The semiarid Chaco plains present one of the highest rates of forest clearing and agricultural expansion of the world. In other semiarid plains, such massive vegetation replacements initiated a groundwater recharge and salt mobilization process that, after decades, raised regional water tables and salts to the surface, degrading agricultural and natural ecosystems. Indirect evidence suggests that this process (known as dryland salinity) began in the Chaco plains. Multiple approaches (deep soil profiles, geoelectric surveys and monitoring of groundwater salinity, level and isotopic composition) were combined to assess the dryland salinity status in one of the oldest and most active agricultural hotspots of the region, where isolated forest remnants occupy an extremely flat cultivated matrix. Full vadose moisture and chloride profiles from paired agriculture-forest stands (17 profiles, six sites) revealed the following: a generalized onset of deep drainage with cultivation (32 to >87 mm year À1 ), full leaching of native chloride pools (13.7 ± 2.5 kg m À2 ) down to the water table after >40 years following clearing and differential groundwater table rises (0.7 to 2 m shallower water tables under agriculture than under neighbouring forests). Continuous level monitoring showed abrupt water table rises under annual crops (up to 2.6 m in 15 days) not seen under forests or pastures. Varying deep drainage rates and groundwater isotopic composition under agricultural plots suggest that these pulses are strongly modulated by crop choices and sequences. In contrast to other dryland salinity-affected areas of the world, forest remnants in the study area (10-20% of the area) are not only surviving the observed hydrological shifts but also sustaining active salty groundwater transpirative discharge, as evidenced by continuous water table records. The overall impact of these forest remnants on lowering neighbouring water tables would be limited by the low hydraulic conductivity of the sediments. As highly cultivated areas of the Chaco evolve to new hydrological conditions of shallower saline water tables, innovative crop rotations that minimize recharge, enhance transpirative discharge and tolerate salinity will be needed.

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During the last century, the massive conversion of Australian dry forests to crops and pastures triggered the massive soil and groundwater degradation process known as dryland salinity.Currently, South American Chaco's dry forests are undergoing a similar transformation, leading global deforestation rates. The goal of this study was to review existing ecohydrological information about natural and cultivated systems in the Chaco to assess the dryland salinity risks. We review deep soil water, salt stocks, and groundwater recharge from agriculture or native dry forests stands located in a precipitation range of 450-1100 mm. We complement this with water table level records and geoelectric profiles together with personal observations. We use data from 15 Australian studies for comparison. Strong salt leaching, especially after 20 years of forest clearance, indicates the onset of deep drainage following forest conversion to agriculture in the Dry Chaco. Water stocks were more than double in the cleared stands compared to their dry forest pairs, and recharge rates were up to two order magnitude higher in agricultural areas.Although lower atmospheric salt deposition, younger sediments, and relatively high water-consuming agricultural systems in the Dry Chaco attenuate salinization risks compared to Australia, the very flat topography and related shallow water table levels of the South American region could make groundwater recharge and salt mobilization processes more widespread and difficult to manage. The lack of awareness among the general public, farmers, and decision makers about this issue amplifies the problem, making land management plans for the Argentine dry forest territories essential.