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|ŠUMARSKI LIST 11-12/2014 str. 32 <-- 32 --> PDF|
Given that the objective of “timber management” type of forestry is to provide the optimal combination of quantity and quality of timber products that will maximize economic profit, the development of accurate and flexible models is necessary to provide the information required. The variable used in decision-making regarding timber management is volume. The total volume of trees is commonly estimated from regression models using the breast height diameter and the total height as predictors (Van Laar and Akça 2007).
In this study, randomly selected Scots pine trees from the central part of the Rhodope Mountains were measured. Data collected were used as input for the development of regression models that estimate the total tree volume. Development of such models is particularly important, because there are no other models for Scots pine for that area. Also, the effect of nearest trees to sample trees was examined, in an attempt to uncover possible relation between distance and species of the nearest trees and form factor of the sampled trees.
2. Materials and Methods
Materijali i metode
2.1 Study area – Područje istraživanja
The study area was in the central part of the Rhodope Mountains, which is under the management of the Forest Service of Xanthi, Greece. Data covered an area about 3100 ha (longitude 41º19’N and latitude 24º43’E), where altitude range from 1200 to 1500 m. (Figure 1).
In the wider region, stands of Fagus sylvatica L. s.l., Pinus sylvestris – F. sylvatica, Abies borisii-regis – F. sylvatica – P. sylvestris, and F. sylvatica – A. borisii-regis and are mainly occurred (Milios 2000a, 2000b, 2004, Milios et al. 2008). Scots pine species occurs mainly in mixed stands with beech in three productivity sites. The age of Scots pine trees in several cases exceeds 120 years (Milios 2000a, 2000b).
In the scots pine – beech stands, the basal area of scots pine ranges from 17.00 to 41.15 m2/ha and in beech ranges from 0.39 to 26.38 m2/ha. In almost all cases scots pine appears mainly in the overstory. On the other hand, in a rather small totally area beech appears with many trees in the overstory (Milios 2000a, 2000b).
2.2 Data collection – Uzorkovanje
Raw data were collected in the framework of a Master thesis prepared at the Department of Forestry and Management of the Environment and Natural Resources, of Democritus University of Thrace, in Greece (Lipiridis 2013). Sampled trees were selected applying Neyman’s random stratified sampling, with optimum distribution of sampled units to strata (Neyman 1934). Stratification was applied by distinguishing three site types (A, B, C) in the study area (Milios 2000a). Site type A represents the best sites (good site quality), B the intermediate sites (medium site quality) and C the worst sites (poor site quality). The distinction of site types was based on a combination of site attributes and the growth performance of predominant trees, using plots of 500 m2. The site distinction was referred mainly to F. sylvatica that is the main (abundant) late successional species