Comparison of biomass and nutrient content between oak (Quercus petraea) and hornbeam (Carpinus betulus) trees in a coppice-with-standards stand in Chimay (Belgium)

The management of forest stands on acid soils requires information on nutrient exports under various harvesting scenarios. Twenty one oaks (Quercus petraea (Mattuschka) Liebl.) and eighteen hornbeams (Carpinus betulus L.) were destructively sampled from a coppice-with-standards stand located on a dystrochrept soil in the Belgian Atlantic Fagne. Regression equations were developed (i) to quantify the partitioning of aboveground biomass and nutrient (N, P, K, Ca, Mg, S) content between the two component species at the stand level, (ii) to estimate the biomass and nutrient content distribution (stemwood, stembark, branchwood/branchbark from various diameter classes) within the two species as a function of breast height diameter, and (iii) to assess the pattern of nutrient concentrations within and between oak stems. For branches ( dead and alive) and stems, weighted mean concentrations (wood + bark) tended to be higher in hornbeams for all elements except Ca in stems and K in all components. For both species, nutrient concentrations in live branches decreased with increasing branch diameter (0-1 cm up to > 21 cm), except for Ca in oaks. For oaks stems and large branches, a steep increase in Ca concentrations was noted in bark tissues compared to wood. At the stand level, 81% of total biomass and from 67% (Mg) to 87% (Ca) of total nutrient contents were associated with oak trees. Aboveground nutrient contents represented from 30% (Mg) to 270% (Ca) of the 0-40 cm exchangeable soil pools. Assuming the felling of all oak trees, the harvest of crowns and stems was shown to increase nutrient exports from 85% (Ca) to 281% (Mg) in comparison with a stem only scenario.