Adding a Covariate

Covariates are required for many of the traits. Covariates generally indicate the environmental conditions under which a measurement was made. Without covariate information, the trait data will have limited value.

A complete list of required covariates can be found in tab:covariates. For all respiration rates and photosynthetic parameters, temperature is recorded as a covariate. Soil moisture, humidity, and other such variables that were measured at the time of the measurement that may be required in order to standardize across studies.

When root data is recorded, the root size class needs to be entered as a covariate. The term 'fine root' often refers to the <2mm size class, and in this case, the covariate root_maximum_diameter would be set to $ 2$. If the size class is a range, then the root_minimum_diameter can also be used.

To add a new covariate, go to the http:ebi-forecast.igb.uiuc.edu/covariates/newnew covariate page: Covariate $ \to$ new.


Table 7: Traits with required covariates
variable required covariates optional covariates
Vcmax irradiance and temperature (leaf or air)  
any leaf measurement   canopy height
root_respiration_rate temperature (root or soil) soil moisture
root_respiration_rate root_diameter_max root size class (usually $ <2mm$)
any respiration temperature  
root biomass   min size cutoff, max size cutoff
root, soil depth (cm) used for max and min depths of soil, if only one value, assume min depth = 0; negative values indicate above ground
gs (stomatal conductance) A$ _{max}$ \dagsee notes in caption
stomatal_slope (m) humidity, temperature ?specific humidity? assume leaf T = air T?
A list of traits and the covariates that must be recorded along with the trait value in order to be converted to a constant scale from across studies. notes: $ \dag$ stomatal conductance (gs) is only useful when reported in conjunction with other photosynthetic data, such as A$ _{max}$. Specifically, if we have Amax and gs, then estimation of Vcmax only covaries with dark_respiration_factor and atmospheric CO2 concentration. We also now have information to help constrain stomatal_slope. If we have Amax but not gs, then our estimate of Vcmax will covary with: dark_respiration_factor, CO$ _2$, stomatal_slope, cuticular_conductance, and vapor-pressure deficit (VPD) (which is more difficult to estimate than CO$ _2$, but still possible given lat, lon, and date). Most important, there will be a strong covariance between Vcmax and stomatal_slope.




Subsections
David 2011-10-07