Developing a prescription for brush control in the Chaco region, effects of combined treatments on the canopy of three native shrub species

Abstract

Shrub encroachment is frequent in grazing lands in the Chaco region, Argentina. Fire is used by cattlemen to reduce the dominance of the shrub stands, improve forage standing biomass and quality, and enhance grazing accessibility. In this research, we assessed the combined effect of roller chopping þ fire on the plant canopy of three native shrub species, Acacia gilliessi, Celtis ehrenbergiana, and Schinus bumelioides. We used a randomized design, with three factors, year, burn dates, and fine fuel load. Before the burn, the area received a roller-chopping treatment. Canopy volume reduction was assessed using, DifV ¼ −1*(V i − V a ) and DifS ¼ −1*(S i − S a ), respectively, where V ¼ plant volume and S ¼ sprout number. Suffixes i and a represent measurements taken before the roller-chopping treatment and one growth season after the fire, respectively. Fire intensity, headfire residence time, woody residues, and initial plant volume were evaluated as covariates. Results indicate a negative fire effect on canopy volume and sprouting. A. gilliesi was more susceptible to fire than the other two species. High fine fuel load and high fire intensity generated a severe effect on sprout number. The same trend was observed for coarse fuels. The canopy volume reduction was greater in A. gilliesi than the other species, reaffirming its high susceptibility to fire. Head fires were faster in 2009 than in 2008 and in the late than in the early burn dates. These results suggest that mechanical þ fire treatments can be useful management tools for controlling shrub encroachment in the western Chaco.

Aerial Bud Bank and Structural Changes of Woody Species from Argentine Chaco in Response to Disturbances

“…In this work, the significant differences in the ABB size among studied species (p < 0.0001) seem to affirm our first hypothesis, and this aspect added to bark thickness should be considered when defining the woody species tolerance to physical or mechanical disturbances as wildfires, prescribed fires and roller-chopping as vegetation management techniques [9,14]. Schinopsis lorentzii and S. mistol were the tree species with greater resprouting ability than A. quebracho-blanco at least from epicormic buds in juvenile individuals, in agree with Bravo, et al [9].…”

“…Disturbances affecting aerial plant structures could increase the initial plant cover through expression of buds in new shoots and thorns [2]. Therefore, management activities destined to shrubby stratum control by physical or mechanical methods [13] should consider the ABB size and resprouting ability from basal and underground organs, since these treatments could even increase the initial plant cover of shrubs [14,27]. The intensive roller chopping application reduced exclusively the biomass of Larrea divaricata whereas it increased the number of individuals of Condalia microphylla and S. fasciculatus [28].…”

“…Fire is used from pre-Colombian times to promote new growth of grasses and to control shrubby encroachment in Chaco savannas [13]. Silvopastoral systems in native Chaco forests involve management roller-chopping as mechanical removal method of shrubby vegetation, combined with prescribed fires to diminish woody residues and to control shrub encroachment [14].…”

Impacto del fuego en la defensa de las plantas: Rasgos funcionales y síntesis de metabolitos secundarios en especies leñosas del Chaco semiárido de Argentina

“…La respuesta de la vegetación a este disturbio depende del régimen de fuego y los parámetros que lo definen (la intensidad, severidad, frecuencia, estacionalidad de los fuegos yextensión de las áreas afectadas) (Keeley, 2009), así como de la tolerancia y resistencia de la vegetación frente a este disturbio (Bravo et al 2014;Ledesma et al 2018). El actual escenario de cambio de uso de la tierra y de cambio climático, ha producido alteraciones en los regímenes de fuego a nivel global.…”

“…Las mediciones de inflamabilidad de las especies seleccionadas se realizaron a través de quemas experimentales en parcelas de 2 x 2 m. Cada planta individual (con DAP <15 cm) , se encontraba ubicada en el centro de cada parcela. Cada parcela se quemó con una carga de combustible baja (4.000 KgMs.ha -1 ) Esta metodología se describe con profundidad en el tercer capítulo y sigue las técnicas propuestas por Beutling, Batista, Stolle, y Tetto Giongo Alves, (2012), Bravo et al, (2014) y Ledesma et al, (2018).…”