Zoochorie et premiers stades de la régénération naturelle après coupe en forêt guyanaise

Résumé En

Processes leading to forest regeneration in a mature rain forest of French Guiana were studied on six plots representing initial stages of regeneration, from 2 to 10 years following clear-cutting. The first woody species to appear in plots after tree felling are light demanding species growing from seeds remaining dormant in the rain forest soil. Such a «seed bank» is very heterogeneous, its composition being strongly influenced by the proximity of forest gaps and tree falls. Burning and increased soil compaction can prevent dormant seeds from germinating. Other seeds are disseminated by frugivorous bats and birds, yet other by wind. A few other regenerating plants are sucker shoots from cut stumps of shade tolerant species of the undergrowth, which grow easily beneath the canopy of pioneers. The pioneer vegetation (Table I) is characterized by a low species richness : no more than 15 species (out of a grand total of 113 found 3.5 years after clear cutting), contribute to 85 % of the woody community. The seeds of these pioneer species are dispersed by bats and birds. Twenty species of frugivorous bats were observed in the study area, out of which only 4 (Table II) were abundant in the regenerating forest. Forty species of birds (Table III) also contribute to seed dispersal, out of which 16 species are restricted to second-growth. Some of these birds have a limited flight range and tend to disperse seeds more or less evenly around feeding trees. Other birds, particularly «lek» forming species (Pipridae), tend to defecate mainly around their traditional display grounds and generate a more aggregative dispersal of seeds. Some generalist species with a mixed insectivorous and frugivorous diet (Turdus albicollis and Ramphocelus carbo) are the first birds to colonize newly formed gaps in the forest. The «seed rain» generated by bats during the night and by birds during the day, was measured (Table IV) both in the open and under the trees, using plastic collecting sheets. Only bats defecate in the open in a 50 metre wide belt bordering the forest edge. Seed rain generated by birds was observed only under isolated trees used as perches in the open, and to a lesser extent in the undergrowth of the mature forest.