Stem and branch respiration of beech:: from tree measurements to estimations at the stand level

Stem and branch respiration of 30-yr-old Fagus sylvatica trees was measured in a temperate forest for 1 yr to estimate the annual flux at the stand level. The seasonal response of respiration to air temperature was determined using infra-red gas analysis (IRGA) systems. Annual respiration was derived from half-hourly temperature recording and allometric relations established for the same forest. The basal respiration rate at 15 degreesC (R15) increased greatly during the growing season. On a volume basis, monthly means of R15 were higher for branches than for stems. For stems, Q(10) was relatively constant throughout the year, with an annual average of 1.7. Estimated annual respiration was approx. 325 g C m(-2) ground surface area yr(-1) with 50% of this amount attributed to growth respiration. Stem and branch respiration played a major role in the annual carbon balance of the beech stand. It represented approx. one third of the ecosystem-level carbon loss from respiration. The magnitude of crown respiration makes it obvious that information on branch respiration characteristics is required for reliable estimations at the stand level.