Vusić Dinko, BSc.

The goal of the research was to determine the biomass yield and fuel properties of ten different poplar clones. The research was conducted in an experimental plot established in Forest Administration Osijek, Forest Office Darda, in the spring of 2014. The layout of the plot consisted of three repetitions per clone with 40 plants per repetition in spacing 3x1 m. Based on the DBH distribution, in the early spring of 2018, one sample tree of an average DBH per repetition was selected, thus forming a sample of 30 trees.

Average survival rate of the investigated trees after four vegetation periods was 74.54 ±13.85% ranging from 52.08% (Koreana) to 91.67% (SV885 and SV490). Average DBH of the sample trees was 8.2 ±1.9 cm, height 9.3 ±1.8 m and root collar diameter 10.7 ±1.9 cm. Moisture content in fresh state (just after the felling) ranged from 51.6% (Hybride 275) to 55.9% (SV885). Bark content averaged 18.4%, from 15.4% (Baldo) to 21.1% (V 609). Average nominal density of the sampled trees amounted to 383.5 ±35.9 kg/m3. Bark ash content was on average ten times higher (6.44 ±0.65%) than wood ash content (0.64 ±0.07%) resulting in average ash content of 1.7 ±0.1% (taking the bark content into account).

The clone SV490 showed the highest biomass yield with 15.8 t/ha/year, while the lowest biomass yield was recorded for the clone Hybride 275 with 2.8 t/ha/year.

High inter-clonal productivity variation stresses the importance of selection work to find the most appropriate clones with the highest productivity potential for the given area where the poplar SRC plantations are to be established.

Due to high initial moisture content, if direct chipping harvesting systems are preferred, wood chips could be efficiently used in CHP (Combined Heat and Power) plants that operate on the principle of biomass gasification (where a gasifier is coupled to a gas engine to produce electric power and heat). In several CHP gasification plants operating in Croatia, wood chips with high initial moisture content (from traditional poplar plantations) are used as a feedstock that has to be pre-dried using the surplus heat. In this respect SRC poplar wood chips could make an ideal feedstock supplement.

Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) are both economically and ecologically important coniferous tree species in Europe. Due to climate change, both of them are affected by dieback. This paper examines the quantity, quality, and value of roundwood produced from healthy, severely defoliated (61–99%) and dead Norway spruce and silver fir trees. The study was conducted in four subcompartments located in the Forest Administration Delnice, Management Unit »Milanov vrh«. In total, 81 trees of silver fir (208.77 m3 of gross volume) and 83 trees of Norway spruce (208.43 m3 of gross volume) were measured. Study results showed that the measured gross volume of silver fir was by 8.29% higher than predicted by the harvesting plan, while the measured gross volume of Norway spruce was slightly higher by 0.90%. The determined assortment structure showed a negative correlation between tree crown defoliation degree and the share of highly valuable assortments for both researched species. Healthy trees of silver fir had the highest share of veneer logs, while dead silver fir trees had the highest share of pulpwood. Silver fir dead trees also had the highest share of waste (22.19%), while healthy and severely defoliated trees had 18.69% and 18.47%, respectively. In the case of Norway spruce, healthy trees had the highest share of veneer logs, while dead trees had the highest share of pulp wood. At the same time, the share of waste remains almost the same regardless of the tree crown defoliation degree (from 17.97% for dead trees to 18.17% for healthy trees). Results of the determined assortment structure reflected on the average tree value, which was also negatively impacted by the tree crown defoliation degree. In the case of silver fir, the value of dead trees along DBH classes was 25.6% to 41.6% lower than for healthy trees, while in the case of Norway spruce, the value of dead trees was 22.4% to 36.3% lower than that of healthy trees. The initial hypothesis that average tree value decreases in the order: healthy trees > severely defoliated trees > dead trees was confirmed. To improve harvesting plans, the inclusion of a tree crown defoliation degree as an additional predictor of assortment structure is strongly supported by the results of this study.

Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) are both economically and ecologically important coniferous tree species in Europe. Due to climate change, both of them are affected by dieback. This paper examines the quantity, quality, and value of roundwood produced from healthy, severely defoliated (61–99%) and dead Norway spruce and silver fir trees. The study was conducted in four subcompartments located in the Forest Administration Delnice, Management Unit »Milanov vrh«. In total, 81 trees of silver fir (208.77 m3 of gross volume) and 83 trees of Norway spruce (208.43 m3 of gross volume) were measured. Study results showed that the measured gross volume of silver fir was by 8.29% higher than predicted by the harvesting plan, while the measured gross volume of Norway spruce was slightly higher by 0.90%. The determined assortment structure showed a negative correlation between tree crown defoliation degree and the share of highly valuable assortments for both researched species. Healthy trees of silver fir had the highest share of veneer logs, while dead silver fir trees had the highest share of pulpwood. Silver fir dead trees also had the highest share of waste (22.19%), while healthy and severely defoliated trees had 18.69% and 18.47%, respectively. In the case of Norway spruce, healthy trees had the highest share of veneer logs, while dead trees had the highest share of pulp wood. At the same time, the share of waste remains almost the same regardless of the tree crown defoliation degree (from 17.97% for dead trees to 18.17% for healthy trees). Results of the determined assortment structure reflected on the average tree value, which was also negatively impacted by the tree crown defoliation degree. In the case of silver fir, the value of dead trees along DBH classes was 25.6% to 41.6% lower than for healthy trees, while in the case of Norway spruce, the value of dead trees was 22.4% to 36.3% lower than that of healthy trees. The initial hypothesis that average tree value decreases in the order: healthy trees > severely defoliated trees > dead trees was confirmed. To improve harvesting plans, the inclusion of a tree crown defoliation degree as an additional predictor of assortment structure is strongly supported by the results of this study.