Karaszewski Zbigniew, PhD.

Harvester use in broadleaves has recently become more effective economically. However, difficulties
with delimbing have shown that not all harvesting heads are suitable and efficient for
broadleaved species. The typical obstacles are mainly large tree sizes, bends and forks in the
trunks and large branches. For these reasons, it is difficult to obtain specific log lengths according
to the settings in the harvester on-board computer. The objective of the research was
to determine: 1) the accuracy of the log lengths from the bottom, middle and top parts of oak
trees, and 2) harvester efficiency in the utilisation of the trunk for logs. The research was carried
out on 61-year-old oaks from which logs with an expected length of 250 cm were processed.
To achieve this length, a margin of error was set in the harvester computer with minimum
and maximum lengths of 252 and 257 cm. For thinning operations, a Ponsse Ergo harvester
with a H7 harvesting head was used. After harvesting, manual log measurements were carried
out on 280 logs: 69, 142 and 69, from bottom, middle and top parts of the trees, respectively.
The largest share of assortments satisfying the minimum requirement of 250–257 cm was
obtained from the middle part of the trees (93%), followed by bottom logs (91%) and top logs
(88%). The highest frequency of logs, which were too short, were found to be the top logs (9%),
while bottom logs were most often too long (6%); therefore, different length settings should be
applied to limit such inaccuracies. Analysis of the last log from the highest part of the tree
indicated a strong goodness of fit between the top diameter and the DBH; the mean value of
the top diameter was 13.3 cm over bark.

Harvesters have become a common solution for wood harvesting in coniferous and broadleaved
stands. Unfortunately, not every customer will accept logs with damage on the lateral surface
of the roundwood caused by feed roller spikes. The extent of the wood damage caused by the spikes
of harvester heads depends mainly on the type of feed rollers and tree species. The objective of the
study was to investigate the external damage to pine (Pinus sylvestris L.) roundwood from
harvester head spikes depending on the season of the year and harvester engine RPM, as well as
the significance and potential consequences of such damage. The scope of the study also included
an analysis of wood damage depth in three stem sections. The experimental plots selected
were all in an 85-year-old pure pine stand. Logging was performed using a Ponsse Beaver harvester
with an H60e harvester head manufactured in 2006. The mean depth of wood damage at
all the points of measurement was 4.1 mm, while the maximum depth of wood damage totalled
5.3 mm. The depth of wood damage depended on the season of the year in which the logging work
was performed, the harvester engine RPM and the stem section from which the log was processed.
The damage was the deepest during summer operations and the shallowest during winter and
springtime. The differences were statistically significant, however, the difference in the depth of
damage was only 1 mm in average. Deeper wood damage was found at a lower engine RPM.
Wood damage depth differed axially, and the least damage was found in the bottom logs.

Silver birch (Betula pendula Roth) is a popular tree species forming stands in nearly the whole of Europe. In Poland, birch is one of the most representative broadleaved species growing on rather poor soils, very often as a mix species with Scots pine (Pinus sylvestris L.). In Central Europe, birch forms trunk often with sweeps, and at the older age with thick branches. Due to that, a harvester thinning operation in birch stands can be challengeable when trying to process logs from the top part of trees, which can finally impact on productivity. The objective of this research was to determine harvester productivity for birch with particular attention to production of logs from the top part of a tree. The research was carried out in stands of North and North-West Poland. All together 21 tests were completed in 16 stands, in which 9 harvesters were used (8 different models). The mean diameter of harvested trees was 23.7 cm with the mean height of 21.7 m. Obtained productivity without delays was on average 21.98 m3 h-1 and varied from as low as 5.14 to maximum 44.66 m3 h-1, and depended mainly on harvested tree size. It was also confirmed that top diameter of the last log depended on diameter at breast height (DBH). The model developed based on that relationship can be used for prediction of biomass volume from birch stands when harvesters are used for thinning.