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Mednarodna skupnost za anatomijo lesa žaluje, ker nas je zapustil prof. dr. Pieter Baas (28. april 1944–29. april 2024) iz Nizozemske. Bil je ključna osebnost Mednarodnega združenja lesnih anatomov (IAWA) in desetletja urednik revije IAWA Journal. Več kot štiri desetletja je izjemno prispeval k razvoju anatomije lesa. S svojim življenjem, delom in izjemnimi osebnostnimi lastnostmi je prispeval k rasti in povezanosti svetovne skupnosti IAWA.

The present study focuses on the cambium and the anatomy of secondary tissues (xylem – wood and phloem) of Siberian poplar (Populus sibirica) and Siberian elm (Ulmus pumila) grown in a plantation in the semi-arid Mongolian steppe. Stem and root microcores from both species were collected and subsequently processed to obtain cross-sections for light microscopy by paraffin embedding, sectioning with a rotary microtome, and staining with safranin and astra blue. The results present the anatomy of the secondary xylem and phloem of stems and roots of both species, along with the characteristics of the youngest xylem and phloem annual rings. We discuss the critical aspects which need to be considered when using the microcoring methodology, along with the need for further studies on wood and phloem formation of less-commonly studied tree species and their characteristics when grown in semi-arid environments.

We present a technical note that supplements published procedures on optimal sample preparation for performing wood and phloem formation analyses. Before beginning sampling, it is important to learn about the characteristics of the tree or shrub species to be investigated. Some tips are given how to use the Trephor tool in the best way, how to remove the outer hard bark (periderm), how microcores should be handled after removal from the tree, and how they should be oriented for embedding in paraffin, and cutting thin sections for microscopy. Possible defects that may result from improper handling are illustrated and discussed. We also present optimal images to accurately identify different cell development stages in phloem and xylem, which is particularly challenging in hardwoods and Mediterranean tree and shrub species.

Wood in outdoor applications is exposed to abiotic and biotic factors. If we want to slow down the decay, the wood must be protected. In the past, biocidal products based on copper, chromium, and boron compounds (CCB) were one of the most important solutions for wood protection under extreme conditions. Although CCB is in practice no longer used in the EU, it can serve as a reference for the evaluation of new biocidal products. At the field test site of the Department of Wood Science and Technology, Biotechnical Faculty, an experiment has been carried out under real conditions for 14 years, in which impregnated samples are exposed to the weather according to a double-layer test. In the case of treated wood, we often find that the wood decays faster than expected. In this work we want to determine what contributes to decay based on the analysis of decayed impregnated wood from the field test site. The results show that sufficient retention and penetration of the active substances into the wood ensures the planned service life.

Temporal variability of leaf senescence (autumn phenology) was observed in 2020 in 11 European beech (Fagus sylvatica) trees in Tivoli, Rožnik and Šišenski hrib Landscape Park in Ljubljana, Slovenia, and also observed for spring phenology in the same year. General leaf colouring, BBCH94, occurred between 19 and 24 October 2020, with lower inter-individual variability than that of leaf unfolding, BBCH11. The trees had active leaves (time between leaf unfolding and leaf colouring) between 177 and 199 days. In only three trees total leaf fall, BBCH97, occurred before 19 November 2020. Leaf colouring of the tree included in the long-term monitoring program of the Slovenian Environment Agency ARSO occurred on 24 October 2020. This is 7 days later than the 65-year average of the same tree/location and is ascribed to weather conditions. Investigation of tree tissues showed that the width of the last formed tree-ring in the wood varied between 0.39 and 9.61 mm and in the phloem between 0.09 and 0.26 mm, and that the tissues reflect the health condition of the trees.

Wood identification of barbecue charcoal from commercial packages of three retailers (B1, B2, B3) in Slovenia and Croatia was performed with help of Confocal Laser Scanning Microscopy (CLSM). CLSM enabled us to image key identification features of charcoal wood that were compared with light micrographs of wood from the reference collection. Product B1 contained charcoal made exclusively of beech wood (Fagus sylvatica) and the declaration indicated the address of the producer, in Serbia which allowed traceability of the wood. The selection of wood species in product B2, consisted of red oak (Quercus cerris or Q. rubra), black locust (Robinia pseudoacacia), and cherry (Prunus avium), which could originate from Serbia, and it did not contain tropical wood as stated on the package. Product B3 contained wood from at least four (sub)topical species which could not be exactly identified to species/genus level. The declaration on the product did not allow traceability of wood. As the risks of illegal logging are high for wood of (sub)tropical origin, our results support the initiative that the monitoring of the charcoal trade should be covered by the EUTR - European Timber Regulations.

We used the Confocal Laser Scanning Microscope (CLSM) Olympus LEXT OLS5000 for non-destructive observation and image analysis of wood anatomy traits in growth layers of tree species from different climatic zones. In European beech (Fagus sylvatica), where tree rings can generally be recognised, we discuss the changes in tree-ring structure due to adverse effects (insect attacks). Growth layers in Mediterranean Aleppo pine (Pinus halepensis) from south-eastern Spain are not always annual and contain numerous intra-annual density fluctuations (IADFs). Ocote pine (Pinus oocarpa) growing at high elevation in Honduras showed growth layers with clear growth ring boundaries and IADFs. In both pines, CLSM allowed us to recognise and measure tracheid parameters to define density fluctuations. In tropical true mahogany (Swietenia macrophylla) from Venezuela and cedrela (Cedrela odorata) from Costa Rica, we studied the growth layers with variable dimensions of vessels demarcated by marginal axial parenchyma.

Exact wood identification is usually based on observation of wood features under the microscope. For this, we have to take a sample of the wood from the object and cut thin slides, possibly of all three anatomical sections. Such destructive sampling is often not possible on valuable historical objects, and therefore there is a need for non-destructive approaches. The objective of the study is to present the potential of Confocal Laser Scanning Microscopy (CLSM) using an Olympus LEXT OLS5000 for the identification of wood. We present work on an example of a gothic sculpture, “St. George Defeating the Dragon”. Conventional sampling and microscopical wood identification showed that St. George is made of Norway spruce (Picea abies), and the dragon of poplar (Populus sp.) or willow (Salix sp.). We present crucial features needed for the identification of these species and the limitations with identification if the samples are too small. Finally, we demonstrate the possibility of wood identification of the abovementioned species using CLSM on wood samples without special preparation of the surfaces. CLSM enabled us to observe all the features needed for wood identification.

Before the Second World War, a large underground fortress was built around Goli vrh. Some wood remains in the fort from the time of construction, and some wooden objects have been exhibited in the fort. Several years after the opening of the fort, large scale decomposition was observed on the wood. A sensor for monitoring the relative air humidity and temperature was installed. In addition, a few samples of wood were isolated and examined by X-ray fluorescence spectroscopy and laser confocal linear microscopy. The analysis confirmed the high humidity of the wood and the presence of wood decay fungi on all wood objects, with the exception of wooden ammunition boxes.

A tree ring is defined as a band of xylem-cell layers produced in one year. In Mediterranean trees cambium often produces several bands of alternating early- and latewood during one calendar year, resulting in Intra-Annual Density Fluctuations (IADFs). We present some characteristics of growth layers in Pinus pinea (stone pine) growing on Vesuvius Mountain (near Naples, Italy). The trees showed uninterrupted wood production from January 2015 till the end of January 2016. The ring formed in this period contained five different layers of wood types. Therefore, the wood formed between January and March 2015 would be falsely ascribed to latewood of the tree ring 2014, and the wood formed between March 2015 and the end of January 2016 would be classified as tree ring 2015. We also showed differences in cambium activity in late autumn between years: in November 2015 and 2018 the cambium was still active and not active anymore, respectively. Furthermore, we present the structure of the wood formed in the year 2017 affected by a wildfire in July. Such cases where the growth layer cannot be exactly ascribed to a calendar year should be considered in dendrochronological studies of Pinus pinea and other Mediterranean species.

A local tree-ring chronology of sessile oak (Qercus petraea) was constructed for the site Klanec pri Kozini (KLA), Slovenia (45.59° N, 13.92° E, 450 m a.s.l.) located on the Karst edge on the transition from the sub-Mediterranean climatic to temperate Continental zones. The chronology is 93 years long and covers the period 1925–2017. A comparison with four local oak chronologies from Slovenia and 38 from the surrounding countries (distance 65–220 km) showed that KLA agreed best with the local oak chronology of Rožnik, Ljubljana (ROZ), and two other oak chronologies from central Slovenia (the surroundings of Novo mesto and Ljubljana), one from Croatia and one from Austria. Dendroclimatological analysis showed that the main factor affecting tree-ring variation is June temperature (negative effect) and March precipitation (positive effect), which to a great extent explain the relation to other chronologies. The negative effect of June (maximal) temperature has become increasingly significant in the last few decades, which can be ascribed to warming related to ongoing climatic change.

We present xylem formation in Norway spruce (Picea abies (L.) Karst.) in 2015 at Panška reka, near Ljubljana, Slovenia (ca. 46°00’N, 14°40’E, 400 m a.s.l.) with a temperate climate. The research was a part of a long-term project, which involves different sites and tree species. We measured the widths of cambium and the formation of xylem growth rings with differentiating cells in postcambial (PC) and secondary wall formation (SW) phases, and mature cells (MT). The results for 2015 were compared with those for previous years (2009–2011) in the same species and site, and with the published data from wood formation studies in conifers from all over Europe. The latter were used in two-factor regression models which confirmed the effects of latitude and altitude on the critical dates of onset, end, and duration of xylem production. The models thus helped us to predict/reconstruct phenology of wood formation in conifers in Europe.