Dynamics of organic matter and nutrient return from litterfall in stands of ten tropical tree plantation species

Abstract

We studied the rates and patterns of carbon and nutrient fluxes in litterfall in ten tropical tree plantation species grown at the USDA Forest Service Arboretum in the Luquillo Experimental Forest, Puerto Rico. The stands were 26-years old and grew under similar climatic and edaphic conditions. Individual plantation species ranked differently in terms of their capacity to return mass and specific nutrients to the forest floor, and with respect to their efficiency of nutrient use. The species that returned the most mass did not return the most P, N, or cations. Moreover, species differed according to the amount of N and P resorption before leaf fall. These differences reflect the variation in the ecophysiological response of each species to edaphic and climatic conditions. The difference between average and minimum resorption values of the species studied indicate that other environmental factors, such as heavy winds or the physical effects of heavy rains, can force the shedding of non-senesced leaves. This higher quality material, although not very much in quantity, can provide a small pulse of available nutrients to the forest floor community. The same holds true for other high nutrient/low mass fractions of litterfall such as reproductive parts and miscellaneous materials. In areas with no prevalent or strongly seasonal water limitations, temporal variations of leaf litter on the forest floor are the combined result of the rate of fall and decomposition of the falling material, and the diverse responses of species to different environmental cues. Leaf fall was inversely correlated to reduced water availability in three of the species studied. Leaf fall of the other species was correlated either to daylight duration or minimum temperatures. The results highlight the importance of understanding species performance relative to nutrient and mass metabolism before selection for plantation use, or for rehabilitation of degraded lands.