The climate has changed significantly over the past few decades around the globe. To make meaningful comparisons between changes occurring over time in the tree world, comprehensive databases on the most important species and their evolution must be created. It is essential to consider latitude, longitude, altitude and local relief when analyzing data. Given the extensive distribution of oak, hornbeam and ash, a sequence analysis was conducted to definitively examine the characteristics of these species in West Plain, West Hills, Apuseni Mountains and Transylvania's Tableland. The data for all the regions comprised a total of 708511 ha, which were subjected to rigorous analysis to determine characteristics such as yield class, volume, increment, structure and participation percentage. The data was analyzed using the most appropriate modern statistical programs, including correlation matrices, ANOVA, principal component analysis, matrix data analysis and the cluster method. In relation to the altitudinal variation, oak is present at average altitudes of 200–250 m in West Plain, 400–500 m in West Hills and Transylvania's Tableland, and 900–950 m in Apuseni Mountains. Hornbeam has a similar spreading with oak, but records its presence in slightly higher altitudes of West Hills (400–700 m) and lower in Apuseni Mountains (700–750 m). Volume is also an important indicator, as it is susceptible to climate change. Oak has the highest age-volume, over 95 years, while ash and hornbeam have it less than 90 years. The results are crucial for understanding the ecological requirements of oak, hornbeam and ash, as well as for effectively managing these forests.

Agroforestry systems are gaining increasing attention worldwide due to their several benefits both for landowners and also for the environment. Even though Romania has a great potential for adopting these systems on a large scale, only a few examples exist. The aim of this research was to highlight the main agroforestry systems that could be introduced in plain regions across Bihor County, Western Romania. A selection of the most suitable woody species and cereals was carried, based on available data and information. In order to select the most suitable combination, a set of eight criteria was considered and an Analytical Hierarchy Process Analysis was performed, with the aid of the Expert Choice Desktop (v. 11.5.1683) software package. The combinations that had the black locust as the main tree species scored better in comparison with the ones that had pedunculate oak as a main species. This research should be regarded as a first and important step in the analysis of several combinations of agroforestry systems that could be implemented across plain regions of Bihor County. Lastly, this proposed model could be replicated in similar studies aimed at selecting the most suitable agroforestry systems for certain sites. Future research should also consider criteria that account for various aspects, including the functional relationships of these future green spaces with nearby areas.

Atmospheric pollution is a major problem in urban environments. Pollutants with various sizes of particulate matter result from long-term anthropogenic sources, including industrial emissions and the combustion of fossil fuels by vehicles and commercial and residential buildings. Pollutants affect both humans and green areas. Trees are good indicators of pollution due to their longevity, easy identification, and geographical distribution in urban areas. Recently, due to climate change, all EU member states have agreed to measure heavy metal pollution in urban areas using plants as bioindicators. This study aimed to analyze heavy metal concentrations (Pb, Cd, Mn, Fe, Cu, Zn) in the leaves of monumental trees (both evergreen coniferous and deciduous) in the Carpathian Arch. Leaf samples were collected in the summer of 2022 from 37 specimens across 12 sites in nine counties - Alba, Brasov, Harghita, Mures, Sibiu, Satu Mare, Bistrita Nasaud, Maramures, and Cluj. The leaf heavy metal contents correlated with a low level of atmospheric pollution. Of the six heavy metals analyzed, only four were highly accumulated in the leaf samples and exceeded the toxicity threshold. Of the nine counties sampled, heavy metal pollution above the toxicity threshold was detected only in two sites - the city of Baia Mare, Maramures county (Zn and Cd), and the city of Cluj-Napoca, Cluj county (Fe, Zn, Cd, and Cu). The response of the tree species to changes in atmospheric heavy-metal concentrations confirmed that trees are suitable bioindicators of air pollution in urban areas. Monumental trees can also be used for environmental restoration and to promote sustainable urban development, decrease pollution, and increase urban environmental health.

Secular trees have an important contribution to today’s communities, not only due to cultural or historical reasons but also to recreational aspects. Management of such species can be done after a thorough analysis is done related to their health status. In most cases, a visual inspection to determine the health status can lead to unsatisfactory results. Modern technology, such as computer tomography, has results that are accurate and valid. A total of 17 secular oak trees (Quercus robur) were sampled and analyzed with Arbotom 2D (Arbotom 2D, Rinn Tech, Heidelberg, Germany) by using sensors on the tree trunks. Besides this, it is imperative to compare the results in the field with the view of the community related to their local symbol. Results revealed severe internal decay (75%–80% damaged wood) in eight oaks, while in the core of the trunk (10%–50% damaged wood), it was seen in seven oaks. Only two oaks have good health status. Survey results indicated the oaks as moderate healthy; only 18.8% respondents from the community consider the oaks unhealthy or in visible decline. This can lead to serious injuries to bystanders. The results have demonstrated a great link between technical and social research so decision-making stakeholders can apply a tailored management for their area.