Data from: Convergence, consilience, and the evolution of temperate deciduous forests

The deciduous habit of northern temperate trees and shrubs provides one of
the most obvious examples of convergent evolution, but how did it evolve?
Hypotheses based on the fossil record posit that deciduousness evolved
first in response to drought or darkness and preadapted certain lineages
as cold climates spread. An alternative is that evergreens first
established in freezing environments and later evolved the deciduous
habit. We monitored phenological patterns of 20 species of Viburnum
spanning tropical, lucidophyllous (subtropical montane and warm
temperate), and cool temperate Asian forests. In lucidophyllous forests,
all viburnums were evergreen plants that exhibited coordinated leaf
flushes with the onset of the rainy season but varied greatly in the
timing of leaf senescence. In contrast, deciduous species exhibited tight
coordination of both flushing and senescence, and we found a perfect
correlation between the deciduous habit and prolonged annual freezing. In
contrast to previous stepwise hypotheses, a consilience of independent
lines of evidence supports a lockstep model in which deciduousness evolved
in situ, in parallel, and concurrent with a gradual cooling climate. A
pervasive selective force combined with the elevated evolutionary
accessibility of a particular response may explain the massive convergence
of adaptive strategies that characterizes the world’s biomes.