FIRE EFFECTS
SPECIES: Pinus edulis | Colorado Pinyon 



IMMEDIATE FIRE EFFECT ON PLANT : 
Pinyons are generally very susceptible to fire mortality [12,40.  Tree
mortality, however, is largely determined by the extent to which trees
dominate a site.  Where pinyon trees have recently invaded grassland
communities, young trees less than 4 feet (1.2 m) tall are easily
killed.  As tree dominance increases and the understory is gradually
suppressed, the ability of the understory to carry fires intense enough
to kill larger trees also decreases [57]. 


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Colorado pinyons reestablish from seed cached by rodents and birds after
fire.  Reentry into the plant community depends upon perennial nurse
plants associated with mid-successional and late-successional stages.
Although trees become established 20 to 30 years after burning,
coverages and densites are relatively low until approximately 60 years
after fire, at which time tree dominance begins to exceed that of the
understory.  Pinyons dominate a site within 100 to 150 years of burning
[30,56].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Since pinyons usually require protected sites near the base of 1- to
2-foot-tall (0.3-0.6 m) shrubs for successful establishment, pinyons can
be expected to reestablish sooner on sites where mid to late seral
stages existed prior to burning.  Pinyons begin to dominate sites very
early in the sere, usually when trees are only 3 to 6.5 feet (1-2 m)
tall.  As tree roots grow into moisture supplies, understory species
decline at an increasingly rapid rate.  Areas converted to grasslands
should be burned every 20 to 40 years depending on the rate of pinyon
reinvasion [57].


FIRE MANAGEMENT CONSIDERATIONS : 
Prescribed fire is no longer an effective managment tool on many
pinyon-juniper sites where prolonged tree dominance has not only reduced
the ability of the understory to carry fires but has also seriously
lowered the ability of the understory to respond to fire.  When fires do
occur in closed stands, intensities are often so severe and the soil
seed reserves so depleted, that without successful seeding, highly
flammable annual grass communities are often established [13,54].  On
many overgrazed woodlands, seeding burns is the only way to restore a
desirable perennial grass stage.

Prescribed fire can be used on some sites, depending on stand structure
and understory composition.  In open stands with 700 to 1,000 pounds per
acre (786-1,123 kg/ha) of fine fuels, low-intensity spring fires are
very effective in eliminating pinyon less than 4 feet (1.2 m) tall.
Mortality of taller trees in open stands is relatively low unless fuels
have accumulated around tree bases (12,57].  Optimal burning conditions
in open stands are:  air temperatures of 70 to 74 degrees Fahrenheit
(21-23 deg C); relative humidiy of 20 to 40 percent; and wind speed of
10 to 20 mph (16-32 km/h).

Closed stands with little understory are extremely difficult to burn and
carry fires only on hot summer days when burning conditions are often
hazardous:  air temperatures of 95 to 100 degrees Fahrenheit (35-38 deg
C); low relative humidity; and wind speed of 8 to 20 miles per hour
(13-32 kmh).  Burning under these conditions usually results in
extremely intense crown fires.  Fires carry better as tree density
increases and as the proportion of pinyon to juniper within a stand
increases.  This increased ease of burning has been attributed to both
the greater flammability of pinyon and the increased site potential
associated with pinyon-dominated stands [7].

In the Great Basin woodlands, the best candidates for effective
prescribed burning are ecotonal areas where trees have invaded
sagebrush-grassland communities; sites usually have a shrub and tree
cover ranging from 45 to 60 percent [8].  These sites can be burned
effectively with low-intensity spring burns which eliminate the tree
overstory; in most cases, reseeding is not required for adequate
postfire understory response [13].

Related categories for Species: Pinus edulis | Colorado Pinyon