Watersheds and Fire

Where conditions are not too dry or too wet and where accumulated carbon from photosynthesis will not oxidize slowly or rot, fire cycles Carbon.

Watersheds and Fire

Where fire cycles Carbon, the effect on the watershed is natural only if fire regimes are natural (within the natural range of variability).

Types of natural fire regimes:

• Stand replacing forest fires where few if any trees survive and most new plants grow from seed.

• Over burning where all plants burn, overstory species die or resprout, and most understory plants survive to grow rapidly.

• Over burning where all plants are burned along with a lot of litter but few plants die.

• Under burning where trees survive and most understory plants survive to grow rapidly.

Short-term Watershed Effects are Proportional to Fire Intensity

• Decreased ET increasing runoff• Hydrophobic soils repelling water and increasing

runoff and erosion• Released nutrients, creating water pollution problems• Erosion of bare soil releasing sediments to streams

and lentic wetlands• Increased or decreased coarse woody debris for

energy dissipation and sediment detention • Diminished shade allowing insolation and thermal

pollution

Long-term Effects are Inversely Proportional to Fire Naturalness

• Changes to water flow adjusting the size of the channel• Erosion of bare soil diminishing soil water storage and

site productivity.• Sediment slugs entrenching or otherwise adjusting the

form of the stream or lentic wetlands• The temporal sequence of increased or decreased coarse

woody debris for energy dissipation and sediment detention

• Changes to vegetation, including invading species, interacting with the watershed and future fires

Riparian Fire/watershed Hypotheses

• Fire is as natural in riparian systems as it is in upland systems

• Fire frequency is lower where green leaves, water, and moist soil increase humidity and cause upland fires to stop or burn around riparian areas

• A high water table and floodplain access diminishes riparian fire intensity and frequency

• Accumulated woody fuel in the absence of fire may increase fire intensity, heat, and consumption of coarse woody debris needed by streams for energy dissipation and sediment retention.

Pinyon Juniper Fire/watershed Hypotheses:

• PJ has expanded into many sagebrush areas with the diminished fire frequency of the past 130 years

• PJ and adds fuel increasing fire heat fire size and watershed effects

• PJ diminishes the understory decreasing release of native perennial plants after fire

• Increased ET before the fire and decreased soil volume after a PJ and fire history in a watershed watershed can dehydrate springs and riparian areas

Invasive Annuals Fire/watershed Hypotheses:

• Annuals, especially cheatgrass, increase fire frequency and size while they decrease fire perimeter/unit area

• The loss of shrubs alters snow catch and the seasonality of ET

• Frequent fires increase the exposure of soil to wind and water erosion.

• Annual weeds facilitate perennial weeds which are not good at protecting soil.

Trigger Event ?

Alternative State --Annuals & Frequent Fire

Cycle--