A study at the Norbury Park Estate (adjacent to BIFoR-FACE) highlights the role that soil plays in offsetting carbon sequestration, and how this might undermine afforestation initiatives.
Since the industrial revolution the atmospheric concentration of greenhouse gases (GHGs) like carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) have risen significantly, driving climate change and representing one of the most pressing environmental challenges of our time.
To address the growing climate crisis, numerous global initiatives have been implemented, such as afforestation projects aimed at enhancing carbon sequestration. Enhancing carbon sequestration might seem simply a case of growing the fastest-growing trees as fast as possible. However, the overall effectiveness of carbon offsetting by afforestation depends on several variables. Such variables include soil management and ecosystem resilience, which are critical for achieving long-term climate goals.
At the Norbury Park estate, adjacent to the BIFoR-FACE LTE, a team at the University of Birmingham is looking at using intensive silvicultural practices to speed up tree growth, namely irrigation and fertilization. This estate is a newly afforested site that was established in 2019 from former arable land. Unlike traditional forest management, these intensive silvicultural practices actively accelerate forest growth rates. But their impact on GHGs requires careful evaluation, especially when converting from arable land into woodlands.
The team investigated the combined influence of N-based fertilizer and irrigation on sandy loam and loam soils. Through this, the results demonstrate how changes in soil-borne GHGs emissions could potentially undermine the intended goal of afforestation.
Afforestation project at Norbury Park Estate, Staffordshire. Photo credit: Andrea Rabbai
Despite increased tree growth, key findings indicated:
1) A significant rise in soil CO2 emissions.
2) An almost fourfold greater emission factor for N2O compared to the official IPCC estimates.
3) A shift of the Norbury Park sites from being a sink to a source of another powerful GHG: CH4.
These factors positively contributed to higher GHGs emissions. This highlights the detrimental effects of coupled irrigation and fertilization practices on biogeochemical cycles.
This research sheds light on an often-overlooked piece of the afforested ecosystem chessboard: the soil. Rabbai et al. (2024) advocate proper site evaluation when designing local-to-global afforestation initiatives and silvicultural strategies. While public attention focuses on the apparent benefits of accelerated green growth, this study offers a reminder of the critical importance of considering the “dirt” beneath our feet.
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