Rapid wood decay and nutrient mineralization in an old-growth bottomland hardwood forest

Abstract

Downed woody debris is an important component of the forest floor, responsible for long-term storage of nutrients in many ecosystems. In large floodplain forests of the southeastern United States, wood loads are relatively low, suggesting these landscapes may promote rapid decomposition and nutrient turnover rates. The goals of this study were to identify the major factors responsible for wood decomposition and associated nutrient dynamics in an old-growth floodplain forest at Congaree National Park, South Carolina (USA). In situ decomposition and nutrient dynamics were quantified for 700 days (April 2011–March 2013) using wood from a common overstory species, red maple (Acer rubrum L.). During the study period, regional drought conditions allowed red imported fire ant (RIFA, Solenopsis invicta Buren) colonization and infestation of the study wood after 183 days in the field. Carbon (C) content decreased throughout the study, indicating net mineralization was occurring year-round. Invertebrate activity contributed to extremely fast decomposition rates (mean k 0.650 ± 0.02 year−1) and wood turnover times (mean 4.79 ± 0.15 years). In contrast to C, wood nitrogen (N) and phosphorus (P) content increased following RIFA infestation, displaying net nutrient immobilization. The rapid turnover rates measured at CONG indicate that the C storage function of woody debris may be diminished, but availability of mineralized N and P may also have increased the importance of wood stocks to support forest net primary productivity.