Germination and development of sown mahogany (Swietenia macrophyllaKing) in secondary tropical dry forest habitats in Costa Rica

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Abstract
Effects of irradiance, root competition and water availability on germination and seedling establishment ofSwietenia macrophyllaKing were investigated in tropical secondary dry forests in the Guanacaste Conservation Area, Costa Rica. The fate of seeds sown in the beginning and the middle of the rainy season was studied in abandoned pasture, and in deciduous and semi-evergreen secondary forest. In the pasture, experimental treatments were mown and unmown grass. In the forest sites, thinning to increase light and trenching to reduce root competition were combined in a factorial design. Effects of moisture availability on germination were tested by supplementing natural rainfall in the initial rainy month. Germination at the beginning of the rainy season was not influenced by the supplementary water and was higher in the semi-evergreen forest than in the deciduous forest and pasture. In the forests, germination was little affected by irradiance or root competition. More seeds germinated in unmown than in mown pasture during the initial rains, but were not influenced by mowing when sown in the peak of the rainy season. Seedling mortality was low (>10%) during the initial months, but increased greatly in the dry season. Seedlings germinating early in the rainy season had a higher survival than those germinating later. The relatively slight effects of the different treatments and habitats on seedling establishment suggest that this species is rather insensitive to the large microsite variation in secondary vegetation.