Spring and Fall leaf phenology observations have been made at 9 locations at the Hubbard Brook Experimental Forest since 1989. Timing and progression of spring leaf out and fall senescence are recorded for 3 dominant tree species, sugar maple, yellow birch, and beech, in treated and untreated watersheds and high and low elevations. Weekly measurements are taken during the active period of the fall or spring season. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station.