Droughts accompanied by high temperatures are becoming increasingly frequent across Europe and globally. Both individual trees and entire forest ecosystems are exposed to drought stress, with prolonged drought periods leading to increased tree mortality. Therefore, continuous monitoring, data collection, and analysis of tree mortality are essential prerequisites for understanding the complex interactions between climate and trees. This study examined the effects of short-term and prolonged (multi-year) droughts on the mortality of individual trees and forests in Serbia. The analysis was based on datasets from our previous research on the influence of drought and drought duration on individual tree mortality in Serbian forest ecosystems, supplemented with new data collected through the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). Additionally, we incorporated data from the public enterprise (PE) “Srbijašume”, which manages forests in Central Serbia, focusing on random yields resulting from natural disasters (droughts). These data enabled a comparative assessment of the findings on increased mortality and drought impact at both the individual tree level and the stand level. This study identifies key similarities and differences in tree mortality trends based on drought duration and examines their correlations within the same time frame (2004–2023). By analysing climatic conditions across Serbia, we provide evidence of the interaction between drought periods and increased forest mortality, which we further confirmed by calculating the Standardized Precipitation Evapotranspiration Index (SPEI). We also address the tree species that were most sensitive to the effects of drought. Our findings indicate that prolonged (multi-year) droughts, accompanied by high temperatures, have significantly contributed to increased tree mortality over the past decade. Successive multi-year droughts pose a substantial threat to both individual trees and entire forests, producing more severe and persistent responses compared to those caused by single-year droughts, which forests and individual trees are generally more capable of tolerating. Moreover, due to prolonged drought stress, trees weaken, leading to delayed mortality that may manifest several years after the initial drought event. The observed increase in tree mortality has been found to correlate with rising temperatures and the growing frequency of prolonged droughts over the past decade. Especially, intense droughts in the growing season (April–September) have a very negative impact on forests.

The wood of northern red oak (Quercus rubra L.), considered to be a very high-quality material for processing in the wood industry, has not been tested in Serbia so far. To date, there are only small areas under northern red oak in Serbia, but there are significant stands of this species in the vicinity of Belgrade. In this paper, the basic physical and mechanical wood properties of northern red oak in Serbia were tested. The examined 57 years old tree was located in the forest of Lipovica, near Belgrade. The tree was cut down and two small logs were taken to the laboratory for analysis. The results show that the properties of wood of northern red oak do not differ significantly from the properties of native oak species in Serbia - sessile and pedunculate oak. In addition, the values of basic mechanical properties of wood of northern red oak in Serbia were similar to the relevant values obtained by other researchers in Europe and the USA. Thus, the utilization of wood of northern red oak in the local wood processing industry should be considered.

Forty-two trees of northern red oak (Quercus rubra L.) were examined in the area of the municipality of Savski Venac, Belgrade, to assess the condition of this allochthonous species in Serbia and its adaptability to urban environments. Physical measurements were taken and ratings of vitality and decorativeness were given. The analyzed trees are in very good condition based on their health status (80.95% of trees without visible indication of disease) and the mean values of ratings for vitality (4.45) and decorativeness (3.88). The obtained values of vitality and some physical measurements were greater than those stated in the literature, suggesting that the species has adapted well to the urban environment of Belgrade and it should be considered a suitable landscape tree species for planting in urban areas of Serbia.

Accurate assessment of the physiological and mechanical condition of trees in urban environments represents a key component of risk management and the planning of protection measures. This study presents the integration of four methodological approaches - multispectral UAS (drone) analysis, a photogrammetrically generated 3D model, Visual Tree Assessment (VTA) and acoustic tomography (Arbotom) - applied to an old lime tree (Tilia platyphyllos) located in the courtyard of the Bishop's Palace of the Šabac Eparchy. Multispectral analysis was used to calculate the NDRE index of physiological activity, while the 3D trunk model was employed for precise positioning of the Arbotom sensors. Tomographic measurements performed at heights of 40 cm and 200 cm identified degradation zones with a reduction in load-bearing cross-sectional area of 27-39% (lower section) and 43-52% (upper section). The NDRE index indicated localized areas of reduced physiological activity within the crown, while the VTA method confirmed the presence of fungi of the genus Ganoderma. The integrated results indicate that the tree currently maintains a stable mechanical structure, with localized degradation zones that do not yet affect its static stability. The presented multi-sensor approach is highlighted as an efficient tool for detection, evaluation, and risk management in urban forestry, however as this research was conducted on a single Tillia platyphyllos specimen, the findings should be interpreted as a case study and methodological demonstration rather than as results directly generalizable to a broader population of urban trees.

A total of 179 Douglas fir trees (Pseudotsuga menziesii /Mirb./ Franco) were examined in the municipality of Savski Venac, Belgrade, to assess the condition of this non-native species in Serbia and its adaptability to urban environments. Tree measurements (trunk diameter, tree height and crown diameter) were taken, and the trees were rated for vitality and decorativeness. The trees were found to be in a very good condition, with 89.05% of them showing no visible signs of disease. The average vitality rating was 3.94, and the average rating of decorativeness was 3.57. The results for vitality and some physical measurements exceeded values reported in the literature, suggesting that Douglas fir has adapted well to the urban environment of Belgrade. Although further research is needed, it can be concluded that Douglas fir is a suitable species for landscape planting in urban areas of Serbia.

Fifty-six Populus spp. trees were examined in Belgrade, Serbia, with a focus on assessing vitality and decorativeness using the Visual Tree Assessment (VTA) method and measuring wood sound velocity. The study aimed to explore the connection between visual indicators of tree condition and internal structural properties based on sonic wave velocities. Vitality and decorativeness ratings ranged from 2 to 5 (out of 5), with mean values of 2.80 and 2.93, respectively; wood sound averaged 788,39 m/s. Statistically significant correlations (r = 0.52 for vitality, r = 0.53 for decorativeness) confirmed the possibility of integrating VTA and sonic measurements. Mathematical models were developed that successfully predict tree vitality and decorativeness based on sound velocity. It can be concluded that this combined approach improves tree health assessment accuracy, supports timely interventions, and contributes to sustainable urban greenery management.