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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - RESILIENCE (Understanding the resilience of Amazonian floodplain ecosystems)

Teaser

Summary

Context
In the Amazon basin, the most severe droughts on record all occurred in the last two decades, each associated with large-scale forest fires. The frequency and severity of drought is predicted to increase further in the future as climate change progresses. Forest fires during drought years, appear to have an especially strong and destructive effect in blackwater floodplain forests. Across the Amazon basin, low-relief alluvial floodplains are covered with dense forests, which are inundated for periods of up to six months each year. These floodplain forests therefore connect the most biodiverse terrestrial and aquatic environments on the planet. They also store vast amounts of carbon in their tree stems and root mats, and play an important role in the regional hydrological cycle. Recent work has shown that blackwater floodplain forests are remarkably susceptible to burn during drought years and can also be particularly slow in recovering after fire. Floodplain forests may exhibit a very low resilience to fire perturbations, and with repeated fires appear to transition to an open, savanna-like state in at least some regions.

Societal importance
Degradation of Amazonian floodplain forests will have far-reaching effects on several ecosystem functions. A staggering number of freshwater fish species, a biodiversity twice as high as that of the entire great barrier reef, depend on the existence of Amazonian floodplain forests. A transition from tree-dominated to grass-dominated vegetation will likely disrupt several ecosystem regulating functions, including regional rainfall and temperature conditions as well as rates of carbon sequestration and storage. Furthermore, as fish form the main protein source for thousands of people living in the Amazon basin, loss of floodplain forests will ultimately have a significant impact on human welfare in the region.

Hypotheses and objectives
Previous research suggests that seed dispersal limitations may play a fundamental role in understanding the resilience of blackwater floodplain forests to fire perturbations. Fire destroys the seed bank completely, and the input of new tree seeds during the high-water season might be a crucial bottleneck for the recovery of floodplain forests. In Amazonian floodplain forests, fish play a important role as dispersers of tree seeds during the high-water period. We hypothesize that major disturbances in floodplain forests break-down the interactions between trees and fishes, and that the input of new tree seeds during the high-water season can become a crucial bottleneck for the recovery of floodplain forests after burning. In particular, high tree mortality in burned floodplain forests likely reduces food availability and increases predation risk for fruit-eating fish. As a consequence, seed-dispersing fishes may avoid burned areas, creating a strong seed-dispersal limitation that prevents tree establishment and forest recovery. This project has two main objectives: (1) to evaluate how disturbances in floodplain forests cascade to fish communities, and (2) to evaluate the contribution of seed dispersal limitation (of tree seeds by fish) in explaining arrested succession of burnt Amazonian floodplain forests.

Preliminary conclusions
Our preliminary analyses indicate that forest fires, and subsequent degradation of Amazonian floodplain forests, result in marked changes in fish communities. Such changes included a change in species composition and diet, as well as a lower fish diversity in burned floodplain forests. These changes likely contribute to the low resilience of these forests to anthropogenic disturbances.

Work performed

Data collection
We completed extensive field sampling during the high water period (May to July) of two consecutive years (2018 and 2019). During each year, we sampled fish communities using standardized protocols in 27 research sites previously selected based on their fire history: nine burned floodplain forests, nine control (unburned) floodplain forest, and nine â€œcampinaâ€ (savanna-like) sites. These sites are located within 100 km radius from the village of Barcelos (0.58Â°S, 62.55Â°W). Stomach contents were retrieved for all fishes. We also performed basic limnological measurements at all sites, including water visibility, pH, oxygen levels, and electric conductivity. In addition, we have been able to collate a large dataset on fish and plant communities, and their functional traits, using our previous work and published literature.

Dissemination of results
The research project was presented and discussed at scientific meetings and invited seminars including: (1) Department of Floodplain Ecology, Karlsruhe Institute of Technology (November 2017), (2) International Symposium on phylogeny and classification of Neotropical fishes (23-27 October 2017, Londrina, Brazil), (3) National Institute of Amazonian Research (20 December 2017, Manaus), (4) Aquatic Ecology and Water Quality Management Group, Wageningen University (28 June 2018), (5) discussed at the International Sclerochronology Conference (16-20 June 2019 Split, Croatia). This project also has made possible the PhD research of Arnold Lugo (at the and Wageningen University, the Netherlands, and Instituto Nacional de Pesquisas da AmazÃ´nia, Brazil). Four research papers on the obtained data are currently in progress. These paper will cover the following topics: (1) the effects of floodplain forests loss and â€œsavannazationâ€ on fish communities, (2) changes in seeds dispersal (comparing burned, unburned and campinas) and the implications for forest resilience, (3) changes in trophic relationships in fish communities after floodplain forests degradation, and (4) the spatial patterns in floodplain forests resilience across the Amazon basin, and the abiotic and biotic drivers underlying such patterns.

Final results

Our preliminary results have been used to obtain three subsequent grants that have facilitated expanding our work: (1) National Geographic Explorer grant (consumables for second field expedition); (2) Wageningen University, The Netherlands (two-year postdoc fellowship to Peter van der Sleen), (3) Wageningen University, The Netherlands ( Sandwich PhD for Arnold Lugo, 2018-2022). We believe that the research line that was initiated by the Marie Curie fellowship, and that will continue with the funding of the Wageningen University during the next years, will allow developing solid knowledge to guide conservation strategies by: (1) showing the sensitivity and fragility of this forest system to anthropogenic change, (2) the cascading effects of changes in floodplain forests to fish communities, (3) feedback mechanisms that link Amazonian terrestrial and aquatic ecosystems. Furthermore, we expect we will be able to identify regions where floodplain forests may be especially vulnerable to climate- and land-use change, and that should receive conservation priority.