Pyric‐based restoration of C₄ grasses in woody (Prosopis glandulosa) encroached grassland is best with an alternating seasonal fire regime

Abstract

Prescribed fire is a management strategy for limiting or reducing woody plant invasion on grasslands and savannas. However, in dense mature woody stands several fires may be necessary to overcome woody dominance and facilitate grassland restoration. Here we determined if a concentrated series of fires could stimulate recovery of C 4 perennial grasses in Southern Great Plains, U.S.A., grasslands that had become dominated by a fire tolerant woody legume, honey mesquite (Prosopis glandulosa).Our study included six treatments: three winter fires in 5 years (3WF), three alternating season winter-summer-winter fires in 4 years (3AF), three alternating season fires in a more compressed (extreme) timeframe (3AFX), two summer fires in 3 years (2SF), two summer fires in consecutive years (2SFX), and a no fire "Control." Cattle grazing was excluded during the study. Treatments with summer fire were most effective at top-killing mesquite, but no treatments root-killed >5%. All top-killed mesquite resprouted. Only the treatments that alternated fire seasons (3AF and 3AFX) increased C 4 mid-grass cover, most from stoloniferous vine mesquite (Panicum obtusum) and not C 4 bunchgrasses. The 2SF treatment increased C 4 short-grass cover but not C 4 mid-grass cover. Because none of the treatments root-killed mesquite, grass recovery declined as woody regrowth increased. Drought also contributed to the decline. Without additional fire disturbances to suppress mesquite regrowth or anthropogenic inputs to root-kill mesquite, transition from woodland to savanna or grassland stable states was not possible.

Stability of C3 and C4 Grass Patches in Woody Encroached Rangeland after Fire and Simulated Grazing

“…Earlier research conducted on the same site as this study (and before any fire treatments occurred) concluded that this region of the SGP would always be dominated by Buchloe, regardless of the presence of Prosopis [5]. We have subsequently found that alternate season fire treatments in the absence of grazing significantly increased the cover of C 4 mid-grasses [31,43]. This included C 4 mid-grass species, such as Bouteloua curtipendula and Panicum obtusum, that are valued as forage for cattle.…”

“…Several combinations of the competitive effects of these three species are suspected to have caused the decline of C 4 mid-grasses as a percentage of total ground cover and/or biomass production of individual plants in the SGP [5,31]. We hypothesize that prior to the European settlement that introduced domestic cattle grazing, much of the SGP frequently burned [32,33] and was open grassland-dominated by C 4 mid-grasses with smaller portions of C 4 shortgrasses, like Buchloe.…”

Impact of soil residual auxin herbicide on seedling emergence and biomass differs between soil types, water pulse event, and seedling species

“…Common management approaches to reduce woody plant cover include mechanical removal (Mndela et al 2023), prescribed fire (Limb et al 2016;Ansley et al 2022), and chemical shrub treatment (Tunnell et al 2006;Eddy et al 2020). Target specificity, cost-effectiveness, and restoration efficacy vary by method (Hamilton 2004).…”