Prof. Dr. Kai Jensen

Welcome

Global change (land use change, urbanisation, climate change) affects biodiversity on all levels of organization. Genetic diversity within populations and species, species diversity of communities and habitat diversity in landscapes have all been reduced due to human activities in many regions of the world. At the same time, strategies for the preservation of biodiversity have been established on the global, on continental and on national scales. Biodiversity affects numerous ecosystem functions, many of them are mainly mediated by vegetation. Carbon sequestration is affected by vegetation properties and the presence of specific plant species has tremendous effects on nutrient cycling.

Understanding interactions between site conditions, human activities and biodiversity is one major focus of the research group ‘Biodiversity and ecosystem functioning’. Furthermore, we address the role of certain components of biodiversity for ecosystem functioning and the potential to deliver ecosystem services. We mainly focus on wetlands and on urban ecosystems as models. While these ecosystems differ in many respects, they both do not only offer habitat for plant and animal species, but play also important roles for the delivery of ecosystem services. Currently, we investigate effects of land-use change and of climate change on biodiversity and ecosystem services in different ecosystem types in the framework of several third-party funded projects.

Coastal Ecology

Junior-Research-Group INTERFACE - Interaction of fish, plants, carbon & sediment: Management and ecosystem functions of Wadden Sea salt marshes

The Junior-Research-Group INTERFACE aims to analyze effects of drainage and livestock grazing on the morphology, vegetation, hydrology and sedimentation in salt marshes of the Wadden Sea National Parks (work package A - Dr. Stefanie Nolte). Furthermore, carbon sequestration of salt marshes (work package B, Peter Müller) and carbon fluxes across the aquatic-terrestrial ecotone (work package C - Hai Do Thi) are quantified. Finally, the suitability of salt marsh creeks as habitat for fishes is analyzed in work package D (Julia Friese). The results of all work packages will be used to develop recommendations for a sustainable management of Wadden Sea salt marshes.

[see more]

Junior-Research-Group BASSIA – Biodiversity, management, and ecosystem functioning of salt marshes in the Schleswig-Holstein Wadden Sea National Park (2009-2013; completed)

The Junior-Research-Group BASSIA addressed the effects of salt marsh management on (i) plant species and vegetation diversity, on (ii) breeding birds and on (iii) Si-cycling and sediment deposition and accretion rates. The Junior-Research-Group was head by Dr. Antonia Wanner. Frauke Müller and Cynthia Erb were carrying out research for their doctoral theses.

Estuaries

Bio-Geo-Feedbacks in Estuarine Environments of the Anthropocene

The project ‘Bio-Geo-Feedbacks in Estuarine Environments of the Anthropocene’ is funded by the Center for a Sustainable University at Universität Hamburg. The major aim is to put together a proposal for a Research Training Group to be submitted to the DFG (Deutsche Forschungsgemeinschaft). During 2016 and 2017, a consortium of 10 Principal Researchers from the Department of Biology and the Department of Geoscience worked on developing a consistent research plan on the topic ‘Biota-mediated effects on Carbon cycling in Estuaries’. A pre-proposal for the establishment of a Research Training Group was submitted to the DFG in early 2018.

ESTRADE- Estuary and Wetland Research Graduate School Hamburg (2008-2013; completed)

Estuaries and wetlands are among the most biologically productive and diverse ecosystems on Earth. They comprise a huge variety of ecosystem types ranging from tidal salt and tidal freshwater marshes to peatlands and swamps, to riparian ecosystems. All these ecosystems can be seen as models for the analyses of evolutionary processes leading to adaptations to extreme environments (e.g. salinity stress, hypoxia). In addition, estuarine and wetland systems have important ecosystem functions in the water and nutrient budget at the landscape scale. Due to human alterations and climate change, estuaries and wetlands are highly threatened ecosystems. There is an urgent need for interdisciplinary and international research in estuaries and wetlands to develop strategies for the sustainable management of these ecosystems.

The graduate school ESTRADE interconnected 30 researchers from two different universities in Hamburg (University of Hamburg and HafenCity University Hamburg) focusing on research in estuaries and wetlands. Researchers in ESTRADE had a highly diverse scientific background ranging from biology, hydrology, geography, biogeochemistry, and soil science to landscape planning. Three important research areas were investigated within ESTRADE: (i) biodiversity, (ii) ecosystem functions, and (iii) sustainable management.

Floodplains and lake shores

Conservation and management of ‘isoetid vegetation’ along lake shores in Schleswig-Holstein (LLUR; 2016-2019) [Detailed project description only available in German]

Ecosystem processes and ecosystem services of hardwood floodplain forests along the middle reaches of the Elbe (BMBF MediAN; 2017-2023)

Projekt ImpaRT - Impact of hydraulic Redistribution by Trees on Temperate Floodplain Forests (Carlsber Foundation ImpaRT 03/2014-10/2015)

Restoration of degraded lake shores in Schleswig-Holstein (DBU, 2005-2010)

The project aimed at understanding factors contributing to the dramatic decline of aquatic reed stands along lake shores of some lakes in Schleswig-Holstein and at testing measures to restore aquatic reed stands. A lack of water level fluctuations, shading by shoreline tree vegetation and herbivory by geese were identified as factors contributing to reed decline.

Urban Ecosystems

Safeguarding drainage of urban spaces in times of climate change (BMBF STUCK; 2015-2018).

The project consortium is investigating opportunities for safeguarding the drainage of urban spaces in Hamburg in times of global climate change with overall increasing amounts of rainfall and higher frequencies of heavy rainfall events. Within the project, the Applied Plant Ecology research unit addresses ecosystem services of urban flooding retention areas. A major focus is on the importance of retention basins as secondary habitat for wetland plant species.

[see more; Detailed project description only available in German]

Urban trees in times of climate change (BMUB SiK; 2015-2018)

In the temperate zone of Europe, urban trees are faced by less favorable growth conditions than trees at rural sites. Decreased water availability may be a major factor for reduced growth and vitality of urban street trees. In this project, we use sap flow measurements and dendrochronological methods to better understand how certain tree species cope with drought. Based on the findings of the project, recommendations for the management of urban trees in times of climate change will be developed.

[see more; Detailed project description only available in German]

KLIMZUG-NORD (BMBF; 2008-2014)

Within the consortium of KLIMZUG-Nord, the Applied Plant Ecology research unit addressed possible effects of climate change on certain ecosystem types in the metropolitan area of Hamburg. We focused on effects of sea level rise on estuarine marshes, on effects of reduced summer precipitation on floodplain grasslands and bogs and of increasing temperatures on plant communities in urban environments. Based on the findings of the project, recommendations for nature conservation in times of climate change were developed.