We want to test if leaf senescence is triggered by the timing of tree growth cessation, and whether this occurs only when day length has shortened sufficiently. Five sub-hypothesis will be tested:

  1. The onset of leaf senescence is determined by day length if trees stop growing early because of unfavourable environmental conditions (for example drought, poor site fertility, bad weather).
  2. The start of leaf senescence is determined by the timing of growth cessation when trees are not limited earlier by unfavourable environmental conditions.
  3. This mechanism applies to both young and mature trees.
  4. This mechanism applies to all species and genotypes at different latitudes.
  5. The proposed mechanism captures the timing of leaf senescence recorded across the major temperate and boreal forested areas of Europe.