Forests are commonly thought of as arenas dominated by height, where the biggest trees hoard sunlight, hoping to turn their smaller neighbors into shadows.
So violent is the competition in these early years that this stem-exclusion phase plays out brutally: shorter trees die, leaving a canopy dominated by giants.
Trees of vastly different sizes coexist, creating layered canopies that defy the idea that only the tallest can win.
“The competition for light among trees is frequently referred to as an evolutionary arms race, but trees of vastly different sizes successfully coexist in mature forests,” says first author Yusuke Onoda.
This illustrates forest succession into structurally complex, multilayered ecosystems in which diversity is maintained by multiple strategies.
Forests are commonly thought of as arenas dominated by height, where the biggest trees hoard sunlight, hoping to turn their smaller neighbors into shadows. So violent is the competition in these early years that this stem-exclusion phase plays out brutally: shorter trees die, leaving a canopy dominated by giants.
Yet in old-growth forests, something remarkable happens. Trees of vastly different sizes coexist, creating layered canopies that defy the idea that only the tallest can win.
A team from Kyoto University set out to understand this paradox. “The competition for light among trees is frequently referred to as an evolutionary arms race, but trees of vastly different sizes successfully coexist in mature forests,” says first author Yusuke Onoda.
Their approach was to break down growth into two components: light interception efficiency (how much sunlight a tree captures per unit of biomass) and light use efficiency (how effectively that sunlight is converted into new growth).
To validate this framework, they described crown shapes and 3D light profiles for over 2,000 trees across 50 species within 12 forest plots in Japan. And the results showed a distinct trend.
In younger stands, taller trees dominate by sheer capture, forcing rapid stratification. But in older stands, shade-tolerant species grow more efficiently below dense canopies. The time-overlapping coexistence of the vertically transmitted traits provides a solution to close this balance.
The study shifts the paradigm of forest succession from a race to the top to a continuous equilibrium defined by competition for light: capture vs. efficiency, quantified! This illustrates forest succession into structurally complex, multilayered ecosystems in which diversity is maintained by multiple strategies.
The implications reach beyond ecology. They can also help inform climate models, which require accurate representations of forest growth to avoid underestimating future carbon uptake and, more broadly, impacts, and assist with the smart management of forests. The team is now testing their framework on forests in other climate zones, from warm temperate to tropical, and aims to develop a blanket law.
In essence, the study reveals that forests are not just arenas of competition but also of coexistence, where survival depends as much on efficiency in the shadows as on dominance in the light.
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