I have the data from Li et al. 2003 paper "Belowground biomass dynamics in the Carbon Budget Model of the Canadian Forest Sector". I am trying to recreate equation 6 in R so that I can produce the same parameter estimates. (eq. 6), however, Pf has a maximum value of 0.426, as values greater will produce a 0. The paper doesn't state whether a linear or non linear model is used so I am having trouble figuring out how to go about coding this is R.
At first I was thinking something like
But this isn't correct as it won't match the parameters stated in the table 3 for equation number 6.
I know this isn't much to go on but I would appreciate any help. Thanks!