Fig 1.
Illustration of the ‘big-leaf’ concept and main functions included in the bigleaf R package.
d is the displacement height, z0h is the roughness length for heat, z0m is the roughness length for momentum, zh is the average vegetation height, zr is the reference (=measurement) height, u is the horizontal wind speed, Rsw is the surface resistance to water vapor, Rsc is the surface resistance to CO2, Rbh is the canopy boundary layer resistance to heat transfer, Rbc is the canopy boundary layer resistance to CO2 transfer, Ram is the aerodynamic resistance to momentum transfer, esat is the saturation vapor pressure at the ‘big-leaf’ surface, es is the vapor pressure at the ‘big-leaf’ surface, ea is the vapor pressure at reference height, λE is the latent heat flux, Ts is the aerodynamic surface temperature, Ta is the air temperature, H is the sensible heat flux, Ci is the bulk intercellular CO2 concentration, Cs is the CO2 concentration at the ‘big-leaf’ surface, NEE is the net ecosystem exchange of CO2, SW↓ and SW↑ are the incoming and outgoing shortwave radiation, respectively, LW↓ and LW↑ are the incoming and outgoing longwave radiation, respectively, and Rn is the net radiation. Numbers denote the following functions: 1) roughness.parameters(); 2) stability.parameter(), stability.correction(), wind.profile(); 3) surface.conductance(), stomatal.sensitivity(), stomatal.slope(); 4) potential.ET(), equilibrium.imposed.ET(), WUE.metrics(); 5) aerodynamic.conductance(), decoupling(); 6) energy.closure(); 7) surface.conditions(); 8) light.response(), light.use.efficiency(); 9) intercellular.CO2(), photosynthetic.capacity(), biochemical.energy(), energy.use.efficiency(); 10) radiometric.surface.temp(). For details on the functions, see section ‘Package content’ or the respective R package help pages.
Table 1.
Characteristics of the three single-level case study sites.
Fig 2.
Seasonal courses of mean daily values of aerodynamic conductance to heat transfer (Gah), surface conductance to water vapor (Gsw), and decoupling coefficient (Ω) for the year 2012.
Data were filtered for rainfree periods (24h after rainfall excluded), daylight (PPFD > 200 μmol m−2 s−1), and positive λE. Gsw was calculated according to Eq 15, and Ω according to Eq 16. Three different Gah formulations (Eqs 2 and 4–7), denoted by different colors, were used as input variables for the respective functions.
Fig 3.
Median diurnal courses of measured air and respective derived ‘big-leaf’ surface variables for the summer months of all available site years (JJA).
Lines depict median diurnal courses of all available site years and shaded areas the interquartile range. Surface conditions were calculated with Ga calculated from Eqs 2 and 7 (with Dl taken as 0.02, 0.008, and 0.035 m for AT-Neu, DE-Tha, and FR-Pue, respectively). Radiometric surface temperature in panels a-c was calculated according to Eq 14 assuming a constant longwave emissivity of 0.98.
Fig 4.
Surface conductance (Gsw) plotted against .
The slope of the relationship corresponds approximately to the G1,USO parameter (Eq 23). Different colors denote the ratio of bulk intercellular CO2 concentration (Ci; Eq 25) to ‘big-leaf’ surface CO2 concentration (Cs; Eq 13). Shown are data for rainfree periods in the growing season of 2012 (see text for details on data filtering).
Fig 5.
(a) Time series of the stomatal slope parameter G1,USO and (b) underlying water-use efficiency (uWUE) calculated for the whole ecosystem (brown), the grass layer (yellow) and the trees (blue) between December 2015 and March 2018. (c) Time series of minimum, maximum and mean daily air temperature and normalized soil water content for the same period. Grey shaded areas denote dry periods associated with a wilted grass layer.
Table 2.
Median daytime physical ecosystem properties in the growing season calculated with the bigleaf package.
Table 3.
Median daytime physiological ecosystem properties in the growing season calculated with the bigleaf package.