A new HSM 904Z 6WD skidder of a large size was tested in a 140-year-old beech stand in northern Poland. The aim of the study was to analyse machine productivity and impact on the soil (bulk density and cone penetrometer test) and the remaining natural regeneration caused by skidding. Trees were cut by chainsaw and, if possible, felled into the direction of the skidroads. After delimbing, logs with a top diameter of a minimum 7 cm over the bark were prepared. The average skidding operational productivity including piling was 21.0 m³·h^-1. At the same time, the level of damage in natural regeneration was: 18% (38% due to both: felling and skidding). An analysis of the soil after skidding showed that the density had grown by 15-30 g·cm^-3. Increase of penetration resistance was up to 2.77 MPa as the biggest.

The aim of this work was 1) to investigate the genetic diversity of H. annosum s. str. populations, 2) to recognize genets ability of their aggressiveness to Scots pine. The genetic similarity among genets varied from 0% to 74%. Totally different genets were found in 17.9% of cases. The lowest similarity occurred among 20.7% of genets and it was calculated on 18%. Six months after inoculations of Scots pine stems by H. annosum s. str. the distance of wood colonization by mycelium was measured. Wood was colonized to a distance varying from 0.52 cm to 2.06 cm. The most aggressive genets were isolated from stumps, and the less aggressive from trees’ stems. The infections in stands caused by H. annosum s. str. basidiospores and appearance of a new pathogen’s organisms, which might distinguish by high aggressiveness, could increase a damages in these stands. There is still a need to use a biological control against root rot disease to reduce spreading of a new generations of pathogens.

The aim of this study was to determine the virulence of H. parviporum genets with known genetic similarity and representing pathogen’s population, which infested a part of Norway spruce stand. Genets caused average 47% mortality of spruce seedlings in infection experiment in vitro. The mortality rate varied from 16% to 80%. In infection experiment in vivo the mycelium of H. parviporum caused the wood necrosis on distance from 0.8 to 7.78 mm. 56% of genets of investigating population characterized by high virulence, 22% by average and 22% by low virulence.

Oak trees play a significant naturalistic and economic role. Common oaks represent the most valuable forest-creating species in Poland. In the recent years, on the area of the whole country, one can observe a visible deterioration of the health conditions in oak tree stands. It is difficult to indicate the main factor responsible for this phenomenon. Because of the wide range of this observation, it can be assumed that this process is caused by many biotic and abiotic, as well as anthropogenic factors. Studies were out in the Sulęcin Forest District. At the turn of July and August in the years 2009 and 2010, an assessment of the losses in the majority of trees showed a medium degree (49%). Another group of trees showed 36% of leaf loss, while 14% of oak trees did not show any losses at all. A very high degree of defoliation was found only in 1% of trees. The presented data indicate that an average loss in the assimilation apparatus of oak trees amounted to 29.15%.