In Search of Sustainable Livestock Management in the Dry Chaco: Effects of Different Shrub Removal Practices on Vegetation and Soil

Background: In arid and semi-arid ecosystems in Argentina, dominance of shrublands and the search to increase the forage supply for livestock motivates interventions such as roller-chopping and hand-cutting to reduce the abundance of shrubs. However, an integral analysis of the effects of these practices from a sustainability point of view, including not only forage productivity but also other ecosystem service is still missing. We evaluated at the ecosystem level the impact of shrub removal on total production and phenology; at the local level the responses in cover, botanical composition and diversity of vegetation functional groups, as well as the effects on soil physical properties. We combined evaluation methodologies with remote sensing and field sampling in control (woodland, shrubland) and treated (roller chopping, hand cutting) sites in 16 paddocks.Results: In treated sites, grass cover increased significantly compared to untreated sites. However, total production, growing season length were reduced. Tree cover was lower in treated sites, while shrub cover was reduced in the hand-cutting compared to the other treatments. Forbs cover was not modified. In addition, species richness decreased in the treated sites, being higher in roller-chopped sites than in the hand-cut sites, while the species diversity index was only reduced in the latter type of disturbance. Soil mechanical resistance and bulk density were higher in treated sites, while infiltration rate did not change.Conclusions: shrub removal and pasture seeding on woodland and shrubland sites increases herbaceous forage production, but decreases total production and increases its temporal variability and rainfall dependence; it decreases functional diversity and increases surface soil compaction. These responses depend on the intensity of the woody biomass removal disturbance (roller-chopping or hand-cutting). In this respect, roller chopping appears to be a more conservative practice than hand cutting, as it maintains high levels of herbaceous forage production and functional diversity. However, it is necessary to consider the importance of maintaining native forest regeneration, as both types of disturbance affected this process. Our study highlights the importance to design selective interventions in the vegetation, compatible with the maintenance of functional diversity, the regeneration of tree strata and the increase in grass production.