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One ash tree does not make a forest

... it needs company. The FraDiv research project investigates how ash dieback affects the biodiversity of our forests, and which silvicultural measures protect the ash trees, as well as the biological diversity of ash-rich forests. As part of the project, 25,200 trees have now been planted.

Blätter und Wurzel einer Esche
© emer1940/iStock

Can the ash tree be saved? - "This is the wrong question," ecologist Dr Katharina Mausolf made clear immediately. She is the scientific coordinator of the CAU project "The impact of the ash dieback disease on forest ecosystems - strategies for biodiversity conservation", which is known as FraDiv. "Initially, it's about determining the extent to which the great diversity of species in ash-rich forests is affected by ash dieback, and which measures can contribute to conserving this biodiversity. In addition, we want to find out which forest community the ash tree has the best chances of surviving the disease in," explained Mausolf.

In forests in which the European or common ash (Fraxinus excelsior) thrives the most, the biodiversity of fungi, plants and animals is usually very high. In addition, many rare and endangered species live here. However, according to Mausolf, a fungus has been spreading in Europe since the 1990s - Hymenoscyphus fraxineus - which infects nearly all ash trees, regardless of their age. The infection initially causes individual branches of the tree to be cut off from the nutrient supply and die off. In the worst case, the whole tree dies - or often even whole forest populations. This is what happened in a wooded area at the Harzhof estate near Holtsee: a clearing had developed because countless mature ash trees died, or were felled previously. Mausolf and two other project staff, doctoral researcher Katharina Haupt and biology student Franziska Fischer, planted trees in this clearing in different combinations: in addition to new ash trees, they also planted potential replacement tree species such as the European white elm, the European hornbeam, the Norway maple and the small-leaved lime.

Women in a forest
Photo: Karena Hoffmann-Wülfing

Biology student Franziska Fischer distributes young ash trees in a clearing in the forest near Holtsee. This is done strictly according to the planting plan she carries with her on a clipboard.

For FraDiv, a total of 252 one-hundred-square-metre test areas were planted in twelve forests in Schleswig-Holstein, each with one hundred young saplings.

"Today we are planting the last of 25,200 trees," said Mausolf with pride at the beginning of this year - and breathed a sigh of relief. Since December, she and her team from the Institute for Ecosystem Research (ÖSF) were on the move almost daily, to set up and replant the test sites. "Sometimes we were outside for twelve hours a day. On one day, we planted 2,200 trees. I have no idea how we did it," said landscape ecologist Haupt. There are monocultures, as well as mixtures of two, four or all five species. Strictly according to the specifications, the saplings were distributed and planted in the soil. Master’s degree student Fischer kept a log, carrying the plan for each experimental plot with her on a clipboard.

In the coming months and years, the team of scientists led by project leaders Professor Alexandra Erfmeier and Professor Joachim Schrautzer will observe and measure the young trees, record the diversity of plants and fungi, and investigate the soil, in order to analyse the complex abiotic and biotic interactions in this forest ecosystem.

It has often been observed that the greater the biodiversity in an ecosystem, the more robust and resistant it is to disturbances by environmental changes or pathogens. Also with ash trees, we know that some individuals seem to cope better with the fungal disease than others. FraDiv investigates whether the forest community in which the ash tree grows has an influence on its resistance to the fungus. In this way, it should be possible to determine whether ash trees have higher chances of survival with certain mixtures of tree species (from monocultures to polycultures).

In addition to the experimental approaches, the project also includes extensive permanent observation areas in forests located throughout Schleswig-Holstein. The experimental planting will investigate the importance of diversity of trees for the vitality of the forest community. It will also provide insights into optimised forest management.

Author: Karena Hoffmann-Wülfing

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Ash dieback disease

What causes it?Hymenoscyphus fraxineus belongs to the phylum Ascomycota (sac fungi). The trees are infected by the sporocarp (fruiting body) of the fungus, Chalara fraxinea.

Which trees can become infected? The European or common ash (Fraxinus excelsior) and the narrow-leafed ash (Fraxinus angustifolia)

Where has the fungus spread? Germany, Great Britain, Austria, Poland, Switzerland, Scandinavia, Slovenia, Czech Republic

What does Hymenoscyphus fraxineus do? The spores of the fungus infect the still-living leaves, shoots and later also the woody parts of the ash tree.

How does the disease become apparent? Initially, dead spots appear on the twigs and branches, and later the leaves wilt and fall off. Later the top shoots die and snap off. The dead branches show a yellowish or reddish discolouration. The fruiting bodies of the fungus are particularly easy to see on the central midrib of the pinnate ash leaves which have been shed.

Figures, dates, facts

Project name: FraDiv (The impact of the ash dieback disease on forest ecosystems - strategies for biodiversity conservation)

Duration: 02.2019-01.2025

Financial budget: €2.4 million

Funding: by the German Federal Agency for Nature Conservation (BfN) with funds from the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety through the "Biological Diversity" federal programme

Trees planted: 25,200 altogether, with 5,040 of each species

Planting period: 02.12.2019 to 21.01.2020 on 24 working days

Kinds of tree: five species - European or common ash (Fraxinus excelsior), European white elm (Ulmus laevis), European hornbeam (Carpinus betulus), Norway maple (Acer platanoides), small-leaved lime (Tilia cordata)

Planting: in monoculture (one species) or as a mixture

Test sites in Schleswig-Holstein: 12 formerly ash-rich forest areas between Gelting and Eutin in eastern Schleswig-Holstein (project partners: Forstbetriebsgemeinschaft Eckernförder Bucht and Herzoglich Oldenburgische Forstverwaltung forestry associations), covering a total of approximately 14 hectares

Experimental plots (ten metres by ten metres): a total of 264, of which 252 were planted with 100 trees per experimental plot, and 12 control plots without any new trees planted

Team: six to eight people: scientists, foresters and volunteer helpers