Controls on gross production by a semiarid forest growing near its warm and dry ecotonal limit

► Oak and pine forest CO2 uptake was measured near a dry and warm ecotone. ► Winter cold exerted a minor limitation on CO2 uptake. ► Vegetation withdrew water from deep soils to support CO2 uptake during dry summers. ► Warmer winters due to climate change would have a small effect on CO2 uptake. ► Vegetation appears vulnerable to soil moisture depletion beneath 1-2 m depth.