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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 : 2017-04-01 - 2018-03-31

Polyter stands out in that it is a commercially available high quality agricultural hydrogel with a synthetic component of only 5%, the rest being organic material. This makes it more environmentally friendly than conventional agricultural super absorbent polymers. This characteristic makes the application of Polyter to help newly planted tree seedlings in the forest to better survive droughts interesting. It is a big problem of forestry that newly planted tree seedlings do not survive the first or second summer because the root system is still small, making the plants sensitive to drought events. The idea is to add a polymer to the planting pit, as the polymer will absorb large amounts of water that the plant can use during a drought. However, Polyter’s performance in practise and its effect on trees’ roots system and mycorrhiza development is unknown. The proposed research has he following objectives: • to examine the properties of the polymer and its effect on soil moisture; • to test whether addition of the polymer to the planting pit affects plant growth during drought; • to test what is the effect oft he water absorption and the fertilization on plant performance; and • to examine the effect of the polymer on root and mycorrhiza distribution. Two-year-old tree seedlings of Beech (Fagus sylvatica) Larch (Larix Europea) Norway spruce (Picea Abies) and Douglas fir (Pseudotsuga menziesii) will be planted in the pots with 4 different treatments: 1) control with only soil, 2) control with addition of nutrients in the form of slow release fertilizer, 3) polymers without nutrients and 4) polymer with nutrients, which is the product intended to be used. Each treatment will be replicated 12 times. Thus,: 4 species x 4 polymer/nutrient treatments x 2 water levels x 12 replicates = 384 pots + 24 control pots without trees = 408 pots. Tree performance as well and root and mycorrhiza distribution will be monitored/measured.
Research project (§ 26 & § 27)
Duration : 2017-01-01 - 2019-06-30

Forest ecosystem function in the Calcareous Alps is under threat from intensifying natural disturbance regimes, raising serious questions over the future provision of key ecosystem services. It is likely that climate change will drive an increase in windthrow and bark beetle events in Central Europe, with forests of the Calcareous Alps representing potential hotspots of future disturbance occurrence. This represents an alarming issue due to Austria’s dependence on the services from these ecosystems. Evaluating this risk is however currently limited by insufficient understanding of how disturbance impacts on forest carbon (C) cycling. Forest C dynamics regulate a number of important ecosystem services (e.g. atmospheric CO2 sequestration, drinking water provision), and their response to disturbance is an important determining factor of ecosystem resilience. Generalized paradigms of ecosystem disturbance are very limited in their ability to explain the changes and development in forest C stocks and fluxes after stand-replacing disturbance, with evidence indicating that these dynamics are strongly governed by ecosystem-specific factors. Unfortunately, empirical data on disturbance impacts on forest carbon cycling in the Calcareous Alps is severely lacking and fragmented. Considering the huge social, economic, and ecological importance of these ecosystems, we propose a project, “C-Alp II”, which will investigate C consequences of forest disturbance in the Calcareous Alps. The project will employ a chrononsequence approach, synthesizing data on carbon dynamics from test sites in different stages before- and after forest disturbance. The project build upon existing empirical data from previous test sites and an LTER site (LTER Zöbelboden), by conducting new measurements and analyses at these and additional experimental sites. One of the test sites is arranged as a manipulation site which was artificially disturbed in 2015

Supervised Theses and Dissertations