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要旨:
To study the decay of coarse woody debris
(CWD) in forest ecosystems, it is necessary to determine
the time elapsed since tree death, which is difficult at
advanced decay stages. Here, we compare two methods for
age determination of CWD logs, dendrochronological
cross-dating and radiocarbon analysis of the outermost tree
ring. The methods were compared using samples from logs
of European beech, Norway spruce and Sessile oak
decomposing in situ at three different forest sites. For
dendrochronological cross-dating, we prepared wood discs
with diameters of 10–80 cm. For radiocarbon analysis,
cellulose was isolated from shavings of the outermost tree
rings. There was an overall good agreement between time
of death determined by the two methods with median difference
of 1 year. The uncertainty of age determination by
the radiocarbon approach did not increase with decreasing
carbon density, despite incomplete separation of chitin
from the extracted cellulose. Fungal chitin has the potential
to alter the radiocarbon signature of tree rings as the carbon
for chitin synthesis originates from different sources. Significant
correlations between year of tree death and carbon
density of wood were found for beech and spruce, but not
for oak due to relatively small decreases in carbon density
within 50–60 years. Total residence times of CWD were
calculated from these correlations and revealed 24 years
for beech and 62 years for spruce. The uncertainty of total
residence times results mainly from huge natural variability
in carbon density of CWD rather than uncertainty in the age determination. The results suggest that both methods are suitable for age determination of CWD.
