Restoration of oak woodlands and savannas in Tennessee using canopy-disturbance, fire-season, and herbicides

• Herbicides reduced understory woody vegetation and increased herbaceous groundcover.
• Benefits were greatest in association with heavy canopy disturbance and fall fire.
• Repeated fire eventually matched all observed benefits of herbicide applications.
• In the Appalachian region, herbicides may be less economical than repeated fire.

Establishing herbaceous groundcover is essential for oak woodland and savanna restoration. In the Appalachian region, woody vegetation in the understory can persist through many fires and interfere with achieving this goal. Herbicide applications could reduce such vegetation and interact with canopy-disturbance and fire to accelerate restoration. In stands thinned to woodland (16 m2 ha−1, 75% canopy closure) or savanna (5 m2 ha−1, 24% canopy closure) conditions and burned biennially in the fall (October) or spring (March), we economically applied triclopyr (Garlon® 3A) to understory woody plants using foliar and cut-surface techniques in the fall between fires. From 2011 to 2013, only minor differences in vegetation were observed between areas managed with canopy-disturbance and fire (CF) and areas where herbicides were also used (CFH). Small-sapling (≥1.4 m tall, <7.6 cm DBH) density in CF was 2,566 stems ha−1 greater than CFH in 2012. This difference was (1) the only woody control CFH attained beyond CF, (2) only lasted a single growing-season because it was mostly fire-sensitive species top-killed by subsequent fire, and (3) only led to increased herbaceous groundcover in savannas burned in the fall. This included the greatest reported increase in herbaceous groundcover (graminoid +18.2%, forb +8.0%) to be associated with herbicide applications under partial oak canopies in the Appalachian region. Expanding herbicide target constraints, completely removing undesirable seed-sources, increasing triclopyr concentration, exploring tank-mixes, and alternative application timing (e.g., prior to canopy disturbance) could improve effectiveness; however, fire suppression throughout the Appalachian region has increased the dominance of fire-sensitive woody species. Our results demonstrate how such composition can reduce the utility of herbicides relative to fire during oak woodland and savanna restoration.