Grass bud bank responses to fire in a semi-arid savanna system

Authors: HEIRS, QUINN - Collin County Community College; TREADWELL, MORGAN - Texas A&M Agrilife; DICKINSON, MATTHEW - Us Forest Service (FS); KAVANAGH, KATHLEEN - Oregon State University; LODGE, ALEXANDRA - Texas A&M University; STARNS, HEATH - Texas A&M Agrilife; TOLLESON, DOUG - Texas A&M Agrilife; TWIDWELL, DIRAC - University Of Nebraska; Wonkka, Carissa; ROGERS, WILLIAM - Texas A&M University

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2021
Publication Date: 4/7/2021
Citation: Heirs, Q.A., Treadwell, M.L., Dickinson, M.B., Kavanagh, K.L., Lodge, A.G., Starns, H.D., Tolleson, D.R., Twidwell, D., Wonkka, C.L., Rogers, W.E. 2021. Grass bud bank responses to fire in a semi-arid savanna system. Ecology and Evolution. https://doi.org/10.1002/ece3.7516.
DOI: https://doi.org/10.1002/ece3.7516

Interpretive Summary: Increasingly, land managers have attempted to use extreme prescribed fire as a method to address woody plant encroachment in savanna ecosystems. The effect that these fires have on herbaceous vegetation is poorly understood. We examined the immediate below-ground grass dynamics of two dominant grasses, a cool season bunch grass, Nassella leucotricha, and a warm season vegetatively-spreading grass, Hilaria belangeri, following fires of varying intensity in a semi-arid savanna system in the Edwards Plateau ecoregion of Texas. Treatments included high-intensity, low-intensity, and no burn treatments. Below-ground buds were counted, and their activities classified to determine immediate effects of fire on bud activity, dormancy, and mortality. High-intensity burns resulted in immediate mortality of N. leucotricha and H. belangeri buds. Active buds decreased following high-intensity and low-intensity burns for both species. In contrast, bud activity, dormancy, and mortality remained constant in the control. In the high-intensity treatment, 100% of N. leucotricha individuals resprouted while only 25% of H. belangeri individuals resprouted three weeks following treatment. Bud depths were different between the two species and may account for this divergence, with average bud depths for N. leucotricha being 1.3 cm deeper than H. belangeri. Our results suggest that fire intensity may directly affect bud activity and mortality for these two species.

Technical Abstract: Increasingly, land managers have attempted to use extreme prescribed fire as a method to address woody plant encroachment in savanna ecosystems. The effect that these fires have on herbaceous vegetation is poorly understood. We examined the immediate (<24hr) bud bank dynamics of two dominant graminoids, a C3 caespitose grass, Nassella leucotricha, and a C4 stoloniferous grass, Hilaria belangeri, following fires of varying energy (J/m2) in a semi-arid savanna system in the Edwards Plateau ecoregion of Texas. Treatments included high-energy, low-energy, and no burn (control) treatments. Belowground axillary buds were counted, and their activities classified to determine immediate effects of fire energy on bud bank activity, dormancy, and mortality. High-energy burns resulted in immediate mortality of N. leucotricha and H. belangeri buds (P < 0.05). Active buds decreased following high-energy and low-energy burns for both species (P < 0.05). In contrast, bud activity, dormancy, and mortality remained constant in the control. In the high-energy treatment, 100% (n=24) of N. leucotricha individuals resprouted while only 25% (n=24) of H. belangeri individuals resprouted (P < 0.0001) three weeks following treatment application. Bud depths were significantly different between the two species and may account for this divergence, with average bud depths for N. leucotricha being 1.3 cm deeper than H. belangeri (P < 0.0001). Our results suggest that fire energy may directly affect bud activity and mortality for these two species. Synthesis and applications: It is imperative to understand how fire energy impacts the bud banks of grasses in order to better predict grass response to the increased use of extreme prescribed fire in land management.