Research Project Summary: Effects of summer prescribed fires on buffelgrass and spittlebug in Sonora, Mexico



RESEARCH PROJECT SUMMARY CITATION:
Smith, Jane Kapler, compiler. 2008. Research Project Summary: Effects of summer prescribed fires on buffelgrass and spittlebug in Sonora, Mexico. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [ ].

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

Martin, R. M.; Cox, J. R.; Alston, D. G.; Ibarra F., F. 1995. Spittlebug (Homoptera: Cercopidae) life cycle on buffelgrass in northwestern Mexico. Annals of the Entomological Society of America. 88(4): 471-478 [4].

Martin-R., Martha H.; Cox, Jerry R.; Ibarra-F., Fernando. 1995. Climatic effects on buffelgrass productivity in the Sonoran Desert. Journal of Range Management. 48(1): 60-63 [6].

Martin-R., Martha; Cox, Jerry R.; Ibarra-F, F.; Alston, Diana G.; Banner, Roger E.; Malecheck, John C. 1999. Spittlebug and buffelgrass responses to summer fires in Mexico. Journal of Range Management. 52(6): 621-625 [5].

Martin-Rivera, Martha H. 1994. The effect of climate and spittlebug (Aeneolamia albofasciata) on buffelgrass (Cenchrus ciliaris L.) productivity in the Sonoran desert. Logan, UT: Utah State University. 81. Dissertation [7].

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 northwestern Sonora, Mexico, north of Hermosillo (lat 2941' N, long 11557' W) [5].

SITE DESCRIPTION:
Elevation at the study site is 470 m. The area is flat (slope 1-2%), with loam soils 2 to 6 m deep. Soils are basic; pH ranges from 8.5 to 8.9. Mean annual precipitation is 320 mm. Approximately 60% of precipitation falls between July and September, and the remainder falls between October and April. Daytime temperatures average 34 C in summer but frequently exceed 40 C in June and July. Nighttime temperatures average 5 C in winter but can be as low as 0 C in January and February [5].

PREFIRE BIOTIC COMMUNITY:
The prefire plant community was ungrazed buffelgrass (Pennisetum ciliaris) pasture infested with spittlebug (Aeneolamia albofasciata). Buffelgrass is a warm-season grass, introduced from Africa, that is invasive in many desert and semidesert communities [5,7]. Spittlebug is a member of the Cercopidae, a family of insects native to the Neotropics that feed on grasses and can reduce grass forage production by up to 50% [8].

The study was conducted in Sonora, Mexico. The plant community prior to buffelgrass establishment was not described, but it seems likely based on location of the study area that the pre-buffelgrass ecosystem was similar to one or more of those listed in the following table:

Fire regime information on vegetation communities that may resemble the historic condition of the community studied in this Research Project Summary. Fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Model [3]. This vegetation model was developed by local experts using available literature and expert opinion as documented in the PDF files linked from the Potential Natural Vegetation Groups listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Desert grassland Replacement 85% 12    
Surface or low 15% 67    
Desert grassland with shrubs and trees Replacement 85% 12    
Mixed 15% 70    
Southwestern shrub steppe Replacement 72% 14 8 15
Mixed 13% 75 70 80
Surface or low 15% 69 60 100
*Fire Severities:
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.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area
[1,2].

PLANT AND INSECT PHENOLOGY:
Four prescribed fires were conducted in July and August of 1985 and 1986 [5,7]. The fires were scheduled to coincide with specific stages in buffelgrass and spittlebug phenology, as determined by previous research [4,6]. See Fire Description for details.

FIRE SEASON/SEVERITY CLASSIFICATION:
Summer/low-moderate

FIRE DESCRIPTION:
Fire Management Objective: The study objective was to determine how prescribed summer fires affect buffelgrass and spittlebug populations when conducted during different plant phenological and insect developmental stages [5].

Burns were conducted between 0900 and 1000 hours on the same dates in each of 2 years (see table below). Burns were initiated with a backfire that burned vegetation in a 3 to 5 m strip; the remaining vegetation was burned using a headfire. Phenology of buffelgrass and spittlebug and burning conditions were as follows [5]:

Buffelgrass phenology, fuel characteristics, and environmental conditions during 4 burns in each of the summers of 1985 and 1986 in northwestern Mexico [5]

Burning date Buffelgrass phenology Spittlebug phenology Fuel load (g/m) Fuel moisture (%) Wind speed (km/hr) Air temperature (C) Relative humidity (%)
27 July
(7-14 days before summer rains)
Dormant Prehatching 360-495 25-35 7.9-8.0 29.5-30.0 44-46
7 August
(during or after 50 mm precipitation)
Second-leaf stage Hatching 325-450 38 8.0-8.1 31.2-32.0 43-48
23 August Early culm elongation stage 2nd and 3rd instar 340-430 39-42 9.6-12.1 33.8-35.0 38-52
29 August Peak of active plant growth 5th instar and adult 330-470 45-50 9.5-12.5 29.6-32.2 66-70

In the remainder of this Summary, the 4 burn dates are referred to by buffelgrass phenological stage at the time of burning: "dormant", "leaf stage", "culm stage", and "peak growth".

The time needed to burn across the treatment plots ranged from 60 to 300 sec, varying with the moisture content of buffelgrass. Assuming a distance of 50 m across each plot, the rate of spread probably ranged from approximately 0.17 to 0.8 m/sec [5].

Percent removal of buffelgrass aboveground biomass (standing stems and litter) by fire declined from the first to the last burn each summer, decreasing as buffelgrass greened up:

Approximate consumption of buffelgrass aboveground biomass by prescribed burns as related to green-up of buffelgrass pastures in Sonora, Mexico [7].

Burn date
(buffelgrass phenology)

New buffelgrass growth
(% green)
Buffelgrass biomass consumed by fire
(%)
27 July
(dormant)
0 100
7 and 23 August
(leaf and culm stages)
20-35 70-80
29 August
(peak growth)
60 ~50

FIRE EFFECTS ON BIOTIC COMMUNITY:
Burning of buffelgrass pasture at different phenological stages reduced buffelgrass live biomass only when conducted during peak growth, but burning reduced the amount of standing dead plant material during all 4 postfire years of the study. Burning also severely reduced spittlebug populations during all 4 postfire years [5,7].

Fire effects on buffelgrass: The only burn time that reduced buffelgrass was the final burn date, at the peak growth stage. On the other 3 burn dates (dormant, leaf stage, and culm stage), density and live biomass of buffelgrass remained the same or increased relative to control plots for 4 postfire years. In plots burned at peak growth, buffelgrass density and biomass were less than on other burn treatments for all postfire years; this reduction was attributed to low soil moisture after burning at peak growth. Control plots had greater buffelgrass density than plots burned at peak growth for all postfire years. Control plots also had greater biomass in postfire years 1 and 2, but biomass on controls was reduced in years 3 and 4 due to a precipitation-triggered increase in spittlebug populations [7].

Buffelgrass live biomass (g/m) measured on 15 August for 4 postfire years after burning at 4 phenological stages [5].

Burn date
(buffelgrass phenology)
Years after fire
1 2 3 4
27 July (dormant) 165ab* 165ab 160ab 190ab
7 August (leaf stage) 170a 290a 260a 255a
23 August (culm stage) 135bc 170ab 260a 275a
29 August (peak growth) 65c 70c 70c 80c
Control 155ab 120bc 75c 70c
*Values within a row and column with the same letter indicate no significant difference (P<0.05).

In the first year after prescribed burning, no dead biomass from the previous growing season was left standing. In subsequent years, this "recent dead" standing vegetation (yellow in color) was similar to that on unburned control plots, although there was less on plots burned during at peak growth than on plots burned at earlier dates:

Buffelgrass recent dead standing biomass (g/m) measured on 15 August for 4 postfire years after burning at 4 phenological stages [5]
Burn date
(buffelgrass phenology)
Years after fire
1 2 3 4
27 July (dormant) 0c* 50ab 50ab 60ab
7 August (leaf stage) 0c 60a 65a 70a
23 August (culm stage) 0c 45ab 80a 75a
29 August (peak growth) 0c 35b 20b 35b
Control 90a 75a 55ab 55ab
*Values within a row and column with the same letter indicate no significant difference (P<0.05).

In unburned buffelgrass pasture, recent dead biomass deteriorates to "old" dead biomass (gray in color) within 1 to 2 years [4,5]. In the areas burned for this study, burning eliminated old dead biomass for 3 years; in the 4th postfire year, old dead biomass was found in trace amounts but was nowhere near the amount in unburned plots, which averaged 110 to 1,200 g/m [5,7].

Fire effects on spittlebugs: Summer prescribed burns reduced spittlebug habitat quality and spittlebug density through 4 postfire years. The first 3 burns each year (dormant, leaf stage, and culm stage) disrupted the insect life cycle by destroying eggs and nymphs. Habitat for adults was destroyed because fire consumed the standing stems needed for food and the litter needed for egg laying. In addition, the microclimate within the grass canopy was more stressful for spittlebugs: Air movement reduced humidity and dried the soil surface and litter near the exposed bases of buffelgrass plants. No spittlebug nymphs were found on any burned plots during the study, whereas 25 to 30 nymphs occurred per m on unburned plots. Only 2 adult spittlebugs were found in the 4 postfire years on plots burned before peak growth. Burning during peak growth altered fuels and microclimate less than burning earlier in the summer. Adult spittlebugs were found on these plots at densities of 6 to 28/m; this density was less than that on control plots and occurred only in postfire years 1 through 3. Since no nymphs were found on plots burned at peak growth, the authors comment that the adults found there had probably migrated in from adjacent unburned areas. [5].

FIRE MANAGEMENT IMPLICATIONS:
Fire Management Objective: This research was designed to learn if fire could be used to increase productivity of buffelgrass pasture. Managers of wildlands are more likely to be interested ways to reduce buffelgrass productivity.

Summer fires conducted while plants were dormant had little effect on buffelgrass productivity. Burning after growth began (leaf and culm stages) increased productivity in postfire years 2 through 4. Burning during peak buffelgrass growth reduced density and biomass of buffelgrass for 4 years.

Summer fires interrupted the spittlebug life cycle, eliminating any potential for this insect to reduce buffelgrass production [4,5]. Potential effects of spittlebugs on growth and productivity of native grasses could be of concern to managers of natural areas, but these effects were not addressed by the research summarized here.
SPECIES INCLUDED IN THE SUMMARY:
This Research Project Summary contains fire effects and/or fire response information on the following species. For further information, follow the highlighted links to the FEIS reviews of those species.

Appendix

Scientific name Common name
Insect
Aeneolamia albofasciata spittlebug
Grass
Pennisetum ciliaris buffelgrass

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. 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]

3. 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]

4. Martin, R. M.; Cox, J. R.; Alston, D. G.; Ibarra F., F. 1995. Spittlebug (Homoptera: Cercopidae) life cycle on buffelgrass in northwestern Mexico. Annals of the Entomological Society of America. 88(4): 471-478. [70514]

5. Martin-R, Martha; Cox, Jerry R.; Ibarra-F, F.; Alston, Diana G.; Banner, Roger E.; Malecheck, John C. 1999. Spittlebug and buffelgrass responses to summer fires in Mexico. Journal of Range Management. 52(6): 621-625. [69189]

6. Martin-R., Martha H.; Cox, Jerry R.; Ibarra-F., Fernando. 1995. Climatic effects on buffelgrass productivity in the Sonoran Desert. Journal of Range Management. 48(1): 60-63. [24432]

7. Martin-Rivera, Martha H. 1994. The effect of climate and spittlebug (Aeneolamia albofasciata) on buffelgrass (Cenchrus ciliaris L.) productivity in the Sonoran Desert. Logan, UT: Utah State University. 80 p. Dissertation. [70513]

8. Peck, Daniel; Castro, Ulises; Lopez, Francisco; Morales, Anuar; Rodriguez, Jairo. 2001. First records of the sugar cane and forage grass pest, Prosapia simulans (Homoptera: Cercopidae), from South America. Florida Entomologist. 84(3): 402-409. [70523]


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