Impact of climatic and hydrological disturbances on blackwater floodplain forests in Central Amazonia

Abstract

Extreme climatic events and anthropic disturbances affect the hydrological regime of Amazonian rivers and connected floodplain forests. This study aims to investigate the impacts of the Balbina hydroelectric power plant on the floodplain forests of the Uatumã River, in the Central Amazon. For this, tree age and diameter increment from the most abundant tree species of three different topographic levels were obtained and analyzed in the affected area downstream of the Balbina dam (Uatumã River) and compared to an undisturbed site (Abacate River, affluent) considering age structure and mean diameter increments between the topographic levels and the two systems. The occurrence of old trees is much lower at the disturbed site compared to the undisturbed system. Especially at the middle topography of the Uatumã site, we observed tree species with high mean diameter increment indicating a strong disturbance. We suggest that the disturbances may be associated with extreme hydro‐climatic events, such as extreme droughts that occurred during the El Niño years 1925/26 and 1982/83 and that these events may increase vulnerability of igapó floodplains to wildfires. Abstract in Portuguese is available with online material.

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

“…The palm Astrocaryum jauari Mart. (Arecaceae) is the dominant species together with tree species showing low mean tree ages (28-66 years) and wood densities (0.42-0.58 g cm −3 ) and high MDI rates of 3.2-4.8 mm yr −1 , which differed significantly from all other elevations (Neves et al, 2019). At this elevation, Neves Aguas, ANA).…”

“…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).…”

“…In this study, the relative IVIs of the five most important species (IVI Σ1-5 ) of trees >10 cm DBH and seedlings (15-100 cm height) was determined, considering three distinct topographic inundation classes (low, medium, and high). Estimated tree ages and mean diameter increment (MDI) rates of the dominant tree species have been provided by Neves et al (2019), analysing a total of 589 trees at different elevations of the Uatumã and Abacate rivers. In addition, basic wood density of the dominant tree species was considered in the comparison of pristine and disturbed river stretches (Mori et al, 2019;Neves, 2018).…”

“…Owing to the long periods of flooding, litter decomposes slowly and accumulates on the forest floor, which is covered by dense root mats at or near the ground surface (dos Santos & Nelson, 2013), providing a large volume of combustible material. The presence of an approximately 30-year old age cohort of N. amazonum (Neves et al, 2019) and low tree species diversity (Figure 6; Table 1) suggests massive disturbances on the medium elevation in the igapó along the Uatumã River, originating from wildfires occurring during the implementation of the Balbina dam (Figure 7). This species has been characterized as a secondary species of the nutrient-rich and highly dynamic white-water floodplains (várzea) (Wittmann, Anhuf, & Junk, 2002), where it shows low maximum tree age (44 years) and comparatively high MDIs (4.8-14.8 mm year −1 ) (Schöngart, 2003;Worbes, Klinge, Revilla, & Martius, 1992).…”

Growth and establishment of monodominant stands affected by ENSO and flooding in the Pantanal

“…The non-destructive method has been used by several authors (e.g. Schöngart et al 45 ; Fonseca-Junior et al 46 ; Locosselli et al 41 ; Andrade et al 47 ; Neves et al 48 ) in recent research in tropical trees with good results of ring analysis. In December 2016, using the non-destructive method, we extracted cores from the stems of 29 trees (one or two cores per stem, but we used the one that allowed the best view of the rings) using an increment borer (Pressler borer) 5 mm in diameter.…”