Allometric equation for the commonest palm in the Central Congo Peatlands, Raphia laurentii De Wild

Abstract

AbstractThe world’s largest tropical peatland lies in the central Congo Basin. Raphia laurentii De Wild. is a palm which forms dominant to mono-dominant stands across ca. 45 % of the peatland area. However, a lack of allometric equation for this canopy-forming trunkless palm with fronds up to 20 m long, means that this it is currently excluded from aboveground biomass (AGB) estimates for these peatland ecosystems. Here we develop an allometric equation for R. laurentii, by destructively sampling 90 R. laurentii stipes (across six mean petiole diameter size classes of: 2-4 cm, 4-5 cm, 5-6 cm, 6-7 cm, >8 cm) in a peat swamp forest, in the Likouala Department, Republic of the Congo. Prior to destructive sampling, the five parameters were measured for each stipe: diameter at stem base, mean diameter of the palm fronds, total diameter of the palm fronds (TDpf), total height and number of palm fronds. After destructive sampling and before weighing each individual was separated into the stem and the following palm frond categories: sheath, petiole, rachis and leaflets. We fitted a linear model relating AGB to each independent predictor variable separately to assess the best variable, finding that palm fronds represented at least 77 % of the total AGB in each diameter classes. We found that TDpf was the best single predictor variable for R. laurentii AGB. We provide a series of equations, based on sampling R. laurentii with fronds ≥2 cm diameter or ≥5 cm diameters. The best allometric equation was: AGB = Exp (−2.691 + 1.425 × ln (TDpf) + 0.695 × ln(H) + 0.395 × ln (WD).. A monodominant 1 ha plot near the harvesting site had a palm AGB of 60.8 Mg ha-1, similar to the AGB of the trees in the same plot, at 86.2 Mg ha-1. Accounting for the AGB of palms is important, and can now be estimated using the allometric equations developed here.