Thinning Practices Impact Forest Carbon Dynamics, Study Finds

Research from the University of Helsinki reveals that thinning, the forestry practice of selectively removing trees, significantly affects carbon storage and release in different forest types. The study, published on November 5, 2025, investigates the carbon dynamics in two contrasting boreal forest ecosystems: one on mineral soil and another on drained peatland.

The researchers assessed annual carbon accumulation rates and emissions from various components of the forests, including trees, forest floor vegetation, soil, and deadwood, both before and after the thinning process. The findings indicate that the effects of thinning on forest carbon balance can vary notably, influenced by the specific characteristics of each forest type.

Upland Forests Show Quick Recovery

In the upland forest, carbon accumulation in trees initially decreased after thinning but rebounded swiftly. The removal of some trees increased light exposure and space, allowing forest floor vegetation, such as mosses and shrubs, to thrive and sequester more carbon. This transition enabled the forest to revert from being a temporary carbon source in the year of thinning to a carbon sink by the following year.

Associate Professor Anna Lintunen from the Institute for Atmospheric and Earth System Research explained that while carbon sinks typically recover quickly, complete recovery of total carbon stocks requires time, as significant carbon is lost along with the biomass during logging.

Drained Peatlands Face Long-Term Challenges

Conversely, the drained peatland forest, which had already been a net carbon emitter prior to thinning, experienced increased emissions following tree removal. The slower growth rates of trees, compounded by accelerated decomposition of harvested materials, transformed these forests into even greater carbon sources just one year after thinning.

The study found that it may take decades for carbon stocks—comprising carbon stored in standing tree biomass and soil—to return to pre-thinning levels in both forest types. Notably, the drained peatlands continued to show a negative annual carbon stock increase throughout the study period, raising concerns about their ability to regain original carbon storage capacity after thinning.

Gonzalo de Quesada, a doctoral researcher at the University of Helsinki, emphasized the need to adapt forest management practices to the distinct qualities of various forest types. He noted, “Understanding how different forest management practices affect carbon dynamics is essential, especially as Finland and other countries strive to balance timber production with maintaining forests as effective carbon sinks.”

This research underscores the complexity of forest management and its implications for carbon storage, highlighting the critical need for tailored approaches to forestry practices to enhance carbon sequestration and mitigate climate change impacts.