Department of Geography

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Browsing Department of Geography by Author "Alvarez, Miguel"

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    Classification, Characterisation, and Use of Small Wetlands in East Africa
    (Springer Link, 2011) Sakana, Naomi; Alvarez, Miguel; Becker, M.; Boehme, Beate; Handa, Collins; Kamiri, Wangechi; Langensiepen, Matthias; Menz, Gunter; Misana, Salome B.; Mogha, Neema G.; Möseler, Bodo M.; Mwita, Emiliana J.; Oyieke, Helida; Van Wijk, Mark
    Small wetlands in Kenya and Tanzania cover about 12 million ha and are increasingly converted for agricultural production. There is a need to provide guide-lines for their future protection or use, requiring their systematic classification and characterisation. Fifty-one wetlands were inventoried in 2008 in four contrasting sites, covering a surveyed total area of 484 km 2 . Each wetland was subdivided into sub-units of 0.5–458 ha based on the predominant land use. The biophysical and socio-economic attributes of the resulting 157 wetland sub-units were determined. The wetland sub-units were categorized using multivariate analyses into five major cluster groups. The main wetland categories comprised: (1) narrow permanent-ly flooded inland valleys that are largely unused; (2) wide permanently flooded inland valleys and highlands flood-plains under extensive use; (3) large inland valleys and lowland floodplains with seasonal flooding under medium use intensity; (4) completely drained wide inland valleys and highlands floodplains under intensive food crop production; and (5) narrow drained inland valleys under permanent horticultural production. The wetland types were associated with specific vegetation forms and soil attributes.
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    Floristic Classification of the Vegetation in Small Wetlands of Kenya and Tanzania
    (2012) Alvarez, Miguel; Becker, M.; Boehme, Beate; Handa, Collins; Josko, Matthias; Kamiri, Hellen W.; Langensiepen, Matthias; Menz, Gunter; Misana, Salome B.; Mogha, Neema G.; Möseler, Bodo M.; Mwita, Emiliana J.; Oyieke, Helida A.; Sakané, Nomé
    Small wetlands in East Africa are increasingly converted into sites for agricultural production. The resulting changes in land use and cropping systems will impact on the wetlands’ vegetation. We characterized the plant communities in four wetlands of Kenya and Tanzania, each comprising four types of land use differentiated by the degree of anthropogenic disturbance (cropland, fallow, grazing land and unused). Since no syntaxonomical scheme was available as a reference, a first classification of vegetation units and the identification of diagnostic species is proposed. We collected 207 relevés in the representative wetlands in relation to the current land uses. The plant communities were determined using a modified TWINSPAN classification. For each vegetation unit, diagnostic species were selected according to their fidelity index (phi coefficient). Floristic relationships between vegetation units were surveyed by nMDS ordination analyses. We identified 15 plant communities and selected 147 diagnostic species. The communities were differentiated into (1) semi-natural wetland vegetation (associated with less disturbed environments), (2) grassland and fallow vegetation, and (3) weed communities (associated with eu-hemerobic, drained and cultivated cropland). While the semi-natural vegetation was distinctly matched with unused fields, the differential matching of the other plant communities with land use types was less clear. According to the floristic similarity, the weed communities associated with cropland tended to be aggregated in the nMDS configuration while the semi-natural vegetation was dispersed. The results of the ordination did not differ when involving all species or only the selected diagnostic ones. As the plant communities described are rankless syntaxa, the establishment of a comprehensive syntaxonomic classification for African wetlands will require further vegetation surveys as well as their comparison with published data.
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    Seasonal Vegetation Changes in the Malinda Wetland Using Bi-Temporal, Multi-Sensor, Very High Resolution Remote Sensing Data Sets
    (Scientific Research, 2014) Kuria, David N.; Menz, Gunter; Misana, Salome B.; Mwita, Emiliana; Thamm, Hans P.; Alvarez, Miguel; Mogha, Neema; Becker, M.; Oyieke, Helida
    Small wetlands in East Africa have grown in prominence driven by the unreliable and diminished rains and the increasing population pressure. Due to their size (less than 500 Ha), these wetlands have not been studied extensively using satellite remote sensing approaches. High spatial resolu- tion remote sensing approaches overcome this limitation allowing detailed inventorying and re- search on such small wetlands. For understanding the seasonal variations in land cover within the Malinda Wetland in Tanzania (350 Ha), two periods were considered, May 2012 coinciding with the wet period (rainy season) and August 2012 coinciding with a fairly rain depressed period (substantially dry but generally cooler season). The wetland was studied using very high spatial resolution orthophotos derived from Unmanned Aerial Vehicle (UAV) photography fused with TerraSAR-X Spotlight mode dual polarized radar data. Using these fused datasets, five main classes were identified that were used to firstly delineate seasonal changes in land use activities and secondly used in determining phenology changes. Combining fuzzy maximum likelihood clas- sification, knowledge classifier and Change Vector Analysis (CVA), land cover classification was undertaken for both seasons. From the results, manifold anthropogenic activities are taking place between the seasons as evidenced by the high conversion rates (63.01 Ha). The phenological change was also highest within the human influence class due to the growing process of cropped land (26.60 Ha). Much of the changes in both cover and phenology are occurring in the mid upper portion of the wetland, attributed to the presence of springs in this portion of the wetland along the banks of River Mkomazi. There is thus seasonality in the observed anthropogenic influence between the wetland and its periphery.
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    Seasonal Vegetation Changes in the Malinda Wetland Using Bi-Temporal, Multi-Sensor, Very High Resolution Remote Sensing Data Sets
    (2014-03) Kuria, David N.; Menz, Gunter; Misana, Salome; Mwita, Emiliana; Thamm, Hans P.; Alvarez, Miguel; Mogha, Neema; Becker, M.; Oyieke, Helida
    Small wetlands in East Africa have grown in prominence driven by the unreliable and diminished rains and the increasing population pressure. Due to their size (less than 500 Ha), these wetlands have not been studied extensively using satellite remote sensing approaches. High spatial resolu-tion remote sensing approaches overcome this limitation allowing detailed inventorying and re-search on such small wetlands. For understanding the seasonal variations in land cover within the Malinda Wetland in Tanzania (350 Ha), two periods were considered, May 2012 coinciding with the wet period (rainy season) and August 2012 coinciding with a fairly rain depressed period (substantially dry but generally cooler season). The wetland was studied using very high spatial resolution orthophotos derived from Unmanned Aerial Vehicle (UAV) photography fused with TerraSAR-X Spotlight mode dual polarized radar data. Using these fused datasets, five main classes were identified that were used to firstly delineate seasonal changes in land use activities and secondly used in determining phenology changes. Combining fuzzy maximum likelihood classification, knowledge classifier and Change Vector Analysis (CVA), land cover classification was undertaken for both seasons. From the results, manifold anthropogenic activities are taking place between the seasons as evidenced by the high conversion rates (63.01 Ha). The phenological change was also highest within the human influence class due to the growing process of cropped land (26.60 Ha). Much of the changes in both cover and phenology are occurring in the mid upper portion of the wetland, attributed to the presence of springs in this portion of the wetland along the banks of River Mkomazi. There is thus seasonality in the observed anthropogenic influence between the wetland and its periphery.
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    SWEA-Dataveg – Vegetation of Small Eetlands in East Africa
    (2015) Alvarez, Miguel; Möseler, Bodo M.; Josko, Matthias; Becker, M.; Langensiepen, Matthias; Menz, Gunter; Boehme, Beate; Oyieke, Helida; Handa, Collins; Kamiri, Wangechi; Misana, Salome B.; Mwita, Emiliana J.; Mogha, Neema G.; Sakana, Naomi
    SWEA (agricultural use and vulnerability of small wetlands in East Africa) is a multidisciplinary project which task is to evaluate the effects of land use on the ecological and socio-economical functions of small wetlands in Kenya and Tanzania. In order to allow the availability of the collected data for further studies we stored them into SWEA-Dataveg (GIVD ID AF-00-006), a database stored in Microsoft Access (mdb-format). Because this project is dealing not only with vegetation science but also with geography, soil science, hydrology and socio-economy, the database also contains information related to these research fields. Additionally, some functional traits of the plant species occurring in the relevés are included in the species list. The sampling areas are concentrated in four localities, two of them in Kenya (Karatina and Rumuruti) and two in Tanzania (Malinda and Lukozi). The vegetation ecology group is dealing in the project with the classification of the vegetation according to species composition, the correlation of plant communities with environmental factors and land uses, and the survey of potential indicator species for the determination of the resilience of wetlands. Once finished the storage, we are considering an adaptation of SWEA-Dataveg into a TURBOVEG-format as well as its extension to further projects (e.g. SWEA phase II) and relevés collected from publications.