A conceptual model for the spectral-temporal development of a forest stand was developed and tested. The model hypothesizes that reflectance changes for a regenerating forest stand follow a defined path in spectral brightnessgreenness space. Landsat Thematic Mapper imagery and field data collected from the lodgepole pine forest of Yellowstone National Park, USA provided an empirical means by which the theoretical model was tested. Recently disturbed stands are spectrally bright and low in greenness. As a stand progresses to midsuccessional stages, brightness decreases, but greenness of the stand is highly variable. Sites affected by the mountain pine beetle regress back along the brightness-greenness vector as the overstory is progressively thinned by the beetle infestation.