Autumn
THE FALL
Autumn brings a transformation when trees become the most luminous landscape objects - coloured up and adrift in the swirl of falling leaves
But why do deciduous trees lose their leaves and how?
All year long chlorophyll dominates the leaf make up, photosynthesising the sunlight into energy for tree growth. As temperatures drop the production of chlorophyll falls and carotenes (a yellow chemical ordinarily present in the leaf) takes over leaf dominance. At this time of the year Ginkgos and Field Maple, in particular, are startlingly butter yellow. If temperatures remain above freezing, with dry and sunny weather, anthocyanins are also produced and these chemicals are pink and red. The transition through the chemical spectrum in the leaf make-up accounts for a gradual morph from green through yellow and then pink, reds and orange.
As autumn wears on, the long daylight hours shorten, and temperatures fall signalling the end of the growing season. Deep in the trees hormone levels are also changing and as auxin reduces it stops supporting the abscission layer that forms the bond between the leaf and stem, allowing the leaves to break free. The characteristic bare branch structure is the trees’ safeguard through winter, allowing winds to run through without damage, conserving moisture in the deep layers of the trunk and saving energy until the next growing season.
During winter however the trees’ root zone is not static, slow root growth continues, expanding and consolidating mycorrhizal relationships below ground throughout winter where the soil seldom freezes in temperate Europe. This is why planting trees in late autumn leads to the best establishment rates. Young trees will continue to put on root growth through the winter so that by spring they are well anchored and their root spread is ready to boost energy for canopy expansion.
Take advantage of the change in visibility that winter trees give us, when the city is no longer buffered by the soft green of our street trees, and the built fabric of urban streets is laid bare. The city is revealed in greater detail in the winter. Times like this are optimum for carrying out townscape and visual assessment giving assessments maximum clarity and visibility.
NOVELL TULLETT is expert in carrying out landscape and townscape visual impact assessments for new buildings and emerging urban districts. Call us now to discuss your project.
Sources:
University of Antwerp 09 01 2025 https://www.wsl.ch/en/news/roots-keep-growing-in-winter-and-that-is-surprising/
Forestry and Land Scotland 30 10 2020 https://forestryandland.gov.scot/blog/trees-in-autumn
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