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Salicaceen, insbesondere verschiedene Salix-Arten und ihre Hybride, sind weltweit typische Invasoren von Flusssystemen und können schwerwiegende Folgen für heimische Ökosysteme hervorrufen. An den Flüssen Patagoniens nehmen Weichholzauwälder, die von invasiven Salicaceen dominiert werden, an Häufigkeit, Fläche und Artenvielfalt deutlich zu. So beobachtet man entlang des Río Negro in Nordpatagonien eine Invasion verschiedener holziger Pflanzenarten, die in den letzten Jahrzehnten dramatisch angestiegen ist. Dominant hierbei sind die Weiden des Salix alba L. - Salix fragilis L. Komplex, ein Hybrid dieses Komplexes und Salix babylonica L. und Populus spp. Zusätzlich breiten sich in letzten den Jahren Elaeagnus angustifolia Willd. und Tamarix spp. aggressiv aus. Die vorliegende Doktorarbeit liefert Daten zu möglichen Auswirkungen dieser Invasion auf Salix humboldtiana Willd., die einzige heimische Baumart am Río Negro. Vegetative Reproduktion spielt besonders für Salix fragilis und ihre Hybride eine wichtige Rolle bei der Besiedelung neuer Habitate und ist wohl der wichtigste Grund für ihre erfolgreiche Invasion. Diese Hypothese wurde in der ersten Untersuchungsreihe in einem Gewächshausversuch zur vegetativen Reproduktionsfähigkeit der heimischen Weidenart (S. humboldtiana) und der invasiven Salicaceen (S. × rubens, ein S. babylonica Hybrid und Populus spec.) unter verschiedenen Gradienten der Bodenbeschaffenheit und Feuchte getestet (Chapter 2). Beide invasive Weidenhybride zeigten eine bessere Wiederaustriebsfähigkeit und wuchsen signifikant besser als S. humboldtiana und Populus spec. Sie hatten mehr lebende Stecklinge sowie mehr und längere Triebe unter allen getesteten Bedingungen und bildeten mehr Biomasse (über- und unterirdisch) aus. Nach Entfernung der gebildeten Biomasse von den Stecklinge wurde in einem nachfolgenden Experiment die Wiederaustriebsfähigkeit dieser Stecklinge gemessen. Erneut hatten die Stecklinge der invasiven Weiden eine bessere Austriebsfähigkeit und Wachstumsperformance. Diese Ergebnisse zeigen, dass invasive Weiden eine erfolgreichere vegetative Reproduktion als die heimische Weidenart haben und ein höheres Potenzial für ein Wiederaustreiben nach Störungen besitzen. Diese Eigenschaften scheinen ein zentraler Faktor für ihre erfolgreiche Invasion zu sein stellen gleichzeitig eine mögliche Bedrohung für S. humboldtiana durch Verdrängung dar. In einer weiteren Untersuchung wurden Analysen der Altersstruktur und Wachstumsperformance in gemischten adulten Waldbeständen auf Flussinseln durchgeführt (Chapter 3). Die ausgewerteten 20 Bestände hatten ein relativ geringes, aber einheitliches Alter (im Mittel < 15 Jahre), was auf gemeinsame Etablierungsereignisse aller erfassten Arten weist. Die Analyse der Wachstumsperformance (Grundfläche, Baumhöhe, Kronendurchmesser, Kronenansatzhöhe) in adulten Beständen zeigte, dass invasive Weiden und Pappeln durch ihre Konkurrenzstärke in der Lage sind, die heimische S. humboldtiana aktiv zu verdrängen: Im adulten Stadium besaßen die invasiven Weiden beispielsweise deutlich größere Grundflächen und Kronendurchmesser. Adulte S. humboldtiana konnte häufiger am mittleren Flusslauf nachgewiesen werden, während die invasiven Weidenhybride am Flussoberlauf häufiger waren. Dies deutet auf einen flussabwärts gerichteten Invasionsprozess hin. Um das Kokurrenzpotenzial von invasiven holzigen Arten (Salicaceen, Elaeagnus, Tamarix) gegenüber S. humboldtiana zu ermitteln, wurden Habitatmodelle für unterschiedliche Altersklassen (Keimlinge, junge und alte Vegetation) entwickelt (Chapter 4). Dabei sollten die ökologischen Nischen und Zusammenhänge zwischen Artvorkommen und abiotischen Bedingungen (z.B. Überflutungsdauer, durchschnittlicher Wasserstand, Strömungsstärke) identifiziert werden. Daten zu den Arten (Vorkommen/ Nichtvorkommen) und erklärenden Umweltvariablen wurden mit einem stratifiziert-randomisierten Stichprobendesign auf 167 Plots gesammelt. Die Umweltvariablen Überflutungsdauer, Kiesanteil und Ort (Ober- bzw. Mittellauf) konnten am besten das Vorkommen der Arten beschreiben. Für alle Altersklassen ergab sich eine starke Nischenüberlappung der invasiven Arten, insbesondere der nicht-heimischen Salicaceen, mit S. humboldtiana. Auf keinen Standorten konnte ausschließlich S. humboldtiana nachgewiesen werden. Zusätzlich wurden multispektrale Satellitenbilder des Flussoberlaufes aus den Jahren 1986 und 2003 ausgewertet (Chapter 5). Daraus geht hervor, dass in dieser Zeitspanne Weichholzauwälder ihre Verbreitung um fast 150% ausdehnten, was höchstwahrscheinlich an einer explosionsartigen Verbreitung der nicht-heimischen Arten lag. Die Ergebnisse dieser Doktorarbeit können wie folgt zusammengefasst werden: Invasive Weiden haben eine signifikant bessere vegetative Reproduktion und Wiederaustriebsfähigkeit und eine bessere Performance im adulten Stadium als die heimische Weidenart sowie eine starke Nischenüberlappung mit dieser. Diese Ergebnisse verdeutlichen das hohe Konkurrenzpotenzial von invasiven Salicaceen und eine daraus resultierende mögliche Unterdrückung und Verdrängung von S. humboldtiana., 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

The flood of 2000 caused extensive changes within the riparian landscape of the Sabie River, Kruger National Park (KNP). Changes within the riparian landscape and the removal of vegetation resulted in considerable changes in riparian vegetation characteristics. Open patches created by the flood served as a template for the establishment of new species and the regeneration of existing species, which consequently resulted in a patch mosaic. This memorable event encouraged an investigation into the response of the Sabie River ecosystem to the memorable Large Infrequent Disturbance (LID). Riparian ecosystems are driven by varying combinations of environmental factors, such as water availability, disturbance, herbivory, fire and river morphology. This complexity depicts unique vegetation structure and assemblages of associated plant species. The lack of sufficient knowledge on the role of riparian vegetation in the health assessment of surrounding ecosystems along semi-arid rivers prompted the establishment of the Kruger Rivers Post Flood Research Program (KRPFRP). Research conducted through this monitoring program four years after the 2000 flood, revealed no significant changes in the species composition, although the location and density of many common riparian species have been changed. There was a decrease in species density across the macro channel floor (MCF) and an increase in species density across the macro channel bank (MCB). Furthermore, it was reported that the flood altered the distribution of height classes across the macro channel. In general the riparian vegetation was shorter and bushier four years post-flood. These studies furthermore illustrated that the tree to shrub ratio did not change drastically from pre-flood conditions, although a decrease in the number of shrub individuals was reported. The research presented in this dissertation was designed to further explore changes in woody species composition and structure along the Sabie River, KNP at a post flood temporal interval, i.e. between the last survey in 2004 (by the KRPFRP) and 2010. For data compatibility, the sampling and analytical approach of this study conforms to the approach followed by the KRPFRP. Data were sampled within four preselected belt-transects that form part of the larger KRPFRP. All established woody individuals were counted and measured within each contiguous 10 m x 30 m plot within each of the four belt-transects. Log transformed species composition data were analysed through the application of the Bray Curtis dissimilarity index in combination with Ward’s method of clustering. Statistical significant differences between clusters were tested through the application of the Fisher’s exact relationship test. The MIXED Procedure or PROC MIXED model was used to investigate change within the vegetation structural data. Results obtained through the various analytical methods broadly support the findings of the KRPFRP. No significant change in woody species composition could be detected between 2004 and 2010. However, a change in the density (increase and decrease) of certain species across the MCB and MCF was revealed. Species richness and density increased significantly on the MCF oppose to small changes on the MCB. A significant increase in the total number of shrubs on the MCF contributed to an overall increase in woody density for the entire study area between 2004 and 2010. Shrubs therefore remained the most dominant growth form in both sampling years. Trees decreased across the MCB although the total number of established trees remained unchanged between 2004 and 2010. Riparian vegetation structure is directly linked to species assemblages, hence the continued dominance of shrub species along the Sabie River in the KNP The Sabie River riparian landscape is therefore still characterised by short and multi-stemmed woody individuals ten years after the LID. Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013

Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013 The flood of 2000 caused extensive changes within the riparian landscape of the Sabie River, Kruger National Park (KNP). Changes within the riparian landscape and the removal of vegetation resulted in considerable changes in riparian vegetation characteristics. Open patches created by the flood served as a template for the establishment of new species and the regeneration of existing species, which consequently resulted in a patch mosaic. This memorable event encouraged an investigation into the response of the Sabie River ecosystem to the memorable Large Infrequent Disturbance (LID). Riparian ecosystems are driven by varying combinations of environmental factors, such as water availability, disturbance, herbivory, fire and river morphology. This complexity depicts unique vegetation structure and assemblages of associated plant species. The lack of sufficient knowledge on the role of riparian vegetation in the health assessment of surrounding ecosystems along semi-arid rivers prompted the establishment of the Kruger Rivers Post Flood Research Program (KRPFRP). Research conducted through this monitoring program four years after the 2000 flood, revealed no significant changes in the species composition, although the location and density of many common riparian species have been changed. There was a decrease in species density across the macro channel floor (MCF) and an increase in species density across the macro channel bank (MCB). Furthermore, it was reported that the flood altered the distribution of height classes across the macro channel. In general the riparian vegetation was shorter and bushier four years post-flood. These studies furthermore illustrated that the tree to shrub ratio did not change drastically from pre-flood conditions, although a decrease in the number of shrub individuals was reported. The research presented in this dissertation was designed to further explore changes in woody species composition and structure along the Sabie River, KNP at a post flood temporal interval, i.e. between the last survey in 2004 (by the KRPFRP) and 2010. For data compatibility, the sampling and analytical approach of this study conforms to the approach followed by the KRPFRP. Data were sampled within four preselected belt-transects that form part of the larger KRPFRP. All established woody individuals were counted and measured within each contiguous 10 m x 30 m plot within each of the four belt-transects. Log transformed species composition data were analysed through the application of the Bray Curtis dissimilarity index in combination with Ward’s method of clustering. Statistical significant differences between clusters were tested through the application of the Fisher’s exact relationship test. The MIXED Procedure or PROC MIXED model was used to investigate change within the vegetation structural data. Results obtained through the various analytical methods broadly support the findings of the KRPFRP. No significant change in woody species composition could be detected between 2004 and 2010. However, a change in the density (increase and decrease) of certain species across the MCB and MCF was revealed. Species richness and density increased significantly on the MCF oppose to small changes on the MCB. A significant increase in the total number of shrubs on the MCF contributed to an overall increase in woody density for the entire study area between 2004 and 2010. Shrubs therefore remained the most dominant growth form in both sampling years. Trees decreased across the MCB although the total number of established trees remained unchanged between 2004 and 2010. Riparian vegetation structure is directly linked to species assemblages, hence the continued dominance of shrub species along the Sabie River in the KNP The Sabie River riparian landscape is therefore still characterised by short and multi-stemmed woody individuals ten years after the LID. Masters

Riparian areas are among the most threatened habitats in the world, due to human activities and land use in adjacent areas. In this study we sought to identify landscape metrics for describing the spatial patterns of riparian vegetation affected by land use. We also hypothesize that land use in the immediate vicinity of the riparian area (considered as a 30-m buffer) can have a greater effect on the structure of riparian vegetation than that in an enlarged buffer (i.e. 200 m). The study was conducted in the highly humanized River Tagus watershed (Central Portugal; Western Iberia), along over 80km of river stretches. Riparian vegetation and land use data were obtained from high-resolution digital images (RGB-NIR 0.5m×0.5 m, spring 2005). Patch analyst was used to calculate landscape metrics related to the spatial configuration, isolation, inter-connectivity, and distribution of patches of three riparian cover classes (tree, shrub, and herbaceous). We quantified and accounted for the global and local spatial autocorrelation of data. Data treatment included redundancy analysis and geostatistic methods. Results showed that only a combined interpretation of various landscape metrics can consistently describe the spatial patterns of riparian vegetation. Riparian vegetation near agricultural areas (irrigation crops, rice fields, orchards, and vineyards), presented a low number of much smaller riparian tree patches with less complex shapes, and a low interspersion of the patch distribution. We found that proximal land use affects the structure of riparian vegetation more than distal land use – an important consideration for the establishment of streamside protection buffers info:eu-repo/semantics/publishedVersion

Mestrado em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia Submitted by Margarida Galamba (galamba@isa.utl.pt) on 2009-07-10T13:29:16Z No. of bitstreams: 1 Tese Mestrado.pdf: 382803 bytes, checksum: 30e3cf1d4d227570197632c888b838fe (MD5) Made available in DSpace on 2009-07-10T13:29:16Z (GMT). No. of bitstreams: 1 Tese Mestrado.pdf: 382803 bytes, checksum: 30e3cf1d4d227570197632c888b838fe (MD5)

Mestrado em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia The present work aims to identify potential landscape metrics that best describe and quantify the riparian structure and evaluate its response to land use pressure. The study was conducted in four rivers of the Tagus fluvial system Data was achieved from the on-screen photo interpretation of airborne digital images. Eight landscape metrics related with the spatial configuration, isolation, inter-connectivity and distribution of riparian vegetation were calculated for the tree, shrub and herbaceous strata. The influence of proximal and distal land use (30 m and 200 m buffers, respectively) in the riparian structure was analysed using redundancy analysis. Geostatistical analysis were used to describe and incorporate the spatial component of the data and to assess the spatial autocorrelation of the riparian structure. The results showed that the combined interpretation of metric values can consistently describe the patterns of riparian structure especially for the tree cover class. Disturbed riparian woods due to major land use pressure, such as agriculture, presented a low number of small patches with simple and homogenous shapes, reduced patch connectivity and a non interspersed patch distribution. Also it is shown that the proximal land use is more determinant in shaping within-stand riparian structure, therefore protection areas should both envelop riparian zones and an adjacent buffer.

Aim Local communities are subject to spatiotemporal contingencies of landscape processes; community assembly is thus often considered to be unpredictable and idiosyncratic. However, evolved trade-offs of species' life histories may set distinct constraints on the assembly of species communities. In plants, the recruitment and invasion success of species into communities depend primarily on the number of propagules available and on their generative or vegetative character. Life-history trade-offs prevent individual plants from producing large numbers of both generative and vegetative propagules, but it is not clear whether this constrains their availability at the landscape scale. We thus tested whether: (1) the observed relationship between generative and vegetative propagules deviates from the null expectation stating that species contributing the bulk of generative propagules to the propagule rain should also contribute the bulk of vegetative propagules; and (2) whether vegetative and generative propagule pressures are negatively correlated once species abundance in the regional pool is accounted for.Location A large riparian landscape in the Netherlands.Methods Analyses were based on an extensive trapping of floating propagules (214,049 propagules of 47 species), and a rough proxy of species abundance across the entire pool. We used both species and phylogenetically independent contrasts as data points, and accounted for variation in size of generative propagules.Results Both hypotheses were confirmed. Numbers of generative and vegetative propagules trapped per species were significantly negatively correlated (r = -0.33; t(45) = -2.61, P = 0.006) and thus strongly deviated from the null expectation. This was confirmed by analyses accounting for variation in species abundance across the species pool, and in the size of generative propagules.Main conclusions The results indicate that plant recruitment and community assembly across streams may be influenced by the way individual plants allocate their resources between competing life-history functions. Life-history evolution across angiosperms might thus have constrained the present-day assembly of local communities.