Methods Based on the standards of the Chinese Phenological Observation Method, three-level Phenological Code (a, b, and c) was used to recode the phenology data. Our data analysis was performed with “pentad” (5-day period) in 24 Solar Terms. Analytical methods include a frequency distribution method to explore the division of phenophases and their dynamic constitution. The frequency distribution statistics in SPSS 20.0 were applied to explore the temporal dynamics in occurrence time and duration for different types of phenophases.

Important findings We found that: The division of phenological seasons and their phenological constitution as: 6th-19th pentad for Spring, with 54.03% of the whole phenophases that are featured with sprouting, leaf spreading and flowering; 20th-45th pentad for Summer, with 12.95% of phenophases that include conclusions of leaf spreading for all trees, intensive fruiting, fewer flowering, and autumn-leaf scenery in late summer; 46th-59th pentad for Autumn, with 27.19% of the phenophases that are characterized with leaf discoloration and defoliation, some fruiting, and very few flowering; and 60th pentad for Winter, with 0.6% of phenophases that are all constituted with defoliation. The temporal distribution pattern of different kinds of phenophases is as follows. The leaf-unfolding phenophases span from 3rd to 23rd pentad and averagely last for 3.27 pentads, with Sorbaria kirilowii as one of the earliest leaf-unfolding species. The leaf coloration phenophases happen between 40th -63rd pentad, with Tilia mongolica and Armeniaca sibirica as the earliest species to show fall-color leaf. The autumn-leaf duration lasts for 8.2 pentads in average, with Euonymus alatusand Sambucus williamsii as the typical species that show longer leaf duration. The leaf period averagely lasts for 44.2 pentads, with Abelia chinensis, Salix matsudana and Kerria japonica holding the longest leaf time. The flowering-type phenophases happen during 1st-53rd pentad, with 8th-23rd pentad as the best ornamental period, and three species (Chimonanthus praecox, Jasminum nudiflorum and Ulmus pumila) as the earliest blooming species and Elsholtzia stauntonias the last one to bloom. The flowering period lasts for 6.7 pentads in average, with Sorbaria kirilowii, Hibiscus syriacusand Lagerstroemia indica showing the longest flowering time. The fruiting-type phenophases happen between 8th-59th pentad, with Ulmus pumila and Lonicera fragrantissima as the earliest species for fruit maturation. The fruiting duration averagely lasts for 29.0 pentads, and those species that do not lose fruits during the winter and some other species with longer fruit holding period though falling fruits completely in winter such as Viburnum melanocarpum and Physocarpus opulifolius ‘Luteus’ have longer ornamental time of fruit scenery. Compared with a counterpart research in the 1980s, this study reveals that spring in 2017 came earlier by a pentad than that 30 years ago while autumn came later by 3 pentads; additionally, autumn duration shortened by 2 pentads while summer duration prolonged by 4 pentads, resulting in larger differences between the duration of the four seasons.