How do wood anatomy and physiological processes influence maximum tree height?

Studying maximum height in plants poses an interesting insight in the possible consequences of changing climatic condition in the next decades. Since trees are long-lived organisms that could reach ages well over 1000 years, researching what are the factors limiting their vertical growth is rather peculiar. The principal hypothesis which will be tested in this thesis states that hydraulic limitations are the main cause of limiting growth in vascular trees. As such, it can be said that theoretically, it exists a maximum height at which the plant is not able to transport water against the increasing forces of adhesion, cohesion, and gravity. The main goal of this thesis is to see if it is possible to determine said maximum height in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst.). In order to do that, a combination between wood anatomical measurements and isotope analysis will be applied to a few trees from both species. More specifically, the lumen area will be measured via image analysis of previously cut microsections. Following that, the hydraulic diameter and the hydraulic conductivity will be calculated using the Hagen-Poiseuille equation. For the isotope analysis, the ratio 13C/12C for whole wood samples will be computed. In the end, it was found that the lumen area, as well as the hydraulic conductivity for the beech samples decreased with increasing tree height. At the same time, the spruce samples did not show the same trend. Instead, they were found to not have any significant height trend. Moreover, for the carbon isotope measurements, both species did not show any particular height related trend. However, it was found that the spruce samples showed constantly higher values of d13C (i.e., less negative) than the beech ones. Finally, it was not possible to determine concretely if hydraulic constraints did indeed limit maximum tree height in both species, while, at the same time, isotopic data did not contribute to that sense