Cost-effectiveness of restoration approaches for above-ground and
soil carbon accumulation
The amount of carbon accumulated per invested US$ in restored forests
increased with time when only implementation costs were considered
(F1,22 = 12.8, P = 0.001), because of the gradual
increase of carbon stocks and the absence of additional costs after the
first years of implementation (Fig. 4A). However, the increase of land
opportunity costs was higher than the increase of carbon accumulation,
which resulted in a decrease of the opportunity cost-effectiveness for
carbon accumulation along the chronosequence (F1,22 =
10.5, P = 0.003; Fig. 4B). These opposing trajectories of implementation
and accumulated land opportunity cost-effectiveness along the
chronosequence nullified changes in total cost-effectiveness with age in
restored forests (F1,22 = 2.8, P = 0.1; Fig. 4C).
Implementation cost-effectiveness was significantly higher for
second-growth forests than for plantations throughout the chronosequence
(F1,22 = 9.4, P = 0.005; Fig. 4A). Opportunity
cost-effectiveness showed a similar trend but the average difference
between plantations and second-growth forests was not significant
(F1,22 = 2.7, P = 0.1; Fig. 4B). Total
cost-effectiveness, i.e. the amount of accumulated carbon standardized
by the total cost of restoration (implementation + opportunity costs),
was significantly higher for second-growth forests
(F1,22 = 9.2, P = 0.006; Fig. 4C). On average,
second-growth forests displayed a total cost-effectiveness that was 60%
higher than plantations (15.1 kgC.US$-1 and 9.4
kgC.US$-1, respectively). Average differences between
second-growth forests and plantations were higher for total
cost-effectiveness than for its components (i.e. implementation and
accumulated land opportunity cost-effectiveness). This indicates that
differences in both implementation and opportunity costs contributed to
the resulting differences in total cost-effectiveness between
restoration practices. We note that one tree planting site was
significantly older (61 years old) than the rest of the restoration
dataset. Removing this site from the analyses did not change any results
or conclusions of this work.