Forest dynamics and tip‐up pools drive pulses of high carbon accumulation rates in a tropical peat dome in Borneo (Southeast Asia)

Abstract

Peatlands of Southeast Asia store large pools of carbon but the mechanisms of peat accumulation in tropical forests remain to be resolved. Patch dynamics and forest disturbance have seldom been considered as drivers that can amplify or dampen rates of peat accumulation. Here we used a modified piston corer, noninvasive geophysical measurements, and geochemical and paleobotanical techniques to establish the effect of tree fall on carbon accumulation rates in a peat swamp forest dominated by Shorea albida in Brunei (Borneo). Carbon initially accumulated in a mangrove forest at over 300 g C m À2 yr À1 but declined to less than 50 g C m À2 yr À1 with the establishment of a peat swamp forest. A rapid accumulation pulse of 720-960 g C m À2 yr À1 occurred around 1080 years ago as a tip-up pool infilled. Tip-up pools are common in the peatlands of northwest Borneo where windthrow and lightning strikes produce tree falls at a rate of 4 trees ha À1 every decade. A simulation model indicates that tip-up pools, which are formed across the entire forested peat dome, produce local discontinuities in the peat deposit, when peat is removed to create a pool that is rapidly filled with younger material. The resulting discontinuities in peat age at the base and sides of pool deposits obscure linkages between carbon accumulation rates and climate and require new approaches for paleoenvironmental reconstructions. Our results suggest that carbon accumulation in tropical peat swamps may be based on fundamentally different peat-forming processes than those of northern peatlands.

How temporal patterns in rainfall determine the geomorphology and carbon fluxes of tropical peatlands

“…We also compared radiocarbon dates in deeper peat to simulated ages at the same locations and depths, excluding basal samples from the mangrove peat before the establishment of the peat swamp forest (Fig. 7 and SI Methods) (1,27). Radiocarbon dates and simulated ages at the same locations and depths matched well (Fig.…”

“…However, including these effects did not affect simulations because these extreme water table heights and depths were neither observed at our site nor predicted by simulations of our site. We also did not include anaerobic decomposition below the water table because analyses of peat cores from tropical sites in Asia (2), including our site (27), do not show detectable loss of waterlogged peat from anaerobic decomposition.…”

Imaging tropical peatlands in Indonesia using ground-penetrating radar (GPR) and electrical resistivity imaging (ERI): implications for carbon stock estimates and peat soil characterization

“…Alternatively, these feature may also be associated with the infill process in a tip-up pool. As described by Dommain et al (2015) for peatlands in Borneo, tip-up pools are commonly formed when lightning strikes a tree inducing its fall and generating a discontinuity in the peat deposit and a pool subsequently infilled with younger material. The horizonal reflectors seem to overlap the tilting reflectors, suggesting that the depression may have formed suddenly, to be later filled up progressively with younger peat.…”

“…The horizonal reflectors seem to overlap the tilting reflectors, suggesting that the depression may have formed suddenly, to be later filled up progressively with younger peat. Although this may represent an isolated feature in our data set, Dommain et al (2015) have recently demonstrated the importance of such features when describing carbon accumulation rates and how it may complicate paleoenvironmental reconstructions.…”

Tropical peat decomposability expressed through physical, chemical and biological properties under varying land management intensities

“…This could be seen in the swamp forest with increasing peat depth and the open sites already at the surface peat as a decrease in particle size composition (I). However, peat decomposition stage does not necessarily increase with depth in the swamp forests, as more decomposed layers in the peat profile may be interspersed with less decomposed layers, due to variation in peat formation speed related to changes in climate and vegetation over time (Page et al 1999;Wüst & Bustin, 2004;Dommain et al 2015). In the surface peat at the open sites, where new coarse litter deposition rates cannot notably support peat accumulation and thus decomposition takes place mainly in the "old" peat, the particle size was smaller than at the forest sites and deeper layers in the open sites.…”