Effect of two different burn treatments on the vegetation of a successional tallgrass prairie site.

Abstract:

Based on pre-treatment comparisons of species overlap and Index of Commonness values, the vegetation in the three survey areas used in this study at the Pony Express Conservation Area near Osborn, Missouri, were considered similar in initial plant composition. Two of the three survey areas were treated as follows: 1.) a spring burn followed by another spring burn after three years and 2.) a fall burn followed by a spring burn after three and one half years. The third survey area remained unburned throughout the study and served as the control. Although Index of Commonness values showed little bluestem (Andropogon scoparius) to be the major species in all three survey areas before and after treatments, commonness results also showed that the study area was undergoing ecological succession during the six years of this study with Jerusalem artichoke (Helianthus tuberosus) and grass-leaved goldenrod (Solidago graminifolia) increasing in all survey areas. In addition, Indian grass (Sorghastrum nutans), a native tallgrass, and the exotic weedy species sericea lespedeza (Lespedeza cuneata) both showed dramatic increases in the treatment survey areas over the control area. Support was provided by the Missouri Department of Conservation.

1. Introduction

Fire on the prairie stimulates the growth of many native prairie plant species, including many native grasses (Towne and Owensby 1984; Svejar and Browning 1988; Howe 1995; Towne and Knapp 1996; Briggs and Knapp 2001) and eradicates invasive shrub species (Gibson and Hulbert 1987). Fire also removes the accumulated dead plant material releasing nutrients back to the soil and allowing more sunlight to reach new growth. Fire suppression is degrading to the tallgrass prairie habitat and may eventually allow a forest to dominate (Collins 1990).

The purpose of this study was to determine the effect of prescribed burns on the flora of a successional tallgrass prairie site. Plants of special concern during this study included all of the native prairie species plus sericea lespedeza, a recent non-native invader in the study area.

This study involved a survey and comparison of plants in the following three survey areas: 1.) an area treated with a spring burn followed by another spring burn three years later, 2.) an area treated with a fall burn followed by a spring burn three and one half years later and 3.) an area left untreated to serve as the control. Floristic surveys before and after treatments were compared in an attempt to quantify the response of plant species to the treatments without the use of statistical analysis.

2. Methods

The area used for this study was a successional tallgrass prairie within the Pony Express Conservation Area near Osborn, Missouri. The climate of this geographical area is subhumid with an average yearly precipitation of 38 inches. The soil is a Clarinda silty-clay loam (USDA Conservation Service 1997). Few land use records for the specific study site were found but it is known that the land was used for agriculture in the past. Missouri Department of Conservation records show that there were no prescribed burns in this area between 1990 and the time that this study began.

The three specific survey areas used in this study were each 20 meters by 100 meters. These three survey areas were adjacent to one another but were separated by plowed firebreaks at least 10 meters wide. A sampling transect was established along the midline of each survey area and 18 one meter by one meter quadrats were positioned 5 meters apart along the transect line (figure 1). All plants within each quadrat were identified and a percent cover value was determined for each species in August of 1993 before any burn treatments. Spring burns were done in April of 1994 and 1997 in one of the treatment areas. In the other treatment area a fall burn was done in November of 1993 and a spring burn was done in April of 1997. All plants within each quadrat were sampled again in August of 1999, two and one half years after the final treatment.

[FIGURE 1 OMITTED]

The ambient environmental conditions required for each burn during this study included a humidity range of 20 to 70 percent, a mid-flame wind speed range of 1 to 12 miles per hour and a temperature range of 20 to 95 degrees Fahrenheit. The ring-head fire method was used for each prescribed burn. Two fire ignition crews would simultaneously start backing fire lines into the prevailing wind from approximately the same point. These two crews would then proceed in opposite directions lighting the edge of the treatment area until both crews met on the upwind side of the treatment area to complete the fire ring. This procedure initiates a backing fire which burns approximately one fourth of the way into the treatment area before a heading fire completes the burn of the entire treatment area.

Flora of Missouri (Steyermark 1963) was used for all identification in this study. Percent cover, frequency and commonness values were determined using the following methods modified from Knoop (1984).

Average Cover = sum of cover values for a species/# of quadrats where the species occurred

Frequency = # of quadrats where the species occurred x 10/total # of quadrats

Index of Commonness = Frequency x Average Cover

3. Results and Discussion

During the pretreatment plant survey (1993) general similarities for the top species by commonness values were observed (Table 1) among all survey transects. Little bluestem (Andropogon scoparius) was by far the most common species on all three transects. The following six other species were in the top ten on all three transects based on commonness values: sericea lespedeza (Lespedeza cuneata), tall goldenrod (Solidago altissima), old field goldenrod (Solidago nemoralis), small ragweed (Ambrosia artemisiifolia), Jerusalem artichoke (Helianthus tuberosus) and Scriber's panicum (Panicum oligosanthes). Although Indian grass (Sorghastum nutans) was found on all transects during the pretreatment survey, its commonness value was much higher on the control transect compared to the treatment transects. Sericea lespedeza (Lespedeza cuneata), another plant found in all three transects during the pretreatment survey, had a dramatically higher pretreatment commonness value on the fall-spring burn transect than on the other two transects. Grass-leaved goldenrod (Solidago graminifolia) was ranked tenth in commonness value on the pretreatment spring-spring burn transect but it ranked eleventh in commonness value on the pretreatment fall-spring burn and control transects.

A comparison of commonness values between pretreatment (1993) and post-treatment (1999) surveys shows little bluestem to be the most common species on all transects before and after treatments (Table 1). Jerusalem artichoke increased on all of the transects during the entire study. Grass-leaved goldenrod also increased in commonness on all transects during the study but showed the greatest increase on the control. Tall goldenrod showed an increase in commonness on the fall-spring burn transect and the control transect but decreased in commonness on the spring-spring burn transect.

Overall, the most dramatic changes during the study were increases in the commonness values of Indian grass, a native warm season tallgrass, and sericea lespedeza, an exotic species that has become a troublesome invader in prairies across the Midwest (figures 2 and 3). During the pretreatment survey (1993) Indian grass was found primarily on the control transect (figure 2); however, over the entire period of the study Indian grass increased in commonness on both burn treatment transects but showed a decrease in commonness on the control transect. An increase in native tallgrasses such as Indian grass is expected in burn treated areas based on some other studies (Town and Owensby 1984; Svejcar and Browning 1988; Howe 1995). Sericea lespedeza showed dramatic increases in commonness on both burn treatment transects but showed a slight decrease in commonness on the control transect (figure 3).

[FIGURES 2-3 OMITTED]

Little bluestem, the other common native warm season grass surveyed in this study, showed the expected increases in commonness on both burn treatment transects but showed a decrease in commonness on the control transect (figure 4).

[FIGURE 4 OMITTED]

The results for sericea lespedeza in this study confirms what other studies have suggested, that is, sericea lespedeza tends to increase with prescribed burns (Whitehead, et al. 1998; Fick 1990). Sericea lespedeza is a nitrogen-fixing perennial legume that was brought to the United States from East Asia in 1896 for erosion control and wildlife food. The first record of the presence of sericea lespedeza in Missouri (the site of this study) dates back to 1936 and its occurrence has been increasing in recent years. Serecia lespedeza is a hardy, disease resistant plant that flowers from early July through October in Missouri and produces large quantities of seeds (1500 seeds/stem) that remain viable for up to twenty years with approximately 15% of the one-year old seeds germinating. The fact that the germination of sericea lespedeza seeds can reach up to 88% (Young and Eddy. 1998) following a fire at least partly explains why sericea lespedeza increases so rapidly following prescribed prairie burns.

Although there is no known effective biological control for sericea lespedeza at the present time, other control methods such as grazing (Escobar 1998) and chemical control (Wehtje et al. 1999) have been suggested. Mowing is especially effective in late July or early August when flowering is well underway and food reserves within the plant are at a critically low point. Whitehead et al. (1998) suggested that a fall burn followed by a burn the next spring is effective in controlling established stands of sericea lespedeza. In our study at the Pony Express Conservation, the transect that was treated with a fall burn followed by a spring burn actually showed a dramatic increase in commonness for sericea lespedeza (figure 3). However, the spring burn came more than three years after the fall burn in our study compared to burns during consecutive seasons in the Whitehead et al. (1998) study. Spring burning to enhance seed germination in sericea lespedeza followed by mowing or hand-applied chemical treatment with a herbicide such as Remedy or Round-up is recommended for future testing as a possible method for reducing sericea lespedeza at the Pony Express Conservation Area.

Table 1. Commonness Values for Top Species on Each of the Three
Transects in the Pretreatment (1993) and Post-treatment (1999)
Surveys.

Transects and Survey Year

                             spring-spring
                             burn transect     control transect

                           (1993)    (1999)    (1993)    (1999)

Andropogon scoparius         3180      3278      4260      3944
Sorghastrum nutans             56      1644       987       267
Solidago nemoralis            584        33       684        22
Ambrosia artimisiifolia       524        44       540        56
Solidago altissima            764       494       520       711
Lespedeza cuneata             772      1533       484       406
Panicum oligosanthes          612       167       424       300
Rubus flagellaris             324       761       416      1461
Helianthus tuberosus          476       839       160       992
Pycanthemum tenufolium        172       411       108       417
Solidago graminifolia         264       600       100      2289
Fragaria virginiana            88       661        24       244
Antennaria neglecta           460       661        12        12

                           fall-spring burn
                               transect

                           (1993)    (1999)

Andropogon scoparius         2940      3389
Sorghastrum nutans             56      1756
Solidago nemoralis            292        22
Ambrosia artimisiifolia       220        11
Solidago altissima            444      1167
Lespedeza cuneata            1396      1994
Panicum oligosanthes          260       144
Rubus flagellaris              92       211
Helianthus tuberosus          392       700
Pycanthemum tenufolium        182      1044
Solidago graminifolia         156      1078
Fragaria virginiana           320       978
Antennaria neglecta           400        44

4. Acknowledgements

Support for this study was provided by the Missouri Department of Conservation.

Special thanks to Marcia Pfleiderer, Craig Crisler, Roland Spilker and Dennis Browning of the Missouri Department of Conservation for conducting the prescribed burns and providing expert advise during this study.

5. Literature Cited

Briggs J. M. and A. K. Knapp. 2001. Determinants of C-3 forb growth in a C-4 dominated grassland. Plant Ecology 152: 93-100.

Collins S. and L. Wallace. 1990. Fire in North American tallgrass prairies. University of Oklahoma Press: Norman and London.

Escobar, E. N. 1998. Performance of goats grazing on sericea lespedeza (Lespedeza cuneata), a noxious weed in Kansas. Journal of Dairy Science, v 81, iss. SUPPL. 1, pp. 106.

Fick, W. H. 1990. Biology and control of sericea lespedeza. Proceedings from the North American Weed Science Society.

Gibson D. J. and L. C. Hulbert. 1987. Effects of fire, topography and year to year climatic variation on species composition in the tallgrass prairie. Vegetio 72: 175-185.

Howe H. F. 1995. Succession and fire season in experimental prairie plantings. Ecology: 76: 1917-1925.

Knoop J. D. 1984. Floristic and vegetation survey of the W. Pearl King Prairie Grove. Proceedings of the 6th North American Prairie Conference. Tri-College University Center for Environmental Studies. Fargo, North Dakota. Pp. 263.

Steyermark J. 1963. Flora of Missouri. University of Iowa Press: Iowa City, Iowa.

Svejcar T. J. and J. A. Browning. 1988. Growth and gas exchange of Andropogon Gerardi as influenced by burning. Journal of Range Management 20: 239-244.

Towne E. G. and A. K. Knapp. 1996. Biomass and density responses in tallgrass prairie legumes to annual fire and topographic position. American Journal of Botany 83: 175-179.

Towne E. G and C. Owensby. 1984. Long-term effects of annual burning at different dates in ungrazed Kansas tallgrass prairie. Journal of Range Management 37: 392-397.

USDA-NRCS. 1997. Soil Survey of DeKalb County, Missouri.

Wehtje G, R. H. Walker and J. D. Jones. 1999. Weed control in low tannin seedling sericea lespedeza (Lespedeza cuneata). Weed Technology 13: 290-295.

Whitehead K., T. Eddy, J. Mayo and J. Young. 1998. Burning Sericea. Unpublished Proceedings of the Sericea Lespedeza Symposium, Emporia State University, Emporia, Kansas.

Young J. and T. Eddy. 1998. Biology of sericea. Unpublished Proceedings of the Sericea Lespedeza Symposium, Emporia State University, Emporia, Kansas.

Sheila Hessler, Terry Elder, Todd Gray, Jerry Hernandez and * John Rushin

Department of Biology, Missouri Western State College, St. Joseph, MO 64507