Integrative landscape modelling requires integrative diagnostics to enable both model developers and model users to calibrate and validate against trusted reference data and to evaluate the consequences of simulation experiments. Land surface phenology can serve as such an integrative diagnostic. What phenology is in general and land surface phenology in particular is reviewed. How land surface phenology is well-suited to model tuning and simulation experiments is then discussed. The paper concludes with an example of modelling future land use change in the Northern Great Plains of North America if large areas of croplands currently in maize/soybean rotation shift to perennial grasses harvested for feedstock to cellulosic ethanol biorefineries.