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Linear interpolation was used to approximate material constants between two samples to provide a gradient of material properties from the corewood to the outerwood. The TRP of cellular properties was investigated using the gradient of elastic constants and Poisson ratios from different samples by applying simulated wind loads to stems with different radial profiles.  While the TRP of \textit{Pinus radiata} usually follows a non-linear increase for density and a non-linear decrease for MFA \citep{burdon_juvenile_2004}, during the first 15 years the trend can be approximated as linear, after this however the non-linear behaviour becomes more prevalent as the properties stabilise. It should be noted that there is much variation between individuals and this is not universal. The TRP was investigated by calculating the appropriate elastic and shear moduli along with Poisson ratios for each point in the stem. The linear interpolation was calculated between two samples chosen to represent corewood and outerwood, Equation \ref{eq:constants} shows the general form.  \begin{equation}\label{eq:constants}  \lambda = \frac{-r}{r_t}(\lambda_i-\lambda_o)+\lambda_i  \end{equation}  Where \(r\) is the stem radius at the current point, \(r_t\) is the total radius at 15 years, \(λ_i\) and \(λ_o\) are the values of the material properties obtained from \citet{Davies_2016} at \(r = 0\) and \(r = r_t\) respectively.  Due to the micro-structure of wood the native coordinate system for describing material properties is not the same as the global coordinates system used to impose external forces on the stem. Transformation between the two systems is needed. The \(rtl\) local system used for experimental work presented in \citet{Davies_2016} is used in combination with the interpolations presented in Equation \ref{eq:constants} and presented as the stiffness matrix in Equation \ref{eq:stiffness_mat} using Voigt (engineering) notation at any point in the stem. Because the stiffness matrix is calculated in the local coordinates it needs to be converted into an \(xyz\) system in order to apply wind loadings in a sensible fashion, Equation \ref{eq:trans_mat} provides the transformation matrix. The use of Voigt notation allows for transformation of the elastic constants into the global system, via Equations \ref{eq:cm_trans} to \ref{eq:stress_tans}. It is assumed that there is no spiral grain occurrence within the stem, the local \(l\) axis is always parallel with the global \(z\) axis. Material constants in the longitudinal direction are parallel with the \(z\) axis, i.e. there is no correction angle applied to account for taper.