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The determination of the age at which a stand reaches harvest maturity is one of the most important decision−making problems in the forest management. The method of determining the rotation age depends primarily on the objectives and management practices (e.g. timber production, carbon sequestration), which determine the optimal age of trees for felling. The paper includes the methodological basis of optimization of the rotation age of stands due to the maximization of the accumulation of carbon in the aboveground woody biomass of forest trees. The research method involves two variants of calculating the optimal rotation age: grouping the stands by site class (W−1) and grouping the stands by management method (W−2). For each of the variants four data processing methods were used to optimize the rotation age of stands: allometric formulas (I−1), formulas for the calculation of the aboveground woody biomass (I−2), information on wood density (I−3), and IPCC method (I−4). The study assumes that the optimal rotation age from the point of view of maximizing the rate of carbon accumulation is when the value of increment in the average aboveground woody biomass production S(t)/(t) equals to the value of the current increment in this biomass production – ΔS. At this age, the standing volume R(t) and the volume of carbon stored in the growing stock Ww was calculated. The optimization method is analogous in all variants and approaches. The proposed method of optimizing the felling age of stands is illustrated on the example of Scots pine stands in 1 st site class (variant W−1, approach I−4). The 2014 data from the Information System of the State Forests were used for the calculations. The results (fig.) indicate that due to the maximization of the rate of carbon accumulation, the optimum rotation age for the Scots pine in 1st site class is 56 years. At that age the stand was characterized by the standing volume R(t) of about 305 m³/ha. The total carbon accumulation S(t) before this age was 85 t/ha.
The paper presents determination of the rotation age in Scots pine stands of 1st site index class on the example of Pisz Forest District (northern Poland). The development of quantitative and qualitative changes in the structure of 10 stands, forming a homologous series ranged between 40 and 130 years was the basis for determining their rotation age. Stand maturity for cutting was determined taking into account three variants of production targets considered alternatively. Traditional criteria and financial indicators were adopted to determine the rotation age. The traditional criteria included the absolute yield of a given variant, the average yield of an assortment per hectare and per year and the percentage share of each assortment group in relation to the growing stock of stands. The financial criteria included the assortment value of the considered variants of production targets, the average change in the value of these assortments, the percentage share of each assortment group in relation to the total growing stock and the average price of one cubic meter of the selected assortments groups.
The selection of the rotation time of a stand (from planting to final felling), i.e. the age at which stand reaches harvest maturity, is a key decision in forest management due to, inter alia, the amount and value of carbon stored in the forest. In this context, the basis for the economic optimisation of the rotation age of forests is to define the goal of forest production and desirable state of forests ensuring the achievement of the adopted aim. Therefore, the choice of the most suitable optimal moment of completing a production cycle and starting the subsequent one is very important in forest management. The aim of the performed analysis is to verify the empirical equations and conversion factors as well as to assess their suitability for determining the volume and value of standing timber and accumulation of carbon in the aboveground woody biomass. The verified equations will be used for modelling the optimal rotation age of forests due to the maximization of the rate of carbon accumulation in the aboveground woody biomass. The input data for the verification of equations and conversion factors were grouped according to the dominant species, 10−years age subclass and site index class. Four methodological approaches were used to analyse and estimate the amount of carbon accumulated in the aboveground woody biomass. With the assumption of a continuous use of forest land for timber production, the generated revenues will be same at the same level of costs in the subsequent production cycles. Analysing the results of the optimization of the age of felling maturity it should be noticed that these are the averaged values relating to the State Forests. They do not take into account local differences in the price of raw wood and production costs including the specific characteristics of individual trees or stands. The accuracy (quality) of calculating the average and current increment of stands and, in consequence, of the amount and value of the accumulated carbon is important for the effectiveness of the optimization of the amount of carbon accumulated in the aboveground woody biomass.
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