Quality and quantity of topsoil organic matter in monospecific and mixed pine forests: role of overstory and understory vegetation

Abstract

Abstract Hypothesis and aims The topsoil organic matter dynamics in mixed vs. monospecific pine stands responds to the vegetation composition. Thus, we tested the effect of the stand type and every under- and overstory species as well as the understory richness in forest floor and topsoil organic matter variability in a fine-scale approach. Methods The study of topsoil (5cm depth), forest floor (25 cm x 25 cm), understory (1 m x 1 m), and overstory (4 m radio) in 180 plots [6 triplets x 3 forest stands (PS: P. sylvestris monospecific stand; PP: P. pinaster monospecific stand; MM: mixed stand of both Pinus species) x 10 plots/stand] was implemented in a triplets’ essay in North-Central Spain. Results The topsoil organic matter quantity (~ TOC) described an expected trend given the overstory composition (PS > MM > PP) but quality (~ - C/N) showed an unexpected trend (PS ~ MM > PP) that we found related to the understory richness. Conclusion The quantity and quality of topsoil organic matter in mixed pine stands respond to the overstory, but also to the understory. Management strategies oriented to understory conservation to maintain dynamics of organic matter that promote carbon sequestration are recommended.