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Hybrid aspen ( Populus tremula L. × 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 −1 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. [ABSTRACT FROM AUTHOR]

Pittosporum undulatum Ventenat (Pittosporaceae) is an invasive tree of forests and woodlands in several regions of the world. In the Azores archipelago it occupies about 30% of the forested areas and efforts to valorize its biomass are underway. Implementing sustainable forest management requires basic information on tree age and growth rate, yet this information was lacking. We used tree-ring analysis to obtain accurate age estimates and growth rates from a total of 982 live trees (1318 samples: 646 increment cores and 336 pairs of stem discs) that were sampled in São Miguel, Terceira and Graciosa islands. Pittosporum undulatum showed distinct annual growth rings with an increase in cell-wall thickness and a decrease in cell lumen of the Fibers, from early to latewood. We found trees with ages at base and at breast height ranging from 5/4 to 131/108 years, respectively. Samples taken at tree base and at breast height allowed to estimate a diameter growth rate of 0.38 cm.year −1 , with an average of 8 years needed to attain breast height, and a rotation period of 26 years to reach the average diameter of 7 cm presently found at the stands. Allometric equations relating tree age and diameter at breast height, tree height, basal area and biomass were found to be significant. Among the models with lowest AIC, equations predicting tree age from diameter at breast height or from biomass showed the best fit (R 2 = 0.65 and for R 2 = 0.70, respectively). The developed methods and the obtained results can now be used to support management of biomass valorization projects but also to better understand invasion dynamics at conservation devoted areas. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the potential stem wood production for Norway spruce was estimated for different regions in Sweden. This was done by using basic physiological relationships of intercepted radiation versus biomass production and knowledge of how a water deficit reduces the potential production, derived from results of field experiments on nutrient optimisation. To scale these relationships up to regional and national levels, data of incident radiation and humidity during the growing season for all of Sweden were used. The figures for potential and attainable production indicate that the temperate to boreal climate allows considerably higher production than the current production, if availability of water and nutrients is non-limiting. In northern Sweden, the attainable production is ca. 300% higher than the current production and in southern Sweden, the yield can be increased by ca. 100%. In absolute numbers, as a mean for a whole rotation period, it is possible to achieve an annual stem-wood dry mass production of 7–9Mgha−1 in southern and central and ca. 5–6Mg in northern Sweden. This increased production would mean that rotation periods can be shorter than they are now by 20–30 years in southern Sweden and by ca. 50–60 years in northern Sweden. [Copyright &y& Elsevier]

• Height growth of Norway spruce and Scots pine were assessed from 1986 to 2018. • Trees grew faster than before, especially after the millennium shift. • Increased growth correlated positively with temperature but not precipitation. • Growth increases may suggest higher forest value and shorter rotation periods. For boreal forests in colder climates, changes in environmental conditions are hypothesised to substantially affect ecosystem processes. In this study, trends of top height growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) were analysed using permanent sample plot data from more than 300 long-term experimental sites distributed from temperate zones to the boreal forest conditions in Sweden. By regression analyses, the effects of temperature-sum and precipitation-sum on top height growth were assessed in the period 1986–2018. A significant upward temporal trend in height growth was observed for both species, with the trend more pronounced after the millennium shift. The magnitude of the annual relative height growth after the millennium was about 16.92% and 9.54% higher than expected, respectively for Scots pine and Norway spruce. A potential climate response on height growth was found for both species with temperature-sum positively correlated with top height growth. No significant effect of precipitation-sum on height growth was observed for either species. Our results suggest improved growing conditions and forest sites became more productive in response to increasing temperature in the northern temperate and boreal regions. The increasing growth trends may offer shorter rotation periods and increased forest value for Norway spruce and Scots pine, coupled with contributions of boreal forests to the emerging bio-economy and the regulation of global atmospheric carbon. [ABSTRACT FROM AUTHOR]