Rozprawa naukowa nr 455

Lasy na gruntach porolnych to jeden z istotniejszych problemów współczesnego leśnictwa. Zalesienia gruntów porolnych były dosyć długo uważane za rezerwuar drewna energetycznego oraz narzędzie ograniczania szkodliwej działalności wiatru. Współcześnie zalesione grunty porolne pełnią funkcje środowiskowe (ochronne), społeczne i produkcyjne. Rola gruntów porolnych w tworzeniu nowych fitocenoz leśnych skłoniła do podjęcia prób wypracowania nowych strategii zalesień gruntów porolnych.
Specyficzne warunki produkcji leśnej na gruntach porolnych mają swoje podłoże przede wszystkim we właściwościach gleby. Duża zawartość azotu w glebie upra­wianej rolniczo, większa wartość odczynu niż w glebach leśnych, obecność podeszwy płużnej, brak korzeni stanowiących nisze ekologiczne dla mikroorganizmów i grzybów antagonistycznych typowych dla gleb leśnych zostały nazwane „zespołem gruntu porolnego”. Na skutek zalesienia gruntów porolnych właściwości gleby ulegają z czasem istotnej modyfikacji. Zmianie ulega przede wszystkim porowatość gleby, pH oraz zawartość podstawowych pierwiastków.

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1. WSTĘP

2. STAN BADAŃ
2.1. Wprowadzenie
2.2. Struktura drewna    
2.3. Biomechaniczna stabilność drzew
2.4. Właściwości drewna
2.5. Hipoteza badawcza

3. CEL I ZAKRES BADAŃ

4. METODYKA
4.1. Założenia metodyczne
4.2. Prace terenowe
4.3. Prace kameralne

5. WYNIKI
5.1. Charakterystyka drzew modelowych
5.2. Allometryczne wskaźniki stabilności drzew
5.3. Właściwości drewna
5.4. Mikrostruktura, ultrastruktura oraz udział ligniny w ścianach cewek
5.5. Współzależności i prawidłowości w związkach pomiędzy badanymi zmiennymi

6. DYSKUSJA
6.1. Stabilność drzew wzrastających w warunkach gruntów porolnych i leśnych
6.2. Właściwości i cechy tkanki drzewnej
6.3. Biomechanika oraz stabilność drzew wyrażona współczynnikiem C_ST

7. PODSUMOWANIE

8. WNIOSKI

9. LITERATURA

SUMMARY

It was assumed in this study that growth and development conditions for trees grow­ ing on former farmland in relation to those found in typical forest sites may have a signif­ icant effect on the formation of tree tissue and thus influence the biomechanical stability of trees. In this study the term tree biomechanics refers to radial and axial variability of wood properties as well as relationships between indexes of tree stability based on biometrie traits and wood properties and its ultrastructure.
Analyses were conducted on production pine stands at felling age, growing on former farmland and on typical forest soils, on sites optirnal for this species in a given nature forest province. Mean sample plots were established in the regions of Poland with high shares of mature stands growing on former farmland. A total of twelve mean sample plots were established in six forest divisions (Warcino, Trzebielino, Olesno, Drawsko, Kaczory and Szczecinek).
A total of 36 model trees were identified and felled (three in each mean sample plot). Selected biometrie traits were measured on each felled tree and next materiał was col­ lected for analyses of physical and mechanical properties of wood. Materiał for wood tissue testing was collected from 50-cm blocks from a distance of 1.30-1.80 m from the kerf plane, next from the middle of the stem and the base of live crown. Mechanical properties were tested on absolutely dry samples and on samples which moisture content exceeded the fibre saturation point. Moreover, 'from each sample tree the materiał for analyses in the form of discs was collected at breast height and in the analyses shares of basie wood components and cell wall width were determined.
In view of many interactions between properties and characteristics of wood tissue at various levels of wood structure a comprehensive and in-depth interpretation of results is not an easy task. Pines growing on former farmland in terms of the biometrie traits analysed in this study resembled trees growing on forest soils. No significant differences were observed between them in indexes of tree stability as described by the slendemess ratio (H/D_1.3), the centre of gravity of a tree (L_K/H) and crown inclination (D_K/H).
Structurally and chemically wood of trees growing on former farmland had signifi­ cantly thinner tracheid walls, lower lignin content in walls and a higher share of the crystalline cellulose fonn. Moreover, in wood of pines growing on former farmland wood density was significantly lower (by approx. 6%) and static bending strength of wood at saturation point and absolutely dry wood was by approximately 12% lower in comparison to trees growing on forest soils. Moreover, compressive strength along the grain was lower by approximately 8% in wet wood and by 13% for dry wood. Differ­ences in wood strength were significant at both tested wood moisture contents. In wood of trees growing on former farmland radial variation in the tested properties was found to be atypical for this species. In this group of trees values of all the investigated wood properties deteriorated within the circumferential stem zone, which was particularly evi­dent in the distribution analysed at breast height and at mid-length of the stem. In both investigated groups of trees all wood properties analysed in this study were significantly correlated. Significant dependencies were also observed between characteristics of trees, together with indexes of stability, and wood properties and structure as well as between the analysed components of wood structure and its properties.
Results indicate a greater biomechanical stability of trees growing on forest soils in relation to pines growing on former farmland. This is confirmed by higher values of mechanical properties in wood at saturation point at similar indexes of stability based on biometric properties of trees. Thus it may be stated that the description of tree and stand stability based solely on coefficients conceming morphological traits of trees is burdened with an error. It results from the fact that these indexes do not take into consid­eration adaptation changes in wood tissue, which may have a significant effect on modification of biomechanical tree stability. In this study biomechanical tree stability was described using the stability index C_ST, taking into consideration both strength quality factor at static bending and slendemess ratio of a tree. It is difficult to extensively apply this index in practice, but such an approach may contribute to a more comprehensive outlook on biomechanical stability of trees and stands.