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Trees have been increasingly considered as modular organisms, with individual shoots forming autonomous units that respond semi-independently to their surrounding environment. However, there is evidence for fairly strict hormonal control of tree crown development. Studies on the hydraulic architecture of trees suggest a closer functional connection between shoots and crown development than is postulated by the theory of branch autonomy. We studied how shoot growth pattern influences growth and crown architecture in young Scots pine trees simulated by the LIGNUM model assuming that (a) the growth of a shoot mainly depends on its light climate and (b) the growth of a shoot is influenced by its position within the crown. We determined shoot position within the crown based on a recently developed vigor index. The vigor index compares the relative axis cross-sectional area from the base of the tree to each shoot and gives a value of 1 to the pathway of the greatest cross-sectional area. All other shoots attain values between 0 and 1 depending on their cross-sectional areas and the cross-sectional areas of the branches leading there from the main axis. The shoot light climate is characterized by annually intercepted photosynthetically active radiation. We compared the results from simulations (a) and (b) against an independent data set. The addition of a within-shoot position index (the vigor index) to our simulation (simulation b) resulted in a more realistic tree form than that obtained with simulation (a) alone. We discuss the functional significance of the results as well as the possibilities of using an index of shoot position in simulations of crown architecture.

The effects of combined production of industrial and energy wood on yield and harvesting incomes, as well as the feasibility of energy wood procurement, were studied. Data for 22 Scots pine (Pinus sylvestris L.) and 21 Norway spruce (Picea abies (L.) Karst.) juvenile stands in Central and Southern Finland were used to compare six combined production regimes to conventional industrial wood production. The study was based on simulations made by the MOTTI stand simulator, which produces growth predictions for alternative management regimes under various site and climatic conditions. The combined production regimes included precommercial thinning at 4-8 m dominant height to a density of 3000-4000 stems ha -1 and energy wood harvesting at 8, 10 or 12 m dominant height. Combined production did not decrease the total yield of industrial wood during the rotation period. Differences in the mean annual increment (MAI) were small, and the rotation periods varied only slightly between the alternatives. Combined production regime can be feasible for a forest owner if the price of energy wood is 3-5 € m -3 in pine stands, and 8-9 € m -3 in spruce stands. Energy wood procurement was not economically viable at the current energy price (12 € MWh -1 ) without state subsidies. Without subsidies a 15 € MWh -1 energy price would be needed. Our results imply that the combined production of industrial and energy wood could be a feasible stand management alternative.

The increase of wood decay due to the fungal pathogen Heterobasidion annosum is expected to increase the vulnerability of tree stands to wind damage due to the decrease in tree anchorage (by wood decay in roots) and stem strength (by wood decay in stem wood). In this work, we developed a framework to simulate the effects of wood decay by Heterobasidion annosum on the vulnerability of Norway spruce (Picea abies (L.) Karst.) stands to wind damage in terms of uprooting and stem breakage. We also demonstrated the model performance by using tree- and stand-level sensitivity analyses. The increase in the amount of wood decay decreased the predicted wind speeds needed for both uprooting and stem breakage of trees and increased the predicted amount of wind damage. The probability of uprooting was higher than stem breakage for infected trees, which was opposite to the findings for the healthy trees. Because of some simplifications in the modelling due to the lack of proper experimental data (e.g., effects of wood decay on strength of roots and stem in Norway spruce), our model may overestimate the risk of wind damage caused by wood decay. Therefore, further model validation is still needed based on experimental research.