Respiratory Costs of Woody Tissues in a Quercus pyrenaica Coppice

Long-term coppicing leads to the development of massive root systems. A disproportionate carbon investment in root maintenance has been pointed as a cause of the widespread decline of abandoned coppices. We aimed at assessing how coppicing has influenced root and shoot development and related carbon loss ascribed to maintenance of woody tissues in Quercus pyrenaica. For this goal, results from published studies on root dynamics, woody biomass and respired CO2 fluxes in an abandoned Q. pyrenaica coppice were integrated and extended to quantify overall respiratory expenditures of above- and below-ground woody organs. Internal and external CO2 fluxes together with soil CO2 efflux were monitored in eight stems from one clone across a growing season. Stems and roots were later harvested to quantify the functional biomass and scale up root and stem respiration (RR and RS, respectively) to the clone and stand levels. Below- and above-ground biomass was roughly equal. However, the root-to-shoot ratio of respiration (RR/RS) was generally below one. Relatively higher RS suggests enhanced metabolic activity aboveground during the growing season, and highlights an unexpected but substantial contribution of RS to respiratory carbon losses. Moreover, soil and stem CO2 efflux to the atmosphere in Q. pyrenaica fell in the upper range of reported rates for various forest stands distributed worldwide. We conclude that both RS and RR represent an important carbon sink in this Q. pyrenaica abandoned coppice. Comparatively high energetic costs in maintaining multiple stems per tree and centennial root systems might constrain aboveground performance and contribute to coppice stagnation.