New research from the University of Birmingham reveals that older trees can significantly increase their wood production in response to elevated carbon dioxide levels, challenging previous assumptions about the role of mature forests in climate change mitigation.
Unlocking the Potential of Established Woodlands
For years, scientists have debated the capacity of mature forests to absorb additional carbon dioxide from the atmosphere. Many believed that older trees had limited ability to respond to rising CO2 levels, potentially diminishing their role in combating climate change. However, a groundbreaking study published in Nature Climate Change on August 12, 2024, suggests otherwise.
The research, conducted at the University of Birmingham’s Institute of Forest Research (BIFoR), utilized a sophisticated free-air CO2 enrichment (FACE) experiment in a 180-year-old deciduous woodland. By exposing mature English oak trees to elevated CO2 levels (40% higher than ambient conditions) over seven years, the team observed a remarkable 9.8% increase in wood production.
Professor Richard Norby, the study’s lead author, emphasized the significance of these findings: “Our findings refute the notion that older, mature forests cannot respond to rising levels of atmospheric CO2, but how they respond will likely depend on the supply of nutrients from the soil.”
The Science Behind Carbon Capture in Forests
The BIFoR FACE experiment provides a unique window into the future of forest-atmosphere interactions. Using laser scanning technology, researchers precisely measured changes in tree diameter, converting this data into wood mass calculations. They also assessed overall forest growth, known as net primary productivity (NPP), by factoring in the production of leaves, roots, flowers, and seeds.
Results showed that NPP increased by 9.7% and 11.5% under elevated CO2 conditions in 2021 and 2022, respectively. This translates to an additional 1.7 tonnes of dry matter per hectare per year, with most of the increase attributed to wood production.
Importantly, the study found no corresponding increase in the production of leaves or fine roots, which typically release CO2 back into the atmosphere relatively quickly. This suggests that mature forests could serve as effective medium-term carbon sinks, potentially storing excess CO2 for decades.
Professor Rob MacKenzie, BIFoR Director and co-author of the study, highlighted the broader implications: “We believe these results, at about the halfway point of our fifteen-year experiment at BIFoR FACE, will prove invaluable for policy makers around the globe as they grapple with the complexities of climate change.”
Why it matters: As the world seeks solutions to mitigate climate change, understanding the role of established forests becomes increasingly crucial. This research suggests that protecting and managing mature woodlands could be a more powerful tool in carbon sequestration efforts than previously thought. It also underscores the importance of preserving old-growth forests as natural climate solutions.
However, the researchers caution against viewing this as a silver bullet. To put the findings in perspective, the extra carbon storage observed is equivalent to just 1% of the CO2 emitted by a single commercial passenger aircraft flying one-way from London to New York, per hectare of forest per year.
The study raises several important questions for future research:
1. How do soil nutrient levels influence the CO2 response in mature forests?
2. Will the observed increase in wood production be sustained over longer periods?
3. How might climate change-induced stressors, such as drought or pest outbreaks, affect this CO2 fertilization effect?
As the BIFoR FACE experiment continues into the 2030s, scientists will delve deeper into these questions, analyzing long-term responses and interactions between forest carbon, other plant nutrients, and the forest food web. This ongoing research promises to refine our understanding of forest ecosystems’ role in climate change mitigation and inform more effective forest management strategies.
While these findings offer hope for the potential of mature forests in carbon sequestration, Professor MacKenzie emphasizes that they should not be seen as a substitute for reducing fossil fuel consumption: “Even if the increase in tree growth translates to a medium-term increase in carbon storage in forests, this in no way offers a reason to delay reductions in fossil fuel consumption.”
As we continue to grapple with the challenges of climate change, this research highlights the complex and dynamic nature of forest ecosystems. It underscores the need for a multifaceted approach to carbon mitigation, combining forest conservation with aggressive reductions in greenhouse gas emissions across all sectors of the economy.
