Issues

Abstract

In Bulgaria, the apple (Malus × domestica Borkh.) has a long history of cultivation, and there is a wide diversity of genetic resources in the country. Wild relatives of this fruit species can be found in forests or other habitats. The local genetic resources are valuable due to their good adaptation to the climate and soil conditions of the natural habitat. In addition, they often have a number of valuable characteristics, such as resistance to diseases and pests, which should be conserved and used as donors for breeding programmes. The aim of the current study was to investigate the diversity of seedlings and local genotypes mapped during expedition studies in the Troyan region, Central Balkan Mountains of Bulgaria, in order to assess their characteristics and select the most valuable ones for future breeding purposes. For these purposes, the fruit size, flesh firmness, the total soluble solids content (°Brix), the skin and flesh colour were measured. All the characteristics studied were highly variable in the population. Fruit flesh colouration varied from white to pinkish. Regarding chemical analysis, very high sugar content was recorded in PM 11 (18.08 %), PM 12 (18.32 %), and PM 25 (17.44 %). All analysed samples had higher invert sugar content and lower sucrose content. Of all the studied genotypes, PM 17 and PM 104 had very low acidity. The studied local forms do not comply with modern market demands but are valuable for preserving biodiversity and for breeding purposes because of their good adaptation to the climatic conditions in the region.

Received: 26 June 2025 / Accepted: 13 December 2025 / Available online: 17 December 2025

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Abstract

The study was conducted on areas where the conservation agricultural systems were applied (No-Till). A crop rotation system of winter oilseed rape and winter wheat has been maintained for the past five years. The present research was carried out over two growing seasons (2019/2020 and 2020/2021). The absence of rotation and differences in the herbicide application, as well as the presence of the same species in the years of the survey, can be considered as the first signs requiring the conduct of annual regular surveys according to the methodology. Such monitoring is essential for the detection of herbicide-resistant weed species. The weed flora monitoring was performed in three agricultural locations: the town of Brezovo and the villages of Streltsi and Varben. A total of 54 weed species were identified, belonging to 22 botanical families, with a ratio of 89:11 (monocarpic : polycarpic). They were assigned to eleven biological groups, comprising 43 annual (monocarpic) and 10 perennial (polycarpic) species. Among the annuals, 6 were monocotyledonous, 36 dicotyledonous, and 1 bulbous species. The family Poaceae was the most abundant in the surveyed areas, represented by 9 species distributed across four biological groups: annual species, from which: winter spring – Apera spica-venti (L.) P.Beauv.; overwintering – Bromus arvensis L.; late spring – Setaria viridis (L.) P.Beauv., Echinochloa crus-galli (L.) P.Beauv., Setaria glauca (L.) P.Beauv.; early spring – Avena fatua L., Lolium temulentum L.; and perennials (rhizomatous weeds) – Sorghum halepense (L.) Pers. and Cynodon dactylon (L.) Pers. The aim of this research was to characterise the weed flora in crop production areas under the crop rotation system of winter oilseed rape and winter wheat.

Received: 21 July 2025 / Accepted: 04 December 2025 / Available online: 10 December 2025

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

Abstract

The aim of this study is to determine the current volume increment of high-stemmed European beech (Fagus sylvatica L.) stands within the territory of Petrohan Training and Experimental Forest Range at elevations ranging from 1400 to 1600 m a.s.l. Permanent and temporary sample plots were established in pure, simple, relatively even-aged stands. Trees within the plots were measured using callipers, and several heights within each diameter class were taken to determine the standing volume. Increment cores from trees of varying diameter classes were taken using a Pressler increment borer to measure the current radial increment over the last ten years. The width of annual rings was measured using CooRecorder software. The current volume increment was estimated using two methods. The first method is based on the difference between the volume measured at the time of the study and the volume ten years ago, while the second method was based on growth tables. Comparison was made between the volume increment results obtained by the two methods. The results indicate that the increment values established in the present study considerably exceed (on average by 5–6 times) the increment levels derived from the growth tables at stand density 1.0. The highest increment rates (8.1 and 8.4 m3∙ha-1) were recorded in stands with a density above 1.0 (1.2–1.3). Equations derived using Gerhardt’s formula for calculating the current increment were developed, which may be applied in beech forests within the enterprise’s territory at the indicated altitudes.

Received: 21 July 2025 / Accepted: 28 November 2025 / Available online: 02 December 2025

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

Abstract

Forests are highly productive ecosystems that act as carbon sinks, where soil organic matter is formed from the residues of biomass decomposition as well as carbon deposited by the rhizosphere. Soil microorganisms play a crucial role in these processes by decomposing plant litter, thereby causing changes in the physical and chemical properties of the soil. This study aimed to determine whether soil bacterial activity can serve as an indicator of soil health and forest condition. In this study, Biolog EcoPlate™ assay was used to analyse the community-level physiological profiles (CLPPs) from spruce forest soils. Samples were taken from two plots in coniferous forests with soils classified as Dystric Cambisols (Sample plot 1, SP1) and Eutric Cambisols (Sample plot 2, SP2) in three depths (0–10, 10–20 and 20–30 cm). Soils were sandy clay loam and clay loam, respectively. Average microbial activity (expressed as the area under the curve, AUC) was nearly twice as high in SP2 as in SP1. In SP1 highest activity was measured at the 10–20 cm depth, while in SP2 it was measured at 20–30 cm. CLPP showed higher bacterial affinity for polymers and lower for carbohydrates. There was a significant difference in the metabolic activity among carbon guilds utilisation (p < 0.05) but not among different depths (p > 0.1). Tween 40, Tween 80 and γ-aminobutyric acid were preferentially utilised, while 2-hydroxybenzoic acid, α-ketobutyric acid and glucose-1-phosphate had the lowest utilisation rates. The strong linear correlation between microbial Shannon diversity and Evenness indices showed that depth influenced these rates, but not the number of utilised carbon sources. Results indicate that microbial activity can serve as a quick and reliable indicator of forest ecosystem functioning.

Received: 24 June 2025 / Accepted: 19 November 2025 / Available online: 21 November 2025

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Abstract

Microbial biomass carbon (MBC) and the enzymatic activities of catalase and cellulase were investigated in soils within Sofia Municipality in an agricultural ecosystem (Vrazhdebna district), forest ecosystems (Vitosha Nature Park, Zheleznitsa, and Dolni Pasarel areas), and urban soil (green area, Dolni Pasarel village), in a seasonal context, with and without the influence of local water sources. MBC and the activities of catalase and cellulase were higher in the agricultural soils than in the forest soils, which is also attributable to the fact that they are tilled and irrigated, with trends of higher microbiological activity in spring compared to summer. In most soils of Vitosha, the inflow of water from local sources creates anaerobic conditions that reduce the accumulation of microbially derived carbon and the enzymatic activity of microorganisms. Soils in Vitosha, Zheleznitsa and Dolni Pasarel are acidic, while those in Vrazhdebna are neutral, suggesting mainly bacterial biomass in the latter and more mould fungi in acidic soils; anaerobic conditions in waterlogged sites further limit mycelial microorganisms. Correlation analysis showed a strong negative relationship between MBC and soil moisture (r ≈ -0.73; -0.69), a weak positive relationship with pH (r ≈ 0.08–0.15), a moderate positive relationship with temperature (r ≈ 0.30–0.38) and catalase (r ≈ 0.50–0.60) and a strong positive relationship with cellulase (r ≈ 0.61–0.66). Catalase activity was moderately negatively correlated with moisture (r ≈ -0.53; -0.45) and moderately positively with pH (r ≈ 0.49–0.52); cellulase showed a weak to moderate negative association with moisture (r ≈ -0.33; -0.27), a weak to moderate positive association with temperature (r ≈ 0.28–0.31) and a moderate negative association with pH (r ≈ -0.21; -0.26). Regression analysis confirmed the role of pH as a stable predictor – positive for catalase and negative for cellulase in both seasons, and showed that in spring catalase was the strongest positive predictor of cellulase, whereas in summer cellulase was significantly influenced by temperature, MBC, depth and catalase.

Received: 30 June 2025 / Accepted: 12 November 2025 / Available online: 19 November 2025

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Abstract

The study aimed to examine the relationship between the occurrence of European mistletoe
(Viscum album L.) and crown defoliation of Canadian poplar (Populus × canadensis Moench) plantations established on coastal dunes along the Central Black Sea coast of Bulgaria. A total of 1,158 trees were assessed for infestation level using a four-class visual scale (no, light, moderate, and heavy infestation) and for crown defoliation following the ICP Forest protocol. Nearly half of the trees (49.8 %) were free of mistletoe, while moderate to heavy infestation occurred in less than 10 %. Defoliation was absent or slight in about two-thirds of the trees, whereas severe defoliation was recorded in 8 %. Statistical analyses revealed a positive correlation between mistletoe abundance and crown defoliation, as well as with stem diameter, indicating that larger and taller trees are more susceptible despite the even-aged structure of the plantations. Although mistletoe did not directly cause tree mortality, it significantly contributed to defoliation and may predispose trees to other biotic and abiotic stressors. A decision-tree model identified threshold values of infestation that predict changes in crown condition, offering a practical tool for assessing host-tree health in dune plantations.

Received: 16 May 2025 / Accepted: 29 October 2025 / Available online: 05 November 2025

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Abstract

Riparian shrub and forest vegetation is widespread across Bulgaria, but its syntaxonomic diversity has not been fully studied, which was the main aim of our study. All published relevés were compiled, and new data were collected from different parts of the country, e.g. 905 relevés. Hierarchical clustering was used for classification from class to alliance levels. Diagnostic, constant, and dominant species were identified for all established syntaxa. This study provides the first comprehensive investigation into the distribution, syntaxonomic diversity, ecological characteristics, and threats to riparian forests and shrublands in Bulgaria. Riparian vegetation was classified into two classes, four orders, and seven alliances: 1) Alno glutinosae-Populetea albae P. Fukarek et Fabijanić 1968, Populetalia albae Br.-Bl. ex Tchou 1949, Platanion orientalis I. Kárpáti et V. Kárpáti 1961, Alno-Fraxinetalia excelsioris Passarge 1968, Alnion incanae Pawłowski et al. 1928, Alno-Quercion roboris Horvat 1950; and 2) Salicetea purpureae Moor 1958, Salicetalia purpureae Moor 1958, Salicion albae Soó 1951, Salicion eleagno-daphnoidis (Moor 1958) Grass 1993, Salicion triandrae T. Müller and Görs 1958, Tamaricetalia ramosissimae Borza et Boscaiu ex Doltu et al. 1980, Tamaricion parviflorae I. Kárpáti and V. Kárpáti 1961. The Mediterranean influence in the country is shown in forests of Alno-Quercion roboris, Platanion orientalis, and Tamaricion parviflorae, found in the southern part of Bulgaria. Alliances Alnion incanae and Salicion eleagno-daphnoidis occur in the semi-mountainous and mountainous regions, whereas phytocoenoses of the Salicion albae alliance are widespread in plains along rivers and water bodies. Alliance Salicion triandrae includes shrub communities dominated by Amorpha fruticosa L. and Salix triandra L. On the other hand, the alliance Alno-Quercion roboris is restricted to rivers in northern Bulgaria and the temperate region. The species composition of the studied vegetation was influenced by continentality, which affects climate patterns, such as light and temperature regimes. Additionally, moisture availability and altitude also played a significant role in shaping the studied vegetation. 

Received: 29 July 2025 / Accepted: 17 October 2025 / Available online: 24 October 2025

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

Abstract

This study aimed to evaluate how different thinning intensities influence the accumulation of organic carbon and nitrogen in soils. We analysed key soil parameters under varying thinning regimes in Norway spruce (Picea abies (L.) H.Karst.) stands, compared with unthinned controls, across six state forestry management units in the Central Balkan Mountains, Bulgaria. On the territory of each management unit, soil samples were taken from three types of plots: unmanaged controls (no silvicultural intervention for over 20 years); light thinning (10–15 %, within the past 10 years); and moderate thinning (20–25 %, within the past 10 years). Soils were examined in depth layers of 0–10, 10–20 and 10–30 cm. We measured bulk density, rock content, soil acidity, and soil organic carbon and total nitrogen stocks. Results indicate that low-intensity thinning (10–15 %) significantly alters soil organic carbon. These findings highlight the need for proactive management strategies to guide thinning practices in Bulgarian forests, with particular attention to soil organic carbon and total nitrogen dynamics.

Received: 15 August 2025 / Accepted: 17 October 2025 / Available online: 24 October

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

Abstract

The rapid and persistent climate change in recent years has amplified the occurrence and spread of various extreme weather events, causing significant socio-economic, ecological, and cultural damages. Forest fires have become constant threat to human life and major challenge to the resilience of forest ecosystems and their ability to recover after severe disturbances. The focus is on the topic of forest vegetation regeneration as first stage of recovery and adaptation. The study, conducted as part of the FIRE-RES project, focuses on the area affected by one of the most severe wildfires near the village of Dabovo (2007), within the jurisdiction of the Regional Forest Directorate Stara Zagora. Due to its characteristics, the area faces constant threat of extreme fires. The objective of the study is to conduct a scientifically grounded assessment of forest resilience and post-fire recovery capacity. To assess regeneration processes, we established methodology for evaluating regeneration and development of understorey vegetation in forest areas affected by fires. Three areas with different exposures, i.e., different types of habitats, were selected within the burned area, where three transects were laid, covering all altitudes within the fire zone. The inventory in the survey plots was carried out by tree species, origin, coverage, and height. The results demonstrate significant relationships between post-fire regeneration dynamics and the structural and ecological condition of the landscape following the disturbance. The real assessment of regeneration after major disturbances allows precise determination of appropriate forestry measures and the creation of a landscape resilient to various challenges. Fifteen years after the Dabovo fire, natural regeneration remains spatially uneven and incomplete, with pioneer species dominating the sun-exposed slopes, emphasising the need for targeted actions to provide ecosystem recovery.

Received: 21 July 2025 / Accepted: 12 October 2025 / Available online: 24 October 2025

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Abstract

In this study, we determined the effectiveness and perceived satisfaction with cultural ecosystem services in Ukraine during the war in six protected areas. The aim of the study was to determine the importance and effectiveness of eight cultural ecosystem services during the war for visitors to six protected parks in four regions of Ukraine. The following methods were used: field survey (route), analytical, systematisation, sociological, socio-psychological and statistical; the Likert psychometric scale was used to survey visitors to protected parks. The data were analysed using descriptive statistics. In all parks, female respondents predominated, their participation ranged from 52.8 % to 69.2 %. Park visitors were mainly young people aged 16–30 (from 30.6 % to 77.5 %) and people aged 51–64. During the war, visitors to all studied parks noted the importance and effectiveness of cultural ecosystem services, such as recreation, aesthetics, and natural history. The age groups 16–30 and 51–64 were the most in need of such services. The effectiveness and importance of the service of inspiration were confirmed, while spiritual enrichment scored the lowest among all age groups in the four parks. Almost one third of visitors in four parks offered suggestions for improving environmental quality, with the greatest demand being for enhanced landscaping and an increase in the number of trees. The quality of vegetation and the location of the parks influenced overall visitors’ satisfaction. The results of this research can be used to improve environment quality through urban green spaces and to address community needs via cultural ecosystem services provided by the studied parks.

Received: 25 July 2025 / Accepted: 11 October 2025 / Available online: 24 October 2025

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

Abstract

The flora of Sakar Mt. is far from well-studied. The territory of the mountain is shared between two floristic regions in Bulgaria – Tundzha Hilly Country and Thracian Lowland. The aim of the study is to improve the knowledge of the floristic composition of these regions. We exploited standard methods widely used in floristic research. Resulting from the study we report eight vascular plant species from Sakar Mt. as new for the Tundzha Hilly Country floristic region incl. Pulsatilla montana (Hoppe) Rchb. and Osyris alba L., and three species as new for the Thracian Lowland floristic region incl. Legousia pentagonia (L.) Thell. assessed as Vulnerable in the Red List of Bulgarian vascular plants. The distribution of four species in the Tundzha Hilly Country floristic region is confirmed. The presence in Sakar Mt. of an interesting member of Campanula rotundifolia group is briefly discussed.

30 June 2025 / Accepted: 09 October 2025 / Available online: 16 October 2025

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

Abstract

Between 2016 and 2018, during a study on deadwood biomass stocks and their role in forest ecosystems of the Berkovski Balkan region (Western Stara Planina Mountains, Bulgaria), we investigated earthworms (Oligochaeta: Lumbricidae) captured using pitfall traps. With the help of 156 pitfall traps set in 13 sampling plots, we collected over 500 individuals belonging to 20 species and 9 genera. There are four new records for the region of the Western Stara Planina Mts.: Dendrobaena balcanica (Černosvitov, 1937), Dendrobaena depressa (Fitzinger, 1833), Dendrobaena hortensis (Michaelsen, 1890) and Dendrobaena rhodopensis (Černosvitov, 1937); three of them are new for the whole territory of the Bulgarian part of Stara Planina Mts. as well. Along with these species, we found three Balkan endemics: Cernosvitovia rebeli (Rosa, 1897), Dendrobaena balcanica, Dendrobaena rhodopensis and one rare species: Dendrobaena hortensis. Zoogeographical analysis showed that the peregrine species dominated, which seems typical for the earthworm diversity of Bulgaria. Pitfall trapping proved to be a suitable method for assessing species composition and collecting ecological data on oligochaete communities. It also shows potential for future use in ecosystem biomonitoring. We aimed to survey lumbricid fauna in the Western Balkan forests using а non-traditional method for collection of earthworms.

Received: 27 June 2025 / Accepted: 08 October 2025 / Available online: 16 October 2025

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Abstract

Oilseed rape (Brassica napus L.) is among the most essential oil crops worldwide. The main limiting factor for its growth and development is the uncontrolled weed infestation. Primary method for weed control is the application of herbicides. If applied improperly they can cause herbicidal phytotoxicity. One phenomenon for this stress is the herbicide drift from one field to another. Therefore, the current study aimed to investigate the response of the conventional oilseed rape variety ‘РТ 225’ to simulated herbicide drift and subsequent ameliorative treatment with plant biostimulant. In this regard, herbicidal drift from a field of Clearfield oilseed rape to the conventional one was imitated. The herbicidal product used was Cleranda SC (17.5 g·L-1 imazamox and 375 g·L-1 metazachlor) used for weed management in Clearfield oilseed rapes. The trial was conducted during 2020/2021 and 2021/2022 on the field of the Agricultural University – Plovdiv, Bulgaria. Treatments of the trial were: 1. Untreated control; 2. 0.40 L·ha-1 (20 % of the rate 2.00 L·ha-1); 3. 0.60 L·ha-1 (30 % of the rate 2.00 L·ha-1); 4. 0.40 L·ha-1 + Amino Expert® Impuls (selected biostimulant) – 3.00 L·ha-1, and 5. 0.60 L·ha-1 + Amino Expert Impuls – 3.00 L·ha-1. The levels of phytotoxicity were evaluated by the 9-score scale of European Weed Research Society. Parameters as total leaf chlorophyll content, number of primary branches, plant height at the end of the growing season, seed yield, weight of 1000 seeds, and seed oil content were studied. The damages caused by the herbicidal drift were more severely pronounced at 30 % of the solution fallen to the plants. The ameliorative treatment with the plant biostimulant Amino Expert Impuls helped the plants overcome the herbicidal stress, and the plants showed higher results for the studied indicators.

Received: 26 June 2025 / Accepted: 02 October 2025 / Available online: 11 October 2025

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