W połowie lat 90. prof. Laurow pisał, że szlaki są popularnym tematem wszelkiego rodzaju konferencji i szkoleń. Obecnie zauważalne jest ponowne zainteresowanie szlakami, co jak się wydaje, wynika z dwóch przyczyn: zdecydowanego zwiększenia liczby specjalistycznych maszyn leśnych do pozyskania i zrywki drewna wymagających szlaków oraz wymogów stawianych w procesie certyfikacji gospodarki leśnej, ukierunkowanych na środowiskowo bezpieczne technologie pozyskiwania drewna ze szlakami operacyjnymi (zrywkowymi). Zainteresowaniu temu towarzyszy brak w praktyce użytkowania lasu wytycznych co do kryteriów i zasad udostępniania drzewostanów dostosowanych do dzisiejszych realiów funkcjonowania gospodarki leśnej. Opracowanie takie powinno bazować na rezultatach krajowych badań, których niestety brakuje. Ostatnie wytyczne dotyczące szlaków powstały w połowie lat 90., a opracowano je na podstawie wyników badań IBL nad wpływem technologii pozyskiwania i zrywki drewna na poziom uszkodzeń środowiska leśnego. Badania te nie obejmowały zagadnień związanych z wpływem szlaków na kształtowanie się np. zasobności drzewostanów, czy też określonych cech drzew rosnących przy szlakach. Tematyka ta coraz częściej staje się przedmiotem zainteresowania leśników-praktyków stojących przed koniecznością, czy też widzących potrzebę, udostępnienia drzewostanów dla maszyn pozyskujących i zrywających drewno w cięciach przedrębnych. Powyższe uwarunkowania legły u podstaw podjęcia przez autora badań, których wyniki są przedmiotem niniejszej pracy.

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1. WSTĘP 

2. PRZEGLĄD LITERATURY I HIPOTEZA BADAWCZA 
2.1. Przegląd literatury 
2.2. Hipoteza badawcza

3. CEL I ZAKRES BADAŃ 

4. TEREN I METODY BADAŃ 
4.1. Teren badań 
4.2. Metody badań 
4.3. Opracowanie statystyczne wyników badań

5. WYNIKI BADAŃ 
5.1. Charakterystyka drzewostanów 
5.2. Redukcja potencjału produkcyjnego drzewostanu 
5.3. Cechy biometryczne drzew 
5.4. Przyrost miąższości, grubości i wysokości drzew
5.5. Wskaźniki jakości technicznej drewna drzew na pniu

6. ANALIZA I DYSKUSJA WYNIKÓW BADAŃ 

7. WNIOSKI 

LITERATURA 

SUMMARY

The research study on the effects of skid trails on the tree stand productive potential was conducted in age class 2, 3 and 4 pine stands during thinning operations. The assessment of these effects was made in the area, volume and quantitative contexts. The biometrical features included tree diameters at breast height, tree heights, tree crown lengths and the heights of the crown base. Growth and increment measurements comprised tree volume, thickness and height, and among various wood technical quality indicators, the following ones were analysed: tree taper, ovality, crooks and knots.
The research study on the tree stand productive potential was carried out between 1998 and 2000 (the skid trails were cut in 1990 and the tree stand was 32 years old at that time). The following wood harvesting and extraction variants were tested in course of the research study:

Cs-PK – tree length method, harvesting with a chain-saw, horse skidding,
Cs-PC – tree length method, harvesting with a chain-saw, extraction with a farm tractor,
S-PF – cut-to-length method, harvesting with a chain-saw, extraction with a forwarder,
S-HF – cut-to-length method, harvesting with a harvester, extraction with a forwarder.

The variants Cs-PK, Cs-PC and S-PF were applied in the age class 2 stand, whereas in the stands of age classes 3 and 4 the following variants were used: Cs-PC, S-PF and S-HF. The distance between skid trails was 30 m in the Cs-PK, Cs-PC and S-PF variants, and it was 20 m in the S-HF variant. The widths of the skid trails were 1.5 m, 2.5 m and 3.5 m for the Cs-PK, Cs-PC and S-PF/S-HF variants, respectively.
The tree stand productive potential reduction related to the area was assessed on  the basis of the area of the skid trails, calculated by multiplying their length and width (1.5 m, 2.5 m or 3.5 m), and the area occupied by the leave (remaining) trees growing on skid trails. The reductions in tree numbers and in wood volume were computed based on the percentages of the numbers and volumes of trees removed from the skid trails.
Measurements of biometrical features, increments and technical wood quality were carried out in the youngest tree stand, opened with 2.5 m and 3.5 m wide skid trails in 1990 (variants Cs-PC and S-PF). The analysis of biometrical features and technical wood quality indicators comprised their mean values for the trees growing in zones that were 0-1 m, 2-4 m and 8-10 m away from the skid trail. The last one was considered the control plot. In the case of ovalities, the geographical directions W-E and N-S, in which these tree form defects occurred, were also taken into account. The biometrical features, ovalities and the stem taper values were analysed twice: in 2005 and in 2010, whereas crooks and knots were measured in 2010 and increments – in 2010-2011. The sample plots, where the technological variants S-PF and Cs-PC were applied had 5 skid trails each. The analysis of the tree diameter distribution was made on all the trees growing along skid trails, while the analysis of the tree height distribution was made on a part of trees and the assessments of knots and tree form defects were made on sample trees.
The analysis of increments was made on 45 sample trees that were felled (3 trees for each zone along all 5 skid trails) in each technological variant. These three trees felled in each zone were selected based on DBH measurements in the course of which the mean DBH value and the standard deviation were calculated, and they had the following DBH values: tree 1 = mean DBH, tree 2 = mean DBH + std. dev. and tree 3 = mean DBH – std. dev. The increment measurements on the felled trees were carried out for one 5-year time period prior to the cutting of the skid trails and for two such time periods after the cutting. The tree volume increments were measured on wood discs taken from the centres of 2-meter wood sections, and the diameter increments were measured on wood discs cut 1.3 m off the butt end of the stem.
For the biometrical features of the trees, tree form defects, knots and increments in volume, diameter and height the basic position and distribution statistical values were computed and the significance of differences between their mean values was tested. In the case of the ovalities, also the relation between the ovality value and the height of its occurrence on the tree was analysed.
The results of the investigation confirmed the effect of skid trails on the production potential of the tree stand and on some biometrical features, increments of trees, and – to a lesser extent – on indicators of the technical wood quality of standing trees. The maximum value of the reduction in the tree stand area, calculated on the basis of the physical area of the skid trails, accounted to 17.9% and it was found in the age class 4 stand, where the technological variant S-HF was applied. It was almost twice as high as the maximum reduction value (the youngest tree stand, variant S-PH) calculated on the basis of the area that would have been occupied by the leave trees on skid trails. The reduction in the number of trees was similar to that of the area reduction, calculated on the basis of the area occupied by the leave trees. The reduction in wood volume was on average about 30% lower than that in the number of trees, and the highest values of the indicators describing the reductions in volume and in the number of trees were found in the age class 2 stand, in the S-PF technological variant, and the relevant values reached 5.8 and 8.8%, respectively. Among the biometrical features of trees, that were analysed, the DBH values and tree crown lengths widely varied. The DBH and tree crown length values on the trees in the 0-1 m zone were statistically significantly higher than the corresponding values on trees in the 2-4 m and control zones. Such differences in tree heights were not confirmed. The cutting of skid trails affected the increments in volume and in diameter. The highest volume and diameter increment values were shown by the trees growing in the 0-1 m zone, but only the differences in diameter increment values for the first 5-year time period, after cutting the strip trails in the S-PF variant were statistically significant. Although the volume and diameter increments on trees growing in the 0-1 m zone were higher than in the other zones, in the case of the tree height the result was reverse – the trees showed lower height increment values. Although the differences were statistically insignificant, the increment values were higher in the variant with wider strip trails (S-PF). In the case of the technical wood quality indicators, analysed on standing trees, significant differences were found for knots only.Trees growing in the 0-1 m zone showed statistically significantly higher diameters of knots, compared to the trees in 2-4 m and 8-10 m zones.
The results of the study showed that the effects of skid trails on the analysed biometrical features of trees, increment values and technical wood quality indicators were limited to trees growing close to the trails (zone 0-1 m). The widths of the skid trails did not affect the results obtained (with the exception of tree thickness and heights increment and the ovality shares in the N-S and W-E directions in 2010, in the S-PF variant).