COS 258-6 - Reduction of cover of the invasive grass Bothriochloa ischaemum by a summer fire still present 12 years later

Background/Question/Methods

Prescribed burning can reduce invasive species and increase native species cover in grasslands, but fire effectiveness depends on the characteristics and timing of the fires. The perennial, non-native grass Bothriochloa ischaemum is invasive throughout the southern Great Plains.

We established 80 randomly located 2x1-m experimental plots at Balcones Canyonlands National Wildlife Refuge in central Texas in 2009. Half of the plots were invasive-dominated (≥ 60% invasive grass B. ischaemum cover) and half were native-dominated (≤ 40% B. ischaemum cover). Approximately half of the plots in each group were burned in July 2009. In 2011, there was significantly less B. ischaemum and significantly more native forb cover in the burned-invasive plots than in unburned-invasive plots. All plots were burned in the winters of 2014 and 2017. We revisited these plots in 2021 to determine whether the treatment differences observed in 2011 were still detectable and whether B. ischaemum had invaded into previously native-dominated plots.

Results/Conclusions

The treatment differences observed in 2011 were reduced, but still detectable, in 2021. Plots that had been burned in summer 2009 still had more native forb cover and greater species richness than plots that had not been burned 12 years earlier.

B. ischaemum had not invaded most of the native-dominated plots even though there were dense stands nearby and all the plots were in full sun (a habitat requirement of B. ischaemum). These native-dominated plots tended to have shallower soil (0-10 cm) than the invasive-dominated plots (10-30 cm). Limited soil moisture and nutrients in shallow soil may prevent B. ischaemum from establishing and/or may give certain native species a competitive advantage.

These results indicate that a prescribed burn conducted in the summer followed by winter fires can control B. ischaemum for up to 12 years. We also found that soil depth, a previously unrecognized factor, influences habitat suitability for B. ischaemum.

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