SEASONALITY OF FLOWERING AND FRUITING IN TEMPERATE FOREST TREES

The phenology of leaf presence and photosynthetic activity together set a potential limit on tree productivity in a seasonal climate; similarly, the seasonal timing of flowering and fruiting can decide tree reproductive success. The capacity for long-term storage of photosynthate appears to override any necessary functional linkage between these two critical aspects of tree phenology. Foliar and reproductive phenology in broadleaf deciduous trees of the temperate zone are only weakly coupled within a growing season, especially in precocious flowering trees that mature their fruits in early summer. In species that fruit in late summer and fall, leaf emergence and flowering can be entrained by shared responses to the progressive warming of early spring but with only limited effect on the timing of fruit maturation. The timing of foliar senescence and fruit maturation is correlated only in fall-fruiting trees but as a common response to fall climate rather than the outcome of foliar retranslocation of resources to developing fruits. The possibility exists that global climate change may disrupt these patterns of foliar and reproductive phenology, but the magnitude of the effect will depend on the poorly studied balance of thermal versus photoperiodic cues for phenological events.