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How does competition for light shape the canopy of a forest?

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Tall giant sequoia trees with reddish bark and thick trunks rise closely together in a dense forest at Sequoia National Park, California. — Tree A stand of giant sequoia trees (*Sequoiadendron giganteum*) in Sequoia National Park, California.

Competition for light is a primary driver of forest structure, as trees compete for access to the aerial environment to maximize photosynthesis. Because trees cannot move to seek resources, they have evolved trunks that allow them to reach upward, leading to distinct morphological differences between open-grown trees and forest trees.1

In a forest, trees compete for growing space, which typically results in a foliage-free trunk (bole) below a limited crown. The aggregate of these crowns forms the forest canopy, which acts as a filter for sunlight; a full-canopied forest may absorb 60 to 90 percent of available light.12

This competition shapes the canopy in several ways:
* Stratification: Depending on the species composition and their light requirements, the canopy may be displayed in a single layer or stratified into multiple stories or layers.12
* Resource Partitioning: Trees partition light in time and space, with some species or life stages (such as seedlings) exhibiting higher shade tolerance than others.1
* Structural Complexity: The intensity and quality of light streaming into the forest dictate its growth, structure, and composition, leading to complex vertical stratification in diverse ecosystems like rainforests.12