River damming affects seedling communities of a floodplain forest in the Central Amazon

Abstract

The flood pulse of black water rivers in the Amazon basin determines the composition of species along the flood gradient in igapó forests. The Balbina dam, built on the Uatumã River, has altered the flood pulse and caused changes in the floristic composition of adult trees throughout the downstream area. There is a lack of studies on how communities of seedlings in igapó forests respond to changes in the flood pulse. This study investigates the response of seedling communities in the igapó forest downstream the Balbina dam and compares it with two pristine areas. The areas were sampled with transects of 1x25 m within 36 plots (25x25 m) along the flood gradient. Richness and dominance were calculated by simple regression and ordination analyses. The pristine areas had the same pattern of richness, dominance and genera distribution along the flood gradient. However, the affected Uatumã area formed different groups of genera by NMDS analysis, which divided them along the flood gradient with significantly increased dominance of three genera. The insertion of the Balbina dam resulted a loss of lateral and longitudinal connectivity for the Uatumã River, and the alteration to seedling communities may alter the future landscape of downstream igapó forests.

The shadow of the Balbina dam: A synthesis of over 35 years of downstream impacts on floodplain forests in Central Amazonia

“…At the level of seedlings, Rocha et al (2019, 2020) observed even higher IVIs for dominant tree species. In the disturbed low igapó, 55% of the total IVI in the seedling stratum was represented by Pouteria elegans (A.…”

“…The assessment of spatiotemporal disturbances along a 35-year time line combines hydrological alterations of the Uatumã River during the post-dam period (Assahira et al, 2017) with mortality patterns based on remote-sensing analyses (Resende et al, 2019), radiocarbon dating, and dendrochronology (Assahira et al, 2017;Resende et al, 2020), as well as data on tree species diversity and ecological characteristics of dominant tree species (Lobo et al, 2019;Neves, Piedade, Resende, Feitosa, & Schöngart, 2019;Rocha et al, 2019Rocha et al, , 2020. Using water level records from the Cachoeira Morena station, approximately 35 km downstream of the dam (Figure 1), Assahira et al (2017) analysed the changes in the hydrological regime , applying the method of indicators of hydrologic alteration (IHA) and range of variability approach (RVA) (Richter, Baumgartner, Powell, & Braun, 1996;Richter, Baumgartner, Wigington, & Braun, 1997).…”

“…Both species can live for up to 500 years in the case of M. acaciifolium (Schöngart et al, 2005) and more than 800 years in the case of E. tenuifolia (Resende et al, 2020) The impacts of the hydrological alterations on tree species diversity and dominant tree species were assessed by comparing the forests along the Uatumã River with those of an adjacent, undammed affluent (Abacate River) (Figure 1). The floristic data available for igapó forests comprised 6 ha in the focal area of the Uatumã River and 3.75 ha of the Abacate River (for further details, see Lobo et al, 2019;Rocha et al, 2019Rocha et al, , 2020Targhetta et al, 2015) (Figure 1). Floristic data were also available for adjacent terra firme forests in both areas (total of 1 ha) (Lobo et al, 2019).…”

“…All plots were divided into 25-m × 25-m subplots (625 m 2 ), where all trees ≥10 cm DBH, including palms, were tagged and identified and the mean duration of the aquatic phase for each subplot was calculated (for further details, see Lobo et al, 2019). In four subplots (625-m 2 plots) at low, medium, and high elevations of the igapó in the Uatumã and Abacate rivers, Rocha et al (2019Rocha et al ( , 2020 established cross transects of 25 m × 1 m (12 transects at each site) to study the species composition of tree seedlings (15-100 cm in height). Based on this floristic data, the tree species diversity for each plot (individuals >10 cm DBH) was estimated by Fisher's alpha (Fisher, Corbet, & Williams, 1943), which was then correlated with the corresponding duration of the aquatic phase by nonlinear regression models.…”

Effect of Seasonal Rains and Floods on Seedling Recruitment and Compositional Similarity in Two Lowland Tropical Forests

“…Our results are congruent with what has been reported for várzea, since Caño Cumaral is a small white-water river flooding the SFF. An additional factor that can influence richness and abundance patterns in SFF is high anthropic intervention, where species dominance is low, compared to areas with low intervention [74].…”