Improved management of forest plantations could absorb up to 230 million tonnes/year of CO2 emissions; research by UC Berkeley, TNC and partners finds mixed species plantations 'promising' when prioritizing multiple values, including carbon storage

The study, from researchers at the University of California, Berkeley, Environmental Defense Fund, Conservation International, The Nature Conservancy and partner institutions, assessed the climate impacts of three common management practices in forest plantations: adding fertilizer to trees, interplanting nitrogen (N)-fixing trees, and tree thinning.

While there is momentum behind restoring forests to fight climate change, the improved management of existing forests may represent a more cost-effective and rapidly deployable natural climate solution, removing 100-230 million metric tons of carbon dioxide from the atmosphere each year.

By specifying the conditions in which fertilization and other activities tend to be the most beneficial for carbon storage, the study provides additional information to practitioners on how to maximize the climate mitigation potential of forest management.

The research found both positive and negative effects of all three management practices. Adding fertilizer in plantation forests boosts tree growth—and therefore carbon sequestration potential—but this benefit is generally offset by emissions from inorganic fertilizers. Tree thinning, or managing the density of the forest stand, results in a strong reduction of aboveground carbon storage, but this effect lessens with time. In contrast, interplanting trees with N-fixing trees initially has no effect, but was shown to boost growth in older tree stands. This highlights the importance of mixed species plantations in climate-smart forestry.

“We generally see a preference for even-aged plantations of single species within ‘conventional’ forestry, as these systems can be optimized for wood production and are relatively easier to manage,” said Dr. Jacob Bukoski, an assistant professor at Oregon State University’s College of Forestry and co-author on the paper.

“However, when we prioritize multiple values of forest plantations, such as carbon storage or nutrient cycling, mixed species plantations become very promising.”

The results of the study emphasize the need for a nuanced approach in plantation forest management for climate benefits. Factors to consider include tree species selection and local conditions such as precipitation, soil moisture levels and previous land use.

“Knowledge of site characteristics and tree silvics will allow land managers to make informed choices and apply the right treatment, at the right intensity, at the right timing and in the right context,” said lead author Cyril Melikov, an analyst at the Environmental Defense Fund at the time of this study.

“Following these 4Rs maximizes the chance of delivering climate benefits via forest management.”

Although not all management actions included in the study provide substantial increases in carbon storage over the entire lifetime of plantation trees, they provide additional ecological benefits, such as enhanced forest biodiversity and soil fertility. They also improve resilience to disturbances such as pests or natural disasters, which is crucial for the durability of carbon sequestered on the landscape, particularly in a changing climate.

“To avoid the most damaging effects of climate change, we need urgent action within this decade in both the energy and land sectors,” said Susan Cook-Patton, co-author and Senior Forest Restoration Scientist at The Nature Conservancy.

“Given limited resources and the urgency of climate change, identifying near-term management actions that can maximize carbon stocks in managed forest stands is of paramount importance.”