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Humus forms in two secondary semi-evergreen tropical forests
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International audience. The dynamics and function of humus forms in tropical forests are still poorly understood. Humus profiles in two secondary semi-evergreen woodlands in Guadeloupe (French West Indies) were analysed micromorphologically. The humus forms are described under the canopy of five dominant tree species at two sites: under Pisonia subcordata and Bursera simaruba in a secondary forest on a Leptosol (Rendzina), and under Swietenia macrophylla, Tabebuia heterophylla and B. simaruba in a plantation on a calcareous Vertisol. In the secondary forest, two distinct humus forms were observed. A calcareous Amphimull, characterized by an OH horizon comprising the faecal pellets of millipedes, is formed under the canopy of P. subcordata, which produces a litter that is rich in nitrogen. A Dysmull with a thick root mat (OFRh horizon) develops under the canopy of B. simaruba, which produces a litter rich in lignin and phenol that is consumed slowly by the soil fauna. In the plantation on the Vertisol, the activity of the endoanecic earthworm Polypheretima elongata has led to the rapid disappearance of litter and the mixing of organic and mineral material. The humus form is a Eumull and is similar under all three tree species present.
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