Leaf phenology has long been thought to evolve to maximize plant carbon gains, and it reflects plant life history strategies for exploiting resources. Extending leaf life span is of great importance for some species of temperate deciduous forests to gain enough carbon needed for plant survival and persistence, because their growing seasons are repeatedly interrupted by cold winters. Leaf life span can be extended by early leafing, late shedding, or both. To examine which approach was employed to maximize leaf longevity, the phenology of leaf emergence and abscission was investigated for species of two deciduous broad-leaved oak forests in Nanjing area, East China, and the relationships between leaf phenological parameters were analyzed.
The timing of leaf emergence differed greatly among species. The earlier the species leafed out, the earlier the species ended the process of leaf emergence; the earlier a species leaf began to abscise its leaves, the longer it took to end the process of leaf abscission. Consequently, the leaf abscission for all species was completed within a narrow time period although the start of leaf abscission differed greatly among species. Both correlation analysis and regression analysis indicated close relationships between leaf longevity and the timing of leaf emergence and abscission, in which a longer leaf life span was related to early leafing and late shedding. The timing of leaf emergence seems more important for plant carbon gain than the timing of leaf abscission, assuming that early leafing has advantages over late shedding for carbon gain for the woody species living in the study region. No significant relationship was found between the timing of leaf emergence and leaf abscission indicating that long leaf longevity could be achieved by either early leaf emergence or late leaf abscission. Early leafing is not necessarily correlated to late shedding for the study species.