Litterfall and nutrient return in seasonally flooded and non-flooded forest of the Pantanal, Mato Grosso, Brazil

Abstract

Seasonally flooded evergreen forests and non-flooded deciduous and semi-deciduous forests of the Pantanal of Mato Grosso, Brazil, were studied to compare their structure and floristic composition, their production of small litterfall and its seasonal variation, as well as the nutrient input into the soil by fallen litter. The litterfall data were used to test the hypothesis that seasonally flooded forests of the Pantanal are more productive than non-flooded forests. Eight permanent plots of 0.25 ha each were established in three forest types. The clayey forest soils had low N and P concentrations, a CEC from 20 to 190 μmol g −1 and a pH from 5.1 to 6.6. All trees of ≥5 cm DBH were identified and their diameters measured. Tree density and stand basal area ranged, respectively, from 368 to 1700 ha −1 and 15.5 to 25.3 m 2 ha −1 in non-flooded and from 725 to 2005 ha −1 and 22.1 to 32.6 m 2 ha −1 in seasonally flooded forests. There were no significant differences in stem density and basal area between non-flooded and seasonally flooded forest. Species richness ranged from 4 to 17 per plot. Small litterfall (leaves, wood≤2 cm, reproductive parts, trash<2 mm) was collected monthly over three years in 25 litter traps on each plot. Dry weights and element concentrations (N, P, K, Ca, Mg, Al) of litter fractions were determined. Concentrations of P, Ca, and Mg were highest in leaf litter from plots with many deciduous species. Accumulated Al (1.4%) was found in litter from Vochysia divergens Pohl. Element accession rates were low in deciduous and high in semi-deciduous and evergreen forest. Total litterfall in non-flooded deciduous and semi-deciduous forest (4.86 to 7.71 t ha −1 year −1) was significantly lower than in seasonally flooded evergreen forest (7.53 to 10.27 t ha −1 year −1). The findings show that, despite seasonal water excess being the prominent feature of the Pantanal, it is water shortage in the dry season that limits forest productivity.