In 2009, the Bavarian State Institute for Viticulture and Horticulture in Veitshöchheim, Germany, started the Urban Greenery 2021 project: a pilot to test new and so far little-used tree species and therefore to provide the widest possible range of tree species and varieties in practice. A range that has good resistance to the city climate and to heat and drought stress. Twenty tree species were chosen on the basis of the following criteria: tolerance to drought stress, resistance to frost (particularly late in the spring), location requirements/high pH tolerance, limited susceptibility to diseases, no known sensitivity to harmful organisms and pests (EPPO list), evaluation in practice and growth form.
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Interim research results
The Urban Greenery 2021 project is in the eighth study year. Every year, the trees are investigated for growth (trunk circumference, side branches, leading shoot), frost damage, drought stress, pests and for phenology (emerging leaves, change of leaf colour, falling leaves) in early July and mid-September. Although there are still four years of the study to go, thanks to the extreme summers and winters over the past years, the results for a group of trees planted in 2009-2010 are good enough for an interim regional evaluation.
Assessment of tolerance to frost and salt for the various study species
| Study species |
KLAM |
Urban Greenery 2021 |
Urban Greenery 2021 |
Tolerance to salt |
| Acer buergerianum | 1 | - | - | + |
| Acer monspessulanum | 2 | + + | + | not specified |
| Alnus x spaethii | 1 | + | + | + |
| Carpinus betulus 'Frans Fontaine' | 1 | + | - | - |
| Celtis australis | 3 | - - | ? | not specified |
| Fraxinus ornus | 4 | + + | + | not specified |
| Fraxinus pennsylvanica 'Summit' | 1 | + + | + | + |
| Ginkgo biloba ♂ | 2 | + | + | + |
| Gleditsia triacanthos 'Skyline' | 2 | + + | + | + |
| Liquidambar styraciflua | 3 | + + | + | not specified |
| Magnolia kobus | 2 | + + | - | - |
| Ostrya carpinifolia | 1 | + | + | - |
| Parrotia persica | not specified | + | + | + |
| Quercus cerris | 2 | + + | + | + |
| Quercus frainetto 'Trump' | 2 | ? | + | not specified |
| Quercus x hispanica 'Wageningen' | not specified | ? | + | not specified |
| Styphnolobium japonicum 'Regent' | 2 | - | + | + |
| Tilia tomentosa 'Brabant' | 2 | - | - | not specified |
| Ulmus 'Lobel' | 1 | + + | + | + |
| Zelkova serrata 'Green Vase' | 2 | - | + | + |
Key:
| KLAM | KlimaArtenMatrix (Climate-tree matrix) |
| 1 | very good winter hardiness |
| 2 | good winter hardiness |
| 3 | problematic winter hardiness |
| 4 | very limited winter hardiness |
| + + | very high tolerance to frost |
| + | high tolerance to frost |
| - | limited tolerance to frost |
| - - | no tolerance to frost |
| + | tolerant to salt |
| - | sensitive to salt |
Gleditsia triacanthos 'Skyline'
Winner: drought stress - heat stress
More information in the TreeEbb
Quercus x hispanica 'Wageninen'
Winner: drought stress - heat stress
More information in the TreeEbb
Styphnolobium japonicum 'Regent'
Winner: drought stress - heat stress
More information in the TreeEbb
Ulmus 'Rebona'
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