Spring versus autumn leaf colours: Evidence for different selective agents and evolution in various species and floras

Red colouration is common in young and old leaves of broadleaf woody species. Assuming that leaf colours are adaptive, we examined, by comparing the colouration in young versus old leaves, the possibility that different selection agents may have operated on spring versus autumn leaf colouration. We observed spring versus autumn colouration in three very different woody floras (Finland, Japan and Israel) in order to allow for a broad ecological and evolutionary spectrum. The null hypothesis was that if the same selective agents operated in spring and autumn, it is expected that when spring leaves are red, they should always be red in autumn, and when spring leaves are green, they should be green or yellow in autumn. We found that green spring leaves are almost exclusively associated with yellow leaf colour at senescence in autumn. Species with red autumn leaves almost always have at least some red colouration in their spring leaves. However, about half of the species with red spring leaves have yellow autumn leaves. Brown autumn leaves were not common in the species we studied. As about half of the species with red spring leaves have yellow autumn leaves but not vice versa, we conclude that there are many cases in which the selecting agents for spring versus autumn leaf colour were not the same.