Historic allées and urban avenues reflect a far-sighted and forward-thinking design attitude. These compositions are the living witnesses of olden times, suggesting permanence. However, the 20th century’s urban development severely damaged the environment, therefore hundred-year-old mature trees are relatively rare among city avenues’ stands. Due to the deteriorated habitat conditions, replantation may be necessary from time to time. However, there are a large number of replanted allées and urban avenues considered historical monuments, according to the relevant international literature in urban and living heritage’s preservation. The renewal often results in planting a different, urban tolerant taxon, as seen in several examples reviewed. Nevertheless, the allée remains an essential urban structural element, though often with a changed character. The Budapest Andrássy Avenue, a city and nature connection defined in the late 19th century’s urban landscape planning, aimed to offer a splendid link between city core and nature in Városliget Public Park. The 19–20th century’s history and urban development are well documented in Hungarian and several English publications, though current tree stock stand and linear urban green infrastructure as part of the urban landscape need a detailed survey. The site analyses ran in 2020–early 2021 created a basis for assessing the allées and the whole avenue as an urban ecosystem and a valuable case study of contemporary heritage protection problems. Andrassy Avenue, the unique urban fabric, architecture, and promenades have been a world heritage monument of cultural value since 2002. The allées became endangered despite reconstruction type maintenance efforts. The presented survey analyses the living heritage’s former renewal programs and underlines the necessity of new reconstruction concepts in urban heritage protection. We hypothesize that urban green infrastructure development, the main issue in the 21^st century to improve the urban ecological system and human liveability, may support heritage protection. The Budapest World Heritage Site is worthwhile for a complex renewal where the urban green ecosystem supply and liveable, pedestrian-friendly urban open space system are at the forefront to recall the once glorious, socially and aesthetically attractive avenue.

Examining the history of garden art since ancient times, we find many examples of linear tree layouts supporting orientation or being used for the purpose of composition. Allées gained special significance during the Baroque as dynamic and grandiose space-forming garden design elements. They mostly consist of trees of taxonomically similar species planted along a regular line equidistant from each other in single or multiple rows. The two-dimensional compositional elements of the layout form three-dimensional longitudinal space forms. During their evolution, both their proportions and openness constantly change. Analyses of the compositional role and functions of allées of exemplary Hungarian Baroque garden complexes in the 18th century provided a basis for setting up a novel typology. Five compositional types have been defined as the primary result of archival research. The significance of the still-subsisting historic Hungarian allées calls for unique protection similar to European heritage protection. Taking a summary of significant, surviving examples of Hungarian Baroque allées into account, methods for allée renewal are defined along with the core question of whether allées are natural landscape elements or strict architectural compositions where authenticity may be an important criterion. The methodological research is partially based on three plans for the renewal of Baroque allées in Hungary that have been worked out by the Author as the chief landscape architect of the projects.

Trees are key components of historic gardens and are valuable sources of genetic diversity that need preservation to enrich native populations’ genetic basis in order to enhance long-term viability, and facilitate the species’ adaptation to changing climatic and environmental conditions. The primary objective of our study was to assess the genetic diversity, structure and relationships of theTilia cordataMill. allée at Széchenyi Castle in Nagycenk (UNESCO heritage site), Hungary, to infer the late-Baroque garden’s rich genetic heritage and conservation importance. The small leaved lime individuals at Nagycenk, with an age of 200 years, maintained high genetic diversity with non-significant inbreeding and high allelic richness and number of private alleles. Genetic diversity was similar to Central European natural populations and slightly higher compared to other plant collections, e.g. Eszterházy Castle garden at Fertőd. The surveyed trees exhibited two age groups unrelated with shallow genetic differentiation indicating the potential seed source origin from the local geographic area. Bayesian clustering of individuals showed significant differences from the individuals growing at Fertőd-Esterházy gardens (approx. in a 15 km distance) and otherT. cordatacultivars. We concluded that theT. cordatacollection of Nagycenk is a unique genetic heritage of the former natural vegetation due to its genetic variability and divergence, which would be a valuable source of future breeding programs and conservation.

Due to their authentic urban and architectural character, the Medinas of Tunis and Marrakesh became listed among the United Nations educational, scientific, and cultural organization (UNESCO) heritage sites in 1979 and 1985, respectively. Nowadays, the urbanization of the surrounding green areas and the climate change impacts on cities are degrading the Medinas’ livability and their characteristic heritage. On the other hand, scientific knowledge and data about the green system in the dense urban cores of Medinas in the Maghreb region is still not a widely apprehended theme in the scientific domain. This research objective is to initiate nature-based and sustainable solutions in these cities by demonstrating the application of the urban green infrastructure (UGI) approach. As a research methodology, an analysis of the historical green system development in the Medinas is given to highlight their tangible and intangible values. The analysis goes over three periods: first, the medieval Islamic era, then the modern period during the French colony, and the contemporary city as a unique urban landscape. Finally, the study proposes a design guideline to prove the applicability of the UGI in the given historical morphologies by implementing the retained historical values of the historic green heritage in Medinas and the aspects of the site.

Climate change may strongly modify the habitat conditions for many woody plant species. Some species could disappear from their natural habitats and become endangered, while others could adapt well to the changed environmental conditions and continue to survive successfully or even proliferate more easily. A similar process can occur within the artificial urban environment as the hitherto popularly planted urban trees may suffer from the extremities of the urban climate. However, among the planted taxa, there are species that spread spontaneously and appear as weeds in extensively managed gardens. In our study, we evaluated the native and non-native species involved in spontaneous spreading in the institutional garden of Buda Arboretum (Budapest) during the COVID-19 period in 2020–2021 when entry was prohibited, and maintenance went on in a restricted, minimal level. We investigated the correlation between spontaneously settling and planted individuals, and then performed multivariate analyses for native and non-native spreading plants for spatial and quantitative data. During our studies, we observed the spontaneous spreading of 114 woody species, of which 38 are native and 76 are non-native. Taking the total number of individuals into account, we found that, in addition to the 2653 woody species planted, a further 7087 spontaneously emerged weeds developed, which creates an additional task in the maintenance.