Xylem Phenology of Fagus sylvatica in Rarău Mountains (Eastern Carpathians, Romania)

Wood colour metrics are increasingly being used in wood technology and ecology studies. Researchers usually determine the colours of the wood after treatment or in different habitats. There is very little research dedicated to the problem of colour variations among one specific species harvested in different forests or regions. The main purpose of the current research is to reveal and estimate the colour variability of oak species. For this study, a total of 89 samples were taken from the heartwood of seven oak species (Quercus robur L., Quercus cerris L., Quercus rubra L., Quercus pedunculiflora K. Koch., Quercus pubescens Willd., Quercus petraea (Matt.) Liebl., and Quercus palustris Muenchh.). The CIELAB system was used for the assessment of the colour differences. To determine the colour groups and variations, K-means clustering was used. The results show that colour variations do exist. According to the cluster analysis, at least five types of oak wood can be distinguished (because in some clusters, very few samples were present) in the investigated forests. The differences are mainly observed in terms of the lightness (L*) and yellowness (b*). Redness is not a feature by which oak wood differs, but the wood can be brighter or more yellow in some of the samples. The density of the Romanian oaks in the sample does not influence the colour coordinates. The only coordinate affected is a*, but with a very small probability.

Sessile oak (Quercus petraea) is a polytypic species comprising three subspecies (Q. petraea subsp. petraea – Qpe, Q. petraea subsp. dalechampii – Qda, and Q. petraea subsp. polycarpa – Qpo) with distinct ecological requirements, posing significant challenges in morphological differentiation. The integration of macro- and micro-morphological analyses plays a crucial role in clarifying the taxonomic uncertainties. This study aimed to characterize phenotypic diversity and identify key leaf descriptors for distinguishing sessile oak subspecies across three peripheral populations, one reference population, and one sessile oak comparative trail from Eastern Romania. A comprehensive analysis was conducted on 227 sampled trees, utilizing multivariate statistical analysis - encompassing 18 macromorphological and 9 micromorphological leaf descriptors. The results revealed distinct traits of Qda and Qpo, including shorter leaves with maximal width in the lower half of the lamina, fewer lobes, ovate shapes, a subcordate basal shape, and a higher intercalary vein frequency compared to Qpe. Furthermore, Qpo could be differentiated from both Qpe and Qda by its shorter lamina lengths, fewer lobes, greater lobe width ratios, and stellate trichomes with shorter rays. The length of rays of stellate trichomes has emerged as a significant micromorphological descriptor. Qda predominated in peripheral populations, likely due to natural selection in drought-affected local ecosystems. This highlights the importance of prioritizing this taxon in breeding programs and conserving it in situ, given its remarkable leaf plasticity and adaptability. Additionally, principal component indicated a fairly high level of morphological similarity among the three subspecies. These findings emphasize the critical importance of comprehensive morphological analyses for precise species classification and deeper understanding of sessile oak taxonomy.