Historical disconnection from floodplain alters riparian forest composition, tree growth and deadwood amount

Riparian forests are among the most dynamic but threatened terrestrial ecosystems. Their dynamism and conservation depend on historical changes in river geomorphology, which can be evaluated through changes in channel sinuosity. However, we lack long-term assessments on sinuosity and how they impact riparian forest composition, tree growth and deadwood amount. To fill this research gap, we reconstructed river sinuosity in 14 sites across the middle Ebro basin, north-eastern Spain, using historical aerial photographs taken in 1927, 1956, 1998-2003 and 2014-2015. Relationships between sinuosity, stand composition and deadwood amount and decay degree were calculated. We also reconstructed radial growth of the major tree species (Populus alba, Populus nigra, Fraxinus angustifolia, Salix alba and Ulmus minor) in two sites to evaluate how coupled it was with changes in river flow after dam building. From 1927 to 2015, sinuosity decreased passing from 1.39 to 1.20. The river dynamics were altered in the 1950s and 1960s after dam and dyke building. Sites with high sinuosity values in 1956 corresponded to mature stands with large P. nigra individuals. Sinuosity was negatively related to F. angustifolia (rs = -0.83, p < 0.001) and P. alba (rs = -0.64, p = 0.02) abundance, whereas sites dominated by P. alba and U. minor presented abundant decayed deadwood. A loss of sinuosity and a contraction of the riverbank gradient increased disconnection of active channel from floodplain, with a mixing of more (e.g., P. nigra) and less phreatophytic species (e.g., U. minor). River flow diversion reduced growth and increased the tree-to-tree P. alba growth coherence. Hydrological droughts contributed to growth decline and dieback of U. minor, which is sensitive to spring river flow. Conservation and restoration of riparian forests must consider historical changes in river geomorphology related to human activities.

Twentieth-century development of floodplain forests in Polish Carpathian valleys: The by-product of transformation of river channels?

Changes in forest extent in the corridors of four rivers of the Polish Carpathians over the last 130 years and their relation to changes in planform river geometry were investigated through the analysis of 1:25000-scale maps from the 1870s and aerial images from the mid-20th century and 2009. Average proportions of river and its geomorphic units as well as floodplain and its land cover features in the total width/area of the analysed river corridors were determined and compared between the three dates. All the analysed rivers narrowed significantly over the study period. This increased considerably the proportion of floodplains in the area of the river corridors, while lateral parts of the former, wide channels became a place of forest development. In the Koszarawa and Raba valleys, forest developed also on parts of the former floodplains following a decline in agricultural and pastoral use of lands with shallow, poor soils. The proportion of forest in the total area of the river corridors increased from 0-7.5% in the 1870s to 28.5-46.5% in 2009, and the forest expansion was mainly driven by the timing and scale of channelization works that reclaimed parts of the former channels from the rivers. A reduction in flow and sediment dynamics of Carpathian rivers over the 20th century enabled development of islands in their active zones. However, channelization works eliminated islands from most river reaches and thus islands persisted only in scarce unmanaged reaches. The expansion of floodplain forests in Carpathian valleys improves functioning of the river ecosystems but the resultant increased delivery of large wood to river channels may generate flood hazard. Optimal river management should avoid removal of riparian trees to maximize the environmental benefits but enable undisturbed transfer of driftwood through bridge cross-sections to minimize the flood hazard resulting from floodplain forest development.

Ethnoecology of miriti (Mauritia flexuosa, L.f.) fruit extraction in the Brazilian Amazon: knowledge and practices of riverine peoples contribute to the biodiversity conservation

BACKGROUND

This article presents, from an ethnoecological perspective, the worldviews, traditional knowledge, and cultural practices of Amazonian riverine people involved in the extraction of miriti fruits (Mauritia flexuosa L.f.), in a context of increasing market demand for miriti fruits and of pressure for the intensification of açaí (Euterpe oleracea Mart.) production on the Sirituba island, in Abaetetuba, Brazil.

METHODS

Methods used were participant observation and non-directive interviews with 22 extractive families of miriti from the Santa Maria and Costa Sirituba communities, on Sirituba Island, in Abaetetuba, Pará, Brazil. Non-structured interviews were used to analyze the knowledge about the species, history of miriti extraction, the traditions, and innovations related to this activity over time. Participant observation took place when riverine individuals were working with miriti fruits, in order to grasp the "codes" that permeate the human-nature relationships embedded in this production system.

RESULTS

It was verified that the riverine peoples have a great knowledge about the palm tree, which is reflected in their own classification systems and management practices that allow the sustainable extraction of the fruits, avoiding, for example, cutting the miriti palms. In addition, a reciprocity relationship was observed between riverine peoples and miriti palm that are personified and preserved, contributing to the conservation of the species in the floodplain, even with the intensification of açaí (Euterpe oleracea Mart.) production. Another important aspect is the collective work involving all the members of the family, which allows the appropriation of the knowledge about the extraction of miriti by the young, allowing the resistance of the tradition that remains strong, contributing to the sustainability of the practice and conservation of biodiversity in the Amazonian floodplain.

CONCLUSION

The k-c-p complex inherent to the riverine universe allows, even in face of the growing commercial demand for miriti fruits and the unchallenged increase in the extraction of this product, the conservation of floodplain biodiversity. Thus, we emphasize the importance of traditional knowledge and practices for biodiversity preservation, and they use them to guide public policies and natural resource management systems, aiming for sustainable ways to manage and use biodiversity.

Coarse- and fine-scale patterns of distribution and habitat selection places an Amazonian floodplain curassow in double jeopardy

Patterns of habitat selection are influenced by local productivity, resource availability, and predation risk. Species have taken millions of years to hone the macro- and micro-habitats they occupy, but these may now overlap with contemporary human threats within natural species ranges. Wattled Curassow (Crax globulosa), an endemic galliform species of the western Amazon, is threatened by both hunting and habitat loss, and is restricted to white-water floodplain forests of major Amazonian rivers. In this study conducted along the Juruá River, Amazonas, Brazil, we quantified the ranging ecology and fine-scale patterns of habitat selection of the species. We estimated the home range size of C. globulosa using conventional VHF telemetry. To estimate patterns of habitat selection, we used geo-locations of day ranges to examine the extent and intensity of use across the floodplain, which were then compared to a high-resolution flood map of the study area. We captured two females and one male, which we monitored for 13 months between September 2014 and September 2015. Average home range size was 283 ha, based on the 95% aLoCoH estimator. Wattled Curassows selected areas of prolonged flood pulses (six to eight months/year) and had a consistent tendency to be near open water, usually in close proximity to river banks and lakes, especially during the dry season. Amazonian floodplains are densely settled, and the small portions of floodplain habitat used by Wattled Curassows are both the most accessible to hunters and most vulnerable to deforestation. As a result, the geographic and ecological distribution of Wattled Curassows places them at much higher extinction risk at multiple spatial scales, highlighting the need to consider habitat preferences within their conservation strategy.

Groundwater salinity in a floodplain forest impacted by saltwater intrusion

Coastal wetlands occupy a delicate position at the intersection of fresh and saline waters. Changing climate and watershed hydrology can lead to saltwater intrusion into historically freshwater systems, causing plant mortality and loss of freshwater habitat. Understanding the hydrological functioning of tidally influenced floodplain forests is essential for advancing ecosystem protection and restoration goals, however finding direct relationships between hydrological inputs and floodplain hydrology is complicated by interactions between surface water, groundwater, and atmospheric fluxes in variably saturated soils with heterogeneous vegetation and topography. Thus, an alternative method for identifying common trends and causal factors is required. Dynamic factor analysis (DFA), a time series dimension reduction technique, models temporal variation in observed data as linear combinations of common trends, which represent unexplained common variability, and explanatory variables. DFA was applied to model shallow groundwater salinity in the forested floodplain wetlands of the Loxahatchee River (Florida, USA), where altered watershed hydrology has led to changing hydroperiod and salinity regimes and undesired vegetative changes. Long-term, high-resolution groundwater salinity datasets revealed dynamics over seasonal and yearly time periods as well as over tidal cycles and storm events. DFA identified shared trends among salinity time series and a full dynamic factor model simulated observed series well (overall coefficient of efficiency, Ceff=0.85; 0.52≤Ceff≤0.99). A reduced multilinear model based solely on explanatory variables identified in the DFA had fair to good results (Ceff=0.58; 0.38≤Ceff≤0.75) and may be used to assess the effects of restoration and management scenarios on shallow groundwater salinity in the Loxahatchee River floodplain.