Black cherry (Prunus serotina Ehrh.) belongs to quite common and the best known invasive woody plants of alien origin occurring in central Europe. On the other hand, little is known about the degree of settling of another North American representative of the Prunus genus from the Padus subgenus – the chokecherry (P. virginiana L.). A considerable morphological similarity of the above-mentioned taxon to P. padus L. is a cause of fairly significant problems associated with its identification. It is not easy to distinguish these related indigenous species, common in forests, as well as in mesophilous thickets in the area of entire Europe. That is why P. virginiana is usually unnoticed and, consequently, it is overlooked in floristic studies. On the basis of the data derived from a variety of sources, mostly collected by the authors in the course of their field trips, supplemented with information from literature, as well as unpublished notes obtained from different persons, information concerning the distribution of secondary P. virginiana sites in Poland is summed up. The article presents a list of 28 such sites together with a map on which their locations have been marked. The discussed species was observed most frequently in the forest environment on eutrophic as well as mesotrophic broad-leaved forest sites in shrub thicket areas at the edge of dense forests. It was also found in broad-leaved and pine coniferous forest underbrush as well as in mid-field thickets. It was established that in Poland, it was not only fully settled in on semi-natural sites but it also encroached upon forest phytocoenoses of natural character. In order to draw attention to possibilities of P. virginiana occurrence in other, hitherto unrecognised synanthropic sites, some remarks and observations concerning morphological features and phenological properties of this taxon in field conditions were included.

This paper presents the results of studies on the influence of soil preparation methods and ways of utilization of logging residues on belowground biomass of 3-year- -old Scots pine saplings, after artificial regeneration. Statistically significant correlations were detected between root biomass and soil preparation methods, while there was no significant impact of logging residues management. Furthermore, interaction of methods of soil preparation and various ways of logging residues management also did not affect the belowground biomass of the plants. The greatest biomass was detected on the area where the soil was prepared by ploughing furrows with the LPz-75 plough. On plots where the soil was prepared by scarifying with rotary tiller, the lowest values of belowground biomass were observed.

The aim of this study was to determine the influence of soil preparation on height of 3-year-old Scots pine plantation. Three methods of cutting residues management and three methods of soil preparation were analysed. Height structure was determined and mean heights in specific variants were statistically analysed. Conducted analysis showed, that the influence of soil preparation method was much greater than cutting residues management. Statistically significant impact on tree height was found in case of scarifying and mixing of topsoil with rotary tiller, where greatest mean height was observed. Ploughing furrows with LPz-75 plough proved to be the most beneficial method of soil preparation. In this case the greatest heights of 3-year-old Scots pines were measured.

The study compared basic density, compressive strength along the grain, static bending strength and modulus of elasticity of juvenile wood in pines from different Kraft’s classes. Analyses were conducted in 8 mature pine monocultures in north-western Poland. In each experimental site a total of 9 trees were selected, thus the analyses were conducted on 72 model trees (with 24 for each social class of tree position in the stand). The highest values of analysed technical parameters were recorded for wood of codominant trees, the lowest were found for predominant trees, while intermediate values were recorded for wood of dominant trees. All the reported differences were statistically significant. Similar dependencies were observed when comparing wood from different sections of stems, with the greatest disproportions, frequently statistically significant, found in their lower sections.

One of the main dendrometric characteristics of Scots pine is the height increment. This characteristic is used to assess the condition of trees and determine radial increments in considered periods. Meteorological conditions have a large impact on the length increments, both during formation of buds and during tree growth. The duration of sunshine is one of the factors influencing the weather, thus the relationship between this factor and height increments was considered in this paper. The correlation coefficients and forward stepwise regression analysis were both used for this purpose. The significant dependences between increments in height of Scots pine and sunshine were shown. The sunshine in the vegetation season (current year) had the largest impact mainly in winter and spring months, as well as in July of the current year.