National Aeronautics and Space Administration

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Weng et al. 2019

Weng, E., R. Dybzinski, C.E. Farrior, and S.W. Pacala, 2019: Competition alters predicted forest carbon cycle responses to nitrogen availability and elevated CO₂: Simulations using an explicitly competitive, game-theoretic vegetation demographic model. Biogeosciences, 16, 4577-4599, doi:10.5194/bg-16-4577-2019.

Competition is a major driver of carbon allocation to different plant tissues (e.g., wood, leaves, fine roots), and allocation, in turn, shapes vegetation structure. To improve their modeling of the terrestrial carbon cycle, many Earth system models now incorporate vegetation demographic models (VDMs) that explicitly simulate the processes of individual-based competition for light and soil resources. Here, in order to understand how these competition processes affect predictions of the terrestrial carbon cycle, we simulate forest responses to elevated atmospheric CO₂ concentration [CO₂] along a nitrogen availability gradient, using a VDM that allows us to compare fixed allocation strategies vs. competitively optimal allocation strategies. Our results show that competitive and fixed strategies predict opposite fractional allocation to fine roots and wood, though they predict similar changes in total net primary production (NPP) along the nitrogen gradient. The competitively optimal allocation strategy predicts decreasing fine root and increasing wood allocation with increasing nitrogen, whereas the fixed strategy predicts the opposite. Although simulated plant biomass at equilibrium increases with nitrogen due to increases in photosynthesis for both allocation strategies, the increase in biomass with nitrogen is much steeper for competitively optimal allocation due to its increased allocation to wood. The qualitatively opposite fractional allocation to fine roots and wood of the two strategies also impacts the effects of elevated [CO₂] on plant biomass. Whereas the fixed allocation strategy predicts an increase in plant biomass under elevated [CO₂] that is approximately independent of nitrogen availability, competition leads to higher plant biomass response to elevated [CO₂] with increasing nitrogen availability. Our results indicate that the VDMs that explicitly include the effects of competition for light and soil resources on allocation may generate significantly different ecosystem-level predictions of carbon storage than those that use fixed strategies.

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@article{we05200z,
  author={Weng, E. and Dybzinski, R. and Farrior, C. E. and Pacala, S. W.},
  title={Competition alters predicted forest carbon cycle responses to nitrogen availability and elevated CO2: Simulations using an explicitly competitive, game-theoretic vegetation demographic model},
  year={2019},
  journal={Biogeosciences},
  volume={16},
  pages={4577--4599},
  doi={10.5194/bg-16-4577-2019},
}

TY  - JOUR
ID  - we05200z
AU  - Weng, E.
AU  - Dybzinski, R.
AU  - Farrior, C. E.
AU  - Pacala, S. W.
PY  - 2019
TI  - Competition alters predicted forest carbon cycle responses to nitrogen availability and elevated CO2: Simulations using an explicitly competitive, game-theoretic vegetation demographic model
JA  - Biogeosciences
JO  - Biogeosciences
VL  - 16
SP  - 4577
EP  - 4599
DO  - 10.5194/bg-16-4577-2019
ER  -

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