Do poplar plantations contribute to soil organic carbon storage? A closer look

Do Poplar Plantations Contribute to Soil Carbon Storage? A Closer Look

Poplar plantations, a cornerstone of Italy’s wood economy, are promoted as a promising tool for carbon (C) farming and climate mitigation mainly due to their capacity to store C in the living biomass. However, it remains uncertain whether these systems are capable of having a positive impact on SOC dynamics. Thus, this study aims to investigate the role of poplar plantations in SOC sequestration, addressing key uncertainties while aligning with broader European agenda on C farming. The primary objective was to examine the entire lifecycle of poplar cultivation and its impact on SOC, employing two complementary methodologies: the SOC stock difference approach and the paired comparison method. Specifically, the study focused on: i) assessing the effect of 30 years of poplar cultivation on SOC using a diachronic approach; ii) comparing SOC levels between poplar plantations and the previous land use (e.g., cropland), and iii) assessing the impact of poplar removal and the reestablishment of cropland, both using the paired comparison method.

Leveraging a thirty-year dataset, we analyzed SOC trends at 0–30 cm soil depth in poplar plantations managed under conventional systems, using data collected from the same locations over time. These systems exhibited significant potential for increasing SOC, likely driven by reduced soil disturbance, the incorporation of organic inputs, extended rotation cycles, and improved biodiversity.

To contextualize these findings, SOC levels in poplar plantations and croplands using paired sampling methods were compared. Interestingly, while the diachronic method suggests absolute SOC accumulation over time in poplar plantations, the paired method revealed less pronounced differences between the systems. This methodological discrepancy highlights the complexity of accurately assessing SOC sequestration and raises questions in qualifying the true advantages of poplar plantations over monoculture cropping systems.

Additionally, the third part of this study focuses on the effects of converting poplar plantations back to croplands, with a focus on fields that have been converted in the past 1 to 3 years. This highlights the challenges posed by reverse land-cover changes on the permanence of SOC. The findings aim to guide the development of effective management strategies to mitigate SOC losses during such transitions, ensuring the long-term sustainability of carbon farming practices.