Factors controlling litter production in a large Mediterranean river floodplain forest

Abstract

Although litter production is an essential floodplain forest function, the drivers and their relative importance remain largely unknown, especially in semi-arid rivers. The influence of forest structure, flooding regime, soil conditions, and litterfall chemistry (a total of 17 variables) on spatial variability of litter production within the Middle Ebro River floodplain forests (northeastern Spain) was examined by monitoring litterfall in 12 forest plots in 2007. Linear mixed effects (LME) models, using stem density (SD), river distance (RD) (or soil total organic C (TOC)), and soil total P (TP) as independent predictors, explained 51% of the variance in litter production, while an alternative LME model using SD and P use efficiency (P-NUE) explained 40%. In particular, litter increased with SD and TP and decreased with RD, P-NUE, and TOC. Based on these results, P limitation appears to be controlling litter production in a rather dry hydrological regime. We hypothesized that a deficient sediment input at the plot scale (especially in the outer floodplain), with flood quality (overbank flooding, ground-water seepage, ponding) being a greater determinant than quantity (flood duration, water table levels), might ultimately be responsible for the spatial variability observed in litter production.