The finding that the optimal carbon rotation was shorter than the
timber-only rotation was in contrast to the results of van Kooten et al.
(1995) and Gutrich and Howarth (2007). The main reason was probably
because the forest owners in this study did not have to pay a carbon
tax when the timber was harvested (or similarly no carbon release at
harvesting was assumed) as in the research by van Kooten et al. The
results of van Kooten et al. suggested that if all sequestered carbon in
timber is released at harvest, it is optimal never to harvest trees; yet if
only a portion of sequestered carbon was released, it is optimal to harvest
trees. That said, as the portion of carbon released from harvesting
becomes smaller, the optimal rotation length will become shorter,
ceteris paribus; and if stored carbon is never assumed to be released as
in this Vietnam-based model, it is possible that optimal overall rotation
age is shorter than optimal rotation age when just considering timber
value. A minor additional reason for the apparent differences in optimal
rotation length between this and other studies could be the inclusion of
soil carbon, which accounted for a large proportion (44 to 87%) in the
total carbon uptake in the first several years (Vo et al., 2009), in this
Vietnam-based model.