DOI: 10.3897/silvabalcanica.26.e159961

Authors: Petar Dimitrov

Abstract: National Forest Inventory (NFI) data provided at the field plot-level represent a valuable data source for Species Distribution Modelling (SDM) as demonstrated by many studies. However, a stand-level forest inventory, conducted in some countries, including Bulgaria, is less appropriate because matching these data to spatial predictor datasets is not straightforward. This study aimed to propose and evaluate a methodology for tree species distribution modelling at a national scale driven by stand-level forest inventory data, focusing on Pinus sylvestris L. as a target species. The forest polygons were filtered using a set of attribute and geometric criteria and transformed to points to generate a presence/absence dataset. Based on the literature, four predictor variables were selected, including growing degree-days above 5° C (DD.5), August precipitation (PPT08), potential yearly global radiation (YRA), and soil volumetric coarse fragment content (CF60), all available as 250 m resolution rasters. Generalised Linear Models with different combinations of linear, quadratic, and interaction terms were tested. The effect of spatial errors in the presence/absence dataset was investigated by randomly shifting the points up to 1 km from their original position. Evaluation statistics were calculated by 5-fold spatial block cross-validation repeated 10 times. The basic model, which included only linear terms, performed the worst. The other models were more or less equal performers. The model, which included a quadratic term for DD.5, was therefore selected as the optimal model as it had the most parsimonious structure. The Area under the Receiver Operating Characteristic curve and the True Skill Statistic for that model were 0.80±0.04 and 0.49±0.08, respectively. The model was relatively robust to spatial errors in the occurrence data as simulated by randomly shifting the points. The modelled distribution was much wider than the actual natural distribution of the species, and all mountain areas were identified as potential distribution areas based on these four predictors. As drawbacks of the approach should be noted the assumption of homogeneity of forest stands, the unknown reliability of the inventory dataset, and the low prevalence. Nevertheless, the study demonstrated successfully the utility of the stand-level NFI dataset for SDM.

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DOI: 10.3897/silvabalcanica.25.e135501

Authors: Ivan Evtimov, Fritz Bergmann, Petar Zhelev

Abstract: Genetic diversity of eleven natural populations of Silver Fir in Bulgaria was studied by means of allozyme gene markers. Within population diversity varied among populations and was generally high, but within the range reported for other European populations of the species. Mean number of alleles per locus ranged from 2.1 to 2.4 and effective allele number – from 1.2 to 1.5. Expected and observed heterozygo-sities were also high (mean values 0.295 and 0.265, respectively), but there was significant heterozygote deficiency in most loci and populations, resulting in positive inbreeding coefficient (mean FIS=0.049). Differentiation among populations was low (FST = 0.027), resulting probably from extensive gene flow and recent divergence. The results are discussed in the light of conservation and sustainable management of Silver Fir natural populations.

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DOI: 10.3897/silvabalcanica.25.e121778

Authors: Lora Kirova

Abstract: The carbon accumulation in forest ecosystems helps to mitigate climate changes, therefore the interest in finding strategies for adapted forest management is a major goal of our time. The artificial plantations of Norway spruce (Picea abies Karst) are part of the Bulgarian project to restore the regulatory functions of forest ecosystems. Due to their low resistance, intensive processes of deposition and degradation take place in them, which emphasizes the need to understand the condition of soils and the amount of accumulated carbon in them. This paper reports results from a study on the thinning in even-aged Norway spruce plantations (Picea abies Karst) and its effect on some soil properties. The study includes two thinned plots and an untinned control: 1) Control – an unmanaged spruce plantation, without any activities in it through the last 20 years; 2) Thinned – managed with regular felling over the years, the last of which was carried out 10 years ago with 25% intensity; and 3) Ice storm – plantation damaged from an ice storm in 2007 (when it was 33 years old), felling followed by removal of all affected trees – over 95%, and afforestation with spruce saplings. The soil was examined by layers from 10 cm to 30 cm depth. The main soil characteristics connected with the carbon stocks in soil are analyzed - bulk density, skel-eton, and carbon content. The results of the experiment show that the performed forestry activities were conducted with abidance of the requirements for habitat protection and the ecosystem’s functionality in the studied sites. No significant changes in coarse fraction content and bulk density of soils were found. There is no statistical difference between the plots in the studied depths, but there is a trend of decrease in the organic carbon content in the managed sites. The differences in the soil carbon stocks are significant for the first two soil layers between the control and the managed trough thinning plot.

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DOI: 10.3897/silvabalcanica.21.e54610

Authors: Margarita Georgieva

Abstract: The brown spot needle blight, caused by the fungal pathogen Lecanosticta acicola, has been the most serious and damaging disease on needles of Pinus spp. in recent years. In Bulgaria, the pathogen was reported for the first time in 2017 in a generative plantation of Pinus sylvestris in the region of the State Forestry Ardino, the Eastern Rhodopes. The newly- established invasive pathogen is considered highly adaptable to new hosts and environmental conditions. The life cycle and symptoms of the disease strongly suggest that the new emerging pathogen has the potential to cause severe damages and is a serious threat to naturally distributed species of Pinus in the country. In the period 2018-2019, a spread of L. acicola from the initial outbreak was established throughout stands of P. sylvestris and P. nigra on the territory of Kardzhali District.

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DOI: 10.3897/silvabalcanica.21.e54605

Authors: Sterja Nacheski, Irena Papazova-Anakieva, Stanislava Lazarevska, Blagoj Shurbevski

Abstract: This study presents results for the dynamic of the populations of the pine processionary moth (Thaumetopoea pityocampa) during the period 2007-2017 and the impact of reducing factors in the Repub-lic of North Macedonia. The population density was determined by the number of larval nests both per tree and per hectare that varied during the research period. The number of individuals went up between 2007 and 2010, while during the following years it rapidly decreased. Since 2011, an overall prograding trend has been recorded in the several subsequent years. This could be explained by the huge number of individuals from the previous years that were in a diapause. The abundance of pest populations continued to grow in 2016 as no measures were taken. During the winter of 2016/2017, the impact of the extremely low temperatures on pest mortality was monitored in 2016-2017 generation. The density of the populations came to latency due to the very large number of dead larvae of second and third larval stages. We recorded a 100% mortality of larvae in plantations of Pinus nigra in the regions near Prilep, Sveti Nikole, Shtip, Kochani and Negotino Villages.

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