A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirement for the degree of Masters of Science (GIS and Remote Sensing) at the School of Geography, Archaeology & Environmental Studies / Tamarix spp, commonly known as tamarisk or salt cedar, belong to the family of Tamaricaceae. It is a phreaphytic halophyte with 55 species in the genus Tamarix. South Africa has one indigenous (Tamarix usneoides) and two exotic (T. ramosissima and T.chinensis). Not only are the exotic Tamarix species becoming infamous invaders, but their hybridisation with the indigenous T. usneoides is also complicating morphological discrimination between the different species, and the prospect of potential use of bio-control agents to curb invasion. Thus, lack of spatial information about the current and the past distribution of tamarisk have hampered the effort to control its invasion. This study aimed at investigating the use of multi-temporal remotely sensed data to map the exotic Tamarix invasion in the riparian ecosystem of the Western Cape Province of South Africa, where it predominantly occurs. Random Forest (RF) and Support Vector Machine (SVM) were tested to classify Tamarix and other land-cover types. Sentinel 2 data and Landsat OLI earth observation data were used to map the current and the temporal exotic Tamarix distribution between 2007 and 2018, respectively. This included mapping the current and the multi-temporal Tamarix extent of invasion using the multi-spectral sensors Sentinel 2 and Landsat 5 and 8, respectively. Sentinel 2 was able to detect and discriminate the exotic Tamarix spp invasion using RF and SVM algorithms. The Random Forest classification achieved an overall accuracy of 87.83% and kappa of 0.85, while SVM achieved an overall accuracy of 86.31% and kappa of 0.83. Multi-temporal Landsat data was able to map the current and previous extent of exotic Tamarix invasion for the period between 2007 and 2018. Six land-cover types were classified using SVM. The overall accuracies achieved for 2007, 2014 and 2018 were 87.66%, 91.10%, and 90.62% respectively, and the kappa were 0.85, 0.89, and 0.88, respectively. It was found that the exotic Tamarix invasion increased from 284.67 ha to 647.10 ha in De Rust area, 74.70 ha to 97.29 ha in Leeu Gamka and 215.01 ha to 544.41 ha in Prince Albert region in a period of 11 years. Sentinel 2 and Landsat data have shown the potential to be used in Tamarix mapping. The results obtained in this study would help in implementation of conservation and rehabilitation plans. / GR 2020

Two studies on Catherine Creek and Meadow Creek of the Upper Grande Ronde River basin, quantified several physical and biotic influences on woody riparian community composition and structure. The Catherine Creek study examined the association of woody riparian species with elevational and geomorphic gradients. The Meadow Creek study examined the influence of mammal herbivory on composition and abundance of woody riparian species. At Catherine Creek, twenty nine plots were established at 50 m intervals of elevation from near the stream origin at 2207 m in the Wallowa Mountains to the foothills of the Grande Ronde Valley at 988 m. Woody plant community composition was associated with the dominant environmental variable, elevation. Distribution of dominant riparian species was strongly associated with fluvial surfaces. Black cottonwood (Populus balsamifera) was associated with gravel and cobble bars proximal to the stream channel, and along with ponderosa pine (Pinus ponderosa) was also associated with elevated boulder bars. Alders (A. incana and A. viridis) and willows (Salix bebbiana, S. boothii, S. exigua, S. lucida, S. melanopsis, S. prolixa, and S. sitchensis) were associated with annual floodplains. At Meadow Creek, grazing by cattle was ended in 1991 on the entire study reach and three deer and elk exclosures were built within the reach adjacent to the creek. Inside deer/elk exclosures from 1991 to 1995, mean heights of tagged cottonwoods, willows, and alders increased by 86% to 180%. Outside exclosures, mean heights of cottonwoods and alders increased 109% and 99% respectively, but willows showed little change in height. Both inside and outside of exclosures mean crown volume of cottonwoods increased over 1000% and mean crown volume of alders increased over 600%. Willow volume inside exclosures increased 376% in root sprouting (clonal) species and 528% in crown sprouting (non-clonal) species, while outside of exclosures volume increased 79% and 144% respectively. On both sides of exclosure fences, beaver herbivory had a significant effect on cottonwood height growth in 1994 and 1995, and on height and crown volume growth of willows in 1995. Over 50% of stem density increase on transects was attributable to expansion within two large clones of Salix melanopsis inside exclosures. Excluding these two clones, overall woody plant density increased by 72% from 3.7 plants per 100 m�� of transect in 1991 to 6.3 plants per 100 m�� of transect in 1995. / Graduation date: 1999