11/18/2015

Elevated CO2 Levels Alter Forest Succession and Carbon Cycling

Summary

Regenerating forests influence the global carbon cycle, and understanding how climate change will affect patterns of regeneration and carbon storage is necessary to predict the rate of atmospheric carbon dioxide (CO₂) increase in future decades. While experimental CO₂ elevation has revealed that young forests respond with increased productivity, there remains considerable uncertainty as to how the long-term dynamics of forest regrowth are shaped by elevated CO₂ (eCO₂). In a recent study, researchers used the mechanistic size- and age-structured Ecosystem Demography model to investigate the effects of CO₂ enrichment on forest regeneration, using data from the Duke Forest Free-Air Carbon Dioxide Enrichment (FACE) experiment, a forest, and an eddy-covariance tower for model parameterization and evaluation. They found that the dynamics of forest regeneration are accelerated, and stands consistently hit a variety of developmental benchmarks earlier under eCO₂. Because responses to eCO₂ varied by plant functional type, successional pathways and mature forest composition differed under eCO₂, with mid- and late-successional hardwood functional types experiencing greater increases in biomass compared to early-successional functional types and the pine canopy. Over the simulation period, eCO₂ led to an increase in total ecosystem carbon storage of 9.7 Mg carbon/ha. Model predictions of mature forest biomass and ecosystem-atmosphere exchange of CO₂ and water were sensitive to assumptions about nitrogen limitation; both the magnitude and persistence of the ecosystem response to eCO₂ were reduced under nitrogen limitation. These simulations demonstrate that eCO₂ can result in a general acceleration of forest regeneration, while altering the course of successional change and having a lasting impact on forest ecosystems.

References

Reference: Miller, A. D., M. C. Dietze, E. H. DeLucia, and K. J. Anderson-Teixeira. 20156. “Alteration of Forest Succession and Carbon Cycling Under Elevated CO₂,” Global Change Biology 22(1), 351-63. DOI: 10.1111/gcb.13077.