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Fig. S1. Crown area vs diameter scaling showing data from angiosperms, conifers and modeled trees.

Fig. S2. Sample trees excluded from the model.

Fig. S3. Relationships between the three pathlength by diameter curves: critical; elastically-similar; and actual.

Fig. S4. K vs V scaling for model trees which follow Olson et al. (2009) crown scaling.

Notes S1. Plants used for empirical Pf: selection criteria and sources.

Notes S2. Derivation of Eqn 8 (pathlength).

Notes S3. Description of the xylem anatomy model.

Notes S4. Derivation of Eqn 13 (critical pathlength).