Defensible space refers to that area between homes and an oncoming wildfire where vegetation has been modified to reduce the wildfire threat. At the same time it allows the opportunity for firefighters to safely defend the structures. If vegetation is properly modified a wildfire can be slowed by reducing flames lengths, heat intensity, and rate of spread and keeps fire on the ground, which becomes easier to control. Low intensity ground fires are a lesser threat to homes, communities, forest canopy and habitats. When creating defensible space and improving forest health, homeowners must also consider insect, disease, and hazard tree management, especially in a recreational community where safety is the highest priority.
Chinquapin on Lake Tahoe is a forest residential community located in Section 33, Township 16 North, Range 17 East, Mount Diablo Base Meridian, Placer County. Approximately four miles east of Tahoe City off of State HWY 28, on the north shore of Lake Tahoe at an elevation of 6229 feet. Aspect is southeast with flat to moderate sloping topography. Lake Tahoe to the south and east, Dollar Point subdivision to the west, and State HWY 28 to the north flank Chinquapin properties.
Vegetation is classified as Sierra mixed-conifer comprising of overstory trees of White Fir, Jeffrey Pine, Lodgepole Pine, Sugar Pine, and Incense Cedar. Understory vegetation is a mix of shrub species common to the Sierra’s and Lake Tahoe region. They consist of Huckleberry Oak, Snowbrush Ceanothus, Greenleaf Manzanita, Mountain Whitethron, Bitterbrush, Sagebrush, Currant, and Sierra Chinquapin. Also included in the understory vegetation regeneration of White Fir, Incense Cedar, and scattered Jeffrey Pine in disturbed open areas. Besides the above mentioned forest vegetation, there is accumulation of dead ground fuels. These fuels consist of needles, tree branches, tree-tops, down trees, and dead shrub species scattered throughout the common areas. All naturally occurring native plants and introduced species utilized in residential forest landscapes is potential wildfire fuel. The type, amount and arrangement of this vegetation (alive and dead) available for burning has a dramatic effect on fire behavior.
In creating defensible space in forest residential landscapes the first step should be looking at a healthy stand of well spaced, existing conifers, where trees do not compete for the three basic needs of light, nutrients and moisture. Where possible trees should be spaced in small groups or spaced so as live canopy are not touching. An expert would evaluate trees to be thinned base on age, size, and vigor.
Trees that have been attacked by bark beetles and show signs of dying should be removed immediately to reduce spread to adjacent trees. Disease is another forest pest that should be evaluated especially root, heart, butt diseases which weaken trees that become safety hazards to life and property. Mistletoe in conifers are parasitic plants whose roots penetrate the woody branches and trunks of trees and extract nutrients. Mistletoe causes branches or trunk to swell and crack open, allowing heart rot fungi to enter thus weakening the tree and increasing to possibility of branches or the entire tree to fall. Trees with heavy mistletoe next to structures should be considered for removal. If trees exhibit mistletoe in the lower branches, 8-12 inches from the trunk, those branches could be pruned reducing or eliminating the parasite and improving tree vigor.
Defensible space and forest health planning on forest recreation and residential sites must also include hazard tree evaluation and control decisions. Understanding probability of failure, target impact, and damage potential is an important concept in evaluating hazard trees in forest landscapes. Examples of trees that may be considered in the hazard category are leaning, multi-top, adjacent to structures and driveways causing damage to property. It is important to evaluate these types of hazard trees by a qualified examiner with experience and knowledge for effective hazard rating and control.
Second step in creating defensible space and a healthy forest landscape is the removal of dead fuels for a minimum of 30 feet and as slopes increase treatment distance would increase up to 100 feet. This management practice can be accomplished by removing dead shrubs, accumulation of dead ground materials, and pruning dead branches for conifers. Maintain clean roofs and decks free of needles and other natural debris. Tree branches that overhang and come in contact with structures should be pruned. Limbs that are within 10 feet of a fireplace chimney are required to be removed. To maintain the health and vigor of trees, pruning of live branches should be done during the late fall/winter when they are dormant. Retaining the upper 2/3 of the live crown height is also important for maintaining tree vigor. It is never recommended to cut the tops of live conifers.
Step three deals with perhaps the most important area for developing defensible space and forest health and that is live vegetation between the home and the surrounding wildland, common areas, and adjacent property. What type of treatment and management done in these areas will determine fire behavior and if the home is defendable by fire crews. Fuels in these high priority areas of both mixed conifers and shrub species that under the proper conditions burn with great intensity and at a rapid rate of spread. Treatment of shrubs should be by thinning, using a pruning technique creating openings or islands free of vegetation. The greater the density and height of shrubs the larger of openings, creating a mosaic landscape effect.
Conifers in these areas should be treated in the same prescription as mentioned in step one. Remembering that pruning is very important of the lower branches to reduce ladder effect of fuels and preventing a ground fire becoming a crown fire.
It is equally important to remember that when creating defensible space the property owner must be cognizant of water quality concerns. Treatments done inappropriately, implementing defensible space concepts could encourage accelerated soil erosion. Furthermore, the removal of all vegetation from the treatment area is aesthetically unacceptable. Thus creating islands in dense brush fields in a mosaic fashion is important. Most shrub species are prolific sprouts so live root systems are still anchoring the soil. When removing forest fuels, do so in a manner, which will result in a minimum of soil disturbance.
Step four address fire resistant landscaping and developing a continuing maintenance program. When landscaping with fire resistant plants they should be selected for their ability to thrive under local soil and climate conditions. Most State Foresters, Cooperative Extension, or a local nursery can suggest those suitable for the area and blend in with the native plants.
Vegetation modification and management programs provide short-term salutation in creating defensible space and healthy forest landscapes. Shrubs and conifers will regenerate new plants, and existing plants increase in size from year to year creating future management decisions. Each year plants naturally produce dead material both on the ground and within the plants, which accumulates and requires a long-term maintenance program. Conifers adjacent to structures may create concerns that may have to be evaluated from year to year by a qualified Forester.
The establishment of the grounds committee providing recommendations on annual work requirements and priorities to meet defensible space and healthy forest objectives is an asset to property owners.
On a yearly basis, a field inspection is conducted of Chinquapin by the Grounds Committee and CHOA staff to evaluate the property in order to make recommendations and set priorities for improving defensible space while creating a healthy forest habitat, and provide safety to the residents of Chinquapin. During this review the area of concern focuses on vegetation issues surrounding the individuals units, recreational facilities, roadways and parking areas. The common area extending out to Dollar Point and up to Dollar subdivision has had past forest management activity and is also evaluated on a regular basis.
Listed below are specific treatments which are done on a regular basis: