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Salix viminalis L. is a broadly cultivated willow species that has been intensively used for breeding purposes, particularly in selection of clones and hybrids for biomass production. The present study aimed to explore and compare growth and adaptability of two basket willow (Salix viminalis L.) clonal varieties - rubra and purpurea - at the specific edaphic and climate conditions and cultivation practice presented in an experimental plantation in North Central Bulgaria. The influence of spacing, genotype, root age and rotation on their productivity were also investigated and allometric relationships for non-destructive estimation of woody plant biomass were suggested. The trial plantation was established in the spring of 2018 as 4 sectors of a Nelder wheel plot with 15 nearly-square spacings, ranging from 0.25 to 9.80 m2 (40000–1020 plants per hectare). The two varieties were arranged in 4 four-spoke sectors (2 sectors per clone). Data collection took place from 2018 to 2020 and comprised 1- and 2-year rotations. The study showed that Salix viminalis var. rubra was more susceptible to desiccation-causing adverse climatic changes, poorly adapted to the specific conditions of the study site and gradually died out during the second and the third year. Salix viminalis var. purpurea exhibited steady survival rate (97 - 77%) and annual biomass productivity varying from 3 to 17 Mg/ha/year across the densities, sectors and years. During the first year of growth purpurea variety had a significantly higher plant weight and sprout number than rubra variety. Growing space affected positively the number of shoots and tree dendromass, and sprouting was reinforced by coppicing that doubled the shoot number during the subsequent rotation. This was reflected in the development of the stump-level allometric models that were differentiated according to rotation. The stump-level allometric model of higher predictive power was based on the main shoot length and shoot number. An exponential relationship to the breast-height shoot diameter was also suggested for biomass estimation of each sprout separately.

Europe has a history rich in examples of successful and less successful introductions of non-native trees (NNT) - trees with an evolutionary origin outside of Europe. NNT have been introduced for various reasons such as ornamental purposes, food production, land reclamation/amelioration and timber production. The use of NNT also causes controversies due to potential negative impacts on natural ecosystems of NNT that become invasive. Many international legal frameworks responded to the presence and use of NNT, such as international treaties and conventions ; and also the European Union deals with the issue of invasive alien species in Regulation (EU) No. 1143/2014. However, especially the national and regional responses to NNT affect current and future management decisions in the forest sector and furthermore shape forest landscapes of Europe. In this comprehensive study of the legal landscape concerning NNT we identified all relevant legislations, the different legal approaches and the regulatory intensity in every European country (except microstates). Hard and relevant soft law items at the national and sub-national (regional) level for 40 European countries were collected and proofed using a targeted questionnaire sent to country experts across Europe mainly coming from the forestry and nature conservation sector. In addition, international and national legislation information systems and databases were consulted to complete the information. Legislations included updates until June/July 2019. In total, 320 national and regional law items were identified to be relevant for the regulation of NNT in the investigated 116 legislative units (countries, and regions with own legislation) in Europe. Countries and regions were empirically categorised according to ad hoc created legislation indicators dealing with the general ban of introduction of non-native species, the generally allowed and prohibited NNT, approval mechanisms, e.g. mandatory forest management plans, and areas and cases where NNT are restricted or completely prohibited. Our study revealed a very diverse legal landscape in Europe, with a large variety of approaches being pursued to regulate NNT, and the intensity of regulation ranging from very little restrictions on the species choice and plantation surface area to a complete ban of NNT in forests.

This study investigated the influence of spacing, parental genotype and harvesting cycle on woody biomass production in open-pollinated families of the locally selected black locust (Robinia pseudoacacia L.) clones ‘Tsarevets’ and ‘Srebarna’ at specific site conditions. A Nelder experiment with 16, varying along the spokes, nearly-square spacings and two black locust families arranged in alternating sectors, was established in North Central Bulgaria. Alternative harvesting options (‘harvesting cycles’), consisting of one, two or three successive coppicings, were applied and the amounts of dry shoot dendromass collected per plant were accumulated to calculate and analyse the total yield of woody biomass, achievable within 2-, 3- and 4-year periods (‘production period’). The one-coppicing cycle proved superior for both families, regardless of the length of the production period. Biomass yield in the family of ‘Srebarna’ exceeded that of ‘Tsarevets’ at the wider spacings, when 1 and 2 year-old shoots were harvested, while dendromass production of ‘Tsarevets’ was substantially higher in the 4-year-old shoots. The woody biomass yield per plant increased with spacing, and growth tended to saturation at the lowest densities, enabling derivation of optimal planting densities. The total dendromass yield per hectare was maximized at growing space of around 0.5 m2 per plant for the 2-year production period, while spacing of 1.2–2 m2 was required for production periods of 3 and 4 years. If the results from this experiment can be reliably scaled up in practice then short rotation crops of ‘Srebarna’ and ‘Tsarevets’ families at comparable site conditions should be able to produce annual biomass yields of 9–11 Mg.ha−1.year−1 within a 4-year period, given the optimal planting densities and harvesting regimes prescribed.

Agroforestry is a multifunctional, environmentally-friendly and modern system of land use by which we can reach economic, environmental and social benefits for the society. Bulgaria has achieved good results in the establishment of agroforestry practices, such as: protective forest belts, forest farming (agricultural use of forest areas), silvopasture (forest-grassland complexes). Moreover there are also legal basis and political understanding for promoting these types of systems. Missing, however, entire Concept and Strategy of supporting the development of agroforestry in the country. There is a strong need for the introduction and elaboration of best practices and new agroforestry technologies in the country where agricultural areas cover 47 % and forest areas 37 % from the territory. As a modern form of land use, agroforestry is a viable alternative for providing good income for land owners in many areas of the country, particularly these which livelihood are formed by a tobacco-production. Agroforestry can pushed up agricultural returns by diversification of production and can give many ecological and social benefits for society. The perspectives are targeted at the production of forest fruit tree species with high value tree timber, and forest farming.

Cultivation of energy crops is concerned with estimation of the total lignified biomass (dendromass) production, which is based on the plantation density and individual plant dendromass. The main objective of this study was to investigate the allometry of aboveground leafless biomass of juvenile black poplar hybrids (Populus deltoides x P. nigra ), traditionally used for timber and cellulose production, and to derive generic allometric models for dendromass prediction, relevant to energy crop cultivation in Bulgaria. The study material comprised a variety of growth sites, tree ages and clones, specific to poplar plantings in Bulgaria. We used three principal quantitative predictors: diameter at breast height, total tree height and mean stand (stock) height. The models were not differentiated by clone, because the black poplar hybrids tested were not equally represented in the data, and the inclusion of tree age as a predictor variable seemed unreliable, because of the significant, up to 3 years, variation, which was possible within the narrow age range investigated. We defined the mean stand (stock) height as a composite quantitative variable, which reflected the interaction between the time since planting (age), site quality and the intrinsic growth potential. Stepwise and backward multiple regression analyses were applied to these quantitative variables and their products and sets of adequacy and goodnessof-fit criteria were used to derive individual biomass models for stem and branches. Then we developed compatible additive systems of models for stem, branch and total lignified biomass in log-transformed form. Finally, the prediction data were back-transformed, applying correction for bias, and were cross-validated. Three systems of generic equations were derived to enable flexible model implementation. Equation system M1 proposes a stem biomass model based on tree and stand heights and stem diameter, and a model for branches including mean stand height and breast height diameter; this model displayed the best goodness-of-fit characteristics. Model system M2 uses only the tree height and diameter and therefore is most relevant to dendromass determination in single trees or harvested saplings, while model M3 allows fast and sufficiently accurate biomass estimation of standing poplar stock, because it employs the average stand height and the individual tree diameters. All models are applicable to predict lignified aboveground biomass of juvenile Populus deltoides x P. nigra trees of diameter up to 21 cm and total height up to 16 m.

The chapter presents information about the legal instruments and institutions concerning the conservation of genetic resources of forest tree species in Bulgaria. Due to the specific circumstances, the vast majority of the Bulgarian forests are state-owned. Therefore, the main regulation documents concerning management of state forests are relevant in the context of tree genetic resources sustainable use and conservation . A brief survey of the most important regulation documents determining the legislation framework for conservation of genetic resources of forest trees is presented.

This paper proposes a new method for obtaining controlling unstable equilibrium point (CUEP) for transient stability analysis in electric power systems. A minimization problem is formulated to attain CUEP by applying the critical trajectory (CTrj) method to the boundary controlling unstable equilibrium point (BCU) method. CTrj method is a unique approach proposed by the authors to obtain critical condition for transient stability problem. The Proposed method simultaneously computes a trajectory on the stability boundary starting from the exit point reaching CUEP. The effectiveness of the method is demonstrated through simulations for various systems.

The rapid growth in demand of electricity combined with intermittent renewable energy sources (RESs) are presenting serious challenges for the optimal network operation. The future perspective of the dramatic increase in renewable generation, such as wind and solar energy, may lead to severe problems related to the load dispatch. Other important aspect is the reduction of controllable resources yielding concerns about the reliability issues of such sources. This paper focuses on a new technique for mitigating the irregularity associated with renewable power generation. A new method is proposed for real-time dynamic economic load dispatch as an efficient solution for real-time management over the limited control resources of a power system. Load following capability will be considered as critically limited. The flexible operational outcome of the proposed approach satisfies the economical requirements and reliability against uncertainties.

We would like to thank the discussers for their valuable discussions. They raised an important issue concerned with the treatment of extreme perturbations of low probable scenarios. Therefore, we would like to discuss how the system security is achieved against such uncertainties in real power system. Hereof, our policy of risk management is presented.

The rapid growth in the electricity demand and expansion of renewable energy (RE) generation are presenting serious challenges for the optimal network operation. The future perspective of the dramatic increase in renewable generation, such as wind and solar energy will lead to severe problems related to the load dispatch. Power system security is threatened due to increase in the uncertainties of RE outputs and the reduction of controllable resources. This paper investigates power system “robust security” in relation with the increase in the uncertainties and the decrease in system control ability. A new concept of robust security and its security regions is defined and then a new technique for real-time dynamic ELD is proposed. It is guaranteed secure operation in the security region and mitigating the irregularity associated with renewable power generation. Key issue is an effective treatment of uncertainties caused by RE forecast and an efficient solution for real-time management over the limited control resources of a power system. The flexible operational outcome of the proposed approach satisfies the economical requirements and reliability against uncertainties. The proposed method is also useful to investigate the limitation of RE under given ability of real-time generation control. Critical problems anticipated in the future are further investigated from the point of view of robust security concerned with the load dispatch. Robust security for West Japan system is also investigated from the present up to 2030 concerned with the transient stability.

Seit Jahrhunderten arbeitet die Wissenschaft an der exakten Festlegung der Begriffe Nation — Staat — Nationalstaat, ohne zu allgemein anwendbaren Modellen zu kommen. Die folgende Darstellung stutzt sich auf ein Verstandnis des Staates als Produkt der Gesellschaft auf einer bestimmten Entwicklungsstufe, als eine aus der Gesellschaft hervorgegangene, aber sich uber sie stellende, sich ihr mehr und mehr entfremdende Macht 1 . Der Staat als „ubernaturliche Fehlgeburt der Gesellschaft“ 2 erfullt seine historische Mission und stirbt unter bestimmten gesellschafts-okonomischen Bedingungen ab. Der Nationalstaat als Variante der geschichtlichen Verwirklichung von Staatlichkeit stellt in dieser Hinsicht keine Ausnahme dar.

The purpose of this study is to facilitate the detection of provenances relevant to the reforestation practice in Bulgaria. Studies were carried out in a Douglas-fir provenance trial plantation established at an altitude of 800 m a.s.l. on the northern slopes of Rila Mountain. To establish the productivity, assess the stands and rank provenances biometric procedures, methods of descriptive statistics and ANOVA were used. The diameter at breast height, average height, dominant height, total growing stock volume, assortment timber structure and survival of trees were analyzed in the stands of 55 Douglas-fir provenances. The provenances were characterized in terms of productivity of forest stands at 20 years of age and their ability to produce high quality timber was evaluated. Provenances: Newhalem No. 4 (Seed zone 402), Darrington No. 7 (Seed zone 403), Parkdale No. 19 (Seed zone 661) and Idanha No. 29 (Seed zone 452) have been recommended. Among the recommended provenances are those with growing stock volume with branches from 296 to 354 m 3 ·ha -1 , mean annual increment from 14.8 to 17.7 m 3 ·ha -1 and dominant heights of up to 17.9 m.