## Appendix A Parametrization of the Global Sensitivity Analyses  
The global sensitivity analysis for the Thornley GPP model was ran over the following ranges: 5.8-19.4 umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) for A\({}_{\text{leaf}}\), 4.58 \(\times\) 10\({}^{-9}\)-1.411 \(\times\)10\({}^{-8}\) kg CO\({}_{2}\) J\({}^{-1}\) PAR for the quantum yield (based on ranges for C\({}_{3}\) species from [69]), 0.5-0.95 for the curvature coefficient of the leaf light response [50], 0.005-0.283 for leaf transmittance, 0-1 for proportion of direct radiation, and 14-65\({}^{\circ}\) for sun zenith angle. The range used for A\({}_{\text{leaf}}\) reflects the community weighted means found at our study sites. The range of leaf transmittance was the minimum and maximum transmittance (averaged over 400-700 nm) obtained from PROSPECT runs varying leaf parameters over the same ranges as those used in the global sensitivity analyses of PROSAIL. The ranges for LAI and canopy mean leaf angle matched those used in the PROSAIL global sensitivity analysis (see below). Beam irradiance was fixed at 435 W PAR m\({}^{-2}\), which approximates 2000 umol photons m\({}^{-2}\) s\({}^{-1}\) (a typical value for full direct sunbeam), and the effect of varying irradiance was taken into account by varying sun zenith angle. The original [PERSON] model does not explicitly include sun zenith angle or mean canopy leaf angle. The sun zenith angle influences the irradiance at the canopy, and both leaf angle and sun angle influence the extinction coefficient of the canopy. Following [PERSON]'s cosine law, the sun zenith angle influences the irradiance \(I\) over a horizontal surface is  
\[I = I_{0}\cdot\cos(\theta sz) \tag{4}\]where \(I_{0}\) is the beam irradiance and \(\theta_{sz}\) is the sun zenith angle. Following [PERSON] [70] and [PERSON] et al. [71], the sun zenith angle and the canopy mean leaf angle \(\theta_{l}\) influence the canopy extinction coefficient \(K\) according to  
\[K\ =\ \frac{\cos(\theta_{l})}{\cos(\theta_{sz})} \tag{5}\]  
Our sensitivity analysis of GPP did not explicitly incorporate the effect of other potentially important variables such as air or leaves temperature. However, previous studies have shown that the important controlling effect of plant traits over GPP holds regardless of variation in these meteorological conditions [15; 62]. We ran the global sensitivity analysis of the PROSAIL model over the following ranges: 9-58 \(\mu\)g cm\({}^{-2}\) for leaf chlorophyll content (see Supplementary Material 5, [72]); 1-4 for the leaf structure parameter [73]; 0.0064-0.0526 g cm\({}^{-2}\) for LMA; 0.0146-0.0771 g cm\({}^{-2}\) for W\({}_{c}\), and 0.1-5 m\({}^{2}\) m\({}^{-2}\) LAI. The ranges of LMA and W\({}_{c}\) were determined by the variation in community weighted mean traits observed at the sites. The range of LAI exceeded the actual ranges observed at the sites (observed range 0.2-3.0 m\({}^{2}\) m\({}^{-2}\) at 5 sites). Ranges for other parameters were 25-63\({}^{\circ}\) for mean leaf angle (based on a review of published values [74], see Supplementary Material 7), 0.0001-0.01 for hotspot (approximate range for the sites according to leaf width divided by canopy height), 0-1 for the soil parameter, 0-1 for proportion of diffuse to direct radiation, 14-65\({}^{\circ}\) for solar zenith angle, 0-60\({}^{\circ}\) for view zenith angle of the sensor, and 0-180\({}^{\circ}\) for the relative azimuth angle between the sun and sensor. The ranges for solar and view angles are based on exploratory analyses of MODIS imagery and MODIS specifications. We ignored variation in carotenoid and brown pigments, given the paucity of field observations and lack of a major effect on reflectance [75]. Previous global sensitivity analyses have used the maximum possible range for mean canopy leaf angles (i.e., 0-90\({}^{\circ}\)), and have shown that leaf inclination exerts a strong control over NIR and vegetation indices such as EVI [20; 54].