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 pre...北温带乔木与灌木的落叶习性是趋同演化（convergent evolution）最具代表性的例证之一，但其演化路径究竟如何？基于化石记录的相关假说认为，落叶习性最初是为应对干旱或遮阴环境而演化形成，并在寒冷气候扩张过程中预先适应了部分演化支系。另一类假说则提出，常绿植物最初在冰冻环境中定植，之后才演化出落叶习性。本研究对分布于亚洲热带、照叶林（亚热带山地与暖温带）及冷温带森林中的20种荚蒾属（Viburnum）植物的物候模式展开了监测。在照叶林生境中，所有荚蒾属植物均为常绿类型，其展叶进程与雨季起始同步，但叶片衰老的时间跨度差异显著。与之形成鲜明对比的是，落叶物种的展叶与衰老过程均呈现严格同步性，且本研究发现落叶习性与全年持续性冰冻现象存在完全相关关系。与预