From progeny trial to stand projections: A modelling approach to genetic gains in silver birch

In the Baltic Sea region, silver birch (Betula pendula Roth) is a key species for plantation forestry, valued for its fast growth, adaptability, and economic importance, particularly in the region's strong plywood industry. This industry produces high-quality, long-lasting wood products that provide an effective means of long-term carbon storage. The study evaluates the impact of genetic improvement and thinning regimes on the productivity, carbon accumulation, and economic outcomes of silver birch plantation in Latvia. Using data from a 12-year-old progeny trial, we modelled stand development under different forest reproductive material (FRM) categories: unimproved (‘source-identified’), moderately improved (‘qualified’), and genetically superior (‘tested’). The simulations incorporated a defined thinning regime and projected growth, stand volume, carbon stocks, and financial returns over a rotation period targeting a mean diameter of 27 cm. The projected mean annual increment reached 14.7–14.9 m³ ha^-1 year^-1 for improved FRM. Results show that commercial thinning reduced rotation periods by 10 years and increased net present value (NPV) by over 1900 %. Genetically improved FRM further enhanced outcomes, with ‘tested’ material achieving the highest NPV (2712.7 EUR ha⁻¹), a 39 % increase compared to unimproved material. These genetic gains were achieved while maintaining high carbon accumulation rates (4.6 t C ha⁻¹ year⁻¹) and reducing rotation periods by an additional 5 years. Furthermore, the enhanced production of high-value veneer products from improved FRM ensures long-term carbon storage, as carbon remains sequestered in durable wood products for decades. The study demonstrates that combining thinning with genetically improved FRM significantly boosts productivity and economic returns, while maintaining carbon accumulation and offering a promising approach for sustainable silver birch plantation forestry in the Baltic region.