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Wildlife, Animals, and Plants |
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FIRE EFFECTS
IMMEDIATE FIRE EFFECT ON PLANT:Alligator juniper appears resistant to the effects of fire [12,74,133]. Consequently mortality of alligator juniper is generally low, even after fires of relatively high severity [107]. The probability of mortality may depend at least in part, on the size of the tree. In many instances the smallest alligator junipers appear to be most susceptible to fire-caused mortality [67]. As many as 32% of alligator junipers < 3 inches (7.6 cm) in dbh were killed after a hot June wildfire in southeastern Arizona [16]. Trees with a dbh of 31 inches (79 cm) or more do not resprout and may be killed by fire. Following a hot June fire in northern Sonora and southeastern Arizona, many of the large alligator junipers suffered severe damage and subsequently died [43]. However, large alligator junipers are not always killed by fire. Researchers have observed fire scars on old alligator junipers which indicate these large trees have survived many surface fires [34,97]. Kittams [74] reports that alligator juniper bark is seldom burned by fires in the Chihuahuan Desert. Irregular strips of the fibrous bark tend to remain attached to the alligator juniper for many years after the plants have been killed by fire [10].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:Alligator juniper mortality following an August wildfire in an oak-juniper woodlands of Arizona was estimated at 28% [67]. Temperatures lethal to alligator juniper tissue vary according to desiccation, and thus season of burn. Site characteristics also may contribute to the specific effects of fire. During a 2-year study, lethal temperatures ranged from 147 degrees Fahrenheit (63.8oC), which was recorded in summer, to 174 degrees Fahrenheit (80.0oC), which was observed during the late fall. Detailed data follow [59]: These findings indicate greatest susceptibility to fire during dry, hot months. Annual variation is also probable.
PLANT RESPONSE TO FIRE:Alligator juniper is capable of prolific sprouting after aboveground vegetation is consumed or damaged by fire [67,107]. Basal sprouts have been observed on trees as young as 1 year [62]. Sprouts generally grow rapidly with favorable weather conditions [133]. Alligator juniper can quickly regain dominance after fire on Arizona rangelands [107]. Approximately 42% of all living alligator junipers sprouted from the base after an August wildfire in oak-juniper woodlands of Arizona [16].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:No entry
FIRE MANAGEMENT CONSIDERATIONS:Prescribed fire is commonly used to reduce juniper dominance. Management objectives include controlling juniper and shrubs, increasing forb production, enhancing habitat diversity, increasing herbivore diversity, enhancing nutritive quality and palatability of forage, and preparing sites for reseeding. On some sites, substantial control of trees by fire may last for up to 50 years, with linear reductions in herbaceous cover as the overstory develops. Where pinyon-juniper cover exceeds 20%, increases in herbaceous plant growth after fire may be low, but where the canopy cover is less, perennial grasses may respond quickly. On sites with high tree cover, however, annuals may quickly invade and can prevent the establishment of a perennial herb community [21]. Alligator juniper may be eliminated in ponderosa pine forests in which underburns occur at 3 to 7 year intervals [71]. Prescribed fire may not be an effective management tool where pinyon-juniper is in an advanced successional state or on sites dominated by exotic annuals. If desirable perennials fail to establish, the site can be left open and susceptible to weed invasion or soil erosion. Fine fuel loading is critical when planning burns in pinyon-juniper woodlands. Sites with < 600 kg/ha fine fuels will be difficult to burn with the intensity needed to scorch and kill alligator juniper [21]. The following methods have been used in attempts to reduce alligator juniper on Arizona rangeland: 1) broadcast burning 2) burning individual trees 3) burning grasslands to kill junipers less than 3 ft (0.9 m) in height 4) burning scattered, wind-rowed, or piled pinyon-juniper slash after mechanical treatment None of these methods has been entirely satisfactory. Broadcast burning in these communities requires a density of 200 to 400 trees per acre, air temperatures around 85 to 90 degrees Fahrenheit (29-35oC), relative humidity of 4 to 8%, and an average wind speed of 10 to 20 mph (16-32 km/h) [107]. Burning individual trees is both costly and labor intensive, and relatively ineffective for sprouters such as alligator juniper [61,107,120]. Blackburn and Bruner [15] have recorded 40% mortality following individual burning of alligator juniper. When mechanical treatment is combined with fire, two-way chaining tends to windrow the slash, producing a better burn which kills more small trees [107]. To increase habitat diversity, several small burns (<20 ha) may be more effective than a single large burn. Disadvantages include increased cost and greater likelihood of damage by grazing. Bunting [21] reports an optimum burn size of approximately 500 to 2,500 acres (200-1000 ha) where hand-firing techniques are to be used, and larger areas where aerial ignition is planned. Where fuel loading is irregular, smaller areas within a larger burn unit can be ignited under conditions of lower temperature and higher fuel moisture, but this often leaves larger amounts of the unit unburned. It is difficult to date fire scars of alligator juniper. It may stop growing when soil moisture is unavailable and resume growth when soil moisture conditions improve. This growth pattern produces "false rings," and makes counting rings extremely difficult [50,97]. Because strips of bark tend to remain on alligator juniper for many years after fire, early utilization of fire-killed trees may be somewhat limited. The use of chemical debarking agents may allow for better immediate utilization of the wood [10]. Palatability of alligator juniper foliage is enhanced by fire [74]. Young shoots may be particularly palatable to herbivores.
Related categories for SPECIES: Juniperus deppeana | Alligator Juniper |
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