Litterfall, litter decomposition and maize bioassay of mulches from four indigenous tree species in mixed and monospecific plantations in Costa Rica.
Plantations of native timber species were established in 1992 on abandoned pastures in the Atlantic humid lowlands of Costa Rica to compare growth and nutrient cycling in pure and mixed stands. As part of the project, leaf litter decomposition, litterfall and accumulation of leaf litter on the plantation floor were studied in young plantations (3.5 yr old) of Pithecellobium elegans, Genipa americana, Vochysia ferruginea and Hyeronima alchorneoides (monocultures of each species and a mixed stand). Of the 4 species studied, V. ferruginea had the highest annual litterfall (867.6 g m-2), G. americana had the lowest (386.7 g m-2), and the mixed plots had an intermediate level (660 g m-2). Leaves of P. elegans decomposed the most rapidly, and those of V. ferruginea the slowest, with the mixed litter decomposing at an intermediate rate. Mulch bioassays testing maize seedling growth showed higher survival and growth rates than the unmulched control in every treatment except for the G. americana mulch. Overall, P. elegans appeared to be a good candidate for agroforestry combinations: the sparse canopy allowed light to penetrate, and its mulch showed the most positive effect on growth of maize seedlings. The large amount of litter produced by H. alchorneoides and V. ferruginea makes them helpful in protecting against soil erosion. A mixed species treatment may combine the beneficial effects of the different species, with the additional advantage of product diversification, especially important for the subsistence-orientated farmers of the region.