Sericea lespedeza (Lespedeza cuneata) was introduced in the United States in 1896 and was once considered valuable as forage for cattle, habitat for wildlife, and prevention of soil erosion.  Expansion of sericea into tallgrass prairie ecosystems has lead to its listing as a noxious weed.  Herbicides are currently the most effective control for sericea, but herbicides are expensive and ineffective as a long-term control method.  Alternate range management practices such as patch-burn management have been found to slow the spread of sericea.  Patch-burn entails burning sections of tallgrass prairie on a 3-year rotation.  We predicted patch-burn management would lead to hotter fires due to more litter accumulation which may have a large impact in sericea lespedeza seed viability and resulting expansion. Our study was conducted at the Bressner Research Site in Woodson County, KS and at the Koger Ranch in Chase County, KS.  Our objective was to evaluate environmental parameter differences between conventional annual burning and patch-burn rotation at these sites to help determine which variables can be linked to the reduced spread. 

Results/Conclusions

We used a respiration test to determine seed viability response to temperature and ran heat treatments with 100 seeds per treatment at 25^oC intervals beginning at 50^oC.  One seed sample was left at room temperature. Our results indicated that sericea lespedeza seed viability dropped significantly at 225^oC and seed viability dropped to zero by 250^oC.  Temperature sensitive paints were applied on tiles and then placed in the burn plots to determine the temperature of the fire at ground level and 5 cm below the surface.  Preliminary tests on fire temperature during burns indicate that surface temperatures during fall burns are insufficient to reduce seed viability, but spring fire temperatures may burn higher.  We found a higher biomass of litter accumulation in the triennial burn plots vs. the annual burn plots and the higher biomass lead to an increase in fire temperature.  The average temperature for the fall burns at the surface was 96.5 ± 6.6^oC with the highest temperature reaching 135^oC.  No buried tiles reached the minimum threshold (79^oC) of the temperature sensitive paint.