Evolution of tree crown shape and the influence of productivity, incident sun angle, and latitude
2016 (English)Manuscript (preprint) (Other academic)
Across the globe, large variations are observed in plant architecture, from bushes in tundra and semi desert, to high top-heavy trees in boreal and tropical forests. Despite recent advances in large scale monitoring of forests, little is known about how crown architecture varies with environmental conditions. We investigate how shading from the plant on itself, and the shading from the forest influence growth, using a dynamic size-structured crown architecture model with mean-field shading and self-shading, based on an established model. We evolve the two traits crown top-heaviness and crown width-to-height ratio.
We report the following findings: (1) Tree crowns are shaped by trade-offs. Top-heavy crowns intercept light well as they can reach high up in the vertical light gradient, but they have low crown-rise efficiency. Wide crowns have a low leaf density per volume giving low self-shading, but a large cost for branches. (2) When coevolving the two traits we find a single evolutionarily stable strategy, far away from the strategy maximizing net primary production. (3) When only sun angle decreases with latitude, both crown width-to-height ratio and crown top-heaviness are decreasing with latitude. When both sun angle and light assimilation response to canopy openness decreases with latitude, crown width-to-height ratio is decreasing significantly only at sites with low productivity, while crown top-heaviness decreases for all sites independent of productivity. Crown top-heaviness increases with increasing site productivity, as a result of a darker forest caused by an increasing density of plants. (4) When varying latitude and sun angle over large ranges we find that crown width-to-height ratio has a maximum at intermediate net primary production or leaf area index, while crown top heaviness is saturating for high net primary production or leaf area index.
Our model approach makes it possible to study evolving crown shapes in high detail, and we can identify trade-offs for crown shape. As expected crown top-heaviness is increasing with site productivity and net primary production, but crown width-to-height ratio has a rich and a more unexpected response due to interactions of self-shading and mean-field-shading.
Place, publisher, year, edition, pages
forest, plant architecture, ecology
Research subject Mathematics
IdentifiersURN: urn:nbn:se:umu:diva-119541OAI: oai:DiVA.org:umu-119541DiVA: diva2:922200