Flammability of Natural Vegetation and Home Landscapes
Wildfires are an important and necessary ecological process in most natural areas of the southern United States. However, with increasing numbers of homes being constructed in close proximity to natural vegetation, risk of wildfire damage to homes in the wildland-urban interface (WUI) is increasing. To reduce WUI fire hazards most effectively, homeowners need to participate in wildfire risk mitigation. To do so they need information on managing their homes and landscapes to reduce flammability.
Two key components of managing fire risk on private property are to understand both the flammability of natural areas surrounding the home landscape and how landscaping design, materials, and plant species selections influence flammability and fire behavior (see fact sheet “Understanding Fire Behavior” available at http://edis.ifas.ufl.edu/FR138). Several studies conducted through a partnership between the Centers for Urban and Interface Forestry and the University of Florida are addressing these critical issues.
Research Projects
Three research studies were designed to address the issues
of wildfire hazard in the wildland-urban interface and investigate
different facets of natural vegetation and home landscape flammability.
These studies provide information to help guide firewise planning
and to improve fire behavior modeling for urban settings.
1) Flammability of native understory species in pine flatwood and hardwood hammock ecosystems
Description:
Regionally specific information on shrub flammability will
improve fire behavior models for wildland-urban interface applications
and allow fire managers to plan fuel mitigation and firefighting
activities more effectively. This study determined the flammability
characteristics of six abundant understory shrub species in
pine flatwood and hardwood hammock ecosystems, which are dominant
vegetation types throughout the southern Coastal Plain. These
ecosystems were selected because they were historically affected
by fire at different return intervals. Fire-prone pine flatwoods
typically experienced fires every 1 to 8 years while hardwood
hammocks typically had 30 to 50 year fire return intervals.
Although these ecosystems contain several of the same understory
species, it was expected that the overall flammability of the
understory shrubs would differ since the fire return intervals
were historically very different.
Findings:
Pine flatwoods shrubs were found to be more flammable than
oak hammock shrubs, which underscores the importance of fuel
management around and within communities surrounded by pine
flatwoods. Saw palmetto (Serenoa repens), gallberry (Ilex
glabra),
rusty lyonia (Lyonia ferruginea) and American holly (Ilex
opaca)
were the most flammable species studied. In addition, flammability
characteristics for saw palmetto and wax myrtle, the two species
that were common to both ecosystems, were similar in the two
ecosystems. However, higher densities of the two species in
the flatwoods may lead to higher flammability levels in that
environment, which illustrates that site and environmental conditions,
such as available light or moisture, may create variations in
flammability within the same species. Therefore, it is important
to remember that in extremely hot and dry conditions, even plants
considered to have lower flammability may become more flammable.
For more information see the research thesis from this study (Flammability of native understory species in pine flatwood and hardwood hammock ecosystems) at: http://etd.fcla.edu/UF/UFE0001167/behm_a.pdf. In addition, the fact sheet “Considering Fire in Florida’s Ecosystems” provides information on fire hazard ratings for other Florida ecosystems and is available at: http://edis.ifas.ufl.edu/pdffiles/FR/FR13700.pdf
2) Quantifying and ranking the flammability of ornamental shrubs in the southern United States
Description:
The shrub species used in home landscaping directly affect
fire behavior and the risk of wildfire damage to the home. Long
flame lengths and high energy release levels from densely planted
or poorly maintained shrubs can easily spread fires into overstory
pines or nearby structures. In order to provide better information
for firewise plant lists for southern WUI landscapes and to
improve WUI fire behavior modeling, this study investigated
the flammability of thirty-four landscape shrubs commonly used
in the South.
Findings:
Twenty-two shrub species were found to have low flammability
characteristics. These shrubs can be safely planted within the
home landscape and are appropriate for addition to firewise
plant lists. The eight species found to be moderately flammable
can also be planted in home landscapes; however, they should
not be planted adjacent to structures and should be isolated
vertically and horizontally from other plantings to reduce the
potential for fire spread. Gallberry (Ilex glabra), yaupon holly
(Ilex vomitoria), Chinese juniper (Juniperus chinensis), and
mountain laurel (Kalmia latifolia) were found to be highly flammable
and were ranked as inappropriate for use within 30 feet of the
home. Because species within the same genus were found to vary
in flammability, it is important for homeowners and landscapers
not to substitute plants on firewise plant lists with other
species in the same genus without verifying flammability characteristics
of the substitute species. All shrubs within the home landscape
should be routinely maintained by removing dead or diseased
branches and foliage.
Flammability Plant List [PDF]
3) Fire spread and structural ignitions from horticultural
plantings in the wildland-urban interface
Description:
A new study, currently in progress, measures the rate of spread
and heat release for fires moving through four common southern
mulches under natural conditions. The mulches are also combined
with gallberry shrubs planted at several densities to determine
how mulches contribute to shrub (and ultimately structure) ignitions.
For each of the mulches and shrub/mulch combinations, several
drying schedules will provide insight into the value of irrigation
for reducing fire risk close to structures. Mulch and shrub
flammability will be repeated under controlled conditions in
a national fire lab and the results of both studies will provide
important information for new models that will be used for predicting
fire spread and structural ignitions in a variety of landscape
conditions.
Upon completion of this study, the knowledge gained about flammability characteristics of landscape plantings will help answer important questions such as: what are the flammability characteristics of plantings with different compositions and heights, how do drought and irrigation affect flammability characteristics, and what are the effects of planting designs on structural ignitions?
Summary
Collectively, these three important flammability studies are
providing critical data needed for modeling WUI fire behavior
as well as information needed by homeowners, community planners,
state forestry agencies, landscape architects, nursery owners,
and extension agents to create effective firewise landscapes
for communities in the wildland-urban interface and fuel mitigation
plans for adjacent natural areas.
Links to Additional Information about Fire in the Wildland-Urban Interface:
- Wildfire Risk Assessment Guide for Homeowners in
the Southern United States – See this guide to
determine whether your property is at risk of damage from
wildfires. It is available
in three formats:
- Download and print as a PDF: http://www.interfacesouth.org/fire/WildfireRAGH.pdf
- View interactive online version: http://www.interfacesouth.org/products/wildfire_ra.html
- Order full color print version: Add
to Cart
- Preparing a Firewise Plant List for WUI Residents – Use
this fact sheet for making local firewise plant lists that
can assist local homeowners with firewise landscaping. It
is available in three formats
- Download and print as a PDF: http://www.interfacesouth.org/products/fact_sheets/Preparing_Firewise_Plant_List.pdf
- View interactive online version: http://www.interfacesouth.org/products/flammability_key.html
- Order full color print version: Add
to Cart
- Reducing Wildfire Risk While Achieving Other Landscape
Goals - See this fact sheet to learn how to achieve
multiple goals with your firewise landscaping. This fact
sheet is available in two formats:
- Download and print as a PDF: http://interfacesouth.org/products/fact_sheets/Reducing_Wildfire_Risk.pdf
- Order full color print version: Add
to Cart
- Selecting and Maintaining Firewise Plants for Landscaping -
Download this fact sheet to learn to choose and maintain low flammability plants for your firewise landscape. This fact sheet is available in two formats:- Download and print as a PDF: http://www.interfacesouth.org/products/fact_sheets/Selecting_Maintaining_Firewise_Plants_Landscaping.pdf
- Order full color print version: Add
to Cart
- Understanding Fire Behavior - See this fact sheet for
an in-depth description of how and why wildfires burn.
http://edis.ifas.ufl.edu/FR138
- Considering Fire in Florida’s Ecosystems - Download this fact sheet to learn about the fire hazards for nine Florida ecosystems. http://edis.ifas.ufl.edu/pdffiles/FR/FR13700.pdf
