Research cooperation at the Monreberg

With the planting, a first step towards establishing an agroforestry system, the sweet chestnut is walking in the footsteps of the Romans, both geographically and historically. The Romans built military camps, settlements, roads and the Limes border wall on the Lower Rhine, which they called Lower Germania. Close to our chestnut plantation was the Burginatium cavalry camp. It is assumed that the Romans brought the sweet chestnut from the Mediterranean region to Germany.

Planting as a climate tree

Castanea sativa, as it is known botanically, thrives in the warmer and milder regions of Germany. It is expected that the sweet chestnut will play a greater role in the future in the context of climate change, as the light-demanding tree – which is much more widespread in Spain, southern France and Italy – copes better with heat and drought than some trees that have been native to us for longer.

Sweet chestnuts boast numerous positive qualities:

•  High nutritional value for humans:
  Chestnuts, which botanically belong to the nut family, contain a lot of starch, B vitamins, vitamin C and minerals.  Their energy density is comparable to that of maize or potatoes. However, in addition to calories, chestnut trees also provide a number of benefits for the environment and agriculture.
• Promotes biodiversity:
  In summer, the flowers provide food for insects such as bees, hoverflies and beetles, so the tree has an important function as a pollen and nectar source. Their fruits, chestnuts, are an important source of food for mammals and birds from autumn onwards. In addition, the bark of older trees with its elongated cracks provides protection for insects.
• Promotes soil build-up:
  The leaves of the sweet chestnut decompose easily and break down quickly. This helps to build up nutrient-rich humus and improve the water retention capacity of the soil.
• Embellishes the landscape:
  The sweet chestnut is known for its bright autumn colours. But the blossoms, which appear from June, also delight nature lovers with their long yellow catkins and white-green flowers. They also exude a pleasant fragrance.

Planting for research

Anna-Lea Ortmann, PhD student in our Agroforestry Living Laboratory team, supervises the cooperation with Jürgen Janssen, on whose farmland the chestnuts were planted. The collaboration with Jürgen Janssen is part of her research work, which includes testing fruit and nuts for local agroforestry systems. The planting of chestnuts involves several aspects. Firstly, there is the variety experiment: five seedlings from a cross between Dorée de Lyon x Marsol and five trees of the cultivar Dorée de Lyon were planted in the field.

‘The Dorée de Lyon chestnut variety is considered to be adaptable and previous experience in Germany indicates that its fruits can still ripen well in this country,’ says Anna-Lea, explaining the selection. ‘Its chestnuts are also considered to store well.’

There is, of course, a reason for planting both seedlings and pure cultivars: while a seedling is grown from a seed, a small tree is used as a rootstock for the cultivar; experts speak of the rootstock on which a young branch, also known as a scion, is grafted from a cultivar tree. In the former case, specialists speak of ‘generatively propagated seedlings’, while the latter is called a ‘vegetatively grafted variety’.

Further differences between the seedling and the cultivar can then be expected in the subsequent plant life of the sweet chestnut. In contrast to the seedlings, the cultivar does not form such a large crown and is generally more restrained in growth. At Monreberg, the cultivar and seedling were planted alternately at a distance of 8.50 metres to allow a direct comparison.

The holes were drilled and dug almost exactly 70 cm deep. The reason for this: The vole, which does not shy away from the roots of the sweet chestnut, is active down to a soil depth of around 50 cm. Therefore, self-made galvanised wire baskets with a 13 mm mesh width were placed around the seedlings at a depth of 70 cm.

When digging the holes, the soil structure was easy to see and understand, even for non-experts. After a relatively short layer of earth, the sandy soil began, as the Monreberg is located on the Lower Rhine ridge, a terminal moraine from the penultimate ice age, the Saale glacial period.

On the one hand, this is an advantage, as the sweet chestnut thrives less well in locations with waterlogged and groundwater-influenced soils, but it is also a disadvantage. Water quickly seeps into the sandy soil. Although the sweet chestnut is considered to be relatively drought-tolerant, young trees in particular with a still weak root system are inherently susceptible in times of drought. If the summer drought persists, it will be necessary to water the trees in the first few years. Even beyond this, a good water supply is important for fruit development and the ultimate yield. This will also be part of Anna-Lea’s research.

In addition, the cultivar Bouche Rouge was planted as a solitary plant in another location. ‘An exciting variety with which we have had positive experiences elsewhere in NRW,’ Anna-Lea reports. At its planting site, it has enough space to grow into a sprawling large tree. Old chestnut trees are within reach for pollination.

Planting for flora and fauna

Jürgen Janssen, the co-operation partner of our Agroforestry Living Laboratory, has a doctorate in agricultural engineering, but does not work in the profession. He has leased the arable land.  Nevertheless, he sought contact early on after the start of our Agroforestry Living Laboratory. ‘I want to help shape the landscape and strengthen resilience in the face of climate change. Even as a child, I was disturbed by the openness of the farmland up here,’ he recalls. He sees agroforestry systems as an opportunity for soil protection, as a contribution to stabilising yields and for biodiversity.

There are many old chestnut trees around the farmstead and in the wooded areas. It made sense to plant more sweet chestnuts in the area that has now been replanted. Jürgen Janssen would like to harvest the fruit and, if possible, market it in a few years’ time. Until the harvest offers marketing potential, he and his family have their own use for the fruit.