Deutsche Agrarforschungsallianz (DAFA)
German Agricultural Research Alliance

Bundesallee 50
38116 Braunschweig
GERMANY
Phone: +49-531-596 1017
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Climate change in dry Mediterranean regions like the Middle East is a potential threat for many people in that densely populated area. Global Circulation Models project higher temperatures and more frequent rain storms but fewer light rains. It is unclear whether this results in more or less rain in total. Using spatially explicit models I have examined what the change in rain distribution means for the natural vegetation and its capacity to provide food for sheep and goats. This work is part of the GLOWA Jordan River project. Some of the results are presented as probability or Bayesian nets.

I programmed a computer model of populations of annual plants simulating the daily rainfall, water dynamics of the soil, plant germination, plant growth of individual plants, resource allocation, and seed bank dynamics in a grid composed of 1 cm²-cells. Simulations using realistic rainfall distributions showed that changes in daily rainfall as projected by climate change scenarios have the same order of magnitude as projected changes in annual volumes.

The results of the annuals model were combined with results of a colleague's shrub model to parameterize a landscape model of vegetation dynamics in a prototypic wadi landscape to assess the effect of topography and climate change on vegetation dynamics and runoff under various grazing regimes. The simulations showed that grazing pressure was more important than climate change for vegetation dynamics. However, climate change and grazing intensity interacted to increase the risk of erosion in semi-arid regions.

Nitrogen is a growth-limiting resource in most temperate and boreal ecosystems. Human activity, especially burning of fossil fuels, releases nitrogen compounds into the air. When the compounds are washed out by rain or simply settle onto plant leaves or soil they act as fertilizers. Using ion exchange resin (IER), I measured deposition of nitrogen from the atmosphere to in six national parks in the prairie provinces. Four parks were in densely populated regions, the others (Jasper, Wood Buffalo) in remote areas. At the same time I measured nitrogen availability in the soil with IER, nitrogen and carbon storage in several vegetation compartments, and nitrogen and carbon isotope ratios in the vegetation. Nitrogen deposition was higher downwind from central Alberta, the isotope ratios indicated that combustion processes were the main source. Historic forest invasion rates, measured from air photographs, were correlated to historic population density and current N deposition rates.

Competition along with its counterpart, facilitation, are though to structure undisturbed ecosystems. If a resource like nitrogen is scarce, plants compete for capturing the nitrogen. More successful plants can grow bigger and replace less competitive plants. I studied the relative competitive ability of woody and herbaceous vegetation in neighbour removal experiments, combined with resource measurements or resource manipulations. Woody vegetation had stronger effects on available nitrogen than herbaceous vegetation, but the effects of both growth forms were similar on light and soil moisture. Accounting for the higher biomass of woody vegetation its effects were always weaker than those of herbaceous vegetation.

To identify processes facilitating the invasion of aspen into prairie, I have conducted litter decomposition experiments with reciprocal litter exchange between habitats and additional shading. In a novel approach I used ion-exchange resin (IER) to measure the nitrogen input and output during the initial stages of decomposition. Litter decomposed faster in sun-exposed treatments, indicating a strong effect of photodegradation. The experiment also showed that atmospheric deposition of N in the prairie was higher than previously thought.

I have used hierarchical sets of vegetation surveys on habitat islands in an agricultural matrix to test predictions of the theory of island biogeography in Sweden. The results showed that the processes predicted by the theory did not contribute significantly to the species-area curve.

Monitoring of engineered nano-particles in the environment
Nano-particles are solid substances in tiny sizes (less than 1 millionth of a gram) that, due to their large specific surface, often have interesting properties much different from those of much larger, conventional units of the same substance. The production of nano-particles is increasing at an exponential rate. Due to the increased application of nano-particles, it is assumed that 5 t/yr nano-silver are released into the environment in Switzerland and 3000 t/yr in the U.S.A. The mobility and half-life of nano-particles can be great. Very little is known about how engineered nano-particles behave in the environment as they accumulate. They might be mobile, aggregate or interact with each other or with other organic pollutants. Past experience with, e.g., asbestos, DDT, chlorofluorocarbons, fossil fuels, teaches that substances that have been considered beneficial or unobtrusive at low concentrations or low amounts may become problematic as they accumulate. It is known that nano-particles applied to clothes can be found in the soil on fields when the particles are washed out with the laundry, accumulate in sewage plant sludge which is spread on arable land. Particles may be washed to the ocean. Other particles may be released into the air. It is not known which nano-particles might accumulate in animals, plants, or humans. In order to detect early signs of accumulation and link these hotspots to potential observed effects, engineered nano-particles ought to be monitored in space and time. The monitoring procedures should be coordinated among the GEO countries.