Critical stem diameter for trees : beyond this diameter, the crown area no longer increases.
\begin{equation}
D_{max} = 0.01 .\left( \frac{k_{allom4}}{\dfrac{k_{allom2}.k_{allom3}}{100^{k_{allom3}}}} \right)^{\dfrac{1}{k_{allom3} - 1}}
\end{equation}
where : \\
\begin{itemize}
 \item  $D_{max}$ is the maximum stem diameter.
 \item  $ k_{allom2} = 40$; \quad  $k_{allom3}= 0.5$; \quad  $k_{allom4}= 0.3$
\end{itemize}

