urban landscapes.

For more information visit: www.zonezerofacts.org and https://bof.fire.ca.gov/projects-and-programs/defensible-space-zones-0-1-and-2. Submit comment on this regulation writing to PublicComments@bof.ca.gov.

Stephanie Landregan, PLA, FASLA 

Stephanie Landregan is a registered landscape architect and senior Southern California director, California Council of ASLA (American Society of Landscape Architects). She is the former director of the Landscape Architecture and Horticulture Programs at UCLA Extension.