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Philipps-Universität Marburg (2015)

Ecological effects of willow and poplar invasions at the Río Negro in northern Patagonia, Argentina

Thomas, Lisa

Titre : Ecological effects of willow and poplar invasions at the Río Negro in northern Patagonia, Argentina

Auteur : Thomas, Lisa

Université de soutenance : Philipps-Universität Marburg

Grade : Doktorgrades der Naturwissenschaften (Dr. rer. nat.) 2015

Résumé partiel
Species of the Salicaceae family, particularly Salix species and their hybrids, are typical invaders of river systems throughout the world with severe consequences for native ecosystems. Along Patagonian streams, riparian softwood forests structured by dominant invasive Salicaceae are increasing significantly in abundance, area and species diversity. The region of the Río Negro in northern Patagonia has been invaded by several woody plant species with a dramatical increase in the recent decades. The most dominant taxa are willows of the Salix alba L. - Salix fragilis L. complex, a hybrid of this complex and Salix babylonica L. and Populus spp. Additionally, Elaeagnus angustifolia Willd. and Tamarix spp. have been spreading aggressively in recent years. This thesis provides information on the possible consequences of these invasions for Salix humboldtiana Willd., the only native woody species along the Río Negro, due to interspecific competition and invasion development. Vegetative reproduction is especially for S. fragilis and its hybrids of great importance for the colonisation of new habitats and probably is the most important reason for their invasion success. In the first study (Chapter 2), a greenhouse experiment was conducted in order to assess the vegetative reproduction capacities of native and invasive Salicaceae (S. humboldtiana, S. × rubens Schrank, a S. babylonica hybrid and Populus spec.) under various soil composition and moisture gradients. The invasive willow hybrids showed better vegetative re-sprouting capacities and performed sinificantly better than S. humboldtiana and Populus spec. They developed more living cuttings as well as more and longer sprouts under all treatment combinations and they generated significantly higher above- and belowground biomass. After completely removing the shoot and root biomass of the cuttings re-sprouting capacities were evaluated in a second experiment. Again, the invasive willows had a superior re-sprouting ability and growth performance. These results demonstrate that invasive willows are able to establish more successfully by vegetative reproduction than the native willow and that they have a higher re-sprouting potential after disturbances. This ability in combination with the advantages of vegetative reproduction compared to generative reproduction seems to be the key factor for invasive success and, simultaneously, a potential threat for S. humboldtiana through out-competition. In a further approach (Chapter 3), age structure analyses were carried out which revealed that mixed adult forest stands are the results of joint establishment events with all Salicaceae taxa involved. The analysed 20 stands on islands had low mean ages <15 years. Investigation on growth performance (basal area, crown diameter, tree hight and crown base hight) of adult stands revealed that non-native willows and poplars are able to actively displace the native S. humboldtiana by competitive strength :


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