10 December 2009: Rasmus Jørgensen

Natural and human caused shifts in dominant vegetation in sub-arctic Greenland in relation to climate changes

Rasmus Jørgesen

dept. Agriculture & Ecology, Copenhagen University


Arctic ecosystems are seen as particularly susceptible to climate change due to their adaptation to cold conditions. Climate change is expected to be strongest in polar regions. In contrast to this, southern Greenland has experienced a 2 degree cooling during the last 50 years. Nevertheless, prognoses for the climate in southern Greenland predict temperature increases for the next 100 years.

In most subarctic regions, shrubs are expanding in range and dominance. This tendency is thought to originate from human-caused climate change and/or an increase in temperature since the Little Ice Age. For South Greenland, it is not known if shrub abundance has changed.

Alnus viridis sp. (green alder) is among the species that have shown the most pronounced expansion rates in NW America with large ecosystem consequences. It is not known what forces connect higher temperatures with increased shrub abundance. Until now, green alder has had a limited range in Greenland – outside the potentially climatologically optimal area. Increased temperatures can have beneficial effects for the species range and dominance in Greenland.

In southern Greenland, the interest for establishing tree plantations with introduced species is increasing. Plans for large-scale plantings are taking form. Increased temperatures and shrub abundance (especially alder) are forces that could facilitate tree growth following afforestation in southern Greenland.

9 December 2009: Anne-Marie Skou

Climate change or naturalized ornamental genotypes? Factors controlling range expansion in an evergreen temperate tree

Anne-Marie Thonning Skou

dept. Agriculture & Ecology, Copenhagen University


Holly (‘Kristtorn’) (Ilex aquifolium) is a dioecious evergreen tree or shrub that grows as a sparse but usually gregarious understory element in deciduous forests of western and southern Europe. In Denmark, the plant is at its northeastern range margin in forests of eastern Jutland, and it seems to be controlled by winter frost, expanding its range eastwards (ca. 100 km within ca. 50 years). However, numerous (frost-hardy) cultivars have been introduced in this region, and the species is an invasive alien plant in Australia and naturalized in New Zealand and western North America. Factors controlling its range expansion include: higher winter temperatures in eastern Denmark (permitting factor), trade and plantations (driving factor), dispersal by birds (100 m per year?); leaf mining; time between planting and fruit maturation (limiting factors). The objectives of my PhD thesis are: to determine propagule pressure of I. aquifolium cultivars in Denmark over time, to investigate genetic differences between native and introduced genotypes of Ilex aquifolium; to analyze the degree of genetic introgression from garden cultivars into native populations; to study the frost tolerance of native and introduced genotypes, and survival in field transplant experiments; to determine whether thrushes have preferences for the fruit of different cultivars; and to assess the effects of introduced genotypes on plant-animal interactions of different specificity.

27 November 2009: Wibke Wille

Evolutionary Agroecology: developing high density, communal crop plants for weed suppression and increased sustainability

Wibke Wille,

dept. Agriculture & Ecology, Copenhagen University


Recent advances in our understanding of the role of size differences in competition among plants suggest that the potential for many crops to suppress weed is greater than generally appreciated. Increasing crop density and uniformity of spatial distribution reduces significantly weed growth and increases cereal yield under weed pressure. This potential can be further enhanced by developing varieties for such an environment, allowing farmers to drastically reduce or eliminate herbicides and energy-intensive forms of weed control.

One hypothesis is that certain forms of phenotypic plasticity that increase individual fitness, specifically the “shade avoidance response”, reduce the potential for weed suppression and high yield in high-density high-uniformity cereal cultivation systems. To test this hypothesis we have grown chemically mutated seeds of spring wheat under green shading selecting for plants deficient in shade avoidance as a potential source of genes to be introduced into high-yielding varieties for crowded, spatially-uniform cropping systems.

A second hypothesis is that there is a large potential for high-density weed-suppressing wheat ideotypes in the existing wheat germplasm, though the genetic characteristics optimizing this potential may have been lost over the past century of breeding cereals grown in rows at low density with mechanical or chemical weed control. We are testing this by growing a large collection of wheat lines from international cultivars and landraces in our high-density high-uniformity system to seek and document natural variation in weed suppression under these conditions.