Root Architecture, Biomass Allocation and Size-Related Allometric Relationships of Porlieria chilensis (I.M. Johnst.) in a Mediterranean Ecosystem of Central Chile

Mediterranean ecosystems in the central region of Chile face seasonal water limitations and increasing aridity. The belowground structure of their woody species remains poorly known. We characterised root system architecture and biomass allocation in 12 adult trees from a single site of the endemic and Vulnerable Porlieria chilensis. These trees had to be removed for the expansion of a tailings dam. Each tree was excavated, and its structural roots (≥0.5 cm) were traced to estimate maximum root length, cumulative root length and potential root exploration area (REA). The aboveground (AB), belowground (BB) and total biomass were determined, and the BB/AB ratio was calculated. The root collar diameter (RCD) showed a positive correlation with the estimated maximum root length (Spearman’s ρ = 0.650), the cumulative root length (ρ = 0.804) and REA (ρ = 0.811), and BB with the cumulative root length (ρ = 0.846) and REA (ρ = 0.797). In contrast, BB/AB decreased with RCD (ρ = −0.713; power-model exponent = −0.080): larger trees had more root biomass in absolute terms but proportionally less relative to aboveground biomass. As roots with a diameter less than 0.5 cm were not completely recovered, BB and BB/AB are conservative estimates. These relationships provide preliminary reference values for non-destructive field assessments, root-zone protection and ex situ planting of this species.