Projects by the working group of Prof. Thomas

Productivity and nutrient relations of trees in deciduous forests with contrasting tree species diversity

(Sub-project B1 within the framework of the Research Training Group [DFG-Graduiertenkolleg 1086]) "The role of biodiversity for biogeochemical cycles and biotic interactions in temperate deciduous forests")


Duration: 2005 - 2008

Funded by: Deutsche Forschungsgesellschaft (DFG)


The Research Training Group (RTG) investigates the role of tree species diversity (1, 3 and 5 species) in broad-leaved deciduous forests of the Hainich National Park (Thuringia, Central Germany) for productivity, carbon sequestration, nutrient and water turnover, deep seepage, nitrate leaching, and biotic interactions among key organism groups as well as for ecosystem services. The sub-project B1 focuses on the role of tree species diversity for the production of above-ground biomass, sizes of nutrient pools, exploitation of soil nutrient resources, and nutrient cycling. The employed methods include the measurements of wood and leaf production, leaf area index, nutrient concentrations in the biomass, and of the rates of litter decomposition.

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Soil and plant water relations in the transition zone between river oasis and desert

(Sub-project within the framework of the INCO-DC project of the European Union "Ecological basis for a sustainable management of the indigenous vegetation in a Central Asian desert")

Duration: 1998 - 2001 (INCO-DC project), 2003 - 2004 (accompanying measures) (completed)

Funded by: European Union

The objective of the project was to deliver basic knowledge for an effective re-establishment and a future sustainable management of the perennial vegetation in the foreland of a river oasis (Qira/Cele) at the southern fringe of the <st1:place w:st="on"><st1:placename w:st="on">Taklamakan</st1:placename> <st1:placetype w:st="on">Desert</st1:placetype></st1:place> (Xinjiang, NW China). In the sub-project, the dynamics of the soil water content as well as the foliar water and osmotic potentials, the xylem sap flow and the stomatal conductance of four perennial species (Alhagi sparsifolia, Calligonum caput-medusae, Populus euphratica and Tamarix ramosissima) and the water use of the stands were measured during two growing seasons. Unexpectedly, the distribution pattern, water relations and productivity of the investigated perennial plant species do not depend on flooding that occurs more or less regularly in the foreland. Instead, the perennial species are in contact with ground water, and do not experience drought stress even in periods with high air temperature, low humidity and extremely low precipitation.


Effects of defoliation and drought on the water relations of sessile and pedunculate oak (Quercus petraea [Matt.] Liebl. and Quercus robur L.)

Duration: 1999 - 2002

Funded by: Deutsche Bundesstiftung Umwelt (DBU)

The project started from the finding that a combination of consecutive defoliation and summer drought plays a significant role in the occurrence of increased mortality of Central-European oaks. Under controlled conditions, young sessile and pedunculate oaks were manually defoliated in two consecutive years and — in the same or in the subsequent growing season — subjected to drought. In addition to growth analyses, measurements of the H2O- and the CO2-gas exchange and hydraulic conductivity as well as investigations into the wood anatomy were conducted. Growth and water relations of the oaks were most severely impaired when defoliation and drought stress were applied simultaneously. In the absence of drought stress, the pedunculate oak regenerated from repeated defoliation within a relatively short time.