Phylogenetic Constraints Do Not Explain the Rarity of Nitrogen-Fixing Trees in Late-Successional Temperate Forests
Figure 3
Character history reconstruction of the weighted shade-tolerance index (STW) for native angiosperm FIA genera.
The shading indicates the character state of STW, with darker shading indicating greater shade tolerance. STW is the proportion of a taxon's saplings in the FIA data that are in the understory relative to the mean shade tolerance across taxa in 2°×2° grid cells (Fig. S3), and is expressed as the number of standard deviations from the overall angiosperm mean (see Methods for details). The six genera that form N-fixing symbioses are starred: Olneya, Robinia, Acacia, and Prosopis (Fabaceae); Cercocarpus (Rosaceae); and Alnus (Betulaceae). Two clades are indicated: the Eurosid I clade and the ‘potentially N-fixing clade,’ the smallest clade that includes all N fixers (the monophyletic subclade of the Eurosid I that excludes the Malpighiales). To create this figure we used the Trace Character History function (parsimony method) of the program Mesquite [66].