Estimation of recent peat accumulation with tree saplings

Abstract

The purpose of this paper is to develop an approach to estimate peat accumulation rates (PAR) over recent decades based on the age and burial depths of roots from pine sapling and to use the newly developed approach to estimate spatial variations of PAR. To this end, we sampled 120 pine saplings growing in three plots at Rėkyva peatland in Lithuania and accounted for the microtopography around each specimen. In the lab, all saplings were cut into 1-cm segments, sanded and analysed. The counting of annual rings allowed dating the germination of each sapling with a yearly resolution and thus also enabled estimation of peat accumulation. The latter was derived by measuring the distance from the original root collar at germination to the ground level (or peat surface) at the time of sampling. The large number of samples selected from three plots also enabled determination of spatial variations in PAR. We obtain averaged PAR values of 1.6 ± 0.72 cm yr⁻¹ across the three plots and over the last decades, but also observe strong spatial heterogeneity in PAR resulting from differences in local hydrology and vegetation. To validate the results, we compared tree-ring derived PAR with radiocarbon-based (¹⁴C) estimates at one of the plots. The results are consistent between the two approaches with PAR estimated to 0.8 and 0.79 cm yr⁻¹, respectively, over the last 20 years. We conclude that PAR can be assessed accurately with tree-ring approaches and that they have clear advantages over radiocarbon dating for shorter timescales as they can be replicated more easily. For longer timescales and larger depths (> 15 cm), however, ¹⁴C dating remains the preferred approach.