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.

Trees in public open spaces are an important part of the urban green space system, which has to adapt to increasingly difficult conditions due to urbanisation, climate change and human activity. Green spaces are a major factor in improving the microclimate, helping to protect biodiversity and playing an important aesthetic role, so they need to be preserved and enhanced. In our country, since the 2000s, a large number of studies and civil initiatives have highlighted the importance of green spaces, but typically from a quantitative approach. However, improving the quality of planting is an equally important task. Our research assesses the canopy cover of trees in open spaces in Budapest in terms of planting density, with a focus on the planting distance of trees in certain squares and streets and the resulting cover values. In our studies, we have considered the quantitative and qualitative variation in crown canopy cover at the time of planting and in maturity, so we can formulate ideal planting suggestions based on the environment, requirements and characteristics (crown shape, growth vigour) of each taxa. In the series of case studies, we first studied the woody species of one of the most important intermodal nodes of Budapest, Móricz Zsigmond Square and Bartók Béla Street. The canopy cover of the square reaches the ideally defined minimum canopy cover of 25-30% in 5-7 years. Considering canopy cover and planting density, it was found that in 2023 the canopy cover of the trees in the Móricz Zsigmond square averages 13%, while at maturity it will cover more than 50%. This means that about half of the tree crowns will be able to have the highest potential impact in terms of ecosystem services.

The world’s big cities, including Budapest, are becoming more crowded, with more and more people living in smaller and smaller spaces. There is an increasing demand for more green space and trees, with less vertical and less horizontal space. In addition, deteriorating environmental conditions are making it even more difficult for trees to grow and survive. Tree species in urban areas have multiple functions and high ecosystem services when in good health. Among taxa with diverse habits, sizes, crown shapes, growth vigor, longevity, urban tolerance, and canopy habit, our research aims to evaluate urban specimens of spherical species with smaller space requirements and sizes but have regular geometric crown shapes in public plantations in Budapest. In the restricted urban habitats, the city’s cadastral records include 4676 specimens with spherical crowns. Among the species examined, eight species with globular crowns (Acer platanoides ‘Globosum’, Catalpa bignonioides ‘Nana’, Celtis occidentalis ‘Globosa’, Fraxinus excelsior ‘Nana’, Fraxinus ornus ‘Mecsek’, Platanus × hispanica ‘Alphen’s Globe’, Prunus × eminens ‘Umbraculifera’ and Robinia pseudoacacia ‘Umbraculifera’) were evaluated in relation to age, health, wood type, crown size, and shade projection in order to show which species are or will be suitable in the future.

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.

A városi zöldfelületek rendszerében kulcsszerepet töltenek be a közterületen álló fák, melyeknek egyre nagyobb kihívásokkal kell szembenézniük az urbanizáció, a klímaváltozás és az emberi beavatkozások hatásai miatt. A zöldterületek jelentősen javítják a mikroklímát, támogatják a biológiai sokféleség megőrzését, és esztétikai értékük is jelentős, ezért védelmük és fejlesztésük kiemelten fontos. Kutatásunk a budapesti szabadterek lombkorona-fedettségét értékeli a telepítési sűrűség függvényében, különös figyelemmel a terek és utcák fás szárú növényeinek telepítési távolságára és az ebből adódó borítottsági értékek összehasonlítására. Vizsgálataink során figyelembe vettük a telepítéskori, jelenkori és a teljesen kifejlett lombkorona arányának mennyiségi és minőségi változásait, hogy az egyes fafajok igényeit és sajátosságait (koronaforma, növekedési erély) figyelembe véve ideális telepítési ajánlásokat fogalmazhassunk meg. Második esettanulmányunk során a Szent Gellért tér faállományát vizsgáltuk. Az értékelés során megállapítottuk, hogy a lineáris facsoportok egyedei – taxontól függetlenül – habitusuk, lombkoronaformájuk és telepítési sűrűségük alapján közel ideális feltételek mellett fejlődnek, és várhatóan a jövőben is jól fejlődhetnek. Ezzel szemben a zöldkazettákban álló fák közül elsősorban a facsoport külső egyedek bizonyulnak hosszú távon is értékesnek az ökoszisztéma-szolgáltatások szempontjából. A jelenlegi nyílt lombfelületek aránya 97%, mely a vizsgált szabadterek között a legjobb értékek közé tartozik, azonban a fák kifejlett korában a zöldkazettában ez az arány 52%-ra, míg a lineárisan ültetett facsoportok esetében 71%-ra esik vissza ezért kijelenthető, hogy a zöldkazettákban álló taxonok a rossz telepítési sűrűség következtében jelentősen akadályozni fogják egymás fejlődését és kedvező hatásaikat sem képesek teljes mértékben kifejteni majd a jövőben.

Urban blight affects billions of city dwellers worldwide. Green spaces and trees are the best way to mitigate the adverse effects of climate change or urban climate, and they raise a wide range of health issues. In addition to pollution, there is increasing talk of allergies, a global public health problem. This article aims to analyse the complex relationship between urban green spaces and allergic diseases, from a medical, horticultural, and landscape architecture perspective. It is becoming increasingly difficult to create a liveable environment around us with few (and fewer) urban 'survivors' to choose from. A recent draft proposal would restrict or ban the planting of any tree species with at least two scientific publications in peer-reviewed journals supporting its allergenicity. Restrictions and bans would primarily limit the use of wind-pollinated plants, while evolution is moving towards wind pollination rather than insect pollination. Restrictions, especially bans, are a very powerful tool that can easily end up having the opposite effect to the original intention. Public health is a fundamental issue for everyone, yet before adopting legislation that can be considered definitive, it is worth considering the arguments from the point of view of tree protection, showing what our environment would be like, what ecosystem services we could expect if we were surrounded only by climate-tolerant but non-allergenic taxa. In addition to reviewing the state of allergy and plant allergy in our country, we also have a strong aim to bring the "two societies" closer together. We believe that by finding common ground between the medical, public health, and green professions, we can move urban plant use in a direction that will create a better, more aesthetic, and above all, healthier and more liveable environment for urban dwellers.