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After approximately 21 years, clear differences had emerged between the two approaches. This study shows that the plantation forests have 16 times more above-ground woody biomass compared to the naturally colonised forests within a period of about twenty years. The plantations had the advantage of being able to accumulate more biomass early in their life due to trees being purposefully planted instead of waiting for them to come naturally as part of the process of succession.
The study ‘ Passive versus active afforestation of agricultural land: Two decades of impacts on tree biomass and ecosystem carbon storage ’ compared agricultural land that had been abandoned and allowed to regenerate naturally with areas that had been actively planted to create plantation forests. Plantation forests had accumulated substantially more tree biomass than naturally colonised forests, demonstrating that deliberate planting can accelerate early forest development and carbon storage. As such, the faster accumulation of biomass led to faster accumulation of carbon in the trees within the early stage of forest development. It is important to note that fast biomass accumulation does not necessarily mean that the plantation mimics all the ecological features of a mature forest. The colonisation that occurred naturally enabled vegetation to grow by the means of ecological succession without any predetermined planting. This process will take more time, but will lead to greater diversity of plants in terms of their species and structure since different plants will colonise certain areas. The Danish study showed that the naturally colonised forests were distinct from the plantation in terms of vegetation and ecology, which proves the necessity of using natural factors in the process of creation of the forest. However, this statement does not mean that plantations cannot be valuable in terms of biodiversity, but only that the structure and composition of such forests differ greatly from the forests developed without planting.
What does the research mean for future forest restoration?
After 21 years, scientists compared naturally regenerated forests with areas deliberately planted with trees. Because plantations would help to achieve faster carbon accumulation, plantations would be an advantageous choice if the aim is to achieve rapid carbon sequestration. Therefore, the scientists show a more complex view of afforestation that does not include only the number of trees planted.
Denmark’s long-running effort to create forests on former farmland has revealed a striking trade-off between carbon storage and biodiversity. Plantations accumulated tree biomass and captured carbon faster, while naturally colonised forests developed greater diversity and more varied ecological structures. The University of Copenhagen conducted a rare long-term comparison of two approaches to forest restoration and found why future reforestation projects may need to balance rapid carbon capture with biodiversity recovery and ecological complexity. The results imply that there is no one particular forest restoration approach that would optimise all of the environmental benefits at once. As for natural regeneration, it would provide greater ecological diversity as the forest develops and could contribute significantly to biodiversity.