Spatio-temporal litterfall dynamics in a 60-year-old mixed deciduous forest

Abstract

To increase our understanding of litterfall dynamics in mixed-species forests, seasonal and annual variations in litterfall mass and nutrient concentrations were assessed for a 60-year-old spontaneously developed forest dominated by silver birch (Betula pendula Roth), pedunculate oak (Quercus robur L.), and northern red oak (Quercus rubra L.) in Belgium. Total quantities and seasonal patterns of most litterfall fractions were similar over the 29-month study period, but the species differed in start and duration of their leaf shedding period. The spatial distribution of litterfall persisted over the years for leaves, but not for total litterfall because of the varying spatial pattern of fallen twigs and reproductive structures. Consequently, predicting humus build-up based on short-term litterfall measurements may be difficult in mixed forests. Nutrient concentrations in leaf litter differed considerably between the species and throughout the year, but the seasonal pattern did not depend on the species. Betula returned significantly more nutrients to the soil per mass unit than Quercus, except for sodium. As the present stand conditions only allow recruitment of Q. rubra, Betula is being outcompeted, which decreases the nutrient return to the soil and may negatively affect biogeochemical cycling.