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



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.

RESEARCH PROJECT SUMMARY CITATION:
Smith, Jane Kapler, compiler. 2010. Research Project Summary: Response of herbaceous vegetation to winter burning in Texas oak savanna. 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/ [].

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

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 LOCATION AND SITE DESCRIPTION:
This study was conducted in a bastard oak-post oak (Quercus fusiformis-Q. stellata) savanna at the Kerr Wildlife Management Area in Kerr County, Texas. Site and soil characteristics were not described.

PREFIRE PLANT COMMUNITY:
The prefire plant community was dominated by grasses, with a very open oak overstory. The study measured abundance of herbaceous vegetation surrounding individual plateau oaks and post oaks. Fuels were measured before and after burning. Species-specific productivity was measured on burned and paired, unburned plots in the first summer after burning (~6 months after fire).

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

Table 1. Fire regime information on the vegetation community studied in this Research Project Summary. Fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Model [4]. This vegetation model was developed by local experts using available literature, local data, and expert opinion as documented in the PDF file linked from the Potential Natural Vegetation Group listed below.
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Oak savanna Replacement 3% 100 5 110
Mixed 5% 60 5 250
Surface or low 93% 3 1 4
*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 [1,3].

PLANT PHENOLOGY:
Herbaceous vegetation was dormant when burned in February; postfire vegetatioin was measured in the growing season after burning (July and early August).

FIRE SEASON AND SEVERITY CLASSIFICATION:
Winter, low severity

FIRE DESCRIPTION:
This research was designed to determine responses of forbs and grasses in a Texas oak savanna to prescribed burning in winter.

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):

Table 2. Average fuel load at 3 distances from the base of each of the dominant tree species.
 
Fuel load (SD) (lb/ac)
Location
Base of tree
Canopy edge
Open grassland*
Plateau oak 1,937 (1,256) 724 (179) 435 (132)
Post oak 2,005 (437) 897 (313) 544 (310)
*Measured at twice the canopy radius from the tree base

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.

FIRE EFFECTS ON PLANT COMMUNITY:
Species richness was less in burned than unburned plots, with burned plots containing 5% to 20% fewer herb species than unburned plots (Table 3). Trailing lespedeza was the only species present near both tree species (post oak and plateau oak) in unburned plots and lacking near both species in burned plots.

Table 3. Richness of forb and grass species in the growing season after a winter prescribed fire.
Dominant tree species
Plateau oak
Post oak
Treatment
Unburned
Burned
% change
Unburned
Burned
% change
Forbs 22 18 -18 25 20 -20
Grasses 20 16 -20 21 20 -5

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.

Table 4. Live biomass of forbs and sedges (lb/ac dry weight) in the growing season after a winter prescribed fire.
Dominant tree species
Plateau oak
Post oak
Treatment
Unburned
Burned
% difference
Unburned
Burned
% difference
velvet bundleflower 4.12 9.50 130.58 5.45 9.05 66.06
catnip noseburn 2.19 1.80 -17.81 1.16 1.21 4.31
saw greenbrier 0.71 2.85 301.41 0.07 3.19 4457.14
Texas snoutbean 0.20 0.00 -100.00 0.68 3.54 420.59
spreading hedgeparlsey 0.01 0.05 400.00 0.00 1.35 N/A
pelotazo 0.06 0.00 -100.00 0.57 1.18 107.02
smartweed leaf-flower 0.69 0.22 -68.12 0.15 0.00 -100.00
slender yellow woodsorrel 0.08 0.03 -62.50 0.07 0.04 -42.86
trailing lespedeza 0.54 0.00 -100.00 0.50 0.00 -100.00
Other forbs
(12 species)
0.97 1.68 73.20 0.72 1.22 69.44
Sedge species 3.32 3.01 -9.34 4.33 3.68 -15.01
Total live forb and sedge biomass 12.95 19.14 47.80 13.74 24.51 78.38

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.

Table 5. Live biomass of grasses (lb/ac dry weight) in the growing season after a winter prescribed fire.
Dominant tree species
Plateau oak
Post oak
Treatment
Unburned
Burned
% difference
Unburned
Burned
% difference
little bluestem 55.54 41.53 -25.23 62.90 46.71 -25.74
Texas wintergrass 40.21 22.87 -43.12 25.80 31.18 20.85
rough dropseed 6.86 8.60 25.36 28.54 29.34 2.80
threeawn species 8.80 11.34 28.86 7.86 4.57 -41.86
grama species 11.98 7.49 -37.48 7.86 16.74 112.98
Edwards Plateau beardgrass 14.72 2.55 -82.68 9.36 9.49 1.39
plains lovegrass 10.08 3.97 -60.62 5.95 5.43 -8.74
Texas cupgrass 0.81 0.63 -22.22 16.48 19.89 20.69
vine-mesquite 2.95 6.85 132.20 6.76 7.31 8.14
curlymesquite 4.73 1.69 -64.27 0.60 0.42 -30.00
cane bluestem 1.25 7.60 508.00 1.51 1.26 -16.56
fall witchgrass 1.34 0.58 -56.72 0.31 0.15 -51.61
Hall's panicgrass 3.56 0.46 -87.08 1.20 0.43 -64.17
Virginia wildrye 0.00 0.00 0.00 2.14 4.77 122.90
Other grasses
(4 species)
1.57 1.51 -3.82 1.19 4.96 316.81
Total live grass biomass 164.47 117.75 -28.41 178.57 182.74 2.34

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).

Table 6. Total standing herbaceous biomass the growing season after a winter prescribed fire.
Dominant tree species
Plateau oak
Post oak
Treatment
Unburned
Burned
Unburned
Burned
Live biomass (lb/ac) 177.42 136.89 192.31 207.25
Dead biomass (lb/ac) 225.60 61.12 145.38 43.68
Percent dead of standing biomass 56% 31% 43% 17%
FIRE MANAGEMENT IMPLICATIONS:
Winter burning may increase forb productivity without adversely affecting grass production, which may improve habitat for deer. The authors speculate that a reduction in standing dead biomass caused by winter fire may increase forb productivity by reducing cover (thus increasing insolation) and by increasing available nutrients in the soil.
APPENDIX: SPECIES INCLUDED IN THIS 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.

Common name
Scientific name
cane bluestem Bothriochloa barbinodis
catnip noseburn Tragia nepetifolia (Tragia neptaefolia)*
curlymesquite Hilaria belangeri
Edwards Plateau beardgrass Bothriochloa edwardsiana
fall witchgrass Digitaria cognata (Leptoloma cognatum)
grama species Bouteloua spp.
Hall's panicgrass Panicum hallii
little bluestem Schizachyrium scoparium
pelotazo Abutilon incanum
plains lovegrass Eragrostis intermedia
rough dropseed Sporobolus compositus (Sporobolus asper)
saw greenbrier Smilax bona-nox (Smilax bonanox)
sedge species Carex spp.
slender yellow woodsorrel Oxalis dillenii
smartweed leaf-flower Phyllanthus polygonoides
spreading hedgeparlsey Torilis arvensis
Texas cupgrass Eriochloa sericea
Texas snoutbean Rhynchosia texana
Texas wintergrass Nassella leucotricha (Stipa leucotricha)
threeawn species Aristida spp.
trailing lespedeza Lespedeza procumbens
velvet bundleflower Desmanthus velutinus
vine-mesquite Panicum obtusum
Virginia wildrye Elymus virginicus
*For species that have undergone scientific name changes, names in parentheses are those used in this Research Paper.

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]

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