In wetland environments, vegetation has an important role in ecological functioning. The main goal of this work was to identify an optimal combination of Sentinel-1 (S1), Sentinel-2 (S2), and Pleiades data using ground-reference data to accurately map wetland macrophytes in the Danube Delta. We tested several combinations of optical and Synthetic Aperture Radar (SAR) data rigorously at two levels. First, in order to reduce the confusion between reed (Phragmites australis (Cav.) Trin. ex Steud.) and other macrophyte communities, a time series analysis of S1 data was performed. The potential of S1 for detection of compact reed on plaur, compact reed on plaur/reed cut, open reed on plaur, pure reed, and reed on salinized soil was evaluated through time series of backscatter coefficient and coherence ratio images, calculated mainly according to the phenology of the reed. The analysis of backscattering coefficients allowed separation of reed classes that strongly overlapped. The coherence coefficient showed that C-band SAR repeat pass interferometric coherence for cut reed detection is feasible. In the second section, random forest (RF) classification was applied to the S2, Pleiades, and S1 data and in situ observations to discriminate and map reed against other aquatic macrophytes (submerged aquatic vegetation (SAV), emergent macrophytes, some floating broad-leaved and floating vegetation of delta lakes). In addition, different optical indices were included in the RF. A total of 67 classification models were made in several sensor combinations with two series of validation samples (with the reed and without reed) using both a simple and more detailed classification schema. The results showed that reed is completely discriminable compared to other macrophyte communities with all sensor combinations. In all combinations, the model-based producer’s accuracy (PA) and user’s accuracy (UA) for reed with both nomenclatures were over 90%. The diverse combinations of sensors were valuable for improving the overall classification accuracy of all of the communities of aquatic macrophytes except Myriophyllum spicatum L.

This paper presents the 2024 research results from the Danube Delta Biosphere Reserve (DDBR), including reed bed mapping and typology for fire management, assessment of sustainable use of vegetal resources, conservation status of invertebrates, fish, reptiles, amphibians, colonial waterbirds, and mammals of Community interest, evaluation of species invasiveness under climate change, and studies on human well-being and ecotourism within a sustainable development framework.

The palatability of a plant refers to the degree of attraction or preference that animals show toward that particular plant. Various factors can influence palatability, including the plant’s chemical composition, texture, taste, aromas, and the circumstances under which herbivorous animals consume it. The study aims to assess the plant species composition in grasslands and pastures within the Danube Delta, Romania. Both old or new references on palatability were considered. The evaluation of plant composition and degree of plant palatability was carried out in 12 grazing areas in the Danube Delta and the surrounding region. The study revealed 121 plant species identified in some pastures. Of these, 31 were “Non-Palatable”, 16 were “Highly Palatable”, 32 were “Mostly Palatable”, 16 were “Less Palatable”, and 26 were “Rarely Palatable”. Animals preferred 60 plant species in their fresh condition, with 29 preferred in fresh and dry. Most animals consumed whole plants (48 species), followed by leaves (43 species), fruits (three species), and inflorescences (two species). By analysing the feeding preferences of animals, it was found that cows exhibited a preference for the broadest range of plants (75 species), followed by sheep (67 species), goats (59 species), and horses (34 species). Domestic animals like goats, sheep, cows, and horses may prefer certain plants based on nutritional content or digestibility while avoiding toxic plants. The study showed that the investigated areas have a diverse flora with a varied supply of plants, including palatable species. The palatability index is essential in assessing the quality of pastures, especially in obtaining average daily gains based on the species of animals living on the pastures. Considering the dynamic climatic conditions and poor pasture quality in the Danube Delta, more detailed and interdisciplinary studies are needed to understand the deltaic biocenoses comprehensively.

Aldrovanda vesiculosa is an endangered aquatic species in Romania which grows in shallow waters where competition with other aquatic species is limited or absent. A comprehensive overview of the species’ distribution and habitat preferences in Romania is currently lacking. In this context, this study aimed to update the distribution and habitat preferences of the species. Localities from Dobrogea, Oltenia, Muntenia, Transylvania, and Crișana represented the study areas. For the vegetation classification, 71 releves with A. vesiculosa were analysed. The size of the sample areas ranged from 4 m2 to 25 m2. Vegetation syntaxonomic assignment was performed by agglomerative hierarchical clustering. The optimal number of clusters was chosen using the corrected Rand and Silhouette indices. Diagnostic species were identified for each cluster based on the indicator value index (IndVal). The study results showed that the dominant majority of the previous populations of A. vesiculosa (89%) were no longer identified from Romania in the 2008‒2021 period. Recently (2021‒2023), they were found only in six localities in the Dobrogea, Transylvania, and Oltenia regions. The causes of the disappearance of the species are eutrophication and the lowering of the water level. From a phytocoenological point of view, 11 plant communities were identified where A. vesiculosa is found. According to the EUNIS classification, this species inhabits wetlands (Q) and inland surface waters (C). In conclusion, translocation is suggested as the primary conservation measure for protecting the species.

New investigations on the flora, vegetation, and natural habitats of the Danube Delta (Romania) were recently carried out. Thus, more than 1,200 vascular plant species were inventoried, phytocoenoses of 253 plant communities, and 32 Natura 2000 habitats were recorded, all mapped on a large scale. As part of the reviewing process of the Standard Form of the Natura 2000 site ROSCI0065 Danube Delta - Romania, the natural habitats included within it were also revised. Thus, it was found that black alder forests were omitted, which was one the purposes of this work, namely to fill this gap. Following the recordings of all black alder forests in the Danube Delta, a phytocoenotaxon is proposed as new for science, namely Ass. Periploco graecae-Alnetum glutinosae ass. nov. The Natura 2000 habitat in the Danube Delta that include this newly proposed plant community is: 91E0* Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae).