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Condition class attributes is an approach to defining and interpreting the importance of fire frequency in ecosystems. This concept is useful in helping wildland fire communicators convey to their audiences the science and management behind wildland fire.
Current "condition class" is defined in terms of departure from the historic fire regime, as determined by the number of missed fire return intervals with respect to (1) the historic fire return interval, and (2) the current structure and composition of the system resulting from alterations to the disturbance regime. Five combinations of fire frequency are defined. Groups I and II include fire return intervals in the 0–35 year range. Group I includes ponderosa pine, other long-needle pine species, and dry-site Douglas fir. Group II includes the drier grassland types, tall grass prairie, and some chaparral ecosystems. Groups III and IV include fire return intervals in the 35–100+ year range; and Group V is the long-interval (infrequent), stand replacement fire regime.
Three "Condition Classes" have been developed to categorize the current condition with respect to each of the five historic Fire Regime Groups. The relative risk of fire-caused losses of key components that define the system increases for each respective higher numbered condition class, with little or no risk at the Class 1 level. Features of each condition class are defined through a qualitative description of the current state of five key ecosystem attributes: (1) disturbance regime; (2) effects of disturbance agents; (3) potential production of smoke emissions; (4) hydrologic function; and (5) vegetative composition, structure, and resilience.
These first two fire regime groups occupy nearly all the lower elevation zones across the United States. They have been most affected by the presence of human intervention and analysis shows that these types demonstrate the most significant departure from historical levels. The departures are affected largely by housing development, agriculture, grazing, and logging. These areas are at greatest risk to loss of highly valued resources, commodity interests, and human health and safety. It is expected that these areas will receive primary focus of wildland management agencies in the future.
| The Five Historic Natural Fire Regime Groups | ||
| Fire Regime Group |
Frequency (Fire Return Interval) |
Severity |
| I | 0–35 years | low severity |
| II | 0–35 years | stand replacement severity |
| III | 35–100+ years | mixed severity |
| IV | 35–100+ years | stand replacement severity |
| V | >200 years | stand replacement severity |
Disturbance Regime
The historic disturbance regime is largely intact and functioning as defined by the historic natural fire regime.
Disturbance Agents
The effects of insects and disease as well as the potential intensity and severity of fire are within historic ranges, but are increasing with length of current fire return interval.
Smoke Production
Smoke production is relatively frequent, but is low in volume and short in duration.
Hydrologic Function
The hydrologic functions are within normal historic range.
Composition, Structure, and Resilience
Vegetative composition and structure are resilient to disturbances from wind, insects, disease, or fire and Do not predispose the stand or its key components to a high risk of loss.
Disturbance Regime
Moderate alterations to the historic disturbance are clearly evident, such as one or more missed fire return intervals.
Disturbance Agents
The effects of insects and disease as well as the potential intensity and severity of fire pose an increased threat to key components that define the system.
Smoke Production
Smoke production has increased both in volume and in duration and has increased potential to affect health and visibility values.
Hydrologic Function
Riparian areas and their associated hydrologic functions show measurable signs of adverse departure from historic conditions.
Composition, Structure, and Resilience
Both the composition and structure of vegetation has shifted towards conditions that are less resilient and are therefore more at risk to loss from wind, insects, disease, or fire.
Disturbance Regime
The disturbance regime has been significantly altered and historic disturbance processes and effects may be precluded.
Disturbance Agents
The effects of insects, disease, or fire may cause significant or complete loss of one or more defining ecosystem components.
Smoke Production
Episodic smoke production is unpredictable and of high volume and long duration, posing signifi-cant impacts to human health, safety, and societal values.
Hydrologic Function
Hydrologic functions may be adversely altered, with significant increases in sedimentation potential and measurable reductions in streamflows.
Composition, Structure, and Resilience
The highly altered composition and structure of the vegetation predisposes the stand or ecosystem to disturbance events well outside the range of historic variability, potentially producing changed environments never before measured. Additional information can be found on these condition classes in Protecting People and Sustaining Resources in Fire-Adapted Ecosystems–A Cohesive Strategy published by the National Wildfire Coordinating Group.
Hardy and other researchers from the USDA Forest Service have provided the research to develop these condition class attributes. This group of researchers has developed a spatial database of historic natural fire regimes for the eleven western states to provide information to support prescription burning. The base-layer spatial data they used was a 159-class Land Cover Classification database derived from seasonal profiles from the USGS EROS Data Center. In order to assign fire regimes to Land Cover Characterization databases they added in biophysical data, Kuchler's unit data (4th code), and the ecological subregions based on Bailey's sections. The resulting knowledge will help decisionmakers determine what level of fire activity may be required. For example, can initial entry fire be used for maintenance? Can fire be used to achieve restoration objectives? Is supplemental mechanical treatment required as a precursor to prescribed fire?
While this level of scientific specificity may be more than many audiences need, communicators must fully brief themselves on emerging scientific thinking in order to more fully explain the science and management of wildland fire.
For more information on this topic contact:
Colin C. Hardy
James P. Menakis
Donald G. Long
USDA Forest Service
Rocky Mountain Research Station
P.O. Box 8089
Missoula, MT 59807
David L. Bunnell
USDA Forest Service
National Interagency Fire Center
3833 S. Development Avenue
Boise, ID 83705