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Research article - Peer-reviewed, 2020

A tree’s quest for light—optimal height and diameter growth under a shading canopy

Fransson, Peter; Brännström, Åke; Franklin, Oskar


For trees in forests, striving for light is matter of life and death, either by growing taller toward brighter conditions or by expanding the crown to capture more of the available light. Here, we present a mechanistic model for the development path of stem height and crown size, accounting for light capture and growth, as well as mortality risk. We determine the optimal growth path among all possible trajectories using dynamic programming. The optimal growth path follows a sequence of distinct phases: (i) initial crown size expansion, (ii) stem height growth toward the canopy, (iii) final expansion of the crown in the canopy and (iv) seed production without further increase in size. The transition points between these phases can be optimized by maximizing fitness, defined as expected lifetime reproductive production. The results imply that to reach the canopy in an optimal way, trees must consider the full profile of expected increasing light levels toward the canopy. A shortsighted maximization of growth based on initial light conditions can result in arrested height growth, preventing the tree from reaching the canopy. The previous result can explain canopy stratification, and why canopy species often get stuck at a certain size under a shading canopy. The model explains why trees with lower wood density have a larger diameter at a given tree height and grow taller than trees with higher wood density. The model can be used to implement plasticity in height versus diameter growth in individual-based vegetation and forestry models.


allocation; growth strategy; life history; optimal control; tree

Published in

Tree Physiology
2020, volume: 41, number: 1, pages: 1-11

Authors' information

Fransson, Peter
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Fransson, Peter
Umeå University
Brännström, Åke
Umeå University
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
International Institute for Applied Systems Analysis (IIASA)

UKÄ Subject classification

Forest Science
Computational Mathematics

Publication Identifiers


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