Effect of initial fertilisation on biomass and nutrient contentof Norway spruce and Douglas-fir plantations at the same site

Abstract

Norway spruce (NS) and Douglas-fir (DF) are among the main species used for production forestry in France. In low-elevation mountains and under-acidic conditions, they often occupy the same ecological situations. It is therefore of paramount interest to have a good understanding of how the two species behave under similar conditions and how they react to site improvement by fertilisation. The study stands are part of an experimental stand located in the estate forest of Breuil-Chenue in the Morvan (east central part of France). Its aim is to compare the impact of change in species on ecosystem functions. Destructive sampling of 10 trees per stand, distributed over the whole spectrum of inventoried classes of circumference at breast height (c1.30), was carried out within four stands, e.g., fertilised and control (non-fertilised) NS; fertilised and control (non-fertilised) DF. Allometric relationships between c1.30 and biomass or nutrient content per tree compartment were calculated. These equations were applied to the stand inventory for quantifying stand biomass and nutrient content on a hectare basis. The standard deviations of results were estimated using Monte-Carlo simulations. Specific emphasis was given to explain the origin of differences observed between species and treatments, i.e., changes in carbon allocation leading to specific allometric relationships, changes in stand structure (tree size distributions) and changes in stand density due to mortality.