The protective effect of forest against rockfall can be quantified thanks to the integration of tree impacts in rockfall simulation models. However, this requires to input spatially-explicit forest data, which is very labor-intensive to collect in operational conditions. Here we compare rockfall simulation results obtained with the RockyFor3D model in three different forest stands, and with different input data sources based on combinations of field and airborne laser scanning (ALS) data. For high rock energies (>200 kJ), the contribution of forest to hazard mitigation is minor compared to topography effects. The rockfall intensity is well estimated (within 16% of reference value) whatever the input data, whereas the frequency is generally over-estimated. Remote-sensing based methods yield a satisfactory assessment of forest protection, but the method based on tree detection has a tendency to under-estimate. ALS turns out to be an interesting option for cost-efficient inventory of high resolution input data for stand-level assessment of forest protection in rockfall simulations. Remote sensing also has potential for a better integration of the spatial heterogeneity of species and stem density, but results have to be evaluated at the hillside level.