Understanding forest tree phenology is essential for assessing forest ecosystem responses to environmental changes. Observations of phenology using remote sensing devices, such as satellite imagery and Unmanned Aerial Vehicles (UAVs), along with machine learning, are promising techniques. They offer fast, accurate, and unbiased results linked to ground data to enable us to understand ecosystem processes. Here, we focused on European beech, one of Europe’s most common forest tree species, along an altitudinal transect in the Carpathian Mountains. We performed ground observations of leaf phenology and collected aerial images using UAVs and satellite-based biophysical vegetation parameters. We studied the time series correlations between ground data and remote sensing observations (GLI r = 0.86 and FCover r = 0.91) and identified the most suitable vegetation indices (VIs). We trained linear and non-linear (random forest) models to predict the leaf phenology as a percentage of leaf cover on test datasets; the models had reasonable accuracy, RMSE percentages of 8% for individual trees, using UAV, and 12% as an average site value, using the Copernicus biophysical parameters. Our results suggest that the UAVs and satellite images can provide reliable data regarding leaf phenology in the European beech.

Climate change’s negative effects, such as rising global temperatures and the disruption of global ecological ecosystems as a direct effect of rising carbon emissions in the atmosphere, are a significant concern for human health, communities, and ecosystems. The condition and presence of forest ecosystems, especially those in peri-urban areas, play an essential role in mitigating the negative effects of climate change on society. They provide direct benefits to the residents of large cities and their surrounding areas, and they must be managed sustainably to protect all their component ecosystems. This research was carried out in the forests of Lunca Muresului Natural Park and Bazos Arboretum, located in the Romanian sector of the Pannonian Plain, near urban agglomerations. The results showed high variability in the stands. Using the height-to-diameter ratio indicator concerning dbh and species, a strong Pearson correlation was registered (between 0.45 and 0.82). These values indicate the high stability of these stands, providing positive human–nature interactions such as recreational or outdoor activities (and a complementary yet indirect use value through attractive landscape views). Protecting these ecosystems offers a so-called insurance policy for the next generations from a climate change standpoint.

The European beech (Fagus sylvatica L.) is one of the most common tree species in Romania, with importance both economically and environmentally. Accurate methods of biomass assessment at the tree compartment level (i.e., stump, stem, branches, and leaves) are necessary for carbon stock estimation. Wood density (WD) is an important factor in determining biomass and, ultimately, the tree’s carbon content. The average tree density was found to be 578.6 kg/m³. For this study, WD was evaluated by the weighting method related to tree volume. Also, to investigate a practical approach to determining the weighted wood density (WWD_st), models were run using density at the base of the tree (WD_Base), density at breast height level using discs (WD_DBH), the wood core density (WD_ic), and the diameter at breast height (DBH) as predictors. The biomass assessment was conducted using different model evaluations for WWD_st as well as allometric equations using the destructive method. From the results, it was noted that using the WWD_st, the total biomass was underestimated by −0.7% compared to the biomass measured in the field. For allometric equations that included DBH and tree height as independent variables, the explained variability was around 99.3% for total aboveground biomass (AGB_total), while it was 97.9% for allometric function using just the DBH. Overall, the distribution of biomass across different compartments was as follows: 73.5% in stems, 23.8% in branches, 1.9% in stumps, and 1.3% in leaves. The study findings offer valuable insights into WD, biomass distribution among different components, and biomass allometric quantification in natural beech forest environments in mountainous areas.

The research objective was to demonstrate the economic impact of using, in afforestation, forest reproductive materials (FRMs) obtained from seed trees selected in the most valuable Norway spruce populations of the FGRs’ (forest genetic resources’) category. The values obtained for the main growth traits (diameter at breast height (Dbh), tree height (Th), and tree volume (Tv)), both in the FGR and in the closest population (with the same age and growth in similar environmental conditions), were compared. Three comparative trials were analyzed, each belonging to different breeding levels: Open-pollinated (Breţcu, 40 years old), half-sib (Măneciu, 25 years), and full-sib (Comandău, 23 years). The difference in volume/hectare between the FGR and an unimproved neighbor population was economically quantified (€), based on the average price per cubic meter (m³) of spruce wood in Romania; the profit at the end of the rotation period (110 years) was projected taking into account the genetic gain that will result from the use of FRM collected from the FGRs. The average FGR growth results were superior to the unimproved neighbor populations, with 8%–13%, 14%–25%, and 26%–79% for Dbh, Th, and volume/ha, respectively, and the differences increased if the best 10% seed trees of the trials were used. For Th, a five times higher family mean heritability was registered for the pendula trees (compared to pyramidalis) in the half-sib trial, while in the full-sib experiment, the pendula trees (both full and half pendula) again registered higher heritability, but for Dbh, which recommends the pendula selection for different traits in the two trials. These results have led to a rate of profitability between 540 and 3366 €/ha, a value that is predicted to increase until the end of the rotation period, when the genetic gain could generate a profit of 7560 €/ha.

Phenology is considered an indicator of environmental changes, with direct implications in the length of the growing season; therefore, it offers essential information for a better understanding of the tree–environment relationships that could lead to the right decisions for forests’ sustainable use and conservation. A better understanding of how European beech (Fagus sylvatica) phenology responds to predicted climate change effects is important for forest management. This study aimed to assess bud burst and senescence among and within beech populations located along a steep elevational gradient. Phenological observations were carried out on 150 beech individuals along an altitudinal transect in the south-eastern Carpathian Mountains, from 550 to 1450 m, in five study sites in two consecutive years. The start of the bud burst, of senescence, and the duration of the growing season varied inversely proportionally to the elevational gradient in both monitored years. Individuals located at the highest altitude need 28 more days to start the growing season than those at the lowest altitude. There is an average difference of 14 days at the start of the growing season in the same beech populations between the two consecutive years. The first stage of senescence (yellowing of leaves) lasted longer in 2021 (21–32 days) than in 2022 (18–25 days), with a difference of 16%–28%, proportional to the increase in altitude. The association of field phenological data with meteorological data indicates that the start of the growing season occurs when the thermal threshold of 10 °C is exceeded, with an accumulation of a least 60 GDD (growing degree days) with a threshold of 0 °C in the last 7 days as a complementary condition. The appearance of the first stage of senescence, the yellowing of the leaves, was also influenced by the temperature and the accumulation of at least 72 SDD (senescence degree days) with a threshold of 0 °C in the last 7 days. Our results confirm that the temperature is the triggering meteorological factor for the onset of bud burst and leaf senescence in European beech.

This study examines the impact of silvicultural and land-use management practices on carbon sequestration in peri-urban forest ecosystems, with a particular focus on human-induced carbon dynamics. The study area’s complex profile spans from a compact native forest to varying degrees of fragmentation. This included areas undergoing secondary succession forest without silvicultural interventions (No-SI) alongside sites subjected to high-intensity (High-SI) and low-intensity silvicultural interventions (Low-SI). The research assessed carbon stocks and sequestration in different carbon pools (living biomass, dead organic matter and soil) using field data, allometric equations and laboratory analysis. Findings reveal a significant correlation between the intensity of anthropogenic interventions and variations in carbon stocks. The CASMOFOR model facilitated the reconstruction of carbon stock and carbon-stock change dynamics over four decades (1980–2022), showing disparities in carbon storage capabilities linked to the structural characteristics of the sites. The Low-SI site had the highest carbon stock in all carbon pools (378 tonnes C ha⁻¹), which is more than double compared to High-SI (161 tonnes C ha⁻¹) or No-SI sites (134 tonnes C ha⁻¹). However, the secondary succession forest (No-SI) demonstrated the highest annual carbon stock change (4.4 tonnes C ha⁻¹ year⁻¹), two times higher than the Low-SI mature stand (2.2 tonnes C ha⁻¹ year⁻¹), emphasising the resilience of forest ecosystems to recover and sustain carbon sequestration capacities after harvesting if forest land use remains unchanged. The study underscores the significant importance of anthropogenic interventions on carbon dynamics, especially for living tree biomass, which has consequences in enhancing carbon sequestration and contributing to emission reduction targets.