The International Association of Horticultural Producers (AIPH) members consist of thousands of growers of flowers and ornamental plants around the world who are together united by one essential goal – promoting the place of plants in people’s lives.
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Gleditsia triacanthos is a very rustic exotic genus and will, with increased probability, provide superior growth performance and, consequently, environmental benefits.
Professor Francesco Ferrini, Full Professor of Arboriculture and Urban Forestry at the University of Florence and President of the Nursery Production District of Pistoia, shares insights on the game-changing benefits of a triple helix approach — a trilateral network of organisational links between university, government, and nursery stock industry. He says plants are the most complex component of urban requalification projects and discusses the need for climate-resilient trees and plants and debates on native versus exotic species.
For Europe, and Italy in particular, 2022 was a disastrous year from a climatic point of view, aggravated by a severe energy crisis and by a summer affected by strong heat waves and prolonged drought, with increasingly damaging and catastrophic effects. The immediate, unanimous, and imperative cry of politicians, public administration and companies more or less responsible for climate-changing gas emissions was: ‘Plant trees’. Not thousands, not millions, but billions of trees. In 2023, however, not even a faint whisper about this emergency has been heard.
Evidently, they have found other solutions or priorities to address what have so far only been called climate anomalies. We wanted to hear the expert opinion on this topic from Professor Francesco Ferrini, Full Professor of Arboriculture and Urban Forestry at the University of Florence and President of the Nursery Production District of Pistoia. Ferrini is an esteemed professional and a shining example of how the university and industry can successfully work together.
Francesco Ferrini is a Professor of Arboriculture and Urban Forestry at the University of Florence and President of the Nursery Production District of Pistoia.
FloraCulture International: I am a great believer in active collaboration between universities and nurseries. Do you think it will bring prestige and credibility to the nursery world? Do you think the politicians consider the time constraints of tree production during talks?
Francesco Ferrini: I have always been close to nurserymen, and with their collaboration, I have undertaken important research. I sincerely hope that my presidency of the most important nursery district in Italy, if not in Europe, will lead to a better dialogue with politicians and the Public Administration. In institutional meetings, we have often explained the shortage of tree production in European nurseries. Still, the Public Administration must contend with the strenuous search for trees like the companies receiving public greenery contracts. Having contracts to honour the industry needs help in completing the work. That is why we have asked to find a solution that can plan production to get the quantities, species, varieties, and correct measures to comply with the commitments undertaken. In this discussion, it is crucial to recognise ‘distractions’, i.e. promises or solutions touted as ‘unique’ or better or whose feasibility and cost-effectiveness are described as far superior to the actual ones. These are often strategies or technologies that are indeed viable but are far from being able to solve a transversal problem such as climate change and which instead risk “distracting” public opinion from the necessary actions for decarbonisation of the energy, industrial, residential and transport sectors. Undoubtedly, ‘planting trees’ is a solution apparently without drawbacks, which appeals to everyone and inspires a positive vision of the future by evoking actual benefits (urban cooling, absorption of pollutants, physical and mental well-being) and others that should be analysed more seriously (carbon dioxide absorption).”
Ailanthus and Robinia in a rather unhospitable urban environment.
By 2030, in addition to the 145 billion square metres of buildings already existing on Earth, there will be a further 73 billion square metres of new buildings. So future city projects are being studied where ‘green’ should play a fundamental role. Does one consider the exceptional changes we have mentioned, destined to become ‘normality’ for the choice of trees? How do you imagine this new scenario?
“Plants are perhaps the most complex component of an urban requalification project; complex because they are living beings, and they change in size (and sometimes even in shape), and, if we reference deciduous plants, they also mutate with each season. The choice to use various botanical species has always been focused on their aesthetic qualities, but today, other parameters, not only technical, must be considered when choosing suitable species for an environment.”
Future research will have to provide answers to important questions. Could one of the first goals be the search for species of trees and shrubs that are less vulnerable and sensitive to extreme drought and heat waves?
“The decision to base our choice on criteria that take into account both technical and aesthetic characteristics becomes significant if, for example, we come to realise that the warmer microclimate of cities can be advantageous in cold climates, allowing the cultivation of species that are less tolerant to low temperatures and hence the choice of a wider range of exotic species and phenotypes than would normally be usable in such climates. But it should also be kept in mind that, somewhat less positively, the warmer microclimate may cause early sprouting or prolong the growing season, making the trees susceptible to late spring frosts or eventual early autumn frosts. And again, in warmer climates, high temperatures and reduced water availability, especially in paved areas, can lead to localised drought conditions and limit the choice of species.”
‘We are well aware that there is no such thing as the perfect tree, but we must strive instead to plant the right tree in the right place and ensure its correct and economically sustainable management’
Robinia pseudoacacia, aka false acacia, or black locust, is a medium-sized deciduous tree originating from the United States. It’s a popular garden tree, although it has naturalised in some parts of North America, Europe, Africa, and Asia and is sometimes considered invasive.
Which species are most affected, and what is the recovery time of urban trees and shrubs suffering from this situation?
“In particular situations, exotic species might perform better than trees that are native to the area but which have evolved in a different climate and would show serious difficulties thriving in our cities, where climatic conditions and soil characteristics may be completely different from those of a ‘natural’ environment. Native plants do not necessarily survive in these conditions better than exotic ones.”
Do you have any actual examples to confirm this?
“One example applies to all: the alder is a typical species found in humid areas and river banks in Tuscany, hence indigenous, but if it is planted even a few dozen metres from the river, where it naturally grows, in a sunny paved square, it will hardly survive. In the same environment, a Gleditsia, a very rustic exotic species, will, with increased probability, provide superior growth performance and, consequently, environmental benefits.”
Is it possible to calculate the mortality rate of the species?
“Certainly, it is possible to predict the mortality rate of the species, using the distribution ranges of the species and the functional traits of the plants, i.e. all the morphological, physiological and phenological characteristics of the plant itself that influence its overall fitness through their influence on survival, growth and reproduction, such as specific weight of wood and its density, plant height, crown size and leaf traits, such as leaf size or area, specific leaf area, relative water content, foliar dry matter content, foliar nitrogen content, foliar phosphorus content, stomatal conductance, photosynthetic rate and intrinsic water utilisation efficiency. It would be necessary to attach microchips to the plant that give data to a server that can evaluate them daily. We are currently researching this project.”
Alnus cordata, aka Italian alder, is a pyramidal, fast-growing, small to medium-sized, deciduous tree that is native to Corsica and southern Italy.
It is necessary to raise a more widespread awareness of how complex this subject is through continuous questioning and increasing studies related to the many issues, such as the species to be used in an urban environment and beyond, the choice of trees with greater retention and storage of CO2, and pollutants, and the native and exotic species capable of coping best with the increase in temperature. Considering all these variables, how do you think interactions between species will change?
“If we must take into account all these factors, we should not rule out a priority use of exotic species. Still, once their potential for new plantings has been assessed and compared with that of native species, we will try to introduce them where they can maximise the benefits they provide in terms of CO2 sequestration and reducing pollutants. On the other hand, it should be emphasised that their excessive use should not lead to a kind of ‘plant globalisation’ to the detriment of species typical of certain areas. Autochthonous, indigenous, or naturalised vegetation can be the ideal backdrop to enhance the ornamental characteristics of certain exotic species, creating contrasting elements that allow the rare species to be fully appreciated. It is not easy to imagine (although it could happen, unfortunately, because of the Red Weevil) our waterfronts in Southern Italy or the Riviera Ligure di Ponente without palm trees (which are all exotic apart from Chamaerops humilis) or the gardens of the islands and almost all coastal strips without Bougainvillea or without other exotic species that have now become part of the classic landscape of our coastal and even lakeside areas. It can, therefore, be stated that a tree which is native or non-native in a different climate has a relative significance. What really matters is whether the characteristics and performance of the trees are compatible, even if they do not enhance the environment where we want to place them, obviously avoiding invasive species. Sometimes, there is confusion and a tendency to associate the term exotic with the potential for invasion of the species. Most non-native or exotic species are harmless. An exotic species is called invasive when it harms the ecosystem, such as the Ailanthus, Paulownia, Robinia or Broussonetia papyrifera. The main difference between exotic and invasive species is that exotic species are harmless to the ecosystem, while invasive species are damaging to the ecosystem. Rather than comply with environmental regulations that exclude the use of exotic species in new projects, it would be more reasonable to stimulate landscape architects to design pleasant green spaces using a greater variety of species, whether native or exotic, seeking out the most suitable or adaptable ones on a case-by-case basis. A 100 per cent native objective, although desirable, may not be the best choice for the site we are dealing with at the time. We are well aware that there is no such thing as the perfect tree, but we must strive instead to plant the right tree in the right place and ensure its correct and economically sustainable management.”
In Italy and Europe, nursery workers and gardeners have achieved high-quality landscaping production, design and creation results. Don’t you think the sector really lacks the economic valuation of greenery? Why can’t we create a European algorithm that can calculate the daily amount of CO2 absorbed by the trees in our gardens?
“It is not at all easy to create the algorithm you mentioned, although many institutions are working on it, and some recently published results are quite encouraging. However, there is still time to say that we have a reliable formula or programme.”
• Professor Ferrini concludes the interview with this note of doubt that is probably dictated not so much by science as by the long-standing knowledge of the world of green operators, often conflicting with the common goals to be achieved. Surely, our united sector would attain unreachable and unimaginable results for everyone.
This interview was first published in the October 2023 edition of FloraCulture International.
