10 Carbon Stocks from Peat Swamp Forest and Oil Palm Plantation …
215
Aboveground C stock was the highest in the primary forests, followed by
secondary forest and oil palm plantations. The mean aboveground C stock was
seven times higher in the primary forests than in oil palm plantation sites (p < 0.001)
(Table 10.3).
Soil
The peat was deeper in the primary forests compared to the oil palm plantations or
secondary forest (Table 10.4). The mean peat depth of primary forest sites was 223
± 10 cm. In contrast, the mean peat depth of three oil palm plantation sites was
significantly lower compared to primary forests, with a mean of 38 ± 3 cm (p <
0.001). The lowest peat depth across sites was observed in secondary forest Tanjung
Harapan (27 cm).
There was a significant difference in soil bulk density between primary forest and
oil palm plantation sites (p < 0.001, Table 10.4), which was apparent throughout all
depths. The mean bulk density across depths was twice higher in oil palm plantations
sites (0.37 ± 0.05 g cm
−3 ) than in primary forest sites (0.17 ± 0.02 g cm
−3 ; p < 0.001).
Bulk density of secondary forests (0.30 ± 0.02 g cm
−3 ) was also twice the value
in primary forests. Interestingly, we did not observe a significant difference in bulk
density between secondary forest and oil palm plantation sites (p = 0.222), suggesting
a clear effect of past forest clearing and agricultural cultivation in the secondary forest
site. Moreover, the higher bulk density and the shallow peat depth in the secondary
forest suggest a slow recovery on the peat layers following abandonment.
In general, bulk density tended to decrease with depth in primary forest and oil
palm plantation ecosystems, but not in the secondary forest. In oil palm plantations
sites, the bulk density at 0–15 cm peat depth was 0.41 g cm
−3 or 1.5 times higher
than the 0.27 g cm
−3 average for peat layer >30 cm. Furthermore, in the primary
forest sites, bulk density at 0–15 cm was 0.25 g cm
−3 or two times higher compared
to 0.13 g cm
−3 at peat layer 50–100 cm.
The mean C concentration across depths was similar in the primary forest (49.42 ±
0.83%) and oil palm plantation sites (48.73 ± 5.05%) (p = 1.0). In both ecosystems,
soil C concentration exceeded 43% C at all depths. Peat in the secondary forest had
a significantly lower C concentration but still relatively high at 32% (p < 0.001). In
general, soil C concentration was not affected by depth in all sites (Table 10.4).
Primary forest conversion to oil palm plantations affected soil N concentration at
all soil depths (Table 10.4). There was no significant difference in N concentration
between primary and secondary forests (p = 0.299). The mean N concentration
in the primary forest, was higher (1.23 ± 0.07%) than at oil palm plantation sites
(0.95 ± 0.13%) (p < 0.001). The difference in N concentration between forest and
oil palm plantation sites was apparent at all depths. Generally, we observed that
soil N concentration decreased with depth in all sites. In the primary forest sites, N
concentration at the 0–5 cm peat depth (1.61%) was about 1.5 times higher than in
the >100 cm peat layer (1.10%). A similar trend was found in the oil palm plantations
215
Aboveground C stock was the highest in the primary forests, followed by
secondary forest and oil palm plantations. The mean aboveground C stock was
seven times higher in the primary forests than in oil palm plantation sites (p < 0.001)
(Table 10.3).
Soil
The peat was deeper in the primary forests compared to the oil palm plantations or
secondary forest (Table 10.4). The mean peat depth of primary forest sites was 223
± 10 cm. In contrast, the mean peat depth of three oil palm plantation sites was
significantly lower compared to primary forests, with a mean of 38 ± 3 cm (p <
0.001). The lowest peat depth across sites was observed in secondary forest Tanjung
Harapan (27 cm).
There was a significant difference in soil bulk density between primary forest and
oil palm plantation sites (p < 0.001, Table 10.4), which was apparent throughout all
depths. The mean bulk density across depths was twice higher in oil palm plantations
sites (0.37 ± 0.05 g cm
−3 ) than in primary forest sites (0.17 ± 0.02 g cm
−3 ; p < 0.001).
Bulk density of secondary forests (0.30 ± 0.02 g cm
−3 ) was also twice the value
in primary forests. Interestingly, we did not observe a significant difference in bulk
density between secondary forest and oil palm plantation sites (p = 0.222), suggesting
a clear effect of past forest clearing and agricultural cultivation in the secondary forest
site. Moreover, the higher bulk density and the shallow peat depth in the secondary
forest suggest a slow recovery on the peat layers following abandonment.
In general, bulk density tended to decrease with depth in primary forest and oil
palm plantation ecosystems, but not in the secondary forest. In oil palm plantations
sites, the bulk density at 0–15 cm peat depth was 0.41 g cm
−3 or 1.5 times higher
than the 0.27 g cm
−3 average for peat layer >30 cm. Furthermore, in the primary
forest sites, bulk density at 0–15 cm was 0.25 g cm
−3 or two times higher compared
to 0.13 g cm
−3 at peat layer 50–100 cm.
The mean C concentration across depths was similar in the primary forest (49.42 ±
0.83%) and oil palm plantation sites (48.73 ± 5.05%) (p = 1.0). In both ecosystems,
soil C concentration exceeded 43% C at all depths. Peat in the secondary forest had
a significantly lower C concentration but still relatively high at 32% (p < 0.001). In
general, soil C concentration was not affected by depth in all sites (Table 10.4).
Primary forest conversion to oil palm plantations affected soil N concentration at
all soil depths (Table 10.4). There was no significant difference in N concentration
between primary and secondary forests (p = 0.299). The mean N concentration
in the primary forest, was higher (1.23 ± 0.07%) than at oil palm plantation sites
(0.95 ± 0.13%) (p < 0.001). The difference in N concentration between forest and
oil palm plantation sites was apparent at all depths. Generally, we observed that
soil N concentration decreased with depth in all sites. In the primary forest sites, N
concentration at the 0–5 cm peat depth (1.61%) was about 1.5 times higher than in
the >100 cm peat layer (1.10%). A similar trend was found in the oil palm plantations