Thomas Janßen

Thomas Janßen
Humboldt-Universität zu Berlin | HU Berlin · Department of Biology

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36
Publications
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Publications

Publications (36)
Article
Full-text available
Plants, fungi and algae are important components of global biodiversity and are fundamental to all ecosystems. They are the basis for human well-being, providing food, materials and medicines. Specimens of all three groups of organisms are accommodated in herbaria, where they are commonly referred to as botanical specimens. The large number of spec...
Article
Questions: Which environmental variables influence grass diversity in West Africa? What are the effects of climate and grass functional traits on the spatial patterns (richness and abundance) of the grass clades Andropogoneae, Paniceae and Chloridoideae? Location: West Africa, demarcated by the Atlantic Ocean in the west and south (20° W and 4° N),...
Article
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ABSTRACT: Though the national Kahuzi-Biega Park be necessarily covered with a forest of well distinguished canopy; it also possesses disturbed areas. This work aims at studying the floristic composition of Ferns and Fern Allies to assess vegetation disturbances in the mountain forests (ranging from 1250 meters to 3000 meters) within the Kahuzi-Bieg...
Article
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Cette étude se focalise sur la vérification de l’hypothèse que l’altitude influence l’occurrence de la flore des Fougères et leurs alliées au sein de l’écosystème forestier des montagnes du Parc National de Kahuzi-Biega. Un échantillonnage de la végétation y a été effectué en considérant 24 parcelles localisées par paires le long de 12 transects in...
Article
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Grass savannas on lateritic crusts are characteristic landscape elements of the Sudanian savannas. In the W National Park and its surroundings in SE-Burkina Faso, plant diversity of savannas on and adjacent to bowé was assessed by a survey of 19 bowal areas with relevés along transects in each of these. The vegetation structure and species composit...
Article
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The West African Vegetation Database (http://www.westafricanvegetation.org; GIVD ID AF-00-001) is an online database that has been designed to securely store, edit and manage phytosociological and dendrometrical relevés from West Africa to provide data for research projects dealing with, but not limited to, plant communities, biogeography, populati...
Article
Full-text available
Cyatheaceae is represented by eight taxa (seven species and one doubtful variety) in Sri Lanka with a high rate of endemism of 75%. Apart from Cyathea walkerae and C. gigantea, the other species are restricted to geographically isolated areas in the country with limited population sizes. Fortunately, all Sri Lankan species of Cyathea occur within t...
Article
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Question: How can quantitative data from vegetation surveys best be assembled in a large regional vegetation database? What effects have intellectual property rights concerns of individual and institutional data holders on data contribution and how can incentives to contribute data be generated?Location: West Africa, with discussion of a possible a...
Article
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An overview is presented of available e-taxonomic products and ongoing projects contributing to Flora Malesiana. This is presented in the context of a strong plea to strengthen the implementation of state-of-the-art e-taxonomy tools to speed up the generation and publication of Flora Malesiana information.
Article
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Biological radiations, e.g., adaptive radiations and rapid radiations, are widely accepted as one of the major events contributing to the diversification of the tree of life, but many aspects of these events are poorly understood (Schluter 2000; Gavrilets and Losos 2009). The classical examples for biological radiations are adaptive radiations, in...
Article
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This study recorded evidence for three independent rapid radiations of scaly tree ferns in Madagascar. These three radiations happened in the late Cenozoic and were likely triggered by the fluctuations of the global climate. It is the first report for this kind of relationships of ferns diversity in the Madagascan biodiversity centre and climate ch...
Article
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Cyathea srilankensis Ranil, a new endemic Sri Lankan tree fern species, is described. It is characterized by large pinnate-pinnatisect leaves, sparse narrowly triangular petiole scales and caducous membranous indusia.
Article
Full-text available
Question: How can quantitative data from vegetation surveys best be assembled in a large regional vegetation database? What effects have intellectual property rights concerns of individual and institutional data holders on data contribution and how can incentives to contribute data be generated? Location: West Africa, with discussion of a possible...
Article
Full-text available
Cyathea sledgei Ranil, Pushpakumara & Fras.-Jenk. is a new tree-fern species from Sri Lanka, morphologically intermediate between C. sinuata Hook. & Grev. and C. hookeri Thwaites. It is easily recognised by its simple but deeply lobed leaves; each lobe has 8-10 pairs of forked veins and 6-9 pairs of sori. It was first recorded as a putative hybrid...
Poster
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Research on conservation and sustainable management of natural resources in West Africa depends on the availability of species occurrence data with good spatio-temporal coverage. Observation data is especially important in this context, because it is widely available in African research institutions and can complement rare species bias in collectio...
Poster
Full-text available
Introduction Poaceae is by far the most important plant family in the African Savanna regions which cover 65% of the continent. The family has been shown to be a good predictor of total plant diversity for the Sahelo-Sudanian region (Schmidt & al. 2007). In the course of studies on coevolution of savanna grasses and large herbivores, the distributi...
Article
The fern family Polypodiaceae plays an important role in Neotropical epiphyte diversity. Most of its American representatives are assembled in a monophyletic clade that, apart from the grammitids, nearly exclusively comprises species restricted to the New World. The phylogenetic relationships of these ferns are still insufficiently understood and m...
Poster
Full-text available
The West African Vegetation Database is an online database that has been designed to securely store, edit and manage phytosociological and dendrometrical relevés from West Africa to provide data for research projects dealing with, but not limited to, plant communities, biogeography, population structure, and vegetation dynamics.
Article
Phylogenetic relationships of the SE Asiatic genus Christiopteris were explored by comparative analysis of sequence variation of four chloroplast genome regions that were successfully used in previous phylogenetic studies of Polypodiaceae. This small genus is nested within the drynarioid ferns, as recovered with good support by each of the methods...
Article
More than 80% of Madagascar's 12,000 plant species are endemic with the degree of endemism reaching as much as 95% in the scaly tree ferns, an important species rich component of Madagascar's evergreen rainforests. Predominantly African or Asian ancestry and divergence times usually postdating the separation of Madagascar from the Gondwanan landmas...
Article
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Introduction. — Extensive field studies over many years, especially in the course of the international research projects BIOTA West Africa (www.biota-africa.org) and SUN (Sustain-able Use of Natural Vegetation, www.sunproject.dk) resulted not only in field data and observations, but also in numerous photographic documentations of research plots, ve...
Article
Based on the examination of herbarium specimens including numerous recent collections and on observations of most species in situ, we herein present a revision of the indusiate scaly tree ferns (Cyathea sect. Alsophila) for Madagascar, the Comoros and the Seychelles. One endemic species occurs on the Seychelles and three taxa (one endemic) are foun...
Article
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Although Africa harbors low species diversity compared to the neotropics or South East Asia, the African fern flora is of interest because of its specific composition and geographic location between the neotropics and Asia. We address the question of how the evolution of the African fern flora may have been enriched by repeated input from the neotr...
Article
A new revision of Cyathea sect. Gymnosphaera in Madagascar and the Comoros is proposed. Two new species, Cyathea impolita Rakotondr. & Janssen and C. rouhaniana Rakotondr. & Janssen, as well as a new variety, C. impolita var. michelii Rakotondr. & Janssen are described. As opposed to all other members of the section in the region, C. rouhaniana doe...
Article
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Historical biogeography of major monocot groups was investigated by biogeographical analysis of a dated phylogeny including 79 of the 81 monocot families using the Angiosperm Phylogeny Group II (APG II) classification. Five major areas were used to describe the family distributions: Eurasia, North America, South America, Africa including Madagascar...
Article
Full-text available
Based on the examination of herbarium specimens including numerous recent collections and on observations of the species in situ, we herein present a revision of the tree fern family Cyatheaceae for the Mascarene Islands. Three taxa are accepted for Réunion, two of which are endemic to the island. Four taxa, including one endemic species and two en...
Article
Ferns with a tree habit are mainly found in the families Cyatheaceae and Dicksoniaceae. Together, they constitute a diverse pantropical group of common to locally dominant elements of tropical floras, especially in montane forests. Many species have very restricted distribution ranges and some are highly threatened. Taxonomic understanding of these...
Article
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Most species of the paleotropic fern genera Aglaomorpha and Drynaria, together constituting a monophyletic clade (drynarioid ferns), possess humus-collecting structures as an adaptation to their epiphytic life form. Humus-collectors are either present as a specialized foliar structure (external leaf dimorphism) or as a specialized leaf part (intern...
Article
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Phylogenetic research on monocots has been extraordinarily active over the past years. With the familial interre-lationships being sufficiently understood, the question of divergence times and crown node ages of major lineages comes into focus. In this study we present the first attempt to estimate crown and stem node ages for most orders and famil...
Article
Full-text available
Thylacopteris is the sister to a diverse clade of polygrammoid ferns that occurs mainly in Southeast Asia and Malesia. The phylogenetic relationships are inferred from DNA sequences of three chloroplast genome regions (rbcL, rps4, rps4-trnS IGS) for 62 taxa and a fourth cpDNA sequence (trnL-trnF IGS) for 35 taxa. The results refute previously propo...
Article
Biogeographic affinities of scaly tree ferns (Cyatheaceae) in the Madagascan region with special reference to adaptive radiation in the Mascarenes
Article
Full-text available
Muséum national d'Histoire naturelle, Département Systématique et Évolution, UMR-CNRS 5202, USM 0602, case postale 39, 57 rue Cuvier, F-75231 Paris cedex 05 (France) and Georg-August-Universität Göttingen, Albrecht-von-Haller-Institut für Pflanzenwissenschaften, Abt. Spezielle Botanik, Untere Karspüle 2, D-37073 Göttingen (Germany) thomas.janssen@b...

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Projects

Project (1)
Archived project
Sustainable Use of Natural Vegetation in West Africa RESULTS IN BRIEF SUN, gathered local and international expertise to create a framework for vegetation management in west Africa. Improved interaction between scientists and stakeholders promises to prevent further deterioration of valuable ecosystems. Anne Mette Lykke The natural vegetation of semi-arid west Africa is of immense importance to local ecosystems as well as the livelihood of the local population. Unfortunately, poor management and unsustainable use is bringing about rapid deterioration of the vegetation. To reverse this worrying trend of destruction of a crucially important resource, a major EU-funded project was set up involving institutions from across Europe and west Africa. The 'Tools for management and sustainable use of natural vegetation in West Africa' (SUN) project aimed to bridge the gap between global initiatives, scientific information and the realities of life in Africa where practical solutions are required. SUN aimed to develop new management tools and solid management strategy to improve sustainable use of natural vegetation. The scientists combined vegetation dynamics and causal factors as well as economic instruments and policies to come up with a recipe for sustainable economic growth. To study human impact on phytodiversity, models were constructed using data from maps of vegetation from land use and protected areas. Overall, the scientists worked to understand vegetation dynamics and the factors that bring this about to identify and protect vulnerable areas and habitats. The scientists derived maps that show the changes in vegetation from 1982 to 2008 from indices subject to evaluation. Growing season peak time, greenness, length of season and shape of the phenological profile were used to correlate plant changes with rainfall and temperature patterns. A comprehensive database at http://www.westafricanvegetation.org/ houses the phytosociological and tree (dendrometric) data as well as lists of flora. Adapted to offline and therefore field use where the Internet may be slow, the vegetation data network allows upload of data sets for registered users. For users, the SUN map server facilitates the use of spatial information in SUN areas in west Africa to input into geographic information systems (GIS) for further processing. The SUN countries folder contains a vast range of data – from cities and villages to vegetation, geology and soils, as well as administrative boundaries. SUN has developed a major information platform for sustainable vegetation management in west Africa. The achievements of the SUN project will be fortified by data input from other projects. One key example is that the SUN map server will be updated regularly with data collected from the follow-on Seventh Framework Programme (FP7) initiative 'Understanding and combating desertification to mitigate its impact on ecosystem services' (Undesert). MORE DETAILED RESULTS Workpackage 1. Maps of vegetation patterns and land use units have been prepared for the project core areas. Extensive vegetation inventories from land use areas and protected areas have been conducted and data are stored in a vegetation database (WP4) and used for modelling of phytodiversity patterns in relation to human impact. Population dynamics of several highly valued species show declining tendencies in land use areas compared to protected areas. An improved understanding of vegetation dynamics and their causal factors will be used to identify and protect vulnerable areas and habitats (WP5). Workpackage 2. Five indices that measure changes in phenology have been developed and evaluated to verify that these indices measure; 1) Changes in the peakedness of the growing season, 2) Changes in the average annual greenness, 3) Shifts in the time of the peak of the season, 4) Changes in the length of the season and 5) Changes in the shape of the phenological profile. These indices have been used to derive maps depicting the changes in phenology that have taken place over the period of the time series used (1982 – 2008) and to analyse the correlations between these changes and changes in the key climate parameters of precipitation and temperature. Changes in vegetation phenology are significantly correlated with changes in rainfall over much of Africa and, occasionally, with changes in temperature. Workpackage 3. Local preferences and needs in relation to vegetation use have been identified and analysed within all the core areas. Economic instruments, such as subsidies, taxation, quotas or property right institutions, have been identified and analysed according to political feasibility as tools for improved management. Cultural and socio-economic impediments to sustainable use of the vegetation are also identified and ways to redress them are explored. Workpackage 4. An online vegetation database has been developed, which allows entry of all major plot types and maximises user acceptance by a flexible access rights approach. The online database concept has the advantage of common standards, facilitated exchange, good visibility of available data and high data security. The synchronization feature with local databases makes it possible to use our database directly in the field and under slow internet conditions. the database has a digitization record of 360028 single observations and 10743 plots. Workpackage 5. Indicators of sustainable use were analysed and identified at different scales (landscape, habitat, species). For identification of vulnerable habitats and species, the Climate Change Severity Index was derived, and the population pressure on the core areas was assessed. Vegetation data were prepared for comparison of land use and protected areas, and data on highly valued species in relation to the nearest settlements were used to identify the use impact on the species. A list of indicator species is in preparation. Workpackage 6. Biophysic data (vegetation, species, landcover/landuse, ecoregions, soils, geology, climate, rivers, watersheds, slope, elevation, satellite images) and socioeconomic data (population density, villages, administrative boundaries, languages, ethnies, borders, protected sites) for the core areas in West-Africa have been gathered, compiled and processed and are available in six File Geodatabases (ESRI ArcGIS). The Map Server has been updated to GeoMoose 2.0. Workpackage 7. A participatory management plan is being prepared for each core area on the basis of vegetation, satellite and socio-economic data. Management of natural resources is being improved by increasing local populations’ awareness of new possibilities for sustainable use of forest resources and by integrating local knowledge in the management plans. The management plans are being prepared in close collaboration between researchers and local communities. Workpackage 8. Restoration activities are carried out in different ecological sites of Benin, Burkina Faso and Niger. A total of 10 ha were reforested using low-cost budget (traditional) techniques and deep ploughing. In total, 2500 saplings of value species were planted. In the Sahelian conditions, Acacia senegal and Faidherbia albida are the best species, and in the Sudanian zones, Combretum micranthum, Jatropha curcas, Bauhinia rufescens and Faidherbia albida are able to grow on degraded soils. The best low-budget techniques are half-moon, zaï and stone walls. More expensive techniques like deep ploughing present more effect on soil restoration and biodiversity conservation. Workpackage 9. Dissemination is an important part of all research activities, and all 20 Ph. D. students will focus on disseminating research results. The dissemination is carried out on various levels: information to international institutions, local governments, natural resource management organisations, NGOs and local communities. The scientific results are published in international journals and in brochures in a simplified form. Presently, 29 scientific publications are published in international reviews and more are on the way. PARTNERS Aarhus University, Denmark (coordinator) Danish Institute of Agricultural Sciences, Denmark University of Cheikh Anta Diop of Dakar, Senegal Johan Wolfgang Goethe University, Germany Senckenberg Research Institute, Germany University of Ouagadougou, Burkina FASO University of Bobo Dioulasso, Burkina Faso University of Abomey-Calavi of Cotonou, Benin University of Abdou Moumouni of Niamey, Niger FUNDING EU-FP6 INCO-dev PROJECT PAGE https://cordis.europa.eu/project/rcn/81309_en.html