• 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:

Moderate or even low-severity fires can top-kill prickly-pear species [7,93,99,106]. Aboveground tissues of Opuntia spp. are easily killed by fire, but some fleshy stem segments usually survive low- to moderate-severity fire and resume growth, even when burned off the parent plant [7,46,49,93,106]. Prickly-pears are vulnerable to mortality from heat generated by fires as well as by actual burning [99]. Hotter fires probably lead to higher mortality, but data are needed [46,93]. 

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

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PLANT RESPONSE TO FIRE:

The succulent stems of prickly-pear species are not combustible and without sufficient fuel may suffer little damage from fire [46]. However, it is reported that a related species, brownspine prickly-pear (O. phaecantha), is easily killed by fire if the plant's height is less than 1 foot (0.3 m) [107]. In west Texas, Heirman and Wright [41] also reported that brownspine prickly-pear less than 2 feet (0.61 m) tall were easily killed by fire because flames readily engulfed the plants. Plains prickly-pear postfire mortality may be delayed for 3 or more years. Secondary effects of fire include insect infestation of weakened plants and increased grazing pressure when spines are burned off [,13,14,77,101,105,107]. Studies in Texas showed that the cactus bug and the blue cactus borer prefer burned cactus pads to unburned pads [20,80,85,101]. This preference may increase prickly-pear mortality after burning [80]. In Wyoming, Smith and others [87] attributed mortality of plains prickly-pear to dehydration following the burn rather than from fire-caused heat damage.

Brownspine prickly-pear experienced high die-off following low-severity fire in Texas. Initial mortality was 20%. Insects entered surviving plants through fire-scarred tissue, spreading bacterial and fungal infections. New sprouts appeared within a few weeks following the fire, but many sprouting plants lost their vascular connection to the root because of insect damage and decay. By the end of the 3rd year, mortality exceeded 70%. Most plants surviving through postfire year 3 had sprouted from the root crown. The authors observed that mortality of both burned and unburned plants of brownspine prickly-pear increased during years of below average precipitation [13].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

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FIRE MANAGEMENT CONSIDERATIONS:

Frequent fire reduces populations of low-growing Opuntia species like plains prickly-pear [7]. Plants that survive in unburned refugia provide parents for regenerating burned areas. Observations of 1,665 plants from 19 succulent species on burned areas Arizona showed that 13% were in unburned refugia [93]; the spatial extent of the refugia was not described.

Fire has been used as a tool to increase the edibility of plains prickly-pear and related species for livestock by burning off spines [32,84]. Wildlife consumption of burned plains prickly-pear is also a consideration. In southern Alberta, pronghorn were attracted to burned areas to graze on plains prickly-pear when spines were singed off green plants [19,88].

Although prescribed burning may effectively control plains prickly-pear in some cases, in dry years desirable forage is lost [105,106]. In a 1965 Wyoming study, burning was among 4 treatments tested for controlling plains prickly-pear. The other 3 methods were chemical, bulldozer blading over frozen ground, and beating with a tractor attachment. Burning was found to be unsatisfactory because, though cactus kill was estimated to be 70%, an unacceptable amount of preferred vegetation was damaged. At that time, the most successful method was thought to be blading, despite vegetation and soil damage [47].

Related categories for SPECIES: Opuntia polyacantha | Plains Prickly-Pear