Allometric equation for Raphia laurentii De Wild, the commonest palm in the central Congo peatlands

The world’s largest tropical peatland lies in the central Congo Basin. Raphia laurentii De Wild, the most abundant palm in these peatlands, forms dominant to mono-dominant stands across approximately 45% of the peatland area. R. laurentii is a trunkless palm with fronds up to 20 m long. Owing to its morphology, there is currently no allometric equation which can be applied to R. laurentii. Therefore it is currently excluded from aboveground biomass (AGB) estimates for the Congo Basin peatlands. Here we develop allometric equations for R. laurentii, by destructively sampling 90 individuals in a peat swamp forest, in the Republic of the Congo. Prior to destructive sampling, stem base diameter, petiole mean diameter, the sum of petiole diameters, total palm height, and number of palm fronds were measured. After destructive sampling, each individual was separated into stem, sheath, petiole, rachis, and leaflet categories, then dried and weighed. We found that palm fronds represented at least 77% of the total AGB in R. laurentii and that the sum of petiole diameters was the best single predictor variable of AGB. The best overall allometric equation, however, combined the sum of petiole diameters (SDp), total palm height (H), and tissue density (TD): AGB = Exp(−2.691 + 1.425 × ln(SDp) + 0.695 × ln(H) + 0.395 × ln(TD)). We applied one of our allometric equations to data from two nearby 1-hectare forest plots, one dominated by R. laurentii, where R. laurentii accounted for 41% of the total forest AGB (with hardwood tree AGB estimated using the Chave et al. 2014 allometric equation), and one dominated by hardwood species, where R. laurentii accounted for 8% of total AGB. Across the entire region we estimate that R. laurentii stores around 2 million tonnes of carbon aboveground. The inclusion of R. laurentii in AGB estimates, will drastically improve overall AGB, and therefore carbon stock estimates for the Congo Basin peatlands

Understory vegetation in fast-growing tree plantations on savanna soils in Congo

The hypothesis that tree plantations may catalyze the regeneration of natural forest biodiversity was tested through studies of floristic diversity and structure in fast-growing tree plantations in the Congo. Study sites included experimental and industrial plantations on poor sandy coastal soils near Pointe-Noire, and experimental plantations on clay soils near Loudima. The effects of plantations species, plantation age (in 6- to 20-year-old eucalypt stands), disturbance due to herbicide use and fire, proximity to natural forest, and soils on understory plant diversity were studied. These plantations were compared to the native savanna ecosystem and to adjacent natural secondary forest stands. Vegetation diversity was assessed through analyses of floristic composition, species richness and frequency. Forest species were dominant in the understory of most plantations, especially in the older stands. However, the forest species established in plantation understories were quite different from those from adjacent natural forest stands. #Preman lucens, #Psorospermum tenuifolium and #Psychotria cf. #peduncularis were the most important forest species found in most eucalypt plantations and in #Pinus caribae and #Acacia auriculiformis plantations. #Alchornea cordifolia, #Anthocleista nobilis, #Barteria nigritiana and #Bertiera cf. #batesii were also important. The savanna species #Eriosema erici-rosenii, #Annona arenaria and #Loudetia arundinacea were encountered in many plots. Herbaceous species were dominant in the younger and disturbed plantation stands. (Résumé d'auteur

Understory vegetation in fast-growing tree plantations on savanna soils in Congo

The hypothesis that tree plantations may catalyze the regeneration of natural forest biodiversity was tested through studies of floristic diversity and structure in fast-growing tree plantations in the Congo. Study sites included experimental and industrial plantations on poor sandy coastal soils near Pointe-Noire, and experimental plantations on clay soils near Loudima. The effects of plantations species, plantation age (in 6- to 20-year-old eucalypt stands), disturbance due to herbicide use and fire, proximity to natural forest, and soils on understory plant diversity were studied. These plantations were compared to the native savanna ecosystem and to adjacent natural secondary forest stands. Vegetation diversity was assessed through analyses of floristic composition, species richness and frequency. Forest species were dominant in the understory of most plantations, especially in the older stands. However, the forest species established in plantation understories were quite different from those from adjacent natural forest stands. #Preman lucens, #Psorospermum tenuifolium and #Psychotria cf. #peduncularis were the most important forest species found in most eucalypt plantations and in #Pinus caribae and #Acacia auriculiformis plantations. #Alchornea cordifolia, #Anthocleista nobilis, #Barteria nigritiana and #Bertiera cf. #batesii were also important. The savanna species #Eriosema erici-rosenii, #Annona arenaria and #Loudetia arundinacea were encountered in many plots. Herbaceous species were dominant in the younger and disturbed plantation stands. (Résumé d'auteur

Changes in biological factors of fertility in managed Eucalyptus plantations on a savanna soil in Congo

Biological factors of fertility were assessed through the study of litter quantity and quality, soil organic matter quantity and quality, soil microfauna, soil macrofauna, organic matter dynamic, particularly decomposition and non-symbiotic nitrogen fixation in an age series of Eucalyptus PF1 and one stand of E. urograndis (E. urophylla x E. grandis). The litter system underwent drastic changes with plot age: litter fall was higher in the older plots than in the younger ones. Soluble carbon and lignin content decreased significantly with plot age and decomposition rate increased. Change in soil organic matter amount occurred in the top layer of soil only and increased with plot age. This enhanced cation exchange capacity. Increase in soil organic matter content was due to the light organic fraction (>0.05 mm), and the amount of C did not change in the organo-mineral fraction. Soil organic matter quality changed also, and the C/N ratio increased with plot age. A drastic decrease in free living nematode density from savanna to young plantations was observed after which it increased slowly with plot age although in the 19-year-plots it was still about ten times lower than in savanna. The importance of Xiphinema parasetariae, a parasite of eucalypts, was confirmed. Its density increased markedly with plot age and the size of the patches where it occurred increased. All soil macrofauna, earthworms, termites and litter inhabiting groups, except the ant group, increased in density with plot age. Termite density decreased in logged stands but no other measured parameters showed any significant difference between plantations and clear felled areas. The long-term effect of harvesting was observed mainly in the litter system and it appeared to be strongly disturbed by previous logging. Previous logging did not affect soil organic matter and nematode populations, either free living or plant parasitic. Soil macrofauna groups slightly increased after harvesting. Total phenolic compounds and fibre content were very different in leaf litter among clones and hybrids