Nature reserve planning models to maximize species protection are typically formulated for a single period using certain data. In practice, however, parcels must be acquired over time. The status of a parcel may change due to conversion to alternate land use. Populations of species to be protected may change, as well. A twostage stochastic program that maximizes expected species protection with annual budget constraints is proposed where parcels available for set aside have associated probabilities of being available for acquisition and species coverage. Runs on hypothetical data show that solutions differ from the single period model and depend strongly on the probability of acquisition in future periods.