This paper presents research results on forest decline in Serbia. The results were obtained through monitoring defoliation of 34 tree species at 130 sample plots during the period from 2004 to 2018. This research aimed to determine whether the occurrence of defoliation and tree mortality were caused by drought. Defoliation was assessed in 5% steps according to the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) methodology. All the trees recorded as dead were singled out, and annual mortality rates were calculated. To determine changes in air temperature and precipitation regimes during the study period, we processed and analysed climatic data related to air temperature and precipitation throughout the year and in the growing season at 28 main weather stations in Serbia. Tree mortality patterns were established by classifying trees into three groups. The first group of trees exhibited a gradual increase in defoliation during the last few years of monitoring, with dying as the final outcome. The second group was characterised by sudden death of trees. The third group of trees reached a higher degree of defoliation immediately after the first monitoring year, and the trees died after several years. Tree mortality rates were compared between years using the Standardised Precipitation Evaporation Index (SPI) and the Standardised Precipitation Evapotranspiration Index (SPEI), the most common methods used to monitor drought. The most intensive forest decline was recorded during the period from 2013 to 2016, when the largest percentage of the total number of all trees died. According to the annual mortality rates calculated for the three observation periods (2004–2008, 2009–2013, and 2014–2018) the highest forest decline rate was recorded in the period from 2014 to 2018, with no statistically significant difference between broadleaved and coniferous tree species. As the sample of coniferous species was small, the number of sample plots should be increased in order to achieve better systematic forest condition monitoring in Serbia. The analysis of the relationship between defoliation and climatic parameters proved the correlation between them. It was noted that the forest decline in Serbia was preceded by an extremely dry period with high temperatures from 2011 to 2013, supporting the hypothesis that it was caused by drought. We therefore conclude that these unfavourable climatic conditions had serious and long-term consequences on forest ecosystems in Serbia.

Various biotic and abiotic factors are the cause of the decline of coniferous forests throughout Europe. Trees weakened by unfavorable weather conditions create an ideal environment for a possible outbreak of bark beetles. The damage caused by bark beetles costs billions of dollars worldwide every year. Extreme climate events are responsible for the enormous forest losses in Tara National Park in the last ten years, leading to a massive bark beetle infestation. The understanding of the diversity and role of mites as biological control agents is still insufficient. In this study, we summarize the current knowledge on the diversity of mites associated with Ips typographus L. in Europe and provide information on the diversity of these mites in Serbia. Paraleius leontonychus, Uroobovella ipidis, Dendrolaelaps quadrisetus, Histiostoma piceae, and Trichouropoda polytricha were detected for the first time in Serbia. Moreover, the occurrence of Paraleius leontonychus represents the southernmost occurrence of this species.

Spatial and urban plans have recently given an increased focus to the sensitive issue of planning the urban resilience of existing and establishing new urban forests. Urban forests are recognised as an extremely important factor of environmental quality, while scientific studies indicate that the health condition of urban forests is threatened by present-day climate change. There have been relatively few systematic assessments of the causes of tree die-back in urban areas in Serbia. Research, forest establishment planning and tree monitoring to estimate possible consequences to existing trees will enable city authorities and managing bodies to raise the issue of urban forest resilience to climate change to a higher level and incorporate it into urban planning. Future scenarios in which urban forests are resistant to potential adverse climate change will depend on the scope of activities of adaptive planning of urban forest establishment and adaptive management of existing ones. Therefore, it is necessary to conduct long-term studies of monitoring the condition of urban forests in the large cities of Serbia (Belgrade, Novi Sad, Niš, Subotica, etc.) in the coming period in order to identify specific problems and remediate the consequences such as deteriorated tree health condition and die-back.

The paper presents the comparative characteristics of the floristic composition in the association of the submontane beech forest (Helleboro odori-Fagetum moesiacae Soo & Borhidi 1960.) and artificially established spruce stands (Picea abies (L.) Karst.) in the area of Kosmaj. According to the obtained results, the cover in the shrub and ground flora layers of the artificially established spruce stands increased significantly compared to the autochthonous beech forests, but the floristic diversity decreased. Regarding the spectrum of floral elements, a higher percentage of mesophilic (51%) and frigophilic plants (11%) was observed in the artificially established spruce stands compared to the beech forests. Significant differences could also be observed regarding the spectrum of life forms since there were twice as many phanerophytes in the artificially established spruce stands (48%) than in the beech forests (23%). This resulted from the open canopy of artificially established spruce stands and the influx of a greater amount of light, which made conditions favourable for an abundant shrub layer to develop in this community. A comparative study of the mean plant indicator values showed that in the artificially established spruce stands, the mean values of the ecological factors for moisture, light and soil nitrogen supply increased, while the value of the ecological factors for temperature and soil acidity decreased compared to the beech forests.

Serbia is one of the countries of Southeastern Europe with significant potentials for using biomass from forests and wood processing industry in the form of wood residues for the production of modern fuels. This type of biomass has not been used efficiently. One of the reasons is the traditional use of firewood for domestic heating needs despite its lower energy efficiency compared to pellets and briquettes. According to FAO methodology, the estimated energy potential of the available biomass derived from forests and wood processing industry in Serbia amounts to 1.53 Mtoe/year. According to the Energy Sector Development Strategy of the Republic of Serbia for the period by 2025 with projections by 2030 together with relevant Decisions on the energy balance determination, the degree of the use of potentially available biomass from forests and wood processing industry is around 1.02 Mtoe/year (66.7%). The remaining unused potential of this biomass is estimated at around 0.51Mtoe / year. Besides the study of the state of biomass from forests and wood processing industry, the paper provides recommendations on how to increase the utilization rate of this biomass in Serbia.