Slide 1
Seasonal leaf loss is a controlled transition
Many deciduous trees shed leaves seasonally. Releasing a leaf is part of a controlled transition, not simply the wind tearing healthy leaves away.
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Leaves lose water through gas exchange and cost resources to maintain. Seasonal shedding can help a tree pass through cold or dry periods when those costs outweigh the benefits.
Slide 2
Losing green pigment reveals other colours
As chlorophyll breaks down, yellow and orange pigments can become more visible. Autumn colour reflects changes within the leaf's chemistry.
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Red pigments may also be produced in some leaves. The display is not one pigment replacing another everywhere, which helps explain differences among species and among individual autumns.
Slide 3
The tree recovers some nutrients before the leaf falls
Before a leaf falls, a tree can move some nutrients into its longer-lived tissues. The leaf's contents are not all discarded together.
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This recovery supports later growth when conditions improve. Fallen leaves still contain material for decomposers, so nutrient transfer within the tree and recycling through soil both occur.
Slide 4
A separation zone releases the leaf and protects the stalk
A specialized zone at the leaf stalk helps the leaf detach. Protective tissues reduce damage at the point of separation.
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Weather can finish the physical release, but the tree has prepared the boundary. This distinguishes ordinary seasonal leaf fall from a branch being broken by a storm.
Slide 5
Fallen leaves feed decomposers and let light through
Fallen leaves cover the ground and become food for decomposers. Their arrival also opens the canopy to more light.
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Plants and animals experience both changes. A forest's seasonal transformation includes ground-level habitat and nutrient pathways, not only the colours visible in the canopy for a few weeks.
Sources
- Why Do Leaves Change Colors in the Fall
National Park Service
- Plant Health: Autumn Leaves
US Forest Service