• 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:

Western juniper is a nonsprouter that is generally killed by severe fires [11]. Younger trees have thin bark and are readily killed by surface fires [87]. Older trees with thicker bark, little fuel near the stem, and higher foliage are moderately resistant to fire [38,87]. Fire may not carry in open stands of mature trees with sparse understory vegetation [15].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

Western juniper foliage is not easily ignited and/or scorched when moist [17]. Western junipers under 4 to 6 feet (1.2-1.8m) tall are readily killed by fire [64,17]. A more severe fire is necessary to kill taller trees [64].

PLANT RESPONSE TO FIRE:

Mature trees are somewhat resistant to fire if the crown is not scorched, so some larger trees may survive low-severity fires and serve as a seed source [67]. Western juniper first becomes dominant 30 to 50 years after fire [15]. Reoccupation of a site occurs fairly slowly through dispersed seed [19,25].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Recovery time depends on the size of burn, location of seed source, stand maturity, and presence of animal dispersers [19]. Postburn succession in western juniper communities depends on season of burn, postfire mortality, and on seed of associated species present in the preburn community. Postfire succession is also related to the effects of competition from herbaceous species and shrubs as well as drought. Large burns and long distances from seed sources slow recovery rates. According to Bunting and others [17] "because these factors vary widely early seral community composition is highly variable." Fire scars have been observed on western junipers found growing in fire-resistant low sagebrush communities lacking perennial grass cover [103].

FIRE MANAGEMENT CONSIDERATIONS:

Western juniper sites with less than 1,322 pounds per acre (600 kg/ha) of fine fuels are difficult to burn [16]. As the crown of an established western juniper expands over time, herbaceous production declines from the combined effects of shading, litter accumulation, and soil moisture [1]. Trees create their own fine fuel break, so these stands may be virtually "fireproof" except under the "most severe burning conditions" [1,103]. Many western juniper woodlands have advanced to a point where prescribed fire is no longer a viable management option. For example, in extremely dense stands, prescribed burning would be both hazardous and expensive. In some cases, weedy annuals prevent the establishment of more desirable perennial species after fire [16].

However, prescribed burning can in some instances be used to reduce western juniper dominance [20,66]. In areas of western juniper invasion, prescribed fire may offer the best means of control [83]. Warm dry conditions are necessary for fire to carry in western juniper woodlands. Often mature open stands can be used as fuel breaks. Steady winds greater than 5 miles per hour (8.1 k/h), temperatures of at least 68 degrees Fahrenheit (20^oC), and relative humidity of less than 25% are generally required for a successful burn [15]. Generally, where tree cover is greater than 30%, there is so little herbaceous understory that extremely high winds are needed to support a burn [70]. Thirty- to 50-year-old western junipers under 10 feet (3.1 m) in height and with an understory are fairly easy to burn, as are dense, uneven-aged mature stands [15].

Western juniper slash can be burned where fine fuels average 400 to 700 pounds per acre (181-318 kg/ha), and where slash fuel ¼ to 3+ inches (0.6->8 cm) totals at least 4 tons per acre (11 Mg/ha). For best results, trees should retain their needles and fuels should be fairly continuous. A rest from grazing followed by a late summer to fall burn can produce better results due to more continuous fine fuels [63].

Western juniper tends to have more resinous foliage than many other species. Ash and heat content values are as follows [97]:

                        foliage   litter   cones   woody fuel

average ash content (%) 4.26      5.31     3.42    1.35-2.80
average heat content
    with ash  (mJ/kg)   23.64     22.53    23.68   20.04-20.27
average heat content 
without ash (mJ/kg)     24.70     23.79    24.51   20.31-20.66 

heat per Unit Area   fireline intensity  flame length	
(reaction intensity)
0.98                 0.95                0.98

Related categories for SPECIES: Juniperus occidentalis | Western Juniper