Marie’s master thesis, titled "Carbon Stocks in Natural Colonized versus Planted Forests", investigates the potential differences in carbon stock levels between naturally colonized and planted forests on former agricultural fields. This research provides valuable insights into the carbon sequestration capabilities of different forest types.

Marie measured and compared three carbon pools: woody biomass, soil organic carbon, and ground/litter layer. The study was conducted at three paired comparison sites in Sjælland, Denmark. Each site consisted of a planted forest (broadleaved) bordering an equally aged, naturally colonized forest.

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Key Findings

• Carbon Stock Distribution: The results showed a difference in carbon stock distributions between the three investigated carbon pools both between treatment and sites. However, the total ecosystem carbon stocks were higher on planted sites.

• Soil Organic Carbon: No significant differences were found in soil organic carbon (0-30 cm) between the naturally colonized and planted sites.

• Development Stages: Naturally colonized sites had developed into different stages, indicating that the rates and trajectories of natural colonization are highly site-dependent.

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There is limited knowledge about the carbon stock levels of naturally colonized forests. Therefore, Marie’s thesis contributes new and important knowledge to the field. This research is directly applicable to land managers, facilitating informed decision-making and sustainable forest and land management.

At Cresco, we encourage more research in this field to increase ecological stewardship.

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In an interview with Marie, she elaborated on her motivation for the project and her recommendations to practitioners and researchers.

My motivation for choosing the thesis topic was to find afforestation methods that support various ecosystem services, including climate change mitigation and biodiversity. In addition, there was limited knowledge about the difference in carbon pools between naturally colonized forests and planted forests, especially in relation to carbon pools other than living biomass.

During the project period, I was surprised to see the large and very clear visual difference between planted and naturally colonized areas. Although my results show that there is a larger carbon stock on planted areas, I recommend that smaller areas will be allocated to natural colonization to achieve higher biological diversity, and because the difference between the carbon pools in naturally colonized forest and planted forests might decrease over time. If land managers decide to let areas colonize naturally, I recommend they patiently commit and ‘let go’ of control to see what happens over time. However, there is limited knowledge about the long-term effects, so I encourage future studies to include longer time series and other parameters such as baselines and previous land uses; soil types; topography; grazing and browsing; and species choice.