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.; (and others), 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. 
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.
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.
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).
Site characteristics in regions of Sonoran Desert where study was conducted 
|Region||Dominant vegetation||Elevation (m)||Annual Precipitation (mm)||Mean annual temperature (ºC)||Soil Textures|
|1||arbosufrutescent shrubland||50-900||250-400||22-26||sand, loamy sand, sandy loam, loam|
|2||arboreal shrubland||70-1200||300-650||22-26||loamy sand, sandy loam, loam, sandy clay loam, clay loam|
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:
|Fire regime information that may pertain to the vegetation community studied in this Research Project Summary. Fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Model . This vegetation model was developed by local experts using available literature, local data, and expert opinion as documented in the PDF file linked below.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Desert shrubland without grass||Replacement||52%||150|
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects [1,3].
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.
|Range of fuel and weather conditions during prescribed burns in one study area dominated by buffelgrass pasture |
|Fine fuel load (tonnes/ha)|
Moisture content (%)
|Soil (surface 5 cm)||0.3-1.8|
Weather at time of burns
|Air temperature (ºC)||26.3-37.5|
|Relative humidity (%)||12.5-26.7|
|Wind speed 2 m above ground (km/h)||3.8-15.9|
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, desert hackberry (Celtis pallida), horseweeds, Anderson wolfberry (Lycium andersonii), and Arizona mimosa (Mimosa distachya var. laxiflora).
Shrub mortality 1 to 3 growing seasons after fire 
|Common Name||Scientific Name||Mortality (%)*|
|Berlandier's Indian mallow||Abutilon berlandieri||76-81|
|whitethorn acacia||Acacia constricta||52|
|sweet acacia||Acacia farnesiana||60|
|ambrosia leaf bur ragweed||Ambrosia ambrosioides||53-58|
|desert hackberry||Celtis pallida||100|
|Sonoran croton||Croton sonorae||31-60|
|sangre de cristo||Jatropha cardiophylla||3|
|West Indian shrubverbena||Lantana urticoides||62|
|Anderson wolfberry||Lycium andersonii||58-100|
|Berlandier wolfberry||Lycium berlandieri||16|
|Arizona mimosa||Mimosa distachya var. laxiflora||51-79|
|desert ironwood||Olneya tesota||21|
|yellow paloverde||Parkinsonia microphyllum||42|
|organpipe cactus||Stenocereus thurberi||46|
|*A single value indicates that mortality was reported for only 1 study site.|
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 |
|Common Name||Scientific Name|
|Abutilon berlandieri||Berlandier's Indian mallow|
|Acacia constricta||whitethorn acacia|
|Acacia farnesiana||sweet acacia|
|Ambrosia ambrosioides||ambrosia leaf bur ragweed|
|Celtis pallida||desert hackberry|
|Croton sonorae||Sonoran croton|
|Jatropha cardiophylla||sangre de cristo|
|Lantana urticoides||West Indian shrubverbena|
|Lycium andersonii||Anderson wolfberry|
|Lycium berlandieri||Berlandier wolfberry|
|Mimosa distachya var. laxiflora||Arizona mimosa|
|Olneya tesota||desert ironwood|
|Parkinsonia microphyllum||yellow paloverde|
|Stenocereus thurberi||organpipe cactus|
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/22.214.171.124/Complete_Guidebook_V1.2.pdf [2007, May 23]. 
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. 
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]. 
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] 
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