Invasion by exotic trees into riparian areas has the potential to impact aquatic systems. We examined the effects of the exotic Salix fragilis (crack willow) on the structure and functioning of small streams in northern Patagonian Andes via a field survey of benthic invertebrates and leaf litter and an in situ experiment. We compared leaf decomposition of the native Ochetophila trinervis (chacay) and S. fragilis in reaches dominated by native vegetation versus reaches dominated by crack willow. We hypothesized that S. fragilis affects the quality of leaf litter entering the streams, changing the aquatic biota composition and litter decomposition. Our study showed that crack willow leaves decomposed slower than chacay, likely related to leaf properties (i.e., leaf toughness). Benthic leaf litter mass was similar between the two riparian vegetation types, though in stream reaches dominated by crack willow, leaves of this species represented 82% of the total leaf litter. Benthic invertebrate abundance and diversity were similar between reaches but species composition differed. Our study found little evidence for strong impacts of crack willow on those small streams. Further studies on other aspects of ecosystem functioning, such as primary production, would enhance our understanding of the impacts of crack willow on Patagonian streams.

Lakes are ideal sites to study environmental changes since they preserve climatic, anthropogenic, and volcanic signals in their sediments. Brazo Blest is one of the most important ramifications of lake Nahuel Huapi and it is an interesting site to study climatic variations as it receives direct discharge of heavy suspended sediments loads from Tronador Glacier through River Frías, as a result of the abrasion of the bedrock, and the runoff from the surrounding Valdivian forest. A short sediment core from Brazo Blest was analyzed for chironomids and diatoms assemblages and pigments in order to reconstruct environmental changes during the last 100 years in the basin under study This multiproxy study also included geochemical and physical analysis and reveals changes in the productivity of the lake over time, showing a shift in 1950s AD from autochthonous to allochthonous organic matter. This modification is related to precipitation changes, and the consequent fluvial runoff from two catchments, River Frías and the Blest-Cántaros basin together with the effects of-rising temperatures, which affected Tronador Glacier. Further, it allows us to link volcanic eruptions to a decrease in the species richness and number of chironomid and diatoms, as a consequence of the reduced light intensities and food availability induced by the high content of suspended sediments in the water column,. This study highlights the effectiveness of multiproxy analyses to reconstruct environmental changes.

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BACKGROUND Understanding the factors that promote the success of invasive species is important for managing biological invasions. Interactions between invasives and other species (e.g. competitors, pathogens, or predators), could favor or limit their success. In recent decades, yellowjacket wasps, including Vespula germanica and Vespula vulgaris, have successfully established in Patagonia. Additionally, the invasive willow Salix fragilis has invaded areas next to watercourses, which in turn are typically colonized by the giant willow aphid (GWA, Tuberolagnus salignus), an additional species characterized as a successful invader in many regions worldwide. Aphid exudate (honeydew) has been reported to be used as a carbohydrate source by social wasps. The aim of our study was to gain a better understanding of the infestation pattern of the GWA in north‐western Patagonia, its effect on exudate availability and its relationship with yellowjacket foraging patterns. The study was conducted under the working hypothesis that the increase in the size of GWA colonies and resulting honeydew production, will fuel an increase in local Vespula spp. populations. RESULTS We found that the aphid honeydew is produced in relatively high amounts in the region (estimated at 1517 ± 139 kg/ha/season), with strong indications that it is used by yellowjackets because of the significantly higher abundance levels of yellowjackets foraging on honeydew compared to nearby areas. CONCLUSION Given its effect on yellowjacket foraging behavior, the interaction of these three invasive species, willows, GWA and yellowjackets, needs to receive special attention to develop future environmentally‐sound mitigation tools of these nuisance pest. © 2023 Society of Chemical Industry.