ProPopulus Team
With the growing demand for high-quality forest products, producing large-diameter timber has become a top priority for the industry. Choosing the right genotype and optimizing tree spacing are crucial to maximizing both productivity and the economic value of plantations. A recent study published in Industrial Crops and Products provides new empirical data that could reshape the way hybrid poplars (Populus × euramericana) are cultivated for this purpose.
The research, titled Enhancing large-diameter timber production: Evaluating poplars by genotype and spacing, authored by Ning Liu, Jan Van den Bulcke, Joris Van Acker, Fenfen Liu and colleagues at Ghent University, examines the performance of twelve hybrid poplar genotypes planted under four different spacing regimes over a 14-year rotation in the Daling River plain in northeast China.
Beyond survival: diameter, volume, and quality
The study shows that while tree height was largely unaffected by genotype or spacing, diameter at breast height (DBH), survival rates, and total stand volume varied significantly.
One of the key findings is that denser planting (2 m × 5 m) achieved the threshold DBH of 24 cm, widely considered the minimum size for large-diameter timber. However, for very large-diameter timber (DBH > 35 cm), wider spacing proved essential, with 4 m × 8 m identified as the minimum effective distance.
Top-performing genotypes and optimal combinations
Using GGE-Biplot analysis, the researchers identified the five best-performing genotypes overall: G2, G4, G11, G1, and G10. Performance, however, varied with stand density. G2 and G11 excelled in high-density plantations, while G4, G10, and G1 delivered the best results under lower densities.
The most productive combination was high-density planting with clone G2 (referred to as D1 × G2), which achieved a total yield of 513 m³/ha, including 288.52 m³/ha of large-diameter timber. This level of productivity is remarkable for commercial poplar plantations, demonstrating that careful genetic and silvicultural planning can optimize both volume and quality.
Early selection: a valuable tool for forest management
Another important insight from the study is the identification of an “optimal window” for early clone selection, between the fourth and fifth year after planting. This finding can greatly support genetic improvement programs, reducing the time and cost involved in evaluating long-term tree performance.
Implications for populiculture
Although conducted in China, the study’s conclusions are highly relevant to regions where poplars are widely cultivated. For the European forestry sector, these results point to new opportunities for orienting plantations toward higher value-added products, particularly as structural timber and engineered wood products gain ground in sustainable construction.
Moreover, prioritizing clones with high survival rates and strong performance under dense planting can help optimize the use of resources such as soil, water, and energy, ultimately improving the profitability of forest enterprises.
Reference
Liu, N., Van den Bulcke, J., Van Acker, J., Liu, F., et al. (2024). Enhancing large-diameter timber production: Evaluating poplars by genotype and spacing. Industrial Crops and Products, Vol. 223, 120148.