Tree species responses of western Amazonian floodplain forests to hydro-geomorphic disturbance as tool for predicting impacts caused through river damming and climate change
Physical Geography
Final Report Abstract
Forests along sediment-rich white-water rivers of the Amazon basin (várzea) belong to the most species-rich floodplain forests on Earth. Beside periodical inundations the forests are influenced by intense erosion and sedimentation processes caused through river-channel dynamics. Many tree species are increasingly threatened through hydro-geomorphic changes that derive from large-scale deforestation, climate change, and the construction of dams for hydropower generation. Therefore, the present project investigates the vulnerability of the most important tree species of várzea forests to hydro-geomorphic changes along three rivers in Bolivia. Each two study areas (one at the upper and one at the lower river stretch) were chosen along the Mamoré, Beni, and Madre de Dios Rivers, where floristic inventories encompassing an area of at least 2.25 ha were investigated (13.6 ha in total). All trees >= 10 cm diameter were measured in diameters and heights and species were identified. From the most abundant species, wood cores were extracted to relate annual wood increment and tree vitality with the environmental variables flood height and duration, physical-chemical soil parameters, and river channel dynamics. The latter was achieved by mapping annual alluvial erosion and sedimentation rates over the last 40 years by means of historical satellite data. In total, 6766 trees belonging to 470 species were inventoried. Flood amplitudes were mostly low (< 2.7 m) and variable. The soils differed in grain size composition and fertility between the upper and lower river stretches. Geomorphic dynamics was much higher along the meandering lower than along the elongated upper river stretches and accounted for 80% of all mobilized sediment at the upper stretches during the last 40 years. Tree species richness and composition are comparable to central Amazonian várzea forests, but in contrast to those they are not dependent on flood height and duration but significantly correlated with edaphic and geomorphic variables. Tree species composition differs mainly between the different successional stages, as well as between the different river stretches. Aboveground wood biomass averaged 255 Mg ha -1, the mean stand ages varied between 16 (pioneer forest) and 136 years (late-secondary forest). Annual wood increment was 2.2 Mg ha -1 and year-1, with maxima of up to 9.6 Mg ha -1 year-1 in the pioneer forests but was neither significantly correlated to inundation nor edaphic variables. The investigated várzea forests are characterized by high species richness but low specificity in species composition, because most of the tree species are also reported to occur in terrestrial forest types of the western Amazon basin. At the landscape scale, most tree species as such can be considered as relatively resilient with respect to potential hydro-geomorphic changes.
Publications
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Surge of peatland destruction by an advancing front of artisanal gold mining in Amazonia. Environmental Research Letters, 20(4), 044001.
Daichendt, Natalie; Janovec, John P.; Tobler, Mathias W.; Wittmann, Florian; Latrubesse, Edgardo M.; Hastie, Adam; Morandeira, Natalia & Householder, J. Ethan
