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Research Project Summary: Effects of spring prescribed fire and chaining on tobosagrass and buffalograss communities in Lynn County, Texas

• RESEARCH PROJECT SUMMARY CITATION
• STUDY LOCATION
• SITE DESCRIPTION
• PREFIRE PLANT COMMUNITY AND FUELS
• PLANT PHENOLOGY
• FIRE SEASON AND SEVERITY CLASSIFICATION
• FIRE DESCRIPTION
• FIRE EFFECTS ON PLANT COMMUNITY AND FUELS
• FIRE MANAGEMENT IMPLICATIONS
• APPENDIX: SPECIES INCLUDED IN THE SUMMARY
• REFERENCES

Sources: Unless otherwise indicated, the information in this Research Project Summary comes from the following papers:

Heirman, Alan L. 1971. Effect of fire on noxious brush species in medium fuel types. Lubbock, TX: Texas Tech University. 55 p. Thesis [2].

Heirman, Alan L.; Wright, Henry A. 1973. Fire in medium fuels of west Texas. Journal of Range Management. 26(5): 331-335 [3].

STUDY LOCATION:
10 miles southwest of Post, Lynn County, Texas
Latitude: 33.17 N
Longitude: -101.40 W
Radius: 5 km

SITE DESCRIPTION:
Elevation: 3,000-3,300 feet
Relief: level to gently undulating
Mean annual precipitation: 19 inches
Soil: deep, hardland soils of the Amarillo loam series with slow surface drainage and medium internal drainage

PREFIRE PLANT COMMUNITY AND FUELS:
The vegetation was desert grassland dominated by "nearly pure" stands of tobosagrass and buffalograss. Honey mesquite were "thick" and tree cholla and tulip pricklypear were scattered throughout both stands. The entire area had been aerially sprayed with herbicide (2,4,5-T) 7 years prior to the study (1963), achieving 95% top-kill of honey mesquite but <5% honey mesquite mortality. The year prior to the fire (1969), when honey mesquite was 3 to 6 feet tall, a portion of the study area was chained. Few trees were killed by chaining. In chained areas, honey mesquite trees were lying on the ground next to their bases [2,3].

The study site is classified in the following plant community and probably historically experienced the fire regime described below:

PLANT PHENOLOGY:
Spring forbs were emerging at the time of the prescribed fire

FIRE SEASON AND SEVERITY CLASSIFICATION:
Early spring (23 March 1970), low severity

FIRE DESCRIPTION:
Objectives of the study were to determine 1) postfire mortality of honey mesquite, tree cholla, and tulip pricklypear the first 2 growing seasons after a March prescribed fire; 2) the percent consumption by fire of honey mesquite logs previously chained; 3) the effects of prescribed fire on the composition and production of grasses and forbs during the 1st postfire growing season; and 4) cattle utilization of tobosagrass and buffalograss in burned and unburned plant communities during the 1st postfire growing season. They also examined the combined effects of chaining and prescribed fire on honey mesquite, tree cholla, and tulip pricklypear during postfire growing seasons 1 and 2.

A headfire was started at 3:30 PM on 23 March 1970, and was completed by 4:30 PM. Three hundred acres were burned. The fire was spotty and incomplete due to insufficient fuels in some areas, especially where buffalograss had been heavily grazed.

Conditions reported during the prescribed fire:
Air temperature: 75 °F
Relative humidity: 25%
Wind speed: 12-20 mph from the southwest [2,3]
Fine fuel loads:

Fuel moisture of grass: 15%
Surface soil moisture: 20%
Maximum soil surface temperature: 460 °F in tobosagrass stands and 220 °F in buffalograss stands [2,3]

Average annual rainfall in the region was 19 inches. A "mild" drought occurred during postfire year 1, when rainfall in the area ranged from 13 to 15 inches. Vegetation green-up occurred in March prior to the fire, which produced "excellent" soil moisture conditions [2]. Precipitation in the area from 1 to 23 March ranged from 2.6 to 3.3 inches [3]. Five days following the fire, precipitation was 0.3 inches. Between 1 May and 15 June, precipitation was 2.8 inches [2]. Thereafter, precipitation was "light" and little vegetation growth occurred [3]. Vegetation green-up occurred again in September when precipitation in the area ranged from 2.3 to 6.4 inches [2]. Precipitation data was not provided for postfire year 2.

FIRE EFFECTS ON PLANT COMMUNITY AND FUELS:
Honey mesquite: No honey mesquite trees were killed by fire. Most were top-killed but sprouted soon after fire. Six months after the fire, sprouts were up to 4 feet tall.

Consumption of honey mesquite logs by fire was greater for large (2-6 inches) than small (<2 inches) logs in chained tobosagrass and buffalograss stands due to the loose bark on large logs giving them a greater surface area to volume ratio of exposed fuel. A greater proportion of logs was consumed in tobosagrass stands than buffalograss stands because of higher fine fuel loads in tobosagrass stands. Log consumption increased linearly as fine fuel loads increased: when <1,200 pounds/acre of fine fuels was present, no logs were consumed; when >1,600 pounds/acre of fine fuels was present, >50% of logs were consumed [2,3].

Tree cholla: During the 1st and 2nd postfire growing seasons, a higher percentage of tree cholla plants had been killed by fire in tobosagrass than buffalograss stands in both chained and unchained areas due to higher burning temperatures in tobosagrass stands (Table 1) [2,3]. During the 1st postfire growing season, many tree cholla plants had sprouted on both sites, averaging 5 sprouts/plant [2]. Tree cholla mortality increased substantially in all stands during the 2nd postfire growing season, although statistical comparisons were not provided. This result was attributed to drought and insect and small mammal herbivory. Short tree cholla plants always had greater mortality than tall tree cholla plants, although differences were significant only in unchained areas. The authors suggested that mortality was statistically similar between short and tall tree cholla plants in chained areas because most tree cholla plants were lying close to the ground [2,3].

Tulip pricklypear: First postfire growing season mortality of tulip pricklypear was similar in chained and unchained tobosagrass stands. In buffalograss stands, its mortality was greater in chained than unchained stands because most pricklypear plants were lying close to the ground in chained areas and because patches of buffalograss were denser, and thus fine fuel loads were greater, in chained than unchained stands. During the 1st postfire growing season, tulip pricklypear mortality in tobosagrass and buffalograss stands was higher for small plants than large plants (Table 2) [2,3].

During the 2nd postfire growing season, tulip pricklypear mortality increased substantially in both stands, with >50% killed in all treated stands. Its mortality in tobosagrass stands was similar in chained and unchained stands. In buffalograss stands, mortality remained higher in chained than unchained stands. Increased mortality during the 2nd postfire growing season was attributed to drought and insect and small mammal herbivory. There were no differences in mortality between small and large plants by the end of the 2nd growing season [2,3].

Tobosagrass: Grass production in tobosagrass stands increased 3-fold the 1st growing season after fire (Table 3). Tobosagrass's unpalatable old growth was removed by burning [2,3]. New growth following fire was tender and succulent and cattle preferred it to buffalograss 3 months after fire. Total tobosagrass grazed by cattle on the burned area 3 months after fire was 2,388 pounds/acre, while only 371 pounds/acre were grazed on the control. Five months after fire, when tobosagrass was dry, cattle preferred buffalograss to tobosagrass and grazed only small amounts of tobosagrass on burned and unburned control stands. Seven months after fire, after vegetation green-up, total tobosagrass grazed by cattle on the burned area was 431 pounds/acre, while only 122 pounds/acre was grazed on the unburned control [2].

Buffalograss: The fire had no effect on grass production in buffalograss stands the 1st growing season after fire (Table 3) [3]. Three months after fire, cattle preferred tobosagrass to buffalograss. Total buffalograss grazed by cattle on the burned area 3 months after fire was 873 pounds/acre, while only 473 pounds/acre were grazed on the unburned control. Five months after fire, when buffalograss was dry, cattle preferred buffalograss to tobosagrass but grazed only small amounts of buffalograss on burned and unburned control stands because cattle had shifted to other grass species. Seven months after fire, after vegetation green-up, total buffalograss grazed by cattle on the burned area was 201 pounds/acre, while 182 pounds/acre was grazed on the control [3].

Forbs: Production (pounds/acre) of several annual herbs, including prairie broomweed and horsetail conyza tended to be lower on burned than unburned areas during the 1st growing season. False mesquite production was higher on burned than unburned areas. Warty euphorbia, western ragweed, and evax occurred on unburned areas but were absent from burned areas (Table 3) [2,3].

FIRE MANAGEMENT IMPLICATIONS:
The authors concluded that spring prescribed fire in tobosagrass and buffalograss communities may help control undesirable herbaceous annuals while increasing tobosagrass production [3]. One objective of this study was to determine the effects of prescribed fire and chaining on honey mesquite, tree cholla, and tulip pricklypear the first 2 growing seasons after fire. Burning did not kill any honey mesquite trees in any treatment during the first 2 postfire growing seasons. Postfire tree cholla mortality was highest in tobosagrass stands, where fine fuel loads were greatest. Tree cholla mortality was generally greater in chained than unchained stands. More than half of all tulip pricklypear plants had died in all treated areas by the end of the 2nd postfire growing season. In buffalograss stands, chaining appeared to increase tulip pricklypear postfire mortality.

This study also aimed to determine the consumption by fire of honey mesquite logs in chained areas. Honey mesquite log consumption increased linearly as fine fuel loads increased [2,3].

Other objectives of this study were to determine the effects of prescribed fire on the composition and production of grasses and forbs and to compare cattle utilization of tobosagrass and buffalograss in burned and unburned plant communities during the 1st postfire growing season. Tobosagrass production increased following fire. Cattle consumed 2,016 pounds/acre more tobosagrass on burned areas than on an unburned control area. Buffalograss production was unchanged after fire. False mesquite production increased after burning, but prairie broomweed and horsetail conyza production tended to decrease [2,3].

REFERENCES:

1. Hann, Wendel; Havlina, Doug; Shlisky, Ayn; [and others]. 2008. Interagency fire regime condition class guidebook. Version 1.3, [Online]. In: Interagency fire regime condition class website. U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; The Nature Conservancy; Systems for Environmental Management (Producer). 119 p. Available: http://frames.nbii.gov/frcc/documents/FRCC_Guidebook_2008.07.10.pdf [2010, May 3]. [70966]

2. Heirman, Alan L. 1971. Effect of fire on noxious brush species in medium fuel types. Lubbock, TX: Texas Tech University. 55 p. Thesis. [35023]

3. Heirman, Alan L.; Wright, Henry A. 1973. Fire in medium fuels of west Texas. Journal of Range Management. 26(5): 331-335. [1119]

4. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: http://www.landfire.gov/downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24]. [66741]

5. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models, [Online]. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: http://www.landfire.gov/models_EW.php [2008, April 18] [66533]