engleski

Natural Drying of Aleppo Pine Biomass

Reduction of forest biomass available in the stand and especially on the forest floor is by many researchers identified as a key component of fire prevention. This especially refers to biomass parts with low moisture content that pose a serious treat either in terms of suitable fuel in the ignition phase of a wildfire or as a fuel feedstock capable to transform ground fire to more destructive and dangerous crown fire. This research was conducted with the goal to determine the structure of the aboveground biomass of Aleppo pine trees and with the goal to determine trends of natural drying of different parts of the aboveground biomass (stem, living branches, dead branches, shoots with needles). Study was established in a mixed Aleppo pine stand near the town of Zadar in Croatia, where the transition from the eumediterranean zone to the submediterranean zone starts. A sample of 20 trees were felled and measured in the period starting from April 15th to September 20th. Additionally, 10 trees were felled in the first week of the research and measured and sampled in two week intervals, starting from April 24th and ending on August 28th. In the observed DBH range (11 cm to 41 cm), the volume of stemwood (> 7 cm overbark) increases from only 0.038 m3 to 1.123 m3. Of this volume 0.017 m3 to 0.784 m3 net volume of wood assortments per tree was produced. The volume of wood with a diameter of 3-7 cm overbark makes about 10% compared to the volume of the wood with a dimeter > 7 cm overbark. In traditional roundwood harvesting this biomass would be left on the forest floor and could pose a threat in terms of wildfire fuel. In addition, it is possible to expect from 11.8 kg to 203.3 kg of bone dry branch biomass (< 3 cm) per tree. Based on the research data it can be concluded that the moisture content of biomass components in fresh state does not depend on the month of the felling (in the investigated period). Duration of natural drying had a significant influence on the reduction of moisture content in some components of the aboveground biomass ; stemwood (samples at the first cross- cutting point) reduced the initial moisture content to just one third, below 20%, and moisture content in living branches was reduced to almost a quarter of the initial value, to slightly above 10%. Moisture content of shoots with needles, in the research period, halved to 15% (but due to variation, statistical difference was not proven). Dead branches had a steady 10–15% moisture content regardless of the drying period. Similar insensitivity to drying period was observed for the stemwood (samples at the base of the stem), but in the wide range of 30–55% moisture content. Research results are expected to have practical application in the field of biomass harvesting in Aleppo pine stands, which is currently still quite limited due to the fact that forests in the research area have a strong protective and recreational function in tourism. But, until intensifying biomass harvesting, the results could hopefully serve as a starting point for forest fire forecast and prevention models.

moisture content, stem, living branches, dead branches, shoots with needles, fire prevention

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