Gerhardt, K.  1994.  Seedling development of four tree species in secondary tropical dry forest in Guanacaste, Costa Rica.  Comprehensive Sumaries of Uppsala Dissertations from the Faculty of Science and Technology 39.43 pp.  Uppsala ISBN 91-554-3279-4.

Abstract

Dry forests constituted about 40% of the lowland forests in the tropics in historical times.  Rapid deforestation and fragmentation of these forests during the last centuries have left few areas of forest intact, and tropical dry forests are today more threatened that tropical rain forests.  Knowledge of regeneration proceses in dry forests is poor, but crucial if these ecosystems are to be restored and successfully conserved.

Seedling development of four canopy tree species, Cedrela odorata L., Hymenaea courbaril L., Manilkara chicle Pittier and Swietenia macrophylla King, were studied in the Guanacaste Conservation Area, north-western Costa Rica.  Nursery-grown seedlings of all four species were planted, and sedes of S. macrophylla were sown, in abandoned pasture, and desiduos and semi-evergreen secondary forest with varying light and root-competition levels.

Seedling mortality was very high during the pronounced dry season.  Seedling survival was positively related to seedling size.  In addition, variation in water availability due to drought spells in the wet season, length of wet and dry seasons, and total annual rainfall, influenced survival and growth.  High light levels during the wet season increased growth, while high insolation during the dry season reduced survival.  Reduced root competition promoted growth in the rainy season and favoured seedling survival.

The germination of S. macrophylla was neither affected by rainfall patterns during the wet season nor by differences in the light levels.  An increasing length of the dry season increased seedling mortality.