Assisted Migration and Large-Scale Restoration in Europe Would Require Over 100 Billion Seedlings

Climate change is expected to profoundly alter the climatic suitability of tree species across Europe, necessitating large-scale reforestation and assisted migration to maintain forest ecosystem services. Here, we present a pan-European projection of potential seedling requirements under assisted migration across three reforestation strategies: conifer-preferred, broadleaf-preferred, and promotion of natural regeneration. Our simulations show that under the moderate-emission scenario (RCP4.5), total seedling requirements range from ~92 billion under the natural-regeneration-oriented strategy to ~144 billion when broadleaves are prioritized. Under the high-emission scenario (RCP8.5), demand rises substantially, reaching up to ~192 billion seedlings across the landscape.

Temporal patterns differ between scenarios. Under RCP4.5, seedling requirements are highest early in the century, with 2035 totals of ~69–72 billion for replacement-focused strategies and ~47 billion for the natural regeneration scenario, declining steadily toward 2095. In contrast, RCP8.5 projections peak at the end of the century, reaching ~76–82 billion seedlings for replacement-focused strategies and ~50 billion under natural regeneration.

Species composition of projected demand varies with reforestation strategy. In the conifer replacement strategy, silver fir, Scots pine, and black pine dominate, together requiring roughly 50–60 billion seedlings, with higher totals under strong warming. In the broadleaf-focused scenario, pedunculate oak, European beech, and sessile oak account for over 40 billion seedlings under moderate warming and exceed 55 billion under RCP8.5. Prioritizing natural regeneration reduces overall demand, though these broadleaf species remain dominant, requiring ~30–35 billion seedlings even under strong climate change.

Spatially, Central-East Europe represents the largest potential market, driven primarily by Poland, Belarus, Ukraine, Romania, and Czechia. Under RCP8.5 with broadleaf expansion, these countries collectively require over 72 billion seedlings, with Poland and Belarus alone accounting for ~23 and ~21 billion seedlings, respectively. Central-West Europe forms the second-largest market, led by Germany (~28 billion seedlings), while Northern, South-Eastern, and South-West Europe show moderate to low demand, rarely exceeding 15 billion seedlings per region.

Our results highlight the scale of effort required to implement assisted migration in Europe and emphasize the critical need for strategic planning in seedling production and distribution. Central and Central-Western Europe, in particular, will likely require substantial increases in nursery capacity and cross-border coordination to meet projected needs. These findings provide actionable insights for policymakers and the nursery sector, supporting the development of climate-adapted reforestation strategies capable of sustaining Europe’s forests under future climate conditions.