Leafless but not dull: trees in winter.

7 Jan 2022 | Uncategorized

The IVN guides had to cancel the monthly walk in the park again. For everybody who would like to look at trees in a different way, we hereby give you a ‘looking guide’ by Henk Wolters. (for pdf:Tekst Henk engels)

Winter time, hold your breath

When the energy-consuming processes of leaf budding, flowering, pollination, fruits, seeds and bud formation are over and the cold and dark winter season has arrived, the trees rest for a few months. They hold their breath, so to speak. With the exception of a few evergreens and most conifers, leaves, flowers and fruits are gone and at first glance appear dull and dead. But is that really so? No, not at all, because at this time of the year there are a lot of interesting things to see that are not or less well visible in other seasons.

Silhouette, the architecture of the tree

Now that the leaves have fallen, the first thing you notice is the silhouette, the architecture of the tree. It is one of the main winter features. Stand at a little distance from a tree and look at the shape. It can be, for example, heart-shaped (linden), spherical (plane tree), columnar (poplar) or capricious (oak). Also look at the structure of the branches. Does the tree form a few heavy side branches that run to the end (horse chestnut, walnut) or are there a number of more or less thin side branches along the trunk and is the image more regular (birch, hornbeam)? Do they make a sharp, blunt or straight angle to the trunk? How are the branches and twigs further branched? And do they run straight (alder) or curved (ash)?

The outer layer, not always reliable

Another important feature is the bark. The same in all seasons, but more visible in winter. In young trees usually smooth, in older trees often grooved (wingnut, elm), sometimes with peeling plaques (plane tree), or smooth (beech). Some have distinctive lenticels, pores in the bark that allow the tree to breathe (cherry, birch). Sometimes thorns (hawthorn) or spines (rose) are present.

Watch out for pitfalls

However, we must be careful with these characteristics. For the silhouette, for example, it can make a huge difference per species whether a tree is in a forest, along the street or is standing solitary. For the bark it is important to know whether we are dealing with a young or an old tree. You often need a combination of characteristics to have some certainty. And watch out for leaves, fruits or seeds that are under the tree, because they can also come from the neighbouring tree.

Where the petiole was attached

The leaf scar, also called leaf mark, is much more reliable. It is the place on the twig where the petiole was attached. Shape and size depend on that of the petiole. In the leaf mark small dots can be seen (usually only with a loupe), the so-called leaf spurs. They are the scars of the broken veins in the petiole. They correspond to the way in which the leaf is constructed. In the leaf mark of the horse chestnut, for example, the number of leaf spores corresponds to the number of leaf segments of the compound leaf.

Buttons, the hallmark par excellence

However, the winter characteristic par excellence, regardless of location, age or anything, are the buds. Always present, reliable and unique for each species. Shortly after flowering, when the plant is still full of energy, they are formed on the twigs as small knobs, then remain on the tree all winter and sprout in the spring when there is sufficient daylight and warmth. Usually the new bud is protected by bud scales against all kinds of threats, such as severe cold, damage, dehydration and rot. Each tree species has its own characteristic bud, which is why it is such a good feature.

You can distinguish buds in many ways What does the bud look like:  pointed, round, bare, hairy, sticky? Is it a naked bud or are there bud scales and what do they look like? How is the bud placed: opposite, alternating, spiraling? How is it situated on the twig: petiolate, sessile, adjacent, protruding? Is it a leaf bud, flower bud or a mixed bud?

It gets tricky when they look a lot alike. Then the distinguishing difference can be found only in a single small detail. For example, the buds of the beech and the hornbeam look almost the same. But in the beech they are protruding from the twig and abutting in the hornbeam.

Witches’ brooms, cork lists and much more

There are countless other features, mostly of an incidental nature. For example, the moment the leaves fall and sprouting can differ considerably per species. Oak and beech retain their leaves for a long time. The hazel sprouts early, the ash and walnut late. Some species have scents in winter, for instance the balsam poplar. Birches are easily identified by their white bark and sometimes have witches’ brooms. There is often a slight twist in the trunk of the horse chestnut. Oaks often have galls. Linden trees make a root shot. Sometimes there are still seeds on the tree (ash, plane tree, alder) or remnants of fruits (maple, laburnum). On the branches of the sweet gum tree we can see striking cork moldings.

A lot of characteristic features can be seen in winter. Do go and have a look in the park!

© Henk Wolters Amsterdam 2021