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

Seasonally flooded evergreen forests and non-flooded deciduous and semi-dec iduous forests of the Pantanal of Mate Grosso, Brazil, were studied to comp are their structure and floristic composition, their production of small li tterfall and its seasonal variation, as well as the nutrient input into the soil by fallen litter. The litterfall data were used to test the hypothesi s 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 concentrati ons, a CEC from 20 to 190 mu mol g(-1) and a pH from 5.1 to 6.6. All trees of greater than or equal to 5 cm DBH were identified and their diameters me asured. 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 20 05 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 1 7 per plot. Small litterfall (leaves, wood less than or equal to 2 cm, repr oductive parts, trash<2 mm) was collected monthly over three years in 25 li tter traps on each plot. Dry weights and element concentrations (N, P, K, C a, Mg, Al) of litter fractions were determined. Concentrations of P, Ca, an d Mg were highest in leaf litter from plots with many deciduous species. Ac cumulated Al (1.4%) was found in litter from Vochysia divergens Pohl. Eleme nt accession rates were low in deciduous and high in semi-deciduous and eve rgreen forest. Total litterfall in nonflooded deciduous and semi-deciduous forest (4.86 to 7.71 t ha(-1) year(-1)) was significantly lower than in sea sonally flooded evergreen forest (7.53 to 10.27 t ha(-1) year(-1)). The fin dings 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. (C) 1999 Elsevier Science B.V. All rights reserved.