Coexisting with Fire in the BCCER

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Fire is the single greatest external force affecting terrestrial ecosystems in Northern California. The last major fire in the Big Chico Creek Ecological Reserve (BCCER) occurred in 1999 and burned about two-thirds of the reserve. Old fire scars and multiple-trunked trees attest to numerous earlier fires. Anecdotes about the Maidu people managing ecosystems with fire coupled with archeological evidence suggest that people set fires in the BCCER area for thousands of years. Reserve ecosystems should be considered to be adapted for periodic fire and expected to change character in its absence.

Fire suppression in the western U.S. has been shown to be inadequate and counterproductive since it allows fuel to accumulate. Each year the amount spent on fire-fighting goes up and so does the damage done by wild fires. Effective habitat management must assume fire will occur and focus on controlling the way fires will affect the ecosystem. Deliberately set and controlled fires can be an important management tool.

Depending on circumstances fire can be a force for change (as causing a stand of trees to be replaced by shrubs) or for stability (preventing shrub encroachment into a meadow or reducing fuel load to a level where mature trees are not damaged by subsequent fires.) In the BCCER we are trying to set up a system where the inevitable fires will act as forces for stability rather than change. Since grasslands and shrublands typically return to their former condition within a few months or years of a fire, our major fuel management activities are concentrated in tree-dominated habitats.

Fire depends on weather, which cannot be controlled, and fuel, which can. While all organic material in an ecosystem could be fuel in a sufficiently hot fire, in most wildland fires only certain fuel components contribute to the fire. Chief among these are small-diameter dead wood not in contact with the ground and thick, waxy or resinous leaves such as those of buck brush, toyon, bay, mazanita, scrub oak, interior-live oak, and needles of conifers. These fuels generate enough quick heat to kill mature trees, which, themselves, are seldom consumed in a wildfire. An equally bad source of tree damage comes from slow-burning ground fuels like duff or dry logs that have accumulated adjacent to trees, particularly on the uphill side, where they generate localized heat for long periods after the passing of the fire front.

Even when the fire is hot enough to kill their leaves, many trees will survive, sprouting new limbs and leaves. However, if the base of the trunk is heated enough to kill the cambium layer, the tree will be effectively girdled and will die in a few years if not immediately. When only one side is heated enough to kill the cambium, bark will eventually peal from the killed spot, permitting invasion of fungus and insects that further weaken the tree. If not felled by wind or gravity, the tree will gradually grow new tissues around the wound and seal it off. A second fire coming before the dead wood is covered may burn into that dead wood and enlarge the wound. Repeated assaults will weaken the tree to the point where it eventually falls.

Several factors influence the ecological value of a native tree:
Placement -- A tree that helps shade the creek is of particular value on the ecological reserve since summer creek temperatures often exceed optimal temperature for trout and salmon. Isolated trees provide forage perches for raptors and flycatchers.
Size -- Larger individuals are more valuable because they provide more ecosystem structure and require a longer time for replacement. However, a range of sizes is important to perpetuate the population. Different ages also provide different resources to other species (for example, juvenile oaks provide deer and rabbit browse while adult oaks yield acorns eaten by many species.)
Scarcity in that area -- Since nearly all species have other species that depend on them for some aspect of their life cycle, presence of even a few individuals of a large organism like a tree may substantially increase local biodiversity.
Living spaces -- Damaged or even dead trees may provide cavities for refuges, dens or food caches.
Cluster -- A group of trees provides a different habitat than does a single tree; therefore a group of trees equates to a valuable resource component.

Snags (standing dead trees) are a valuable component of the woodland ecosystem and should be left whenever practical since they provide perches for birds and food for insects such as beetles and termites that, in turn, provide food for other species. Snags are particularly valuable for woodpecker habitat.

Fuel breaks

Maintenance of a shaded fuel break may be thought of as shifting dominance from shrubs to trees. In the absence of fire, the various tree species gradually overgrow and outcompete the shrubs, which eventually die. If no fires occur for sufficient time the trees get very large and the shrub layer completely decomposes; subsequent fires can run over the ground killing seedlings without hurting the mature trees. However, if a fire comes through while there is still a mixture of shrubs and trees, the shrub layer will burn with enough heat to kill many of the trees. The shrubs will regenerate from the roots or from seeds and, with the fire-killed trees, soon provide enough fuel to carry another fire that will kill still more trees. Thus, a series of fires spaced a few years apart will create a shrub-dominated system.

To create a fuel break we artificially generate a system that mimics the mature forest. We remove shrubs, surface and ladder fuels, selectively leaving trees that will eventually be large enough to suppress shrub growth. Obviously fuel breaks require maintenance, but the amount should decrease as the trees grow.
Fuel breaks don't stop a fire but they create an area of reduced fire intensity, providing a starting line for firefighters or reducing the heat that sweeps into an adjacent habitat. In a properly prepared fuel break, most fires will pass through without substantially changing the ecosystem structure.

See also: BCCER Vegetation Management Plan