Dealing with radar backscattering from trees, the Wong model is a mixing of Gaussian spectra with parameters deduced from considerations on motions of branches and leaves. Very detailed experiments by Narayanan et al. show gaps with this model. We show that autocorrelation functions by Narayanan et al are very well fitted by functions in the form exp[-|τ/τ₀|^α], 0 <; α ≤ 2. In this paper, we prove that the random propagation time theory explains this property. I have shown in other papers that this theory is available to study power spectra in acoustics, ultrasonics, and electromagnetics.