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Research project (§ 26 & § 27)
Duration : 2017-08-01 - 2021-01-31

Seed production, germination and establishment are critical processes determining structure of plant populations and composition of terrestrial ecosystems. In many perennial plants, seed production shows strong inter-annual variation with a gradient ranging from years without seed production to years with heavy seed crops (“masting”). In a number of plant populations, this intermittent production of very large seed crops is synchronized over large areas and sometimes across species. Mast seeding events are common in boreal, temperate and tropical forest ecosystems and have spurred considerable scientific interest. As the number of long-term studies of the phenomenon grows, a new picture of temporal variation in tree seed production is emerging. In particular, many studies have documented both the irregular length of intervals between very large seed crops, and the more frequent production of small or moderate seed crops between the years of peak seed production. To date, there has been little examination of the consequences of these “inter-mast” seeding events for the long-term population dynamics of tree species. The general goal of the proposed research is to understand and predict the consequences of spatial and temporal variation in tree seed rain for long-term population dynamics of tree species. We hypothesize that inter-mast seed production is a bet-hedging strategy for capturing windows of opportunity for successful regeneration after stochastic disturbances for species and sites with longer masting cycles, and that the long-term average abundance of species is increased as a result of inter-mast seed production. We further hypothesize that, for species with palatable seeds, inter-mast seed production is particularly successful when seed predators are driven into hunger cycles by mast years, and subsequent crashes in seed predator populations result in lower than average population sizes during inter-mast years. The hypotheses will be tested using a combination of empirical research, e.g. on seed fate, combined with the parameterization of a spatially explicit individual based tree population model (SORTIE-ND). Detailed age distributions of seedlings and saplings will be characterized in old growth forests of known seed production. Seed fate will be documented by tracking of marked seeds.
Research project (§ 26 & § 27)
Duration : 2000-07-01 - 2002-12-31

Estimating regeneration establishment is a hampered by the difficulty in collecting regeneration data and random impacts in the occurrence of regeneration. Artificial neural networks represent a computational methodology widely used to uncover the structure of a large variety of data. In general, one may recommend the application of neural networks in areas characterized by noise, poorly understood intrinsic structure and changing characteristics. Each of those characteristics is present in predicting regeneration establishment within uneven aged mixed species stands. In this project we develop a design and estimation procedure to predict regeneration establishment using data from the experimental forest, University of Agriculture in Vienna, Austria. The result of the study should provide us with tools to estimate the number of juvenile trees per unit area, the relative percentage of individuals by tree species and the mean regeneration height needed to initialize existing juvenile tree growth models.
Research project (§ 26 & § 27)
Duration : 2014-08-28 - 2015-06-30

As a result of global warming increased exceptional floods and extreme heavy precipitation events take place. So the risk of remobilization of deposits increases. Subsequently radioactive heavily contaminated sediments can be mobilized. At LLC-Laboratory Arsenal radioactivity of the danube compartiments: water (dissolved radionuclides), suspended matter and sediment are continuously monitored based on monthly composite samples and event-related samples during floods since 1984. This is a unique Central European radioecological long time series of measurements. The continuation of this sampling and data collection is of great importance to meet future challenges in radiation protection with regard to potential large-scale environmental contamination.

Supervised Theses and Dissertations