Acta Scientiarum Polonorum
Silvarum Colendarum Ratio et Industria Lignaria

Introduction. Thuja plicata is one of the non-invasive alien species found in Polish forests. It is estimated that the largest forest area covered by this species is located in the Zielonka Forest. The aim of the research  was to determine the current condition of the western red cedar in the Zielonka Forest and to indicate their production potential.
Material and methods. Observations and measurements of T. plicata were carried out in April 2018 in the Zielonka Forest in the Stęszewko Forest Unit, compartment 121 (52°32’15.72”N 17°8’40.92”E). Tree height and DBH were measured and the biosocial position of trees was determined. Statistical analyses were performed using the Kruskal-Wallis test.
Results. The results showed that Kraft’s class II trees dominated the biosocial structure. The infestation of western red cedars with Heterobasidion root disease was observed. The mean tree height was 25.3 m and mean dbh was 36.6 cm. The tallest tree was 33.7 m high, while the thickest tree had DBH of 73.0 cm.
Conclusions. An accurate comparison of the results with previous data was difficult due to the fact that the previous records in Poland has not been preserved. However, it has been shown that the western red cedar is a highly productive species. Currently, in view of the threats posed by climate change and the possible need to include alien tree species in commercial timber production, it is essential to conduct research on the effects of their introduction and methods to improve their productivity. Considering that timber is a renewable raw material, it is necessary to broaden knowledge concerning alien tree species, which would supplement timber production, while at the same time would significantly affect biodiversity of native ecosystems.