Technologies and system for the right management of public green
Urban green areas are increasingly considered as necessary infrastructure to improve the quality of life and enrich the biodiversity of built-up areas. In Italy the average availability of urban green areas is about 30-40 m2 per inhabitant, but with significant territorial differences
In order to counteract the increase in population density in metropolitan areas and to cope with the effects of climate change, greenery is finally being given an important role. Urban greenery is increasingly seen not only as an ornamental element but also as a necessary infrastructure to improve the quality of life of citizens and to increase urban biodiversity. To enhance the value of green areas, however, it is not enough to increase their surface area, but they must also be managed correctly.
Urban and peri-urban green. In Italy the availability of urban green areas is around 30-40 m2 per inhabitant, but with very marked differences, ranging from areas that have more than 400 m2 per capita to others that do not reach 10 m2 . The different types of green spaces can be summarised as follows. Large urban parks. These are large areas (more than 5,000 m2) characterised by the extensive presence of lawns, trees, shrubs and hedges, flowerbeds, equipped areas, etc. They are located both in the centre and in the outskirts of the city, and are used by the public both for leisure and sporting activities. They are generally divided into functional areas for rest, sport, culture and services. Urban trees are trees arranged in rows, generally on both sides of the road. They act as a link between the city and the territory. Wooded areas (urban woods), which are not part of protected natural areas. Equipped green areas, consisting of small neighbourhood gardens with games for children. Urban furniture areas, represented by roundabouts with vegetation, flowerbeds and green barriers. School gardens, represented by the green areas of school buildings. Urban gardens, consisting of land intended for cultivation and entrusted to the care of individual citizens. Outdoor public sports areas. Cemetery greenery. Botanical gardens. Fallow land not intended for agricultural use. Escarpments and river banks. In interventions aimed at increasing green areas, especially with a view to ecological transition, great importance is attached to trees. As part of the Green Deal policy and in pursuit of ecological transition objectives, EU Commission President Ursula Von der Leyen has set an ambitious target of planting 3 billion trees in Europe by 2030. This target was considered by many to be too ambitious, as it would mean planting more than a million trees a day and, above all, already having this amount of plants available and identifying planting sites. However, while we share the doubts about the possibility of achieving this result within the deadline set, we cannot fail to agree with the need and necessity of increasing green areas, especially in metropolitan cities, by increasing urban and peri-urban forestation. Moreover, the theme of the green revolution is also included in the National Recovery and Resilience Plan (PNRR), which envisages the creation of urban and peri-urban forests by planting, mainly in the 14 metropolitan cities, at least 6.6 million trees. This means creating 6,600 hectares of urban and peri-urban forests. This is an unprecedented commitment.
Maintenance work. The main routine maintenance operations concern: cutting grass, lawns and embankments; fertilising and treating, when necessary; stripping and aerating the turf; pruning tall trees; pruning shrubs and hedges; pruning roses and rose bushes; pruning small trees (under 5 m); and collecting leaves. Grass cutting is a very important operation, not only operationally but also economically, as the areas occupied by turf are very large. In an urban park, turfgrass accounts for 40-50% of the plant component. The operation is normally carried out using self-propelled mowers with drivers on the ground and self-propelled machines with drivers on board. These can be combined with brushcutters for trimming operations. In order to evaluate the comparison between ground and ride-on mowers, it is worth mentioning the result of a study conducted in France by Plante&Citè. The survey lasted 4 years and analysed 215 grassed roofs in different situations for a total of 10,000 working hours. The most commonly used machines were ride-on mowers with a working width of between 80 and 275 cm. For these, the average working time was 0.03 min/m2/year, compared to 0.06 min/m2/year for self-propelled mowers with driver on the ground. The overall time is influenced by: the configuration of the borders; the morphology of the site (slope, shape, etc.); the use of unsuitable machines. The finishing operation has an operational impact that depends on the type of lawn, and is between 5% and 70% of the total. Fertilisation is carried out with centrifugal fertiliser spreaders using slow-release fertilisers, while soil stripping and aeration operations are reserved for lawns with compromised vegetation. The shrub and non-grass perennial herbaceous component is important for soil consolidation and environmental and landscape rehabilitation, contributing to increasing the level of biodiversity. Maintenance practices are linked to the different types, i.e. berry, flower and aromatic shrubs. Leaf collection is carried out with blowers and vacuum cleaners.
Extraordinary maintenance operations include: pruning of tall trees: felling of trees; checking stability. Pruning is carried out using stair lifts or, in special cases, tree climbing, whereby the operator, with a harness and ropes, reaches the tree canopy and moves inside it safely. The assessment of resistance to fracture and wind damage is carried out using the VTA method (Visual Tree Assessment) based on analysis at three levels of detail: visual inspection to identify obvious anomalies; detailed visual inspection and instrumental checks (calibre, inclinometer), to assess the danger of the tree and the risk to people and property; advanced assessment with penetrometric (dendrodensimeter) and sonic (3D sonic tomography) instruments, as well as controlled tree pulling tests to assess the resistance of the root system against removal.
Management of public green. The management can be carried out solely by the public authority or entrusted totally or partially to service companies. A very common solution consists in having the maintenance of the most qualified green areas carried out by the authority (the districts may be involved for very restricted areas) and the remaining part entrusted to full service companies. The reason for this is linked to the high investment in machinery, including its maintenance, and the high workload. Taking into account the work schedule, the manpower/area ratio is estimated at: 1 worker/ha, for particularly valuable gardens; 1 worker/4 ha, for less valuable gardens and parks with a fairly intense use; 1 worker/6-8 ha in the case of urban parks and woods in peripheral areas. The different use of manpower can already lead to the application of the concept of differentiated and ecological management, i.e. maintenance operations with different intensity, carried out in relation to the users, the level of use, the type and function of the green space. Ecological management, aimed at increasing biodiversity. Service companies are entrusted with the task by means of tenders that require very detailed documentation regarding the performance of individual operations as well as guarantees of the professionalism and suitability of the companies. The following documents are required for each green maintenance operation: technical report, unit prices, estimated metric calculation, time schedule and economic framework. The guarantee of company suitability is provided both by the DUGE, a single European tender document in electronic format, which is a self-declaration of the company's suitability in terms of competence and financial availability, and by the DUVRI, a risk assessment document, drawn up by the client and accepted by the contractor.