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Research Project Summary: Response of herbaceous vegetation to winter burning in Texas oak savanna

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

Hutcheson, Ann-Marie; Baccus, John T.; McClean, Terry M.; Fonteyn, Paul J. 1989. Response of herbaceous vegetation to prescribed burning in the Hill Country of Texas. Texas Journal of Agriculture and Natural Resources. 3:42-47 [2].

Study sites are classified in the following plant community and probably historically experienced the fire regime described below:

Study sites were burned with a strip headfire pattern between 1230 and 1315 on 1 February 1982. At the time of ignition, air temperature was 55 °F (13 °C), relative humidity was between 42% and 48%, and wind speed ranged from 10 to 32 mi/h (16-51 km/h). Fuel moisture averaged 20% at the time of burning, and the quantity of herbaceous vegetation averaged 988 lb/ac. Fuels were most abundant at the base of trees, less at the edge of the canopy, and even less in open grassland (Table 2):

Burning consumed approximately half of the herbaceous fuel, 455 lb/ac on plateau oak plots and 587 lb/ac on post oak plots. A lower proportion of fuel was consumed at the bases of trees than at other positions, probably because the fire front split at the bases of trees, leaving small unburned patches on the downwind sides.

Maximum temperatures were highest at the litter surface. On plateau oak plots, the average maximum temperature at the litter surface ranged from 138 °F (59 °C) at the tree base to 300 °F (150 °C) in the grassland. On post oak plots, the average maximum temperature at the litter surface was approximately 400 °F (200 °C) and varied little with respect to distance from the tree base. Maximum temperatures at the soil surface averaged 20 to 40 °F (10-20 °C) lower than at the litter surface. Mean temperatures above the litter dropped off "dramatically". At a height of 3 ft (1 m) above the litter surface, average temperatures remained less than 100 °F (38 °C) in plateau oak plots and less than 150 °F (66°C) in post oak plots.

Winter burning increased forb biomass without substantially altering grass biomass. Total forb biomass was 48% to 78% greater on burned than unburned plots (Table 4), mainly due to increases in velvet bundleflower and saw greenbrier. Many species were less abundant on burned than unburned plots near one tree species but more abundant near the other species.

Many grass species were less abundant on burned than unburned plots near one tree species and more abundant near the other (Table 5). Total grass biomass was 28% less on burned than unburned plateau oak plots, with differences mainly due to lower productivity of little bluestem and Texas wintergrass. Vine-mesquite and cane bluestem had substantially greater productivity on burned than unburned plots. On post oak plots, total biomass was virtually the same in burned and unburned plots.

Standing dead biomass was 3 to 4 times greater in unburned than burned plots, comprising more than 40% of total standing biomass in unburned plots and less than 32% in burned plots (table 6).

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. Hutcheson, Ann-Marie; Baccus, John T.; McClean, Terry M.; Fonteyn, Paul J. 1989. Response of herbaceous vegetation to prescribed burning in the Hill Country of Texas. Texas Journal of Agriculture and Natural Resources. 3: 42-47. [17777]

3. 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]

4. 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]