Soil and species effects on bark nutrient storage in a premontane tropical forest

Abstract

Bark contains a substantial fraction of the nutrients stored in woody biomass, however the degree of functional coordination of bark, wood, and foliar nutrient pools, and its relationship to soil nutrient availability remains poorly understood. Bark thickness and nitrogen, phosphorus, potassium, calcium, and magnesium concentrations were measured in 23 tree species present in two premontane wet tropical forests in western Panama differing in soil nutrient availability. Bark data were combined with existing wood and leaf data from the same species. Bark nutrients were positively correlated with leaf and wood nutrients for all elements. The low fertility site had both lower bark nutrient concentrations and thicker bark, driven primarily by species compositional differences between sites, and secondarily by intraspecific variation. Across species, bark nutrient concentration varied 4 to 25 fold, with the highest variation for calcium. Overall, bark accounted for the largest percent of Ca in above-ground biomass nutrient pools (22–82%) and a large fraction of the other nutrients studied (N: 6–53%, P: 5–50%, K: 4–40%, and Mg: 2–35%). Bark represents a substantial, and highly variable, pool of biomass nutrients. The functional role of bark nutrients, the causes and consequences of this variation, and its relation to other bark traits, including bark thickness, deserve further study.