At the end of summer, a tree begins to prepare itself for winter. Deciduous trees, which shed their leaves, start dropping them from this point onward. The exact timing varies by species and is influenced by several conditions. Careful observation of different species can provide valuable insights and contribute to well-designed public spaces. At the same time, leaf fall often causes problems: leaves can clog drains and sewers, and they can make tram and train tracks slippery. By selecting species whose leaves decompose quickly, these issues can be reduced. Landscape architects and green space managers can take this into account by choosing the right species. In this article, we explore several options.
Preparing for Winter
The process of shedding leaves in autumn is not only a beautiful visual spectacle but also a crucial part of the life cycle of deciduous trees. But how does a tree know that winter is coming? The answer differs between species, so let’s look at a few examples.
Many trees commonly planted in cities respond mainly to falling temperatures. This signals them, from September onwards, to prepare for winter. Examples include black tupelo (Nyssa sylvatica), honey locust (Gleditsia triacanthos), and tulip tree (Liriodendron tulipifera).
For species originating from temperate maritime climates, such as the Netherlands, other factors play a role. Here, the weather can suddenly shift from warm to cold, which can catch a tree off guard. Most native trees therefore respond to shorter day length in autumn as their cue to prepare for winter. Some trees also react to changing light conditions, where a low sun combined with cold temperatures signals them to shed their leaves. This is easy to observe in cities: near streetlights, you often see branches holding on to leaves longer. The artificial light confuses the tree, delaying leaf fall. Horse chestnut (Aesculus hippocastanum) is a good example of a tree that responds to day length rather than temperature, shedding its leaves at roughly the same time every year.
The Speed of Leaf Fall
The speed at which a tree loses its leaves depends on multiple factors, with temperature playing a major role. Wind, drought, frost, and sunlight also contribute significantly. Warm temperatures, especially at night, delay leaf fall. This became clear in the unusually warm autumn of 2022: October was warm and dry with little wind, and even into mid-December some oaks (Quercus robur) were still fully in leaf. One night of frost, however, stripped them bare by the next morning. This observation highlights the need for flexibility in municipal leaf-clearing schedules. Choosing species whose leaf fall causes less nuisance can therefore have a positive effect on management.
Conserving Energy
One of the main reasons deciduous trees shed their leaves in autumn is to conserve energy. As temperatures drop and days shorten, photosynthesis becomes less efficient. Photosynthesis is the process in which plants convert sunlight into energy. In autumn, the energy gained no longer outweighs the cost of maintaining the leaves. By shedding them, trees minimize energy use and conserve resources to survive the winter months.
Preventing Drought Stress
Leaf fall also reduces the risk of dehydration. Leaves not only enable photosynthesis but also transpiration, where water evaporates through leaf surfaces. Evergreen broadleaved trees, by contrast, face higher risks: when the ground is frozen and the sun shines, they cannot take up water and may dry out, especially when cold winds add stress. In addition, many evergreen species have low to moderate salt tolerance, which can cause further damage in urban settings. This is why we often see dried-out yew (Taxus) hedges along salted roads, turning brown at the base in spring. Evergreen broadleaved trees also shed leaves annually, but since they continuously produce new ones, they are never bare.
Protection Against Weather
Another important reason for leaf fall is structural protection. In spring and summer, leaves provide excellent shade, but in winter they can become a liability. Snow and ice may accumulate on leaves and branches, increasing the risk of breakage. Without leaves, trees reduce this load and also catch less wind, making them more stable.
Recycling Nutrients
A final, often overlooked aspect of leaf fall is nutrient recycling. Trees do not “waste” their leaves; fallen leaves enrich the soil as they decompose, releasing essential nutrients. This benefits the tree itself as well as surrounding plants, fungi, and soil organisms like worms and insects. Decomposed leaves also improve soil structure, water absorption, and water retention. In public spaces, selecting species whose leaves decompose quickly can be beneficial. Leaves that dry out fast are also easier to clear away.
Semi-Evergreen Trees
Besides deciduous and evergreen species, there are also trees that keep their dead leaves throughout winter. The best-known example is beech (Fagus sylvatica), often used for hedges that remain beautifully bronze-brown all winter. Other species that show this trait to a lesser degree, mainly on younger branches, include hop hornbeam (Ostrya carpinifolia), silver maple (Acer saccharinum), and hawthorn (Crataegus monogyna). As long as a beech hedge is pruned, the plant stays in its juvenile phase and keeps its leaves. This phenomenon may have evolved to deter grazing animals in winter and to protect the bark from sunscald. Just before producing new leaves in spring, the tree finally drops its old ones.
Experience and Design Value
The timing of leaf fall in autumn and leaf emergence in spring strongly affects how a garden or park is experienced. Some species, like Amelanchier lamarckii (Juneberry) and Catalpa bignonioides (Indian bean tree), shed their leaves very early and add little value afterward. Others may be bare in midwinter but leaf out extremely early, shaping the landscape well before spring truly arrives. Examples include Buddleja alternifolia (alternate-leaved butterfly bush) and Crataegus monogyna (hawthorn), which can already be in full young leaf by early March.
A Few Favorites
Early leaf fall: Amelanchier lamarckii, Catalpa bignonioides, Betula pendula, Gleditsia ‘Skyline’, Gymnocladus dioica, Tilia cordata, Tilia pallida
Early leafing: Acer tataricum subsp. ginnala, Alnus cordata, Cornus mas, Crataegus monogyna, Heptacodium miconioides
Semi-evergreen species: Fagus sylvatica, Quercus x hispanica ‘Wageningen’, Quercus x turneri ‘Pseudoturneri’, Quercus imbricaria
Staying green into winter: Sycoparrotia semidecidua, Parrotia persica, Pyrus calleryana ‘Chanticleer’, Alnus cordata, Quercus phellos, Quercus nigra
Some species barely change color in autumn but still drop their leaves while green, such as alder (Alnus glutinosa) and ash (Fraxinus excelsior).
Conclusion
The autumn leaf fall of deciduous trees is a remarkable example of plant adaptation. It enables trees to conserve energy, minimize water loss, and protect themselves against harsh weather. At the same time, leaf fall sustains the surrounding ecosystem by recycling nutrients. What we admire as a colorful spectacle is also a highly functional process. Designers can use these characteristics to make a significant impact in public spaces and landscapes.
