Wood specimens of fir (Abies alba Mill) and beech (Fagus sylvatica L.) were chemically modified using polycarboxylic acids (PCA), cured by convection heating or microwave treatment and analyzed by HPLC. A new non-formaldehyde cross-linking system was composed of citric acid (CA) and 1,2,3,4-butanetetracarboxylic acid (BTCA), which are representative polycarboxylic acids (PCAs). These reagents require phosphono-based catalysts, so a sodium hypophosphite (SHP) catalyst was used in this study. The effects of PCA treatment were compared with a previously introduced 1,3-dimethylol 4,5-dihydroxy ethylene urea (DMDHEU) treatment. The dimensional stability of the modified wood was determined in terms of the anti-swelling efficiency (ASE) using the water soak/oven dry method. The results revealed an improvement in ASE for wood modified with PCA compared to modification with DMDHEU. Qualitative and quantitative determinations of bound acids were performed by HPLC. Further intensification of the wood modification process and an increase in the quality of wood-based materials were achieved using microwave treatment. Among other benefits, the formation of cross-links between the wood and the reagent components led to an improvement in the tensile strength retention, particularly in combination with the microwave treatment.

We investigated the structure and width of the dormant cambium and of the increments of phloem and xylem of Quercus robur to estimate their potential as indicators for tree vitality. The samples were taken from three woodlands, two in Slovenia (KRA and MUS) and one in Croatia (KOB), with reported tree decline. The number of dormant cells seems to reflect the initial capacity of the cambium to accomplish cell division. With the exception of two trees at KRA, cell production was always higher on the xylem side than on the phloem side. The annual phloem increments were narrower, less variable among trees and with clear lower and upper limits. With increased cambial cell productivity, the share of the xylem in the total annual radial increment increased following a curvilinear function. In trees with an annual radial increment > 3.5 mm, the xylem size represented more than 90 % of the total radial growth. The anatomical variables analyzed show that the most limiting environmental conditions seem to prevail at KRA, whereas the conditions at MUS seem to be most favorable in terms of radial growth. Analysis of the width and structure of xylem and phloem increments, the number of dormant cambial cells and their interrelationships can provide additional information on the vitality of oaks.

• Previous articles have shown that modifi cation of wood by citric acid (CA) improves dimensional stability and resistance of wood against fungi attack. However, chemical modifi cation of wood also modifi es its

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• The article presents preliminary results of the biological durability of oil heat treated (OHT) alder wood (Alnus glutinosa) against pure cultures of rot fungi (Postia placenta and Trametes versicolor) in lab conditions. The modifi cation was performed by heating of specimens immersed in soya oil