Milko Milev, Stefan Yurukov, Kiril Lyubenov, and Petar Zhelev

Faculty of Forestry, University of Forestry, 10, Kliment Ohridski blvd, 1756 Sofia, Bulgaria. E-mail: m_milev@abv.bg

Without

Tatiana Stankova^1,2 and Ulises Dieguez-Aranda¹

¹Department of Agroforestry Engineering, Higher Polytechnic School,University of Santiago de Compostela, 27002 Lugo, Spain. E-mail: tatianastankova@yahoo.com
²Forest Research Institute - BAS, 132 Kliment Ohridski Blvd., 1756 Sofia, Bulgaria.

The main objective of this study is to derive a diameter distribution model for Scots pine (Pinus sylvestris L.) plantations in Bulgaria, which predicts with high confidence the allocation pattern of the tree diameters from stand level variables. As the investigated stands showed predominantly unimodal distribution pattern, their diameter distributions were characterized by 2-parameter Weibull function. Six methods for its parameter estimation were examined: two methods for parameter recovery through moments (PRM_L and PRM_S), a method for parameter recovery through the stand basal area (PRM_B), two parameter prediction methods (PPM_NLS and PPM_MLE), and a modified parameter prediction method based on a mixed-effect model (PPM_Mixed). An empirical percentile model, not connected to a predefined functional form of the distribution, was fitted for comparison. The choice of the best performing model involved estimation of ranks based on Kolmogorov-Smirnov test and Error Index values for goodness of fit evaluation, against a fit and a validation data sets. Two of the parameter recovery methods (PRM_L and PRM_S) and one of the parameter prediction methods (PPM_NLS) performed best, PRM_S being the overall outperformer and PRM_L being the simplest for application. The empirical percentile model ranked fourth and was not advantageous for representing diameter distributions of Scots pine plantations. The two best models derived (PRM_L and PRM_S) describe well the diameter allocation pattern of the Scots pine plantations in Bulgaria and can be applied to estimate the diameter distributions from stand level variables in a simple and reliable way.
 

Nadka Ignatova and Sonya Damyanova
 

Department of Plant Pathology and Chemistry, Faculty of Ecology and Landscape Architecture, University of Forestry, Sofia, 10 Kliment Ohridski Blvd., 1756 Sofia, Bulgaria. E-mail: nadia_ignatova@abv.bg
 

Beech forests in the Western part of Bulgaria have been monitored in order to assess the risk of harmful effects of lead (Pb) and cadmium (Cd) pollution by means of Critical Loads calculations and their exceedances by real deposition. Critical loads of Pb and Cd for two sites (Vitinya and Petrohan) have been determined using the 'Steady State Mass Balance' method based on the heavy metal uptake by the biomass and the leaching of the metals in the root zone. Real deposition of Pb and Cd was measured every two weeks during a one-year period by collecting the throughfall in plastic collectors (6 for each site). All samples have been analysed for their Pb and Cd content using atomic emission spectroscopy. The same method has been applied for measuring the content of Pb and Cd in the wood of beech trees. Fluxes of leaching water were measured in grid cells of 10 x 10 km for the entire country. The results obtained show that the critical loads of both Pb and Cd are lower for the Vitinya site demonstrating the higher sensitivity of beech to the pollution of heavy metals in comparison with the Petrohan site. In addition the real deposition of Pb and Cd has been higher at the Vitinya site. Although there were no exceedances of critical loads of Pb for both sites, additional deposition in the future will lead to a sooner exceedance of the critical load at the Vitinya site as compared to the Petrohan site. We conclude that the beech forest at the Vitinya site is at risk of damages by Cd pollution whereas the beech forest at the Petrohan site is more tolerant to heavy metal pollution due to its higher critical loads.

Chris Stuart Eastaugh and Hubert Hasenauer
 

Universitat fur Bodenkultur (BOKU) Institute of Silviculture. Peter Jordan Strasse 82, A-1190 Vienna, Austria. E-mail: cseastaugh@yahoo.com.au

Forest policy and forest carbon accounting systems must be underpinned by appropriately accurate information, yet such information is often difficult and expensive to collect. This has led to the promotion of more cost-efficient forest sampling methodologies, and to the rise of modeling as a means to predict or interpolate changes to forest conditions in response to various stimuli. The accuracy of such modeling is usually determined through comparison with field data, often collected at a relatively limited number of sites.
Large bodies of relevant forest data are collected in National Forest Inventories, but there are inherent methodological problems in using this NFI data for model validation, particularly if such data is collected using angle-count sampling. Angle-count sampling has the advantage of being a relatively fast and cheap method of collecting forest data, but it is generally considered that at least four samples should be taken at a site for the results to be usefully precise. Some NFIs however take only a single angle-count sample at each fixed sampling point. Although at a broad scale these results may give useful figures, their usefulness at the plot scale is severely limited, especially if the intent is to judge plot timber volume increments or prepare forest carbon budgets. The availability of a time series does however allow for some statistical correction to single angle-count estimations. This study demonstrates the statistical uncertainties in using angle-count time series, and develops a method of reducing such 0 to a level that angle-count NFI data may be usefully used for comparisons with forest models.
 

Valeria Messingerova^1*, Miroslav Stanovsky^1**, Stanimir Stoilov², and Michal Ferencik^1***

¹Department of Forest Exploitation and Mechanization, Technical University in Zvolen, Faculty of Forestry, 24 T. G. Masaryka St., 960 53 Zvolen, Slovakia. *E-mail: messin@vsld.tuzvo.sk; ^**E-mail: stanov@vsld.tuzvo.sk; ^***E-mail: ferencik@vsld.tuzvo.sk
²Department of Technologies and Mechanization of Forestry, University of Forestry, 10 St. Kliment Ohridski Blvd., 1756 Sofia, Bulgaria. E-mail: stoilovs@ltu.bg

The aim of this study is to evaluate the wood chips production as fuel for energy sector in the State Forests Enterprise of Slovak Republic logging conditions. Working operations of primary transport are analyzed – ground-based skidding systems that drag or carry logs from stump to landing, transportation of energy wood chips in containers. The main result of the research is the possibility to optimize the energy wood chips transportation methods from environmental and economical point of view. The paper deals with the knowledge and experience of increasing the value of less valuable wood from thinnings.