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Research Project Summary: Effects of June fires in shrubland converted to buffelgrass pasture in Sonora, Mexico

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

Source: Unless otherwise indicated, the information in this Research Project Summary comes from the following paper:

Ibarra-F, Fernando; Martin-R, M.; Cox, J. R.; Miranda-Z, H. 1996. The effect of prescribed burning to control brush species on buffelgrass pastures in Sonora, Mexico. In: Ffolliott, Peter F.; DeBano, Leonard F.; Baker, Malchus B., Jr.; Gottfried, Gerald J.; Solis-Garza, Gilberto; Edminster, Carleton B.; Neary, Daniel G.; Allen, Larry S.; Hamre, R. H., tech. coords. Effects of fire on Madrean Province ecosystems: A symposium proceedings; 1996 March 11-15; Tucson, AZ. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 195-204 [2].

SPECIES INCLUDED IN THE SUMMARY:
Common names are used throughout this summary. For a complete list of the common and scientific names of species discussed in this summary and for links to FEIS species reviews, see the Appendix.

STUDY LOCATION:
The study was conducted in 2 regions of the Sonoran Desert in Sonora, Mexico. Region 1 is in central Sonora, between Carbo and Hermosillo. Region 2 is between Mazatan and Tecoripa.

SITE DESCRIPTION:
The study areas were buffelgrass (Pennisetum ciliare) pastures established in Sonoran Desert shrublands several years prior to the study, where native shrubs were reestablishing. In 2 study areas located in Region 1, buffelgrass pastures were established 4 and 15 years prior to the study. Establishment dates were not given for the other study areas (one in Region 1 and one in Region 2).

PREFIRE PLANT COMMUNITY:
Buffelgrass dominated the study areas before and after burning. In one study area, buffelgrass density ranged from 3.2 to 9.5 plants/m², and cover ranged from 5.4% to 18%.

Brittlebush (Encelia farinosa) canopy cover ranged from 18.6% to 79.8% in the study areas.

Since the study was conducted in Mexico, plant classifications for the United States are not directly applicable. With the exception of planted buffelgrass, many of the species occurring on the study areas also occur in the community indicated in the table below. The study areas may have historically experienced a fire regime similar to that described here:

Burning conditions: Three of the study areas were burned with prescribed fire; the fourth burned in a succession of 3 wildfires during the course of 6 years. All fires occurred in June. Areas to be treated with prescribed fire were fenced to protect them from cattle grazing for 1 year before treatment and 3 years afterward. Burn sites ranging in size from 0.25 ha to 120 ha were surrounded by firelines 6 m wide and burned with headfires. Fuel loads were greater in areas where precipitation was above normal prior to burning. The table below shows fuel loads on 1 of the study areas in arbosufrutescent shrubland (Region 1). Approximately 90% of the area burned. In a study area in arborescent shrubland (Region 2), during a year with above-average precipitation, total fine fuel load was 6.19 tonnes/ha and litter load was 1.67 tonnes/ha. Due to the heavier fine fuel loads, fire spread rapidly in this study area, and burning was more complete (95%) than in areas with less fine fuel.

FIRE EFFECTS ON PLANT COMMUNITY:
Buffelgrass density and cover, measured 1 and 2 growing seasons after fire, were significantly (P≤0.05) greater on burned than unburned plots. Buffelgrass productivity was also significantly greater on burned than unburned plots in most cases, based on data collected 1, 2, and 3 years after fire and on sites burned once, twice, or 3 times within 6 years. There was one exception to this pattern: On a site in which June burning was followed by an unusually dry growing season (76 mm of precipitation, compared with 300 mm the 2nd postfire year), buffelgrass productivity was significantly less on burned than unburned plots in the 1st year; it was significantly greater in the 2nd year (P≤0.05).

Shrub mortality was measured at different times after fire (1 to 3 growing seasons) in different study areas. Variation among areas in preburn vegetation and postburn weather preclude use of the data to examine change over time, so shrub mortality rates are reported here as either a single value (where observations were recorded from only 1 study area) or a range of values (where observations were recorded for multiple study areas). Sangre de cristo (Jatropha cardiophylla) and hillyhock (Callaeum macropterum) showed little mortality after fire. Species for which mortality exceeded 75% in at least 1 study area included Berlandier's Indian mallow, spiny hackberry (Celtis ehrenbergiana), horseweeds, water jacket (Lycium andersonii), and Arizona mimosa (Mimosa distachya var. laxiflora).

Where fine fuels were sparse (less than 0.7 tonne/ha), fires spread poorly and had little effect on brittlebush. In 1 study area treated with prescribed fire, variation in total fine fuel load could be used to explain 93% of variation in brittlebush mortality. In the study area burned by wildfires, brittlebush survival decreased with repeated fires; the species was nearly eliminated by the 3rd fire.

Response of large (>10 cm diameter) and small (<10 cm diameter) brittlebush plants to to repeated June wildfire [2]

REFERENCES:

1. Hann, Wendel; Havlina, Doug; Shlisky, Ayn; [and others]. 2005. Interagency fire regime condition class guidebook. Version 1.2, [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). Variously paginated [+ appendices]. Available: http://www.frcc.gov/docs/1.2.2.2/Complete_Guidebook_V1.2.pdf [2007, May 23]. [66734]

2. Ibarra-F, Fernando; Martin-R, M.; Cox, J. R.; Miranda-Z, H. 1996. The effect of prescribed burning to control brush species on buffelgrass pastures in Sonora, Mexico. In: Ffolliott, Peter F.; DeBano, Leonard F.; Baker, Malchus B., Jr.; Gottfried, Gerald J.; Solis-Garza, Gilberto; Edminster, Carleton B.; Neary, Daniel G.; Allen, Larry S.; Hamre, R. H., tech. coords. Effects of fire on Madrean Province ecosystems: a symposium proceedings; 1996 March 11-15; Tucson, AZ. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 195-204. [28078]

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]