Frank C. Dennis
Colorado State University Cooperative Extension
- With
the growth of Colorado's population, more people
are moving into rural areas, increasing the chances
of wildfire.
- "Defensible
space" is the primary determinant of a structure's
ability to survive wildfire.
- Native
species are generally the best plant materials for
landscaping in the defensible space, but others
can be grown successfully in Colorado.
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Colorado's
population is growing, its urban areas are rapidly expanding,
and more and more homes are being built in what was once natural
forest. Those who move to rural areas often are misinformed
about how to correctly landscape their property.
Improper
landscaping worries land managers and fire officials because
it can greatly increase the risk of structure and property
damage from wildfire. The concern increases when one realizes
that it is a question of when, not if, a wildfire will strike
in any particular area.
Vegetative
clearance around the house (defensible space) is the primary
determinant of a home's ability to survive wildfire. Defensible
space is, simply, "room" for fire-fighters to do their job.
If grasses, brush, trees, and other common forest fuels are
removed, reduced, or modified to lessen a fire's intensity
and keep it away from the home, chances increase that the
structure will survive (see Figure 1). Development of defensible
space is outlined in Service in Action 6.302, Creating fire-safe zones around your forested homesite.
Colorado
has great diversity in climate, geology, and vegetation. Homesites
and cabins can be found from the foothills through 10,000
foot elevations. Such extremes present a challenge in the
development of species recommendations for multiple vegetative
zones. While native plant materials are generally best, a
wide range of species can be grown successfully in Colorado.
Recommended plants are listed in Service in Action 7.201,
Grass planting tips for mountain communities; 7.406, Garden
flower for mountain communities; 7.407, Shrubs for mountain
communities; 7.408, Trees for mountain communities; and 7.413,
Groundcover plants for mountain communities (excluding grasses).
Most
of these species can be used for landscaping in defensible
space if restraint and common sense are used and consideration
is given to plant arrangement and maintenance. Consider the
following factors when landscaping within the defensible space.
Table
1. Genesee Fire Control Seed Mix. |
Grass
| %
by weight
|
Crested
wheatgrass 'Ephriam' |
40 |
Buffalograss,
TREATED seed |
30 |
Arizona
fescue 'Redono' |
13 |
Hard
fescue 'Durar' |
13 |
Blue
grama 'Lovington' |
2 |
Sideoats
grama 'Vaughn' or 'Butte' |
2 |
Sow
at 15 pounds pure live seed/acre, or .5 to 1 pound pure
live seed per 1000 sq. ft. Rake seed in following sowing. |
Mow grasses
low in the inner zones of the defensible space; quite short
closest to the house and gradually increasing in height, outward
from the house, to a maximum of 8 inches. This is particularly
important during fall, winter, and before green-up in early
spring when grasses are dormant and in a "cured" fuel condition.
A "fire
safe" seed mix, developed by the Genesee Forestry Committee
(a homeowner group in the foothills west of Denver), creates
a relatively dense, low-growing, hardy, and easy-to-maintain
turf (see Table 1). The mixture has been used successfully
for several years. (Contact your local Soil Conservation Service
office or district office of the Colorado State Forest Service
for information on seed mixes for your particular area.)
Mow
grasses low around the house and garage, as well as around
out buildings, decks, firewood piles, propane tanks, shrubs,
and specimen trees with low-growing branches.
Wildflowers
bring variety to a landscape and can provide color from May
until frost. Wildflower beds give a natural appearance to
the otherwise manicured look often resulting from defensible
space development. (See Service in Action 7.233, Wildflowers
for Colorado landscapes.) A concern with wildflowers is the
tall, dense areas of available fuel they can form, especially
in dormancy. Plant wildflowers in widely separated beds within
the defensible space to mitigate fire hazard. Do not plant
directly adjacent to structures unless the beds are frequently
irrigated and vegetation promptly removed after the first
hard frost. Use gravel walkways, rock retaining walls, or
irrigated grass areas mowed to a low height to isolate wildflower
beds from each other and from other fuels.
Shrubs lend color and variety to the landscape in addition
to providing cover and food for wildlife. (See Service in
Action 7.407, Shrubs for mountain communities). However, shrubs
concern fire professionals because, as the next level in the
"fuel continuum," they can add significantly to total fuel
loading. They are a potential source of fire brands which,
when carried in the smoke column ahead of the main fire, can
rapidly spread the fire in a phenomenon known as "spotting."
But
the primary concern with shrubs is that they are a "ladder
fuel"--they can carry a relatively easy-to-control surface
fire into tree crowns. Crown fires are very difficult, indeed,
sometimes impossible, to control (see Figure 2). To reduce
the fire spreading potential of shrubs, plant low-growing,
non-resinous varieties close to structures. (Recommended plants
are listed in Service in Action 7.201, 7.406, 7.407, 7.408,
7.413.) Do not plant directly beneath windows or vents, or
where they might spread under wooden decks. Do not plant shrubs
under tree crowns, or use them to screen propane tanks, firewood
piles, or other flammable materials. Plant shrubs individually,
as specimens, or in small clumps apart from each other, and
away from any trees within the defensible space.
Mow
grasses low around shrubs. Prune dead stems from shrubs annually
and remove the lower branches and suckers from species such
as Gambel oak to "raise the canopy" away from possible surface
fires. (See Service in Action 7.205, Pruning evergreens; 7.206,
Pruning techniques for shrubs; and 7.207, Pruning deciduous
trees, for proper pruning techniques.)
Trees
provide a large amount of available fuel for a fire and can
be a significant source of fire brands if they do burn. Burning
trees give off a large amount of radiant heat that can ignite
nearby shrubs, trees, or structures.
Colorado's
elevation and temperature extremes limit tree species selection.
The best species to plant are generally those that are already
growing on or near the site, but others may be planted if
care and common sense are used. (See Service in Action 7.408,
Trees for mountain communities, for species lists.)
If your
site receives enough moisture to grow them, plant deciduous
trees such as aspen or narrowleaf cottonwood. These species,
even when planted in dense clumps, generally will not burn
well, if at all. The greatest problem with these trees is
the accumulation of dead leaves in the fall; remove accumulations
close to structures as soon as possible after leaf drop.
When site and/or moisture availability limits recommended
species to evergreens, carefully consider their placement.
Do not plant trees near structures. Allow plenty of room between
trees, and consider the growth potential of each species.
Spacing within the defensible space should be at least 10
feet between the edges of tree crowns (see Figure 3). Plant
smaller trees initially on a 20- to 25-foot spacing to allow
for tree growth. At some future point, it may be necessary
to thin your trees t retain proper spacing.
Prune
the branches of the trees as they grow (and those of any existing
trees on the site) up to a height of 10 feet above the ground.
Do not over-prune the crowns of smaller trees.
Some
trees (for example, blue spruce) tend to keep a full crown;
trees grown in the open may exhibit a full growth habit. Limit
the number of trees of this type within the defensible space.
Prune others as described above, and mow grasses around such
specimen trees.
Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
Service in Action
6.303
,
Cooperative Extension, Colorado State University. Published
September 1993. Copyright 1993. This Service in Action sheet
was produced in cooperation with the Colorado State Forest Service.
Some recommendations change regularly; contact your county Cooperative
Extension office or local State Forest Service office for current
recommendations or further information.
Frank C. Dennis, District Forester, Colorado State Forest Service.
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