Downed Wood Debris Decomposition and Nutrient Release Two Years after Hurricane Michael

On October 2018, Hurricane Michael a category 5 hurricane roared through the Florida gulf coast and severely damaged trees at Chipola Experimental Forest resulting in huge, downed wood debris (DWD) decomposition (Figure 1). But the influence of decomposition on carbon (C) and nutrients remains unclear. Therefore, the objective of this study was to determine C and nutrient dynamics between pine species [loblolly pine and sand pine], break types [Clean break (CB), Tip fracture (TF), Attached break (AB) and Tip mound (TM)], and tree position [Diameter at Breast Height (DBH) and Tip Top (TT)] at Chipola Experimental Forest. Carbon composition was determined using ¹³C NMR, and C, nitrogen (N) and phosphorus (P) concentration were determined. ¹³C NMR exhibited minimal changes in C composition, with a slight decrease in O-alkyl. Nitrogen increased significantly in the decomposing loblolly pine (p<0.0001) and sand pine (p<0.0001) at DBH position. The highest N was exhibited in TF and TM in loblolly and sand pine, respectively. While P reduced significantly in DWD (p<0001). Carbon exhibited no significant changes across all variables. Increase in N concentrations in DWD resulted in decrease in C:N ratio, however C:N ratio was still >25 indicating N immobilization (Dhanya et al., 2013). The decrease of P concentration in the DWD resulted in an increase in C:P ratio (p<0.0001), the C:P ratio was >300 which exhibited P immobilization (Dalai, 1977). N:P ratio was >30 in DWD and >16 in live trees indicating that P limited both decomposition and plant productivity. In conclusion, the decomposition process was in the initial stage of decomposition as exhibited by dominance of O-alkyl C and non-significant changes in debris total C compared to live tree. There was immobilization of both N and P, and P limited both the decomposition process and plant productivity, indicating the importance of onsite debris decomposition for nutrient cycling and forest sustainability.