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

Fransson P, Brännström Å, & Franklin O ORCID: https://orcid.org/0000-0002-0376-4140 (2020). A tree’s quest for light—Optimal height and diameter growth under a shading canopy. Tree Physiology DOI:10.1093/treephys/tpaa110. (In Press)

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Abstract

For trees in forests, striving for light is matter of life and death, either by growing taller towards 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 towards 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 life-time 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 towards the canopy. A short-sighted 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 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.

Item Type: Article
Uncontrolled Keywords: Allocation; Growth strategy; Life history; Optimal control; Tree.
Research Programs: Evolution and Ecology (EEP)
Ecosystems Services and Management (ESM)
Depositing User: Luke Kirwan
Date Deposited: 07 Sep 2020 07:40
Last Modified: 07 Sep 2020 07:40
URI: http://pure.iiasa.ac.at/16677

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