Cambial and phloem reactivation timing in relation to floral phenology in four co-occurring woody species.

The timing of spring floral production is crucial for plant reproduction and thus fitness. Floral production in spring is a carbon sink, as is the construction of new cell walls for xylem and phloem, and leaf production. As carbon transport is necessary to support any growth in the spring, it is important to understand the timing of the production and resumption of phloem activity in the spring. Phloem and cambial reactivation have been studied in relation to leaf-out, but not in relation for floral phenology. We sampled the stems of three co-occurring temperate broad-leaved woody plants and one shrub to investigate the timing of phloem and cambial reactivation in relation to spring floral production and environmental factors. We find that cambial reactivation is primarily predicted by environmental factors. Wood porosity also is tied to the timing of cambial reactivation. Phloem reactivation, however, was not influenced by environmental effects during the period of our study. We further present evidence that overwintering strategies could be inferred by tracking changes in phloem increment width during spring. Our results underscore the importance of cambial reactivation in supporting floral and foliar spring phenology.