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The exploitation of non-timber forest products has been encouraged in order to reconcile economic uses, biodiversity conservation and the provision of ecosystem services. In this paper we investigate how increments on the açaí palm density (Euterpe oleracea) via forest management change tree assemblages across 47 plots in the Amazon estuarine forest (Brazil). Assemblage attributes were confronted to açai clump density, soil fertility, canopy openness and elevation. Both tree species density and richness were negatively affected by acai, but species richness was also affected by tree abundance. Species-accumulation curves also indicated higher alpha and beta diversity across low-intensity forest patches with high-intensity patches lacking half of the tree species. A small set of species dominated forest patches, but açaí density did not correlate with the abundance of valuable species. Explanatory variables, including açai density, explained a small fraction of the variation on the functional profile of tree assemblages, but functional richness was reduced by a half across forest stands exceeding 600 açaí clumps per ha. Our results suggest that açaí intensification alters the structure of woody plant assemblages in estuarine forest. Tree abundance and species richness consistently declines as açaí clump density increases, with some forest stands being dominated by açaí and almost lacking any tree species. Accordingly, landscapes dominated by high-intensity forest stands are largely impoverished in terms of understory, canopy and emergent tree species. These findings question the current legal regulations and thresholds adopted for açai management, while alert for potential disasters caused by poorly-regulated extractions of NTFPs. • Açaí intensification for enhancing fruit yield represents a complete reorganization of the estuarine forest. • Landscapes dominated by high-intensity forest stands are largely impoverished in terms of understory, canopy and emergent tree species. • Current legal regulations on açaí intensification fail to protect forest integrity and biodiversity. • Açaí represents a key economic opportunity for locals but a real threat for the estuarine forest. [ABSTRACT FROM AUTHOR]

Introduced pathogen microorganisms are important drivers of ecosystem change. This paper highlights the impact of the non-native pathogen mildew multi-species complex on the natural regeneration dynamics of pedunculate oak (Quercus robur). Pedunculate oak is a European keystone tree species, hosting a great amount of biodiversity, but its future role in (near-)natural forests is uncertain due to the lack of natural regeneration. We reviewed historical and recent ecological, pathological and forestry literature on topics related to the impact of mildew on the success of advanced natural regeneration of pedunculate oak in (near-)natural forests. We propose a novel hypothesis, the 'pathogen mildew hypothesis', to explain the failure of natural regeneration of pedunculate oak. Mildew reduces shade tolerance and vertical growth in seedlings and saplings, so sapling vitality and competitiveness have diminished considerably since it was unintentionally introduced to Europe in the early 20th century. Due to mildew infection, pedunculate oak in many cases no longer regenerates well naturally under its own canopy. We found that forest ecologists and conservationists often overlook the impacts of this 'recent' driver, while the 'closed-forest' and 'wood-pasture' hypotheses do not adequately help the management of pedunculate oak regeneration. Nature conservation and forest management plans should thus also consider the impact of mildew in order to improve natural regeneration, promote close-to-nature management of pedunculate oak forests, and support associated diversity. More generally, nature conservation, forest ecology and close-to-nature forestry should pay greater attention to the impact of introduced non-native microorganisms on the dynamics of natural ecosystems. Unlabelled Image • Ecologists and conservationists often overlook the impacts of alien microorganisms. • An alien microfungus impedes natural regeneration dynamics of a keystone species • Oak powdery mildew reduces shade tolerance and growth in seedlings and saplings. • Proposed hypothesis explains the failure of natural regeneration of pedunculate oak. • The alien microfungus threatens the rich biodiversity associated with oaks in Europe. [ABSTRACT FROM AUTHOR]