• 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:

There are conflicting findings regarding the relative impacts of fuels and weather conditions on honey mesquite damage by fire. At the Wagoner Estate near Vernon, Texas, Ansley and Lucia [6] compared 2 plots: plot 1 had 4,085 lbs/ac of fine fuel and plot 2 had 1,861 lbs/ac of fine fuel. On plot 1, 72% of honey mesquite was top-killed and there was a 95% reduction in total canopy; on plot 2, honey mesquite was 15% top-killed and its total canopy cover was reduced 42%.

The influence of mesquite size and fuel loading on fire mortality of velvet mesquite, a closely related species, has been thoroughly studied [41,69,141]. Following a June fire on the Santa Rita Experimental Range in Arizona, velvet mesquite suffered 25% mortality in an area with 4,480 pounds per acre of herbaceous fuel dominated by the exotic Lehman lovegrass (Eragrostis lehmanniana), but in areas with 2,200 pounds per acre of herbaceous fuel dominated by black grama, velvet mesquite suffered only 8% mortality [41]. Prescribed burning on the Santa Rita Experimental Range generally resulted in about 50% mortality of young velvet mesquite that were less than 0.5 inch (1.25 cm) in basal stem diameter, but only 8% to 15% mortality of plants that were greater than 0.5 inch (1.25 cm) in basal diameter [69]. One experimental burn on the Wagoner Estate near Vernon, Texas showed that honey mesquite top-kill was more correlated with relative humidity and air temperature than with amounts of total or fine fuel [11]. Another detailed fire study was undertaken on the Welder Wildlife Refuge of southern Texas. Fire peak temperature and temperature duration at canopy level were found to influence mesquite top-kill more than extreme temperatures at the ground level [10].

Using a propane burner and temperature control to simulate natural fire, Wright and others [190] found that young honey mesquite plants are very susceptible to "moderate- severity" fires until they reach 1.5 years of age, moderately susceptible at 2.5 years, and very tolerant after 3.5 years. In the study, the percent mortality (after 15 months) of various ages of individually burned young honey mesquite plants was observed after 15 months after exposure; results are summarized below :

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

PLANT RESPONSE TO FIRE:

Winter burns often allow regrowth from buds in the crown because fire severity is not great enough to cause complete top-kill. Though percent canopy cover of honey mesquite recovers quickly following these low-severity fires, stand structure becomes more like a savanna than a thicket, which is the most common structure following a disturbance that causes a high rate of complete top-kill [7].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

FIRE MANAGEMENT CONSIDERATIONS:

On some sites honey 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 [61]. In general, fire will not carry in southwestern grasslands unless there is a minimum of 600 pounds per acre (654 kg/ha) of herbaceous fuels. When there is less than 892 pounds per acre (1,000 kg/ha), a wind speed of 8 miles per hour (12.8 km/hr) is needed to carry the fire [189].

Once honey mesquite stands are established, use of stand- replacement fires can cause only minimal reduction in honey mesquite density; regrowth is both rapid and of a thicket-like structure, that is commonly more detrimental to forage production than the pre-burn stand structure [7]. Paysen and others [135] recommend that managers use low-severity fires so that apical dominance is maintained and sprouting is minimized. Ansley and others [7] also support this strategy and recommend winter fires instead of summer fires except when fuel loads are low. The Texas Extension Service recommends the following conditions for prescribed burning (in intervals of 5 to 10 years) in honey mesquite-tobosagrass communities: wind of 6 to 15 mph (10-25 kph), relative humidity between 20% and 60%, temperature between 45 and 70 degrees Fahrenheit (7.2- 21 °C), during late January, February, or early March [2].

It is well-documented that fire can be used as a management tool in tobosagrass and other mesic honey mesquite habitats [2,7,135]. In shortgrass communities, according to Wright [186], fire cannot be "recommended as a tool to control shrubs or increase grass production." In these communities fire, particularly in dry years, can harm black grama and other grasses, thereby increasing the competitive ability of western honey mesquite [37,61,186]. 

Interactions of fire and herbicide effects: Britton and Wright [30] observed 24% mortality in a stand of honey mesquite (20 miles south of Colorado City, Texas) that had been top-killed by herbicides 4 years prior to burning. On the Rolling Plains of Texas, 32% of honey mesquite were killed by fires occurring in March or April soon after a 2,4,5-T herbicide treatment. These mortality rates were unusually high and were attributed to dead foliage and stems that increased fire severity locally. Repeated winter or summer fires did not achieve root-kill greater than 4%. Though there had been an herbicide (2,4,5-T) treatment 17 to 26 years prior to the fire, there were not many dead stems to increase fire intensity and whole-plant mortality [190]. Three to six foot tall (1-2 m) honey mesquite plants, which had survived herbicide (2,4,5-T) spraying 7 years earlier, were top-killed by a late March prescribed fire in western Texas. Most plants survived by sprouting from belowground buds. Resprouts ranged from a few inches to over 4 feet (1.2 m) tall 6 months after the fire [80].

Following controlled spring burning of honey mesquite plants in southwestern Texas that had survived application of 2,4,5-T 4 years earlier, honey mesquite plants were top-killed. Resprouts grew 17 inches (43.2 cm) tall within 4 months [132]. Six years of postfire growth is summarized below; data are means of 15 replicates:

Another study of fire effects on honey mesquite was undertaken in the High Plains of Texas near Colorado City. Fire was prescribed on upland and riparian areas. The season during which fire occurred was not specified but honey mesquite were physiologically active at the time. On bottom lands there was no mortality of large honey mesquite even though they had been sprayed with herbicides (2,4,5-T); well-developed root systems allowed resprouting the following growing season.  On upland sites mortality was up to 50%. Percent mortality was measured up to 5 years after burning, showing that fire-induced mortality is sometimes not immediate. Insect and rodent damage following fire damage causes indirect fire morality. Results and burning conditions were as follows [190].

Related categories for SPECIES: Prosopis glandulosa | Honey Mesquite