Soil physical restrictions and hydrology regulate stand age and wood biomass turnover rates of Purus–Madeira interfluvial wetlands in Amazonia

Abstract

Abstract. In Amazonia, wetlands constitute about 30 % of its entire basin, of which ancient fluvial terraces located in vast interfluvial regions cover a large portion. Although the increased number of permanent plots in the recent years has contributed to improved understanding of regional variation in forest dynamics across the Amazon Basin, the functioning of large lowland interfluvial wetlands remain poorly understood. Here we present the first field-based estimate for tree ages, wood biomass productivity and biomass turnover rates for eight 1 ha plots in wetland and non-flooded forests distributed along the BR-319 Highway along a distance of about 600 km crossing the Purus-Madeira rivers interfluvial region in central-southwestern Amazon Basin. We estimate stand age, wood biomass productivity and biomass turnover rates combining tree-ring data and an allometric equation based on diameter, tree height and wood density and relate these structural parameters to physical soil and hydrological restrictions. Wood biomass and productivity varied twofold among the plots, with wood biomass stocks ranging between 138-294 Mg ha −1 and productivity varying between 3.4-6.6 Mg ha −1 yr −1 . Soil effective depth, topography, structure and mainly soil water saturation significantly affected stand age (64-103 yr) and forest dynamics in terms of annual biomass turnover rates (2.0-3.2 %). On harsher soils characterized by a poor structure, low effective depth and high water saturation, biomass turnover rates were increased and forests stands were younger compared to welldrained sites. We suggest that soil constraints, especially soil water saturation, limit the development of the stand structure, resulting in forests with younger stand ages and higher biomass turnover rates compared to forests growing on welldrained soils. We do not find, however, any relation between physical soil restrictions or hydrology and wood biomass productivity, but there is a trend of increasing wood biomass productivity and phosphorus concentrations at the soil surface. Based on our results we establish hypotheses for different dynamical processes between forests growing on waterlogged and well-drained soils and discuss how these results can be applied in the background of conservation as well as the potential development of forest management plans in this region, which will experience increased deforestation due to the construction of the BR-319 Highway crossing the interfluvial region of the Purus-Madeira rivers.

Different environmental gradients affect different measures of snake β-diversity in the Amazon rainforests

“…Associations between soil texture and patterns of vertebrate community structure are often assumed as indirectly causal, because soil texture affects many factors driving regional species occurrence, such as vegetation density ( Woinarski, Fisher & Milne, 1999 ) and distance from streams ( Bueno et al, 2012 ). The environmental heterogeneity in the Amazon rainforests includes soil texture gradients from poorly drained, seasonally flooded sandy soils ( Cintra et al, 2013 ), in which plants find poor substrate for rooting ( Quesada et al, 2012 ), to well-drained soils that support older well-developed forests ( De-Castilho et al, 2006 ; Emilio et al, 2013 ). Therefore, variation in soil texture across landscapes generates high β-diversity via suitability of the conditions for dispersal and colonization, which has been found in plant ( Costa, Magnusson & Luizão, 2005 ; Costa et al, 2008 ), invertebrate ( Franklin, Magnusson & Luizão, 2005 ) and vertebrate ( Woinarski, Fisher & Milne, 1999 ; Bueno et al, 2012 ; this study) assemblages.…”

“…We evaluated the influence of clay content in the soil on the diversity measures because this gradient affects primary production, which influences the overall trophic network ( Cintra et al, 2013 ). Clay content was measured in a pooled five g sample derived from six subsamples per plot, and we used averages per module.…”

High Species Richness of Scinax Treefrogs (Hylidae) in a Threatened Amazonian Landscape Revealed by an Integrative Approach

“…It covers an area of approximately 15.4 million hectares and contains a complex network of water bodies [24]. The soil is mostly characterized as plinthosols [25], with a predominance of silt [26]. The Madeira river is the main tributary of the Amazon and its basin covers approximately 1.4 million km 2 .…”

The Amazon Tall Tower Observatory (ATTO): overview of pilot measurements on ecosystem ecology, meteorology, trace gases, and aerosols

“…Some of these terrace soils also show signs of anoxia (mottling) in deeper layers. Such impeditive conditions may have an influence on forest structure Emilio et al, 2014) and dynamics (Cintra et al, 2013), thereby possibly restricting tree height or even tree individual biomass storage . …”