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In wetland environments, vegetation has an important role in ecological functioning. The main goal of this work is 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 macrophytes 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.

The assessment of invasive terrestrial plant species in the Romanian protected areas is an important research direction, especially since the adventive species have become biological hazards with significant impacts on biodiversity. Due to limited resources being available for the control of the invasive plants, the modelling of the spatial potential distribution is particularly useful in order to find the best measures to eliminate them or prevent their introduction and spread, as well as including them in the management plans of protected areas. Thus, the present paper aims to assess one of the most disturbing invasive terrestrial plant species in Europe – A.fruticosa in one of the most important natural protected area in Romania, i.e. Mureş Floodplain Natural Park (V IUCN category and RAMSAR –Wetlands of International Importance). The current study is a geographical approach seeking to explain the spatial relationships between this invasive species and several explanatory factors (soil type, depth to water, vegetation cover, forest fragmentation and distance to near waters, roads and settlements) and to assess its potential distribution by integrating GIS and logistic regression into spatial simulation. The resultant probability map can be used by the park’s administration in implementing the Management Plan in terms of identifying the areas with the highest occurrence potential of A.fruticosa according to the primary habitats and ecosystems and setting up actions for its eradication/limitation.

Geographical factors play an essential role in the occurrence and spread of invasive species worldwide, and their particular analysis at regional and local scales becomes important in understanding species development patterns. The present paper discusses the relationships between some key geographical factors and the Invasive Terrestrial Plant Species (ITPS) distribution, and their environmental implications in a few protected areas in Romania. The authors focused their attention on three of the foremost invaders (i.e. Amorpha fruticosa, Ailanthus altissima and Fallopia japonica) making use of the information provided by the scientific literature and some illustrative examples developed in the framework of the FP7 enviroGRIDS project. The study is aimed to increase the knowledge of the ITPS and, specifically, to contribute to the geographical understanding of the role played by the driving factors in their distribution and spread in various habitats and ecosystems. The results will further support the control efforts in protected areas where, often, valuable native species are at risk of being replaced by non-native species.

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