Background
Forest resilience should be improved to promote species adaptation and ensure the future of forests. Carbon stock is considered an indicator of resilience, so it is necessary to determine forest carbon stocks and how to improve them through forest management. The main objective of this study was to analyse biomass production and distribution among the components of four-year-old Pinus pinaster and Pinus halepensis trees. Young trees from a Nelder wheel experimental site were harvested and analysed. The effect of density could be included in the biomass analysis thanks to the Nelder wheel design. We tested densities from 1000 to 80000 seedlings/ha and analysed biomass by fitting different equations: (i) linear regressions to analyse biomass production; (ii) Dirichlet regressions to estimate the biomass proportions of each component and (iii) allometric equations to predict the biomass content of each component.
Results
Results from this innovative approach showed that density was a significant factor for Pinus halepensis. We observed a general increase of total biomass at lower densities and this positive effect increased root biomass proportion at the expense of aboveground biomass. Also, a new set of equations was developed for estimating above- and below-ground biomass in young Pinus pinaster and Pinus halepensis trees.
Conclusions
we note the importance of belowground biomass and its value in total biomass production (approximately 20% of total biomass for both species). The effect of density on biomass production was only significant for Pinus halepensis, but the effect of density would have been different if root biomass had not been considered in the present study. Lower densities increased root biomass proportion at the expense of aboveground biomass. Currently, this positive effect is especially important in promoting management to improve tree resilience.