Our city is home to natural talents who have a lot to offer.
Winter lime tree, Aachen Brand market square
Linden trees quickly win our hearts; the winter linden is even called the "heart-leaf linden" due to its distinctive leaf shape. And lime trees really are linden trees, i.e. trees with gentle and tender characteristics. They put up with a lot and yet are tough and can live for over a thousand years. Linden trees were often planted in villages and towns because they were something of a "bread and butter" tree. Their bast provided material for ropes and clothing, while the leaves, which were low in bitter substances, served as food for humans and animals. The trees were regularly pruned for harvesting: Similar to pollarded willows, branches were always sawn off at the same point. Lime trees can be willingly shaped by pruning, which is how the popular dancing lime trees came into being, with the dance floor located in their low crown between the snowy shoots. Even today, linden leaves and blossoms are sold as health-promoting animal feed. Lime blossom tea tastes good and is often drunk to calm the body and treat colds. At flowering time, the abundance of nectar in the flowers is noticeable through the buzzing of the numerous bees and bumblebees. The excrement of aphids and cicadas is also harvested by honeybees, with one tree yielding up to two kilograms of honey. The soft wood is ideal for carving and is popular for making instruments.
But how can such a heavily harvested tree actually survive? Lime trees form a strong rootstock and have an enormous capacity for deflection. This is precisely why we should protect their roots particularly well, as they do not tolerate soil compaction, paving or injury. If the soil provides sufficient moisture, the winter lime tree is heat tolerant.
But lime trees are not only food trees for humans and livestock, they also provide food for numerous wild animals. Their seeds are popular with birds and small animals. In addition to the numerous flower visitors that collect nectar and pollen, many herbivorous insects live here. Researchers have found forty species of butterfly caterpillars, such as the linden yellow owl or the beautiful linden sicklewing, as well as over twenty species of beetles such as the linden hornworm. The lime tree aphid and lime tree masked cicada are among the species that excrete the abundance of sugar in their food as honeydew. No wonder that many bird species gather food for their young here and bats catch moths at night.
Sal- and Silberweide, Vennbahn Aachen Brand
Willows are at the top of our animals' hit list. Researchers have found over 500 species of animals and fungi that find food here. In the case of the silver willow, there are still around 300 species, including 78 butterfly species alone. The caterpillars of the poplar hawkmoth, which is almost 10 centimetres tall, and five different glasswinged moths nibble here. But 74 species of beetle also live on silver willows, 30 of which alone belong to the particularly beautiful longhorn beetles. Their larvae feed on living or dead wood.
Willows love damp or wet locations, a habitat that promotes the survival of fungi and bacteria. The many predators are countered by defense mechanisms that ensure that willows are among the particularly fast-growing woody plants despite their strong integration into the food web. One substance that plays a major role in the defense against pests and also in the response to stress such as drought, heat, cold or solar radiation in plants is salicylic acid. This plant hormone boosts the metabolism of plants and ensures, for example, that the respiratory openings are closed during stress. It also has a direct effect against bacteria, fungi and sucking insects. No wonder that this substance, which is highly effective biochemically in plants, also has numerous effects in our bodies. Salicylic acid has an analgesic, blood-thinning and anti-inflammatory effect. Applied externally, it softens calluses and makes corns disappear. Some plants of wetland habitats, namely meadowsweet, poplars and willows, contain particularly high levels of salicylic acid. Meadowsweet and willow bark have therefore been used in medicine since time immemorial. The flavonoids in willow bark also have an antioxidant effect, neutralizing cell toxins. However, salicylic acid also causes bleeding in the gastrointestinal tract due to its blood-thinning effect. At the end of the nineteenth century, it was possible to develop a production method for pure acetylsalicylic acid, a similar substance that was named "aspirin" after the meadowsweet, which is also known as spirea, and does not have such strong side effects on the stomach.
Willows flower early and the seeds with their fluffy appendages are already sailing through the air in early summer. Many people mistake this "plant snow" for pollen. The clearly visible stamens of the male willow flowers also often lead to the assumption that willows are allergenic. Fortunately, willows are pollinated by insects and therefore hardly release any pollen into the air, making them suitable for a low-allergen garden.
Maple-leaved plane tree, Aachen Brand comprehensive school
In our increasingly hot world, the shade of large trees is a blessing. Plane trees grow quickly into large and stately trees that shade streets and squares like halls and provide natural air conditioning for outdoor spaces through the evaporation of their leaves. They can grow up to 30 meters high and 25 meters wide.
Plane trees sprout late, so the warming spring sun reaches the ground for longer. However, this robust tree species can also be adapted to confined spaces by pruning, provided that the trees are trained accordingly as young trees, which keeps the pruning wounds small. This results in roof plane trees or the striking and therefore popular box plane trees.
What is particularly interesting about plane trees is their bark, the outer layer of which is shed at regular intervals. The trunk has interesting patterns of yellow, greenish and gray-brown, depending on how old the outer layer of bark is. Sycamore trees have an intensive and resistant root system that can tolerate overcrowding or construction work relatively well. Compacted soils and exhaust fumes have little effect on the trees, which is why they are well suited as street trees. However, the roots are happy to take what they need, even from sewage pipes. And if slabs or paving are in the way, they like to be lifted. Pipes in the vicinity of plane trees should therefore be tight and well protected. Paving can be shielded by root-repellent edging.
As a hybrid of two exotic species, the American sycamore (Platanus occidentalis), which has inherited its winter hardiness, and the Oriental sycamore (Platanus orientalis), the maple-leaved sycamore only serves as food for a few insects; researchers found eight different species here.
Silver birch, Brander Bahnhof Aachen Brand
Popular with insects and birds alike, the birch is a typical pioneer tree. Like willows, birches are often the first to appear on green roofs and abandoned railroad tracks. The extensive root system supplies the plants very well even in dry conditions.
Birches then quickly grow into medium-sized trees. In May, their light-colored bark and flexible light-green leaves shine brightly and spread springtime cheer. However, the roots of the birch are also highly sensitive. Even light and localized overcrowding, such as a raised bed in the root area or an earth mound, can cause a birch to die. Birches also do not tolerate transplanting well. As a result, birch trees grown from seed can easily survive periods of summer heat, whereas planted birch trees will die even in slightly dry conditions. Birches should ideally be allowed to develop from spontaneous sowing. Then they can also be easily planted on sticks, i.e. managed in a similar way to a coppice forest. In this way, light and cheerful birch groves can be permanently maintained even in small areas.
In the past, leaf hay was obtained from such birch groves as animal feed. However, birches were also used for human consumption, not only the birch sap obtained in spring by drilling, but also young leaves, buds, fruit and the bast of the trees.
But anyone who cares for a birch tree also creates an important habitat. Researchers found over 380 different animal species that feed on birch leaves or other parts of the trees, for example the caterpillars of 161 different butterfly species. 25 different species of aphids suck on the shoots, almost all but two of which occur only on birch trees. 32 bird species eat the seeds of birch trees, but the many caterpillars and aphids that the bird parents find here for their chicks are particularly important for most bird species.