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You are here >1Up Info > Wildlife, Animals, and Plants > Plant Species > Shrub > Species: Prosopis velutina | Velvet Mesquite
 

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FIRE EFFECTS

SPECIES: Prosopis velutina | Velvet Mesquite
IMMEDIATE FIRE EFFECT ON PLANT : Fire mortality of velvet mesquite is generally low. Following most fires, plants sustain little or no damage, have their aboveground foliage partially destroyed, or are completely top-killed. Only a small percentage are killed. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : Based on observations following prescribed fires and wildfires, top-kill and mortality appear to be most influenced by the size of the velvet mesquite plant and the intensity of the fire. Size of the plant: Percent top-kill and mortality of velvet mesquite following fire are inversely related to plant height and basal stem diameter. At the Santa Rita Experimental Range in southern Arizona, fall burning on areas with 303 pounds per acre (340 kg/ha) of herbaceous fuel and about two burroweed plants per meter square resulted in greater than 80 percent top-kill of velvet mesquite plants up to 2 inches (5 cm) in basal stem diameter. The percentage of plants top-killed, on a size class basis, gradually decreased to near zero as basal stem diameter increased to 10 inches (25 cm) [79]. Evaluation of several other prescribed fires at Santa Rita showed that young velvet mesquites less than 0.5 inch (1.25 cm) in basal stem diameter suffered about 50 percent mortality, but only 8 to 15 percent of plants greater than 0.5 inch in basal stem diameter died [51]. In southern Arizona, an accidental June fire in Lehman lovegrass (Eragrostis lehmanniana) resulted in 30 percent mortality of velvet mesquite less than 0.5 inch in basal stem diameter and 18 percent mortality of plants with basal stem diameters from 2 to 6 inches (5-15 cm) [20]. At Santa Rita, 4- to 6-inch-tall (10-15.5 cm) seedlings were burned in a "good stand" of grass. Of the 8-month-old seedlings burned in March, 67 percent were killed and 23 percent were top-killed only. Of the 12-month-old seedlings burned in June, 65 percent were killed and 25 percent were top-killed only [19]. The effects of fire on velvet mesquite 10 months following a June prescribed fire (mesquites in bloom at time of burn) in an area with 40 percent grass cover dominated by curly mesquite (Hilaria belangerii) is summarized below [8]: basal stem diameter (inches) fire effects 0-.5 .5-1 1-2 2-3 3-4 >4 total (number of plants) no crown damage 1 4 5 7 8 12 37 partial top-kill 16 14 8 1 0 1 40 total top-kill 73 11 1 0 0 0 85 dead 8 1 0 0 0 0 9 total 98 30 14 8 8 13 171 Fire intensity: In some locations, velvet mesquite has displaced grasses to the extent that the herbaceous fuels are insufficient to carry anything but a cool or spotty fire [104]. Low intensity fires occur under these circumstances and usually inflict no damage or only partially kill the aboveground crown. High intensity fires may kill many young plants, but mature plants are often only top-killed and then resprout. Fire intensity is influenced most by the amount of herbaceous fuel and the time of year burning takes place. Plants seem to be more susceptible to burning during late spring and early summer, which is the hottest and driest time of the year in Arizona, than during other times of the year [22]. At the Santa Rita Experimental Range, about 29 percent of velvet mesquites were killed on areas burned in June, compared to about 10 and 4 percent on areas burned in November and February [51]. Following a June fire at Santa Rita, velvet mesquite suffered 25 percent mortality in an area with 4,480 pounds per acre of herbaceous fuel (4,973 kg/ha) dominated by Lehman lovegrass, but on areas with 2,200 pounds per acre (2,465 kg/ha) of herbaceous fuel dominated by black gramma (Bouteloua eriopoda), velvet mesquite suffered only 8 percent mortality [20]. The fire effects on velvet mesquite on the Santa Rita Experimental Range as influenced by plant size and season of burn are summarized below [51]. Since herbaceous fuels were lacking, barley hay was added to increase the fine fuel to 800 pounds per acre (896 kg/ha). basal stem diameter Month and fire effect Feb June Nov Oct up to 0.5 inch top alive 3% 1% 13% --- top-kill 74% 39% 66% --- dead 23% 60% 21% --- 0.5 to 1.0 inch top alive 35% 5% 12% 5% top-kill 50% 62% 73% 90% dead 15% 33% 15% 5% 1.0 to 2.0 inches top alive 50% 6% 41% 28% top-kill 50% 74% 52% 62% dead 0% 20% 7% 10% 2.0 to 5.0 inches top alive 78% 20% 63% 62% top-kill 22% 65% 32% 31% dead 0% 15% 5% 7% over 5.0 inches top alive 82% 40% 82% 90% top-kill 18% 49% 18% 10% dead 0% 11% 0% 0% PLANT RESPONSE TO FIRE : The response of velvet mesquite following fire depends on the amount of damage the fire inflicted on the plant. Plants may initiate new growth from either aerial crown or underground stem buds. Following low-intensity fires which only partially top-kill plants, velvet mesquite often sprouts from axillary buds on the branches of the crown. Following severe, top-killing fires which char or completely consume the crown, plants survive by producing numerous basal stem sprouts [20,126]. Some plants which are lightly or moderately damaged survive by both refoliating undamaged portions of the crown and by producing basal sprouts. In general, smaller plants receive more crown damage and thus tend to recover by basal sprouting, while larger plants tend to produce crown sprouts. Cable [20] observed that basal sprouting predominated on trees with a stem diameter less than 2 inches (5 cm), while crown sprouting predominated on plants with basal stem diameters less than 2 inches. Following a fall burn at Santa Rita, heights velvet mesquite resprouts were 105 percent of preburn levels in 4 years. Six years after burning, some resprouts flowered and set seed [79]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : Prescribed burning has not been effective in controlling velvet mesquite because of the species' fire survival strategies. On grasslands in good condition with a low density of velvet mesquite, repeated prescribed fires have the potential to kill small plants under 0.5 inch (1.25 cm) in basal stem diameter and keep others low in stature and from producing seed [22]. However, on some sites velvet mesquite has reduced the native grass cover to the extent that there is now insufficient fuel to carry anything more than a "spotty" or "cool fire" [42]. In general, fire will not carry in Southwestern grasslands having less than 600 pounds per acre of herbaceous fuel (654 kg/ha) unless there is a good stand of burroweed present [127]. When there is less than 892 pounds per acre (1,000 kg/ha), a windspeed of 8 miles per hour (12.8 km/hr) is needed to carry the fire [127].

Related categories for Species: Prosopis velutina | Velvet Mesquite

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Information Courtesy: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Fire Effects Information System

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