Another variable that was expected to explain the likely aboveground
carbon offset additionality of mixed indigenous plantation
forest is stand structure. However, stem density, which is one of
the attributes of stand structure, was ruled out. Mixed indigenous
plantation forest did not have a significantly higher stem density
than other forest types. Similarly, young secondary forest, which
had a significantly higher stem density than other forest types
had the least aboveground carbon stock. Nonetheless, stand basal
area was found to have a strong influence on aboveground carbon
stock. The results indicated that forest stands with larger basal area
had relatively more aboveground carbon stock than those with
smaller basal area. Since stand basal area is a function of both stem
DBH and stem density, and the latter had been confirmed to have
negligible effect on aboveground carbon stock, the results suggest
that the contribution of basal area was attributable to stem DBH.
This observation is consistent with those of Chaturvedi et al.
(2011), Omeja et al. (2011) and Ifo et al. (2014), which reported
that large trees, though less abundant, often store more aboveground
carbon than smaller ones, which are normally significantly
more abundant in tropical forest stands.
There were instances where plantation forest stands with larger
basal area did not hold more aboveground carbon stock than secondary
forests. For instance, B. javanica and M. eminii monoculture