Modelling root system development for anchorage of forest trees up to the mature stage, including acclimation to soil constraints: the case of Pinus pinaster

Abstract

A reliable root architectural model is required to study tree anchorage, including secondary root growth, from seed to the mature stage. We calibrated the generic RootTyp model for the seven root types of Pinus pinaster. We determined most parameter distributions from the means and standard deviations of corresponding features in 92 excavated root systems of various ages. We set the remaining parameters using the literature or an optimisation method. The simulated root systems were compared to 22 additional root systems for validation. Branching varies as a function of the distance from the root base, and the growth capacity decreases with branching order. These damping properties had to be implemented in the model to yield realistic outputs beyond the juvenile phase. Diameter growth was satisfactorily modelled from the apex diameter and a tapering-by-branching coefficient. Nevertheless, the diameters of the simulated roots were underestimated near the stump. Growth alterations due to soil constraints were accurately reproduced using the calibrated soil module. Root architecture of large-size and long-living plants can be appropriately modelled with the modified RootTyp model. We suppose that diameter underestimation was due to selective acclimation to the prevailing wind, a facet not taken into account at this calibration step.