Fig. 1. An illustration of day length patterns in the northern and southern parts of the eastern deciduous region of North America. If a critical day length is shorter than on the spring equinox (the point where the two lines intersect), then moving a plant to the south means this requirement is met later, and vice versa. If the critical day length happens after the equinox, these patterns are switched. The triangle and circle denote day length when many trees are growing new leaves in the north and south, respectively (see text in Section 3).
| Table 1. A summary of common garden studies synthesized in this paper. All encountered studies of temperate or boreal trees reporting leaf-out observations were included. ‘Leafing Pattern’ gives the order of leaf budburst: L→H means low latitude/elevation genotypes leaf out earliest, while H→L indicates high latitude/elevation genotypes leaf first. Species nomenclature and authorities follow the referenced publications except where noted. The ‘Range’ column gives the extreme lower and upper values of elevation or latitude and the difference between these values. Key to ‘Wood Anat.’ column abbreviations: DP = diffuse porous, RP = ring porous, NC = narrow coniferous. View in new window/tab. |
Fig. 2. The relative frequency of reviewed studies showing different leafing patterns in (A) conifers, (B) ring-porous angiosperms, and (C) diffuse-porous angiosperms. All angiosperm species with any large vessels (see Table 1) were included in the ring porous category. High→Low means leaf out happened in order from highest to lowest elevation/latitude and Low→High indicates the opposite; the Other category includes all other patterns including nonlinear, undifferentiated and no pattern at all (see Table 1). Only for ring porous species did binomial tests reveal statistical differences below or near traditional cutoffs between the High→Low and Low→High categories for latitude (p = 0.070) and elevation (p = 0.021).