PNNL

Abstract

Litterfall is crucial for forest maintenance, serving as a primary mechanism for nutrient return to the nutrient-poor soils of tropical forests. Foliar nutrient resorption likewise represents an important nutrient-conservation mechanism. Yet, little is known about how these processes vary between fast- and slow-growing species in post-logging areas of the Amazon forest. The objective of this study was to quantify litterfall production and the resorption of foliar nutrients in fast-growing and slow-growing tree species of the Central Amazon, in a forest that was experimentally logged in 1987. The study was conducted from May 2022 to April 2023. Litterfall was collected biweekly using four collectors that were systematically distributed beneath the canopy of each monitored tree, totaling 72 collectors. Three fast-growing and three slow-growing species were selected, each with three replicates, totaling 18 monitored individuals. Species-specific samples of fresh (green) and senesced (litter) leaves were collected and analyzed for their nutrient content and resorption efficiency. Fast-growing species had a monthly leaf litter deposition of 13.53?±?1.6?g?m-2 month-1, compared to 2.59?±?0.4?g?m-2 month-1 for slow-growing species. The average annual litter production across both functional types was 8.6?±?2.6 Mg ha-1 year-1. Nutrient inputs through litterfall were higher in fast-growing species for all elements, particularly nitrogen (N), with 21.92?±?4.9?kg?ha-1 year-1. Phosphorus (P) and potassium (K) exhibited the highest foliar resorption. P resorption efficiency was 68.3?% in fast-growing species and 57.8?% in slow-growing species. For K, efficiencies were 59.0?% and 41.7?%, respectively. These results highlight the substantial role that fast-growing species play in restoring forest productivity in managed Amazon forests, both through higher litter deposition and nutrient fluxes, and through nutrient conserving-mechanisms such as foliar nutrient resorption.