Figure 1. Measured vs. predicted values from Model 3a (universal D and species-specific μ).

Dash lines are 1∶1. The model explains between-species variation in all four cases (area- and mass-based Amax and Rdark). The amount of within-species variation explained is greatest for Rdark_area (Figure 1a) and least for Amax_mass (Figure 1d). Units for per-area Amax and Rdark are µmol CO₂ m⁻² s⁻¹, and units for per-mass Amax and Rdark are 10⁻⁴ µmol CO₂ g⁻¹ s⁻¹. Species code: GB = gray birch, WA = white ash, SM = sugar maple, WP = white pine, EH = eastern hemlock.