Aboveground and soil carbon in novel forest ecosystems in Singapore: A case study of abandoned plantation secondary forests

Societal Impact Statement Novel forest ecosystems consist of forest ecosystems dominated by non‐native tree species that are difficult to restore to their pre‐human disturbance states. Nevertheless, novel forests can provide numerous ecosystem services, such as carbon sequestration and storage. We quantified the aboveground living tree and soil carbon stocks in four novel forest sites in Singapore using forest inventory and airborne LiDAR data, and soil core data, respectively. We found that the carbon stored in the four sites is comparable to tropical secondary forests elsewhere. Our results show that novel forests can be protected as carbon stores. Summary Forest succession after the cessation of intense human land use may result in ecosystems with biotic or abiotic properties that differ from their historical states before anthropogenic activities. These ‘novel ecosystems’ often consist of communities dominated by non‐native species that are costly to restore to their original state. As novel ecosystems become more ubiquitous, there is a need to understand the opportunities and challenges in managing these ecosystems and the implications for the ecosystem services they provide. Here, we evaluated the role of novel forest ecosystems in Singapore, a tropical city‐state in Southeast Asia, in regulating carbon stocks and flows. Specifically, we mapped the distribution of aboveground carbon density (ACD) in living trees of four post‐agricultural, non‐native‐dominated forest sites across two time periods using a combination of field measurements (2013, 2023) and airborne LiDAR scans (2014, 2019). Soil carbon stock was estimated from soil cores collected at each site. We find that field‐estimated ACD in our plots can reach 129.8 Mg C ha −1 , with a mean sequestration rate for each site ranging between 0.3 and 2.6 Mg C ha −1 yr −1 . Soil carbon can be as high as 127.9 Mg C ha −1 down to 200 cm, comparable to the soil carbon found in other non‐wetland forest ecosystems in the region. Our study highlights the role of novel forests as carbon stores. Therefore, there is a need to consider management options for these ecosystems in highly urbanized landscapes.