How Frequent, How Hot, How Big
Fire in the ApplegateEcosystem health is dependent on change. Suppressing change, like suppressing fire or freedom, is a short-term solution. As we are witnessing, fire may be temporarily suppressed, but it will return even stronger than before. Fire suppression can also open the way for disease or infestations. Rather than being passive observers of this process, however, we can collectively work to help select the agent(s) of change, be it us, fire, diseases, insects, or some acceptable combination of them all.
The basic patterns and processes of ecosystems are shaped not only by life cycles of plants and animals but also by nonliving disturbances such as fire, drought, and wind. The place and time of such forces are often unpredictable, but all these forces help maintain the differences in the natural communities and increase the natural variability of ecosystem structure, composition, and function (Kaufmann, et. al. 1994). Fire as one of these forces is not only unpredictable; its results are often not repeatable (Lavern 1996).
Fire has played an integral part in creating the forest environment of the Pacific Northwest (Agee 1981) and a particularly significant function in shaping plant communities in southwestern Oregon (Atzet and Wheeler 1982). Overall, the Applegate watershed should be considered a fire-dependent ecosystem with numerous fire-adapted species of plants and animals dependent on fire to recycle nutrients, regulate plant succession and wildlife habitat, maintain biological diversity, reduce biomass, and control insects and diseases.
As we take a new and closer look at our relationship with fire here in southwestern Oregon, we need to consider the following elements:
* Historic fire regimes: a term used to refer to the frequency, intensity, seasonality, duration, and extent of fire
* Condition classes: a classification system using key components of the ecosystem to describe the degree of departure from historic fire regimes
* Fire hazard: the likelihood of a specific area to have a catastrophic wildfire, based upon five physical elements (vegetation, canopy cover, slope, aspect, and elevation)
* Fire risk: the chance of fire starting as determined by the presence and activity of causative agents
* Fire occurrence: the average number of fires in a specified area during a specified time.
All of these elements play a role in determining a fire plan for any given piece of land. What follows is a discussion of each of them.
Fire Regimes
The behavior of fire - how often it occurs, how hot it burns, how big it is, in which season it occurs, and whether it is a crown, surface, or ground fire - defines the fire regime. The fire regime depends on the physical, climatic and biological (including human) environment.
Each vegetative type is adapted to its particular fire regime (Agee 1981). The plants that existed in the Applegate watershed prior to Euro-American settlement were adapted to a different fire regime from the current one. Years of fire exclusion and climatic change have caused a shift in vegetation away from the more fire-adapted species that formerly predominated. Attempting to restore the vegetation associated with a past climate may not be appropriate.
Several classifications and descriptions of fire regimes have been developed. The one chosen for this document was based on national and regional scales (Heinselman 1981, Davis and Mutch 1994, Agee 1981) and developed by the Oregon BLM State Office and the Pacific Northwest Region of the Forest Service.
Natural areas within the Applegate watershed fit generally into three classes and one sub-classification of the seven categories of fire regimes. The following is an identification of each of these fire regimes in the Applegate along with a general discussion of the plant community, fire type, and fire severity of each. As you read, keep in mind these two important considerations:
(1) Categorization produces simplification, exceptions abound, and combinations of fire regimes are likely to apply to single ecosystems. For example, the Quartz Fire area, at the high elevations, contains regimes 6 and 1.
(2) Almost all fires have various proportions of severity and intensity. Thus, under-burning and crown fires might occur in the same event.
Fire Regime #1: 0-35 years between fires, which are of low severity. Typical climax plant communities of this regime include ponderosa pine, eastside and dry Douglas-fir, pine-oak woodlands, Jeffery pine on serpentine soils, oak woodlands, and very dry white fir. Large stand-replacement fires can occur under certain weather conditions but are rare events (i.e. every 200 years or more). It is more probable that fire will occur frequently and be of low intensity, and most of the dominant trees are adapted to resist such fires. One such adaptation is the development of thick bark at a young age. This adaptation means that a fire will affect mostly small trees in the under-story, limiting over-story mortality. Fires in a low-severity regime are associated with ecosystem stability, as the system is more stable in the presence of fire than in its absence (Agee 1990). Frequent, low-intensity fires keep sites open, which are then less likely to burn intensely even under weather conditions conducive to severe fire.
Fire Regime #2: 0-35 years between fires, which are usually stand-replacing. This category includes true grasslands (Columbia basin, Palouse, etc.) and savannas, where fire typically returns every ten years or less. It also includes mountain shrub communities (bitterbrush, snowberry, ninebark, ceanothus, Oregon chaparral, etc.) where fire returns every 10-25 years. Fire severity is generally high to moderate. Grasslands and mountain shrub communities are not completely killed in a fire but are usually only top-killed, and they usually re-sprout without difficulty.
Fire Regime #3: 35-100 or more years between fires, which are of mixed severity. This regime typically results in heterogeneous landscapes. Large, stand-replacement fires may occur, but rarely. Such fires may destroy large areas of vegetation (10,000-100,000 acres), but subsequent mixed-intensity fires are important for creating heterogeneity in the landscape. Within these landscapes a mix of ages and sizes is important; generally the landscape is not dominated by one or two age classes.
Fire regime subcategory of #3: Fires occur every 50 years or less and are of mixed severity. Typical plant communities include mixed conifer, very dry west-side Douglas fir, and dry grand fir. Lower severity fire tends to predominate.
Certain species of plants and animals in southwestern Oregon have been able to exist here for millennia because of their adaptations for fire survival - adaptations to a particular ecosystem and its specific fire regime (Kauffman 1990). If the regime is altered, the capacity for that species to survive in the environment may be greatly changed. Hence, if an area has a fire regime of frequent fire and if, through suppression, that regime has been altered, then the hazard of catastrophic fire has been increased and such a fire poses a greater risk to adjacent land and to the inherent value of the land itself.
Prolonged fire exclusion in ecosystems of the Pacific Northwest ended the pattern of frequent, low-intensity fires which used to keep the forest free of dead limbs, downed trees, and over-abundant under-story vegetation. Years of fire suppression have created a trend towards increasing amounts of fuel in the forests and higher intensity, stand-destroying fires rather than the historic low-intensity, stand-maintenance fires.
Condition Classes
Historically, wildland fire frequently burned in most areas of the Applegate watershed. In recent decades, however, the nature of fire on these lands has changed, and, due to fire exclusion and other human activities such as grazing and timber harvest (Kaufmann et. al., 1994), the ecosystems have also changed dramatically. The extent and impact of this change can often be correlated to the fire regime itself. Thus, fire exclusion would have less impact on the ecology of an area characterized by a combination of infrequent crown fires and severe surface fires than on an area that typically experienced light surface fires every one to twenty-five years. An aggressive fire suppression program that has been in place for approximately sixty years would have more impact on an area where fire historically occurred at low intervals than on an area that historically hosted fire every 100 to 300 years.
The detrimental effects of fire suppression in these latter regimes will take longer to appear. Old, dense stands, covering a large portion of the landscape in these higher frequency regimes, can dramatically increase the size and severity of wildfires (Barrett et al. 1991) and insect epidemics (Mutch 1994).
A series of Condition Classes has been developed to describe the extent the current fire regime has deviated from "normal" (Hardy et al, 2000). These are based on changes in the species composition, structure, age, and density of a stand and are used to quantify the condition of the land resulting from fire exclusion and other influences (timber harvesting, grazing, insects, disease, and the introduction and establishment of non-native plant species). This analysis attempts to quantify the extent of the fire management problem and the degree of required restoration and maintenance treatments.
Below is a summary of the three condition classes, the attributes of each class, and general management options.
In Condition Class 1, fire regimes are within or near the historical range; fire frequencies differ from historical rates by no more than one return interval, and the vegetation's species composition and structure are intact and functioning within the historical range. The risk of losing key ecosystem components is low. Where appropriate, these areas can be maintained within the historical fire regime by treatments such as fire use.
In Condition Class 2, fire regimes have been moderately altered from their historical range; the frequency of fire differs from historical rates by more than one return interval. This change results in moderate changes to landscape patterns and/or to fire size, frequency, intensity, and severity. Vegetation has been moderately altered from its historic state. The risk of losing key ecosystem components has increased to moderate. Where appropriate, these areas may need moderate levels of restoration treatments, such as fire use and hand or mechanical treatments, to be restored to the historical fire regime.
In Condition Class 3, fire regimes have been significantly altered from their historical range; fire frequency is greatly different from its historical pattern. This change results in dramatic changes to landscape patterns and/or to fire size, frequency, intensity, and severity. Vegetation has been significantly altered from its historic state, and the risk of losing key ecosystem components is high. Where appropriate, these areas need high levels of restoration treatments. Hand or mechanical treatments may be necessary before fire is used to restore the historical fire regime.
Roughly 30% of the Applegate watershed currently fits into Condition Class 3, mostly due to fire exclusion. Fire exclusion has created vegetation and fuel conditions for large and catastrophic fires that are more difficult to suppress than smaller fires. Throughout the watershed, our forests present a continuous fuel supply both vertically, in small, thin trees and dead branches (ladder fuels), and horizontally, in an abundance of dead and down material. When a fire gets started in such a forest, the dead branches, sticks, twigs, and other material increase fire intensity and, with ladder fuels present, provide great opportunity for the fire to reach the forest canopy, resulting in a stand-killing crown fire. These conditions also affect the means in which prescribed fire and fuels treatment are applied to the landscape.
Fire Hazard
Why do some fires spread faster than others? A number of factors important to a fire's ability to spread determine the "fire hazard" of an area and also affect the difficulty or ease we have in suppressing the fire. Various schemes for rating fire hazard have been developed; the one used in this analysis is based on five elements chosen by all agencies: vegetation, canopy cover, slope, aspect, and elevation.
Vegetation directly influences rate of spread, flame length, fire line intensity, heat per unit area, and other elements of concern in the suppression of wildland fire. A hillside with lots of highly volatile ceanothus, for instance, has a higher hazard rating for vegetation than one with more fire-resilient species such as Madrone or Douglas-fir.
Canopy cover and ladder fuels are closely related when it comes to hazard rating. A greater percentage of ladder fuels means a greater likelihood of a surface fire moving into the crown canopy, increasing the difficulty of suppressing the fire. An area with a thick shrub cover has a higher hazard rating than a grassy area, which has neither canopy cover nor ladder fuels. A conifer or conifer/hardwood mixed forest has a higher hazard rating than a hardwood forest if both have the same amount of ladder fuels. If there are no ladder fuels present, a closed canopy will not, by itself, cause a crown fire.
Gravity dictates that many if not most things travel downhill faster than uphill. Not so with fire, which defies gravity in obedience to other laws of physics (warmer air rises). Thus, slope is a factor in the rate of fire spread. As the slope becomes steeper, fire increases in speed. On flat terrain, the spread of fire relies more on wind.
Aspect affects fire spread in that southern aspects are drier and warmer, promoting a more active fire, whereas the typically cooler and damper northern aspects have a lower level of fire behavior.
The last element to consider in rating fire hazard is elevation. Lower elevations get a slightly higher rating than higher elevations because they receive less precipitation. A number of factors come into play with elevation such as length of fire season, variations in weather conditions (cool, damp, warm, wet), density of vegetation, etc.
Once all five elements have been determined for an area, it can be given a hazard rating: the higher the rating, the worse the hazard. Thus an area dominated by a thick canopy of shrub with a steep, south slope at a lower elevation would have a higher hazard rating than a grass meadow with a slight northerly slope at a high elevation. Hazard, combined with other considerations such as risk and value-at-risk, can be useful in understanding and planning for fire management problems, identifying opportunities, and prioritizing areas to meet goals, objectives, and desired future conditions for the watershed.
The map following page 22 shows fire hazard ratings for the Applegate watershed as computed by local agencies using the most recent data for vegetation and canopy closure. Each of the five elements is given point scales; ratings reflect the total points an area receives.
Fire Risk in the Applegate
Although we watch the skies anxiously when summer thunderstorms threaten to rain lightning into our dry forests, it seems it might be wiser to watch ourselves. When it comes to fire risk in the Applegate, human beings are more dangerous than lightning.
"Fire risk" is a self-explanatory term - how much chance is there that a fire will start? - but it also has a technical definition: the chance of fire starting as determined by the presence and activity of causative agents.
Human activity is certainly one of these causative agents, so human actions greatly influence the pattern of fire risk - as well as the number of fires - in the watershed. In fact, human activities are highest on the list of causative agents and include mowing, landscape maintenance, "backyard" burning, farming, ranching, timber management, light manufacturing, mining and quarry operations, recreation, tourist and travel activities, and electrical transmission. Typically, a human-caused fire in the watershed starts at low elevations along roads and in the wildland-urban interface and burns up to the ridge tops. When these fires occur under conditions of high and extreme fire danger, they are often costly, difficult to suppress, and highly damaging. Because of the frequent threat to life, property, and other resources of high value, they require a large and complex response to suppress them.
Lightning occurs in the watershed on a moderate to high frequency with, typically, at least two or three lightning storms every summer. Typically, but not exclusively, lightning-caused fires occur in the ridge-top areas and on the upper portions of the slopes.
Fire Occurrence
Fire occurrence (or fire incidence) is also self-explanatory - and also has a technical definition: the average number of fires in a specified area during a specified time. In the Applegate between 1970 and 1999, a specified time period with available data, fire occurrence averaged about 78 fires per year. 56% of the 2,257 fires in the Applegate watershed during those 29 years were human caused. The remaining 44% were started by lightning. (See map following page 22.)
In assessing an area's complete fire situation, all the factors discussed above need to be considered: the historical fire regime, the area's history of fire occurrence, the area's current condition class and fire hazard rating, and the area's fire risk. Some of these we can affect and change if we so choose.