Ecology - Wildland Fuel Fundamentals and Applications - page 90

Table 6.2 The eleven terms often used to describe disturbance regimes
Disturbance characteristic Description Example

Agent Factor causing the disturbance Mountain pine beetle is the agent that kills trees

Source, cause Origin of the agent Lighting is a source for wildland fire

Frequency How often the disturbance occurs or its return time Years since last fire or beetle outbreak (scale dependent)

Intensity A description of the magnitude of the disturbance agent Mountain pine beetle population levels; wildland fire heat output

Severity The level of impact of the disturbance on the environment Percent mountain pine beetle tree mortality; fuel consumption in

wildland fires

Size Spatial extent of the disturbance Mountain pine beetles can kill trees in small patches or across

entire landscapes

Pattern Patch size distribution of disturbance effects; spatial hetero-

geneity of disturbance effects

Fire can burn large regions but weather and fuels can influence fire
intensity and therefore the patchwork of tree mortality

Seasonality Time of year of that disturbance occurs Species phenology can influence wildland fires effects; spring

burns can be more damaging to growing plants than fall burns on
dormant plants

Duration Length of time of that disturbances occur Mountain pine beetle outbreaks usually last for 3-8 years; fires can

burn for a day or for an entire summer

Interactions Disturbances interact with each other, climate, vegetation,

and other landscape characteristics

Mountain pine beetles can create fuel complexes that facilitate or
exclude wildland fire

Variability The spatial and temporal variability of the above factors Highly variable weather and mountain pine beetle mortality can

cause highly variable burn conditions resulting in patchy burns of
small to large sizes