Tree species do not influence local soil chemistry in a species-rich Costa Rica rain forest

Abstract

In a now classic study, Zinke (1962) showed that a single Pinus contorta tree growing on a sand dune along the coast of California modified the chemistry of the soil underneath its crown. He found distinct patterns of pH, exchangeable cations and nitrogen (N) content moving from the bole outward to the crown drip zone, because the acidic bark and stemflow were concentrated around the bole (Zinke 1962). Subsequent studies in temperate forests have also found tree species to affect soil chemical properties such as pH, organic carbon (C) and rates of N mineralization (Boerner & Koslowsky 1989, Boettcher & Kalisz 1990, Finzi et al. 1998). Presumably, these species-specific effects are caused by inter-specific differences in organic acid exudation, nutrient uptake, litter quality or quantity, decomposition rates or nutrient outputs (Binkley & Giardina 1998, Knops et al. 2002, Rhoades 1997). Regardless of the causes, species-generated soil heterogeneity has implications for stand-level estimates of biogeochemical processes such as soil C storage and N-cycling as well as implications for plant diversity and regeneration (Finzi et al. 1998). Although a number of studies have demonstrated that tree species modify soil environments in temperate forests or monospecific tree plantations in the tropics (Fisher 1995, Rhoades 1997), few studies have investigated these processes in species-rich tropical forests (but see Rhoades et al. 1994).