• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

IMMEDIATE FIRE EFFECT ON PLANT:

Common juniper is generally killed or seriously damaged by fire [24,25]. Patchy fires may allow individual plants to survive in protected areas such as on rocky cliffs. More rarely, portions of a lightly-burned plant may survive. The amount of damage this species incurs increases with increasing fire severity [120].

In the boreal forest of Quebec, at least 37% of common junipers survived fire. Although the dominant fire regime here is crown fires or "important surface fires covering large areas," common juniper often survives on sites made up of exposed bedrock or where protected by lakes and island complexes. Survival can occur if fire affects only part of an area or where fires are of low intensity. In some cases, fires of low intensity "can allow sections of the plant to survive and reproduce vegetatively" [31].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

In a Scottish study, common juniper was killed by 1,472 ^oF (800 ^oC) heat treatment when heath was burned. Plants made only "feeble regrowth" when burned at 1,112 ^oF (600 ^oC). However, following treatment at 752 ^oF (400 ^oC), new shoots were produced [82].

PLANT RESPONSE TO FIRE:

Common juniper does not sprout after disturbance. Surviving individuals serve as sources of seed for adjacent areas. Postfire regeneration is more frequent in proximity to existing populations of common junipers [31]. Regrowth can generally take place after fire if some of the basal branches remain alive [82], which only occurs in fires of low severity or where spread is patchy.

Common juniper also reestablishes after fire through off-site seed dispersed by birds or mammals. Poor seed dispersal from existing stands along with low germination rates can explain why some favorable sites are not readily occupied by common juniper [31].

It is possible that seed protected by overlying soil can survive at least some fires. After low-severity fires, some seed may germinate. However, Mallik and Gimingham [82] observed that high temperatures did not increase germination in common juniper seed and little seed germinated after fire.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Following "light" (less than 50% litter reduction) fires in forested areas of western Montana, burned sites often exhibit minimal shrub damage and have at least some surviving common juniper [120]. Common juniper averaged 6.7% cover 3 years after a light burn in Montana [120]. Laboratory heating experiments on common juniper plants from Scottish heath showed that growth could take place after heating only if some of the basal green branches remain alive [82]:

effect of temperature* on vegetative regrowth after heating
                               400oC   600oC   800oC
mean # sprouts per plant
3 months after treatment        5        4       0

height of veg. regrowth (cm)
17 months after treatment       8        6       0

oven-dry biomass per plant of
veg. regrowth (grams)           3      0.8       0
17 months after treatment 

*"temperature maintained for about 2 minutes"

Postfire recovery of common juniper is generally slow. The following table gives the density and frequency of occurrence for common juniper in stands of different ages in 2 Colorado forest types [21]:

Stand    Spruce   Freq.   Stand  Lodgepole  Freq.
age      -fir             age    density
after    density          after
fire                      fire       
-----------------------------------------------
  1      ---        ---     1     ---       ---
  2      ---        ---     2     ---       ---
  8      ---        ---     8     ---       ---
  8      0.2         20     8     ---       ---
 18      0.2         20    18     0.2       20
 74      2.7         70    18     0.8       20
200      0.2          8    18     0.4       20
280      0.6         40    45     0.8       40        
290      0.4         20    85     2.0      100 
                           85     0.8       60
                          108     0.6       60
                          115     0.4       40
                          190     1.4       60 
                          248     0.8       20
                          251     1.3       30 
                          257     3.4       85 
 

FIRE MANAGEMENT CONSIDERATIONS:

In a north-central Colorado study of fire behavior in quaking aspen stands, common juniper patches burned more intensely and released more heat than adjacent herbaceous areas. A caloric analysis of 5 foliage samples yielded an average low heat content of 5064 kcal/kg. Common juniper fuels tended to be deeper and heavier than herbaceous fuels and flames were longer and deeper in common juniper patches. Fire removed almost all litter, standing herbs, and common juniper foliage, leaving only bare branches. The moisture of green common juniper foliage averaged 112% of oven dry weight on 2 burns [117]. Fuel loading for common juniper can be estimated as follows:

branch load (kg/m2) = .000191* crown height above duff
(cm) ** 2.135

foliage load (kg)   = 6.456* crown volume (m3) ** 1.93

Related categories for SPECIES: Juniperus communis | Common Juniper