<p>This study was carried out at the La Mancha Coastal Research Center (CICOLMA) in tropical semi-deciduous forest, secondary forest and two locations in coastal dune scrub (crest and slack). The aim was to study the carbon and organic nitrogen dynamics of the soil to quantify organic matter mineralization and nitrogen supply. In the laboratory, soil samples were incubated at 25 °C for 97 days and over this time 10 samples were analyzed to monitor the soil’s carbon (CO₂-C) and nitrogen ( , ) dynamics. The results reveal that mean cumulative organic carbon content was: dune slack (2.70 mg g^-1) &gt; secondary forest (2.0 mg g^-1) &gt; semi-deciduous forest (1.9 mg g^-1) &gt; dune crest (1.2 mg g^-1). A comparison of the means using Tukey’s test (α = 0.05) detected differences only between the dune slack and the crest. Mean cumulative inorganic nitrogen content was: secondary forest (1284 mg kg^-1) &gt; dune slack (1140 mg kg^-1) &gt; semi-deciduous forest (1021 mg kg^-1) &gt; dune crest (302 mg kg^-1), with significant differences only between the dune crest and the other treatments. In general, organic matter mineralization was higher in the dune slack and nitrogen supply was higher in the secondary forest. We conclude that organic matter mineralization and nitrogen supply are depending on the type of ecosystem and soil properties.</p>