Abstract

Competition among plants of the same species often results in power-law relations between measures of crowding, such as plant density, and average size, such as individual biomass. Yoda’s self-thinning rule, the constant final yield rule, and metabolic scaling, all link individual plant biomass to plant density and are widely applied in crop, forest, and ecosystem management. These dictate how plant biomass increases with decreasing plant density following a given power-law exponent and a constant of proportionality. While the exponent has been proposed to be universal and thus independent of species, age, environmental, and edaphic conditions, different theoretical mechanisms yield absolute values ranging from less than 1 ton early 2. Here, eight hypothetical mechanisms linking the exponent to constraints imposed on plant competition are featured and contrasted. Using dimensional considerations applied to plants growing isometrically, the predicted exponent is−3/2 (Yoda’s rule). Other theories based on metabolic arguments and network transport predict an exponent of−4/3. These rules, which describe stand dynamics over time, differ from the “rule of constant final yield” that predicts an exponent of−1 between the initial planting density and the final yield attained across stands. The latter can be recovered from statistical arguments applied at the time scale in which thesite carrying capacity is approached. Numerical models of plant competition produceplant biomass-density scaling relations with an exponent between−0.9 and−1.8 depending on the mechanism and strength of plant-plant interaction. These different mechanisms are framed here as a generic dynamical system describing the scaled-up carboneconomy of all plants in an ecosystem subject to differing constraints. The implications of these mechanisms for forest management under a changing climate are discussed and recent research on the effects of changing aridity and site “quality” on self-thinning are highlighted.

Keywords

constant final yield; mono-specific stand; plant biomass; plant competition; plant density; power-law; self-thinning

Published in

Frontiers in forests and global change
2020, Volume: 3, article number: 62

SLU Authors

• Vico, Giulia

  • Department of Crop Production Ecology, Swedish University of Agricultural Sciences
    

Sustainable Development Goals

Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss


UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.3389/ffgc.2020.00062

Permanent link to this page (URI)

https://res.slu.se/id/publ/108583