We present surface ablation threshold investigations on Al2O3 (corundum) after single- and multiple-laser pulse irradiation at 800 nm in the picosecond and subpicosecond duration range. Scattered light monitoring was utilized for in situ damage detection and irradiated spots were inspected by optical and electron microscopy. We obtained fluence thresholds for two distinctively different etch phases. The threshold for ablation drops sharply for multiple-laser shot irradiation, due to material-dependent incubation effects. The threshold reduction for increased number of laser shots is related to defect accumulation.