Changes in carbon and nutrient dynamics in tropical forests: The importance of litter

Litter has long been known to be an important source of soil nutrients and soil carbon in temperate forests. Further it is generally accepted that recycling of nutrients from litterfall in tropical forests explains why highly productive forests have grown indefinitely on soils, which if converted to agriculture result in poor crop growth in only a few years. We have experimentally investigated the importance of litterfall in maintaining the carbon and nutrient balance of soil and the supply of nutrients to trees in semi-evergreen rainforest in at Barro Colorado Nature Monument in Panama. After four years of continuous litter removal and addition the concentrations of NO3 and NH4 in the soil (0-10 cm) in litter removal (L-) plots have decreased, while in litter addition (L+) plots the concentrations of Ca, Zn, NO3 and B in the soil have increased significantly. The concentration of Ca in live leaves has decreased in L- plots, while in L+ plots there were no changes in leaf nutrient concentrations. Litterfall nutrients are unchanged in the L- plots but litterfall N has increased by 18% in L+ plots relative to controls. Thus, even in the relatively fertile soils of BCNM, where forest nutrient use efficiencies are average to low, over four years litter removal has lowered soil fertility, and litter addition has increased soil fertility; changes in nutrients in trees are beginning to appear. We suggest that there would be even stronger responses in forest on less fertile tropical soils.