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Research project (§ 26 & § 27)
Duration : 2018-03-01 - 2019-05-28

Due to their presumed drought tolerance and fast growth rates, the non-native tree species Douglas fir (Pseudotsuga menziesii) and Grand fir (Abies grandis) have emerged as viable silvicultural alternatives to Norway spruce (Picea abies) in Austrian forests. However, the effect of these species on the forest soil carbon (C) cycle remains uncertain. If the contribution of these tree species to the forest composition increases in the near future, this information is urgently needed in order to lower the uncertainties of C sequestration estimates for the forestry sector. This project will, therefore, investigate soil C stocks and litter decomposition under Douglas fir and Grand fir in comparison to Norway spruce. Genecological field sites of the Department of Forest Genetics, Austrian Research Centre for Forests (BFW) will be utilized for a field study in 2018. Soil C stocks and litter decomposition will be determined for Norway spruce, Douglas fir and Grand fir plots in Lower and Upper Austria. Litter decomposition will be analyzed by means of a novel mass loss approach. The method will be developed in the project and allows for an in situ partitioning of litter mass loss into CO2 efflux, leaching of dissolved organic C and litter fragments. By means of the method litter decomposition will be linked to soil C stocks under the respective tree species. It is hypothesized that tree species with a higher partitioning into leaching of dissolved organic carbon have higher soil C stocks. This is one of the first studies investigating the effects of non-native tree species on soil C stocks in Austrian forests. Furthermore, it is the first in situ study partitioning mass loss during litter decomposition in forest ecosystems. The results will be an important information for forest managers which intend to use non-native tree species as an alternative to Norway spruce. The research will also give new insights into the complex process of litter break down and its role in the soil C cycle.
Research project (§ 26 & § 27)
Duration : 2018-03-01 - 2022-02-28

Ozone is a serious health problem in many cities during hot summer days. The ozone causes breathing problems as well as heart diseases and WHO has lately lowered the recommended limits exposure concentration. City trees can both increase and decrease the ozone levels depending on the environmental conditions. The increase of ozone is caused by the release of volatile organic compounds (VOC) which in the presents of NOx produce ozone. On the other hand leaves can decrease ozone levels trough deposition processes. The trees influence on both production of ozone and absorption depends on species but also on the physiological status of the tree such as drought or salt stress. By measuring the VOC production as well as the ozone absorption of species commonly used as street trees we can identify species that at high temperatures has a large capacity to decrease ozone concentrations. Further we can test how the influence on the ozone concentration is affected by drought and salt stress and how the response differs between species. The results will be used to model the ozone concentrations in Vienna The findings and the improved model can in the future be used as decision tools when planning the urban landscape to minimize ozone peaks.
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.

Supervised Theses and Dissertations