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The Middle-spotted Woodpecker is an indicator of structurally complex deciduous forests, typically associated with mature oak stands but occasionally found in beech dominated forests, including at elevations exceeding 1,000 m. Although standing dead wood is often used for nesting and foraging, its necessity for the species’ occurrence remains debated. This study examined the relationship between D. medius presence and standing dead wood characteristics in beech-dominated low-mountain forests of the Perșani Mountains, central Romania. Standardized national woodpecker monitoring protocols were applied at 25 fixed points. Standing dead wood variables (density, diameter at breast height (DBH), height, volume, and basal area) were measured across three habitat categories: all forest types, mature and old stands (> 70 years), and stands containing at least 10% oak. Snag density did not differ significantly between plots with and without Middle-spotted Woodpecker, yet occupied plots contained taller and thicker snags, with predicted occurrence probabilities highest at DBH > 60 cm and height > 25 m. No significant differences were found for basal area or volume. In predominantly beech stands, the species’ presence appeared to be influenced by the availability of standing dead wood and the presence of rough-barked species. These findings confirm the species’ strong association with mature deciduous forests, particularly where oak is present. The increasing probability of occurrence with higher oak proportions in standing dead wood underscores the ecological importance of conserving large, old trees and mixed forest structures for Middle-spotted Woodpecker persistence.

The white-backed woodpecker (Dendrocopos leucotos) is one of the bird species which depends on dead and dying trees as their most important habitat resource. Because of this, it is affected by forest management that removes deadwood and changes the structure of old stands. In Romania, its relations with the structures of forests with and without management, including standing deadwood, are not known. The main objectives of this study were the analysis of the most representative elements of snags in its specific habitat – mainly beech forest in low mountains from central Romania. Based on the presence-absence of species, by applying the standard woodpeckers monitoring protocol using a total of 25 fixed points we compared deadwood variables (snag density, volume, basal area) for the entire study area, regardless of forest structure and management, and for stands over 70 years old, as potentially suitable or optimum habitat for the species. The comparison between plots with and without analysed species shows several significant differences especially regarding the number of snags, volume and basal area mainly for stands older than 70 years. The PCA of the variables for the trees with a DBH > 10 cm explained 74.4% of the variance, but for the very large trees (DBH > 40 cm) this percent is the highest one (89.9%). At the same time, the values of several variables (e.g. snag volume, basal area) are similar or higher than those in various areas of Europe. As a main conclusion, these forests are suitable or optimal for white-backed woodpecker and the Romanian forest management can be considered \"closer-to-nature\" at least for beech stands but for maintaining and improving the species typical habitat structure a few conservation measures should be applied in addition.

Forest ecosystems provide invaluable ecological, economic, and social benefits, making them essential for global well-being. However, these ecosystems face various threats, including biological invasions by alien species. Among these, the oak lace bug (OLB), an invasive North American insect, has rapidly spread in Europe, impacting oak forests and raising concerns about its adaptation to new environments. OLB feeds on the undersides of oak leaves, extracting sap and causing chlorotic discoloration. Severe infestations lead to premature defoliation, increased susceptibility to diseases or pests and can also result in a substantial reduction in photosynthesis activity. This study aims to analyse OLB’s invasive behaviour in Romanian forest ecosystems, with a specific focus on the differences between thermophilous and mesophilous oak forests. The analysis covers 6 years of data and reveals critical insights. In the initial 4 years, OLB predominantly inhabited the extracarpathian regions of Romania, with concentrated presence in the southern, western, and northwestern areas. Forest ecosystems mainly affected between 2017 and 2020 were characterized by thermophilous oak forests in southern and western regions. However, in the last 2 years (2021–2022), OLB presence increased, particularly in lowland ecosystems, albeit with reduced damage intensity. The analysis also unveiled an adaptation and expansion of OLB in mesophilous forest ecosystems. Climatic factors, specifically temperature and precipitation, significantly influenced OLB’s behaviour, points with severe attacks exhibiting specific climatic conditions. In summary, this study provides crucial insights into OLB’s behaviour, emphasizing the role of climatic and environmental factors in its invasive tendencies.

To control a forest pest, it is necessary to understand the biotic and/or abiotic factors that can lead to population regulation. Such knowledge is even more critical if the pest is an invasive alien species. This is the case for Corythucha arcuata (Say, 1832), commonly known as the oak lace bug (OLB), an alien insect species that has invaded oak forests on a large scale, both in Romania and other European countries. In this study, we set out to examine the relationship between adults of this species and meteorological factors, such as air temperature and humidity. The study lasted for two years (2019–2020) and was performed on three plots in Romania, in Ilfov, Giurgiu, and Călărași counties. In the first year, the seasonal dynamics of the OLB populations and the meteorological factors potentially influencing those were studied, whilst in the second year, the dynamics of the diurnal activity of the insect population were examined. We found that Corythucha arcuata experienced two population peaks—in July and August—and a diurnal population dynamic that reached a maximum at midday. Data analysis indicated that, for most of the time, the adult activity was influenced by both temperature and humidity. In addition, the population dynamics were not constant over the course of the day, preferring relatively high temperatures and low humidity but not exceeding certain thresholds of thermal discomfort.

In this paper, site-specific allometric biomass models were developed for European beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.) to estimate the aboveground biomass in Șinca virgin forest, Romania. Several approaches to minimize the demand for site-specific observations in allometric biomass model development were also investigated. Developing site-specific allometric biomass models requires new measurements of biomass for a sample of trees from that specific site. Yet, measuring biomass is laborious, time consuming, and requires extensive logistics, especially for very large trees. The allometric biomass models were developed for a wide range of diameters at breast height, D (6−86 cm for European beech and 6−93 cm for silver fir) using a logarithmic transformation approach. Two alternative approaches were applied, i.e., random intercept model (RIM) and a Bayesian model with strong informative priors, to enhance the information of the site-specific sample (of biomass observations) by supplementing with a generic biomass sample. The appropriateness of each model was evaluated based on the aboveground biomass prediction of a 1 ha sample plot in Șinca forest. The results showed that models based on both D and tree height (H) to predict tree aboveground biomass (AGB) were more accurate predictors of AGB and produced plot-level estimates with better precision, than models based on D only. Furthermore, both RIM and Bayesian approach performed similarly well when a small local sample (of seven smallest trees) was used to calibrate the allometric model. Therefore, the generic biomass observations may effectively be combined with a small local sample (of just a few small trees) to calibrate an allometric model to a certain site and to minimize the demand for site-specific biomass measurements. However, special attention should be given to the H-D ratio, since it can affect the allometry and the performance of the reduced local sample approach.

The historical loss of natural wetlands in Romania is significant. The building of lakes, ponds, and dams has compensated for some of these losses, as was the case in the study area, the artificial wetlands designated as the Natura 2000 (special protection area, SPA) and Ramsar sites. In this context, to evaluate the conservation status of colonial waterbirds (cormorants, herons, and egrets), we analyzed actual distributions, habitat selection, features, and population sizes. Standardized counting of colonial species was used, supplemented by nest counting and colony-area estimation during winter, and drone footage. All species and their colonies were built in artificial or anthropically influenced habitats. Concerning distribution and population sizes, Phalacrocorax carbo and Microcarbo pygmeus were found to nest only in central Romania. The pair numbers of Ardea alba, Ardea purpurea, Ardea cinerea, and Nycticorax nycticorax in the area exceeded 1% of the national minimum breeding population. There was a statistically significant positive trend of breeding populations for Ardea alba, Nycticorax nycticorax, and Egretta garzetta. In conclusion, these artificial wetlands offer optimal breeding conditions for a relatively large diversity of colonial bird species over areas that are not very large.

Research Highlights: Past disturbances occurred naturally in primary forests in the Southern Carpathians. High- and moderate-severity disturbances shaped the present structure of these ecosystems, which regenerated successfully without forestry interventions. Background and Objectives: Windstorms and bark beetle outbreaks have recently affected large forest areas across the globe, causing concerns that these disturbances lie outside the range of natural variability of forest ecosystems. This often led to salvage logging inside protected areas, one of the main reasons for primary forest loss in Eastern Europe. Although more than two-thirds of temperate primary forests in Europe are located in the Carpathian region of Eastern Europe, knowledge about how natural disturbances shape the forest dynamics in this region is highly essential for future management decisions. Material and Methods: We established our study in a primary forest valley situated in the centre of the largest temperate primary forest landscape in Europe (Făgăraș Mountains). A dendrochronological investigation was carried out to reconstruct the natural disturbance history and relate it to the present forest structure. Results: The dendrochronological analysis revealed high temporal variability in the disturbance patterns both at the patch and stand level. Moderate severity disturbance events were most common (20–40% of canopy disturbed in 60% of the plots) but high severity events did also occur (33% of the plots). Regeneration was spruce-dominated and 71% of the seedlings were found on deadwood microsites. Conclusions: We conclude that the current structure of the studied area is a consequence of the past moderate-severity disturbances and sporadic high-severity events. The peak in disturbances (1880–1910) followed by reduced disturbance rates may contribute to a recent and future increase in disturbances in the Făgăraș Mts. Our findings show that these disturbance types are within the range of natural variability of mountain spruce forests in the Southern Carpathians and should not be a reason for salvage logging in primary forests from this area.

In a field study, we measured saplings of beech, ash and maple growing in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy with 3-60% of above canopy radiation reaching the saplings. Under low light conditions, maple and ash showed a slight lead in recent annual length increment compared with beech. With increasing light, ash and maple constantly gained superiority in length increment, whereas beech approached an asymptotic value above 35% light. A suite of architectural and leaf morphological attributes indicated a more pronounced ability of beech to adapt to shade than ash and maple. Beech displayed its leaves along the entire tree height (with a concentration in the middle crown), yielding a higher live crown ratio than ash and maple. It allocated biomass preferentially to radial growth which resulted in low height to diameter ratios, and expressed marked plagiotropic growth in shade indicating a horizontal light-foraging strategy. In addition, beech exhibited the highest specific leaf area, a greater total leaf area per unit tree height, a slightly greater leaf area index, and a greater plasticity to light in total leaf area. Ash and maple presented a “gap species” growth strategy, characterized by a marked and constant response in growth rates to increasing light and an inability to strongly reduce their growth rates in deep shade. In shade, they showed some plasticity in displaying most of their leaf area at the top of the crown to minimize self-shading and to enhance light interception. Through this, particularly, maple developed an “umbrella” like crown. These species-specific responses may be used for controlling the development of mixed-species regeneration in shelterwood systems.

In addition to the classic biotic and abiotic factors that have disrupted the health of forests throughout history, lately, the balance of forest ecosystems has been disturbed by different phenomena such as climate change, pollution, and, especially, biological invasions of invasive alien species. One of the alien species that has invaded Europe relatively quickly is an insect species of North American origin, the oak lace bug (Corythucha arcuata Say, 1832 Heteroptera: Tingidae). In the context of the rapid spread of infestations and the severity of attacks on oak trees in infested forests, this paper aims to assess measures to manage this species in the future. Namely, the effect of aerial chemical treatments on oak lace bug has been investigated with two influencing factors: the mode of insecticide action (contact and systemic) and the treatment volume (low volume and ultra-low volume). The experiment was conducted in two forests over a total area of 350 hectares. The results show that the reduction of the nymph population varied from 91% to 96%. However, the residual population was sufficient to allow differentiated re-infestations over time, more quickly after contact insecticide sprays (22 days after treatment) and slowly after systemic insecticide sprays (more than a month after treatment). This re-infestation time difference had implications on attack intensity as well, with stronger leaf discoloration observed in areas treated with a contact insecticide compared with those treated with a systemic insecticide.

Forest structure as an effect of forest dynamics can be used to characterize biophysical processes, biodiversity and ecosystem functions. This study examines the structural components of old-growth forest stands located in the Caspian forests, north of Iran. We measured forest-related attributes in five plots located in the Kheyrud Forest, Mazandaran Province, Iran in 2004 and 2014, respectively. The mean stand density was of 338.6 tree ha-1, the mean volume was of 389.2 m3 ha-1, and the volume of deadwood accounted for 34.1 m3 ha-1. The mean stocking volume per hectare was for beech: 3.95; hornbeam: 7.00; oak: 1.39; maple: 0.60 and other species: 2.55 m3 ha-1. Meanwhile, the mean volume of the felled trees, other cuttings, snags and logs were 31.3, 1.1, 12.6, and 21.5 m3 ha-1, respectively. The mean abundance of gap size on small (<200 m2), intermediate (200-500 m2), and large (>500 m2) classes were calculated as 53.5, 37.9, and 14.1%, respectively. No significant difference in size gap distribution was detected over 10 years, neither any gap size class. The coarse woody debris (CWD) percentage from total deadwood volume varied from 67% to 93%, whereas the fine woody debris (FWD) amount was estimated ranged between 7 and 33%. No significant differences between 2004 and 2014 was found for CWD and FWD. Comparison of spatial pattern results of tree species in 2004 and 2014 implies that there were no significant changes in the mingling index, uniform angle index, or diameter differentiation at species and stand levels, except oak and maple species that showed a significant change in diameter growing. In other words, despite the harvesting of the trees, spatial pattern indices have not changed significantly. These results indicate the performance of ecological forestry programs by foresters in the Hyrcanian Forest stands and their increasing consideration to the ecological principles of the forest. The results are useful in the sense that they characterize the stand structure components which are fundamental to performing silvicultural treatments based on the emulation of natural forest structural dynamics.