Net ecosystem production of a tropical secondary forest in Jengka, Pahang, Malaysia

Secondary tropical forests are important contributors to atmospheric carbon exchanges in tropical regions. However, our understanding of how secondary succession affects carbon cycling and carbon sequestration in these ecosystems is limited. We studied carbon cycling and net ecosystem production (NEP) in a secondary lowland forest using a full biometric-based flux measurement (2018-2019) and a partial biometric-based measurement (2017). Net primary production ranged from 6.01 to 8.37 Mg C ha-1 year-1 (2018-2019). This was partitioned in changes in aboveground biomass (0.98-3.66 Mg C ha-1 year-1), coarse roots (0.23-0.88 Mg C ha-1 year-1), litterfall (2.74-3.94 Mg C ha-1 year-1) and fine roots (0.86-1.09 Mg C ha-1 year-1). The total annual soil surface CO2 efflux was 10.56, 8.90, and 12.23 Mg C ha-1 year-1 for 2017, 2018, and 2019. The net ecosystem production of the forest was -2.89 and -3.86 Mg C ha-1 year-1 for the years 2018 and 2019. Litterfall exhibited the highest percentage of change (32%-58%) followed by aboveground biomass (14%-44%) and fine roots (13%-14%). The negative NEP values showed that the site is a C source and may be partially influenced by forest fragmentation. Seasonal variations also influence the dynamics of NPP and NEP.