资源环境科技发展态势分析平台

Hybrid aspen (Populus tremula L x P. tremuloides Michx.) has recently been introduced commercially in the Nordic and Baltic forestry. The hybrid is suitable for biomass production under high latitude conditions and the productivity is promising. Regeneration may be based on vigorous root sucker sprouting. Management strategies for root sucker stands are important for the outcome, but are still under development. Our study examined dynamics, productivity and sustainability of root sucker generations with three different management regimes: 4-year rotation (4YR), 8-year rotation (8YR) and intended 16 year rotation (8+YR), which was halfway in this study. Thinning measures were performed in the two longest rotations, i.e. corridor cleaning in 8YR, and corridor cleaning followed by thinning to ca 1100-1200 stems ha(-1) in the 8+YR rotation. The study comprised a mid-term evaluation eight years after clear cutting of the initial planted stand.

Total woody biomass production during eight years was 98.3, 92.6 and 87.2 Mg DM ha(-1) in the 4YR, 8YR and 8+YR treatments, respectively, but without significant differences. Mean annual increment (MAI) raised rapidly and reached a level of 10-12 Mg DM ha(-1) year in all regimes two years after clear cutting. Stem diameter development was strongly promoted by thinning measures and height development was also positively affected by reduced stand density.

Sustainability in biomass production is essential when relying on sprouting after harvest. We could not see any productivity decline in the two consecutive 4-year cycles included.

Thinning measures often cause a decreased production until canopy closure is reached, but our study showed no decrease, which may be due to the very rapid growth of root sucker stands. The root sucker number was 77,000-124,000 ha(-1) after the first season. Self-thinning was reached after one year leading to a rapid reduction in living shoots in unthinned plots where the share of dead shoots constituted 46-56%, but only 5.0-9.1% of biomass, at the end of the 4-year rotations.

We concluded that different management strategies affected biomass production weakly, but influenced diameter development strongly, which suggests a large flexibility where different management strategies may be selected for various purposes without substantial initial loss of biomass. (C) 2017 Elsevier B.V. All rights reserved.