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Forests are integral to the global land carbon sink, which has sequestered ~30% of anthropogenic carbon emissions over recent decades. The persistence of this sink depends on the balance of positive drivers that increase ecosystem carbon storage—e.g., CO2fertilization—and negative drivers that decrease it—e.g., intensifying disturbances. The net response of forest productivity to these drivers is uncertain due to the challenge of separating their effects from background disturbance–regrowth dynamics. We fit non-linear models to US forest inventory data (113,806 plot remeasurements in non-plantation forests from ~1999 to 2020) to quantify productivity trends while accounting for stand age, tree mortality, and harvest. Productivity trends were generally positive in the eastern United States, where climate change has been mild, and negative in the western United States, where climate change has been more severe. Productivity declines in the western United States cannot be explained by increased mortality or harvest; these declines likely reflect adverse climate-change impacts on tree growth. In the eastern United States, where data were available to partition biomass change into age-dependent and age-independent components, forest maturation and increasing productivity (likely due, at least in part, to CO2fertilization) contributed roughly equally to biomass carbon sinks. Thus, adverse effects of climate change appear to overwhelm any positive drivers in the water-limited forests of the western United States, whereas forest maturation and positive responses to age-independent drivers contribute to eastern US carbon sinks. The future land carbon balance of forests will likely depend on the geographic extent of drought and heat stress.
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Understanding forest dynamics by integrating age and environmental change
Summary How much carbon a forest ecosystem can sequester is determined by both postdisturbance regrowth and environmentally modified growth. Disturbance causes sharp declines in the short term and is followed by regrowth in the long term. Environmental change may alter carbon accumulation through increasing CO2, nitrogen deposition and climate change. Regrowth and modified growth occur simultaneously, yet they are usually studied separately and assessed using an additive approach. Alternatively, an interactive approach using hierarchical models can address their concurrent nature and evaluate their joint effects. Hierarchical models are informed by forest age data, which have recently become available at global scales. The age‐based hierarchical framework provides a coherent and feasible way to integrate regrowth and modified growth in understanding forest dynamics.
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- Award ID(s):
- 1926438
- PAR ID:
- 10372557
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 228
- Issue:
- 6
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 1728-1733
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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