DEVELOPING FLOOD RESISTANCE IN THE ARGENTINIAN CHACO BY SURROUNDING FIELDS WITH FOREST STRIPS

The Gran Chaco is South America’s second largest forest after the Amazon, and is one of the fastest developing agricultural frontiers on the planet. The dry forest is being converted for corn and soybean production in an effort to meet growing global demand. This landuse conversion is triggering hydrologic change in the Chaco of northern Argentina. The region has an extremely low topographic gradient and annual potential ET rates exceed precipitation, resulting in almost no surface water runoff. Under pre-development conditions, the deep roots of the perennial dry forest are able to take up all water before it can percolate through the root zone and recharge groundwater. When annual row crops replace the dry forest, recharge occurs during fallow periods or when large wetting fronts penetrate below the shallow-rooted crops to initiate groundwater recharge. However, groundwater recharge in the landscape is problematic because the landscape is so flat and poorly drained that as the watertable rises, it ultimately approaches the surface and causes inundation. Regionally, stripes of remnant forest ~100m in width called cortinas are left as borders around the fields in an effort to help preserve native ecosystems and minimize wind erosion. We present field and modeling evidence that these strips of remnant forest perform an unrecognized ecosystem service in that they make the landscape more resilient to flooding by suppressing the watertable mounds that develop within the fields.