A hard-to-keep promise: Vegetation use and aboveground carbon storage in silvopastures of the Dry Chaco

Abstract

In dry woodland regions, silvopastures have emerged as a promising option to balance cattle production, carbon storage and biodiversity. However, one of the major challenges in these systems, particularly when implemented in a matrix of natural vegetation, is the preservation of tree populations in the face of management actions implemented by ranchers to control woody encroachment. Here, we investigate the extent of that tradeoff by analyzing the impact of woody encroachment control practices on carbon storage in silvopastures of the Argentine Dry Chaco. First, we analyze tree density and carbon storage in aboveground woody biomass for silvopastures and woodlands at 24 sites in five properties across the Argentine Dry Chaco. Then, we characterize vegetation management goals and actions of ranchers who have adopted silvopastures in that same region, combining field assessments, high-resolution imagery analysis, characterization of site history, and surveys. We find that woody biomass in silvopastures retains an average of 64 % of the carbon present in aboveground biomass in intact woodlands (28.8 Mg C ha−1). However, we also find that this storage capacity decreases by 12 % with each woody encroachment control intervention, due to these interventions’ negative effects on tree density. Ranchers expressed concern about tree mortality, but also indicated low profitability of wood products and highlighted woody encroachment as a major issue for livestock production. Therefore, ranchers feel they have no choice but to continue preventing woody encroachment, even if this implies the gradual depletion of tree populations. Understanding how ranchers manage silvopastures, and how that management affects the provision of ecosystem services, is essential and will require more careful long-term monitoring and evaluation. This is particularly true in agricultural frontiers such as the Argentine Dry Chaco, where silvopastoral systems have the potential to mitigate the seemingly irremediable conflict between commodity production and nature conservation.