Propriétés des structures produites par les ingénieurs écologiques à la surface du sol d’une savane colombienne

Fourteen types of physical structures produced by ecosystem engineers were sampled at the surface of a savanna soil of Colombia. Invertebrates implicated in the creation of these structures were identified. Some physical (aggregate size and stability, bulk density) and chemical (C, N, P contents, pH, etc) properties of structures were assessed. Three large groups of structures were identified: (i) earthworm casts characterised by a high bulk density (1.3–1.4 g·cm^–3), constituted of aggregates (7–10 mm), high in organic C (3–4 %) and assimilable nutrients; (ii) termite mounds with low bulk density (0.6–0.9 g·cm^–3), constituted of aggregates (8–9 mm), high in organic C (3.5–10 %) and assimilable nutrients; and (iii) slightly compact (0.4–0.7 g·cm^–3) and granular (aggregate size < 1.5 mm) termite superficial channels and ant mounds low in organic C (less than 1.5 %) and assimilable nutrients. These results underline the large diversity of the biogenic structures produced at the surface of the studied soil. They suggest the feasibility of a functional classification of engineer organisms that would take into account simultaneously the different functional attributes reflected by these structures.