Vegetation composition and structure changes following roller-chopping deforestation in central Argentina woodlands

Abstract

Driven by the pressure of increasing forage production for cattle, dry forests and woodlands of Argentina are suffering one of the highest deforestation rates in the world. In this study we combined field work and a remote sensing approach to assess the successional trajectory in terms of functional group diversity and ecosystem phenology, following roller chopping deforestation in a woodland of central Argentina. The first year after disturbance, shrub cover decreased at the same proportion than grass cover increased while tree cover was drastically reduced. After 3 years, shrubs recovered 70% of the original cover and grasses maintained a relatively high proportion, but tree cover remained low. Roller-chopping favoured early over late successional species in the case of woody plants, but had the inverse effect in the case of grasses. At ecosystem scale the length of the growing season was drastically shortened by 100 days following disturbance. Roller chopping improves ecosystem services of provision by enhancing forage's offer but at the same time deteriorated the system by reducing functional plant diversity

Interception loss, throughfall and stemflow by Larrea divaricata: The role of rainfall characteristics and plant morphological attributes

“…This means that L. divaricata is an "efficient species" at rainfall partitioning, which results a very important aspect in dry regions where water is a limiting factor for plant growth. There is evidence that L. divaricata is the main species in increasing its aboveground biomass production after clearing in Dry Chaco rangelands (Marchesini, 2011;Steinaker et al, 2016). So far, this situation have been explained by: (a) the high abundance of L. divaricata previous to the disturb due, in part, to the fact that it is a nonpalatable species (García et al, 2017), (b) the adaptation to support high temperatures without decreasing its photosynthetic activity respect to similar shrubs (Salvucci & Crafts-Brandner, 2004) and (c) the capacity to uptake water from the soil at very low water potentials (exceeding−8 MPa) (Marchesini, Fernández, & Jobbágy, 2013).…”

“…Therefore, our results suggested that the high stemflow inputs, combined with very low interception losses, represent another argument to explain the capacity of L. divaricata to generate more encroachment than other similar shrubs in Dry Chaco rangelands. The most common land use change of Dry Chaco rangelands are the replacement of native dry forest by buffelgrass (Cenchrus ciliaris) pastures using roller chopping technique (only aboveground shrub layer is removed) (Steinaker et al, 2016). However, buffelgrass is frequently displaced by L. divaricata, especially in the southern edge of this region, limiting the long-term forage production of the system (Figure 1).…”

Litter is more effective than forest canopy reducing soil evaporation in Dry Chaco rangelands

“…Under practical conditions, reference evapotranspiration, rainfall inputs, and soil type are not controllable factors, but the amount, distribution, and persistence of litter (or crop residues in agricultural systems) are amenable to be controlled by management practices (Klocke et al, 2009;Steiner, 1989;Van Donk et al, 2010). Our results, and some experiences from local farmers, highlight the underlying litter effects that would potentially explain the effectiveness of the roller chopping practice based on favouring those key species that produce a large quantity (amount) of litter, such as Prosopis flexuosa trees (Blanco et al, 2005;Marchesini et al, 2015;Steinaker et al, 2016). 500-600 mm/year) such as the southern great plains in United States or the northeast plain in China (Ji & Unger, 2001).…”

“…Native woody vegetation consists of 7-m high canopies dominated by Prosopis flexuosa and Aspidosperma quebracho-blanco trees and Larrea divaricata shrubs (Marchesini, 2011). A large fraction of native dry forests has been converted to pastures by traditional deforestation or roller-chopping over the past 30 years (Boletta, Ravelo, Planchuelo, & Grilli, 2006;Hoyos et al, 2013;Steinaker et al, 2016).…”

“…where it is more difficult to define such contrasting phases, yet ecohydrological process are shown to respond to more gradual cover shifts (Bisigato, Villagra, Ares, & Rossi, 2009;Breshears & Ludwig, 2010;Magliano, Breshears et al, 2015). The South American Dry Chaco is an example of these ecosystems dominated by a vegetation cover gradient at the patch scale that presents two challenges for assessing evaporation dynamics in relation to vegetation changes: (a) the predominance of extensive livestock production systems that continuously transform spatial vegetation patterns (Magliano, Murray et al, 2015;Rueda, Baldi, Verón, & Jobbágy, 2013;Steinaker et al, 2016) and (b) the occurrence of regional land cover changes at high rates, in which native forests are replaced by planted pastures to intensify livestock production (Houspanossian, Giménez, Baldi, & Nosetto, 2016;Hoyos et al, 2013;Murray, Baldi, von Bernard, Viglizzo, & Jobbágy, 2016). Understanding how the spatial heterogeneity of vegetation patches can affect evaporation dynamics may represent an avenue to improve livestock production of Dry Chaco rangelands.…”