Environmental Sensitivity and Impact of Climate Change on Leaf-, Wood- and Root Phenology for the Overstory and Understory of Temperate Deciduous Forests

To synthesize new information regarding the environmental sensitivity and impact of climate change on leaf-, wood-, phloem- and root phenology of deciduous forests of the temperate (and boreal) zone, comprising overstory and understory, and both woody and herbaceous species. The environmental sensitivity and impact of climate change on spring leaf phenology are relatively well understood, with ongoing efforts focusing on the spatial and temporal variability in both overstory and understory. Autumn leaf phenology and cambial phenology have received increasing attention in recent years. The drivers of senescence progression are well understood (current temperature), while the drivers of the onset of senescence are still uncertain but likely relate to spring temperature, water availability and light conditions. Studies on cambial phenology of angiosperm trees have focused on the variability across populations and years, while studies on phloem remain scarce and synthesis studies are unavailable. For fine root phenology, asynchronicity with leaf phenology and high variability among species have been demonstrated, but large uncertainty remains regarding the drivers of the onset and cessation of their growth. Studies on woody and herbaceous understory highlight the importance of microclimate differences within the stand. Future phenology research should focus on (i) onset of leaf senescence, (ii) fine roots, (iii) the relationships between overstory and understory species not only regarding leaves, but also wood and fine roots, (iv) variability across multiples scales (e.g. individuals, stands), and (v) interannual legacy effects and connections among phenophases of different organs and forest compartments.