Phenology
Phenology is the study of the timing of vegetation life-cycle events, such as budburst, flowering, leaf colouring, leaf fall.
Most plants that are evergreen (perennial, never entirely without green foliage), deciduous (leafless for a certain period during the year), mixed deciduous/evergreen, or semi-evergreen/semi-deciduous, whichever is dominant.
Unit: day of the year (DOY)