Tree of the month

In the next few months we will present you various heat-tolerant trees.

The walnut tree

Everyone knows walnuts, the fruits of the walnut tree, which are especially popular at Christmas time. Around 60 species make up the walnut family. The walnut tree thrives in many different landscapes, in the mountain valleys of the Balkans and the Himalayas as well as on the plantations of California.


In Germany the heat-loving and light-seeking tree is widespread in rural areas and in wine-growing regions, occasionally at the edges of forests. As a forest tree, it occurs in Southwestern Germany as well as in France and Switzerland.    

The walnuts ripen in September, their green fruit shell contains a brown-coloring juice. Inside is the light brown nutshell that protects the nut core. The heavy seeds (walnuts) are often hidden by the squirrel and the jay up to several hundred meters away from the mother tree as a winter supply. Since their hiding places are not always found again, this promotes the further spread of the tree.


Being one of the heat-loving trees, it is a suitable candidate for forest conversion in times of climate change. However, it is sensitive to late and early frost, therefore it is important to plant varieties that are adapted to these conditions in endangered areas.

The hornbeam

The genus of hornbeams consists of about 30 species and occurs only in the northern hemisphere. Its distribution ranges from North America through Europe to the Near East and East Asia, as it tolerates both hot summers and severe frosts.


The hornbeam is not a beech, as its German name suggests, but belongs to the birch family. It reaches a height of up to 20 meters, a trunk thickness of up to one meter and a maximum age of 150 years.


Flowering time is in April and May, the catkins form small nuts in autumn, which fall off during winter. Roe deer can cause some problems for the hornbeam, as deer love the tips of its young branches, and mice can damage the roots.

It is a forage plant for butterflies and important as a bird protection and nesting wood. In gardens it is often used as a hedge plant, where it also makes a valuable contribution to biodiversity as a nesting place and forage plant.


The wood of the hornbeam is particularly hard and is traditionally used for tool handles. It has one of the highest calorific values of our domestic hardwoods. In forestry, the hornbeam is often used as a mixed tree species in oak forests. It can cope well with these shady locations thanks to its shade tolerance and it promotes the natural cleaning of the branches of oak trunks.


Due to its deep root system, it has both a high tolerance to periods of drought and resistance to storms and can become more important in times of climate change.

The silver birch

The genus Betula includes around 40 species, the predominant species in Central Europe is the silver birch, which is also called white birch. Its distribution in different climatic zones extends from Scandinavia to southern Italy and from France to Russia due to its resistance to drought and extreme frost.


After the Ice Age it was the first tree species to settle in Europe as a pioneer tree. In the northern countries it is primarily a forest-defining tree species with up to 30 percent.

In Germany, the fast-growing silver birch is often the first tree to settle on fallow land, thus preparing the ground for other tree species. As a shade intolerant species, however, it will soon be supplanted. It reaches heights of 25 meters and the trunk reaches a thickness of up to 90 centimeters.

Its white, smooth bark is an outstanding feature. The blooming period is in April and starts at an early age of the tree’s life. The catkins develop a lot of tiny winged nuts.


Because of its thin crown the silver birch provides a habitat for many shrub and herb species making a valuable contribution to biological diversity. It is one of the most favorite trees for insects, particularly popular with many species of butterflies. Birch sap and leaves are mainly used in cosmetics and herbal medicine.

In Germany it is the most common tree species in the early phase of reforestation and at extreme locations. Because of its modesty and robustness, it can be of great use for future silviculture.

The oak

The oak is one of the most important tree species being found in nearly every continent.


Powerful and solid – the oak has existed for at least ten million years. With around 600 different species it has adapted to numerous diverse living conditions and can be found all over the world.


As climate change creates new challenges for our forests, such as longer periods of drought or the increasing occurrence of storms, the oak plays an important role in future generations of forests.

It has a high drought stress tolerance – not least due to clever adaptation mechanisms. Its deep taproots make it storm resistant and it can temporarily endure backwater and floods.


The oak also has great significance in terms of biodiversity –  it creates habitats for numerous other species such as small mammals, birds, insects and other invertebrates such as mushrooms and mosses.

The wild service tree

The wild service tree is one of the largely unknown tree species in Germany and is rarely found in forests. Its distribution extends from the Caucasus, Turkey and the Balkans to Central Europe with focus in France. After the last ice age the wild service tree came back to our regions from France about 10,000 years ago.

Wild Service Tree

The fruits of the wild service tree, also called “checkers”, are a favorite food of birds who eat them in the crown, so that hardly any fruits fall off.  Growing up to 25 meters tall it stands out due to the early and bright scarlet color of its leaves in autumn. The slowly growing wood is used for making high-quality furniture and musical instruments.


The wild service tree loves dry and warm locations. With its widely branched root system, it is firmly anchored in the ground making it stable against storms. Pest infestation has a minor significance in the entire distribution area.


As it copes well with higher temperatures and is able to withstand longer periods of drought, the service tree can play an important role in times of climate change.

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Your Audi Environmental Foundation Team