A recent study looking at the dynamics of carbon accumulation and loss in forest ecosystems in the Pacific Northwest region of the United States concluded that young forests accumulate the most carbon before canopy closure and old-growth trees play a minor role in additional carbon accumulation. Factors such as increased decomposition-related losses of dead wood contribute to declines in carbon accumulation rates in older stands.
The study, conducted across 8,000 plots across 9.1 million hectares of national forest, aimed to understand how factors such as stand age, plant community type, and site productivity affect carbon accumulation rates and maximum carbon stocks. Researchers determined that while forests in the Pacific Northwest are indeed accumulating woody carbon, the rates vary significantly depending on site productivity and stand age.
They found that while old-growth forests vary in their carbon storage based on productivity, most forests accumulate around 75% of their maximum carbon by age 127. Interestingly, in older forests over 400 years old, the growth of trees balances out with mortality, resulting in minimal change in carbon levels. While forests between 200 and 400 years old still accumulate carbon modestly, smaller trees play a bigger role in overall carbon accumulation, particularly in younger forests.
This study suggests that while old-growth and large trees are significant carbon stores, their contribution to additional carbon accumulation is relatively minor compared to smaller trees, challenging recent ideas about their importance. The findings underscore the complexity of carbon dynamics in forest ecosystems and highlight the importance of considering various factors such as stand age, productivity, and tree size. Understanding these dynamics is crucial for accurately assessing carbon stocks and fluxes, particularly in the context of climate change mitigation strategies.