Large green spaces: function, management and maintenance
The constant increase in the population living in cities and urban centres brings to the fore the topic of maintenance of parks and public areas used for sports and recreational activities. The combination of agronomic techniques, environmental protection methods, and mechanical and electronic technologies enables the optimal management of urban green spaces. Fleets of robots able to intervene in a timely manner and controlled from a remote location are on their way
Green spaces play an important role in the area of sustainable development. The same sustainability assessment approach applies to these spaces too, using an integrated vision of the three aspects that characterize it: respect for the environment, social justice and economic efficiency.
This article focuses on large green spaces. In particular, it focuses on cities, where human presence is increasingly concentrated (in 2050, 75% of the world’s population will live in a city) and, therefore, where there is greater pressure on the environment and on quality of life. In Italy, the average prevalence of public urban green space is about 32 m2/inhabitant.
However, there are cities that do not reach 9 m2/inhabitant; conversely, in the northern regions, more than 40% of the regional capitals have an average public green space per capita higher than the national average. In assessing green spaces, we need to look beyond the average data per inhabitant.
Besides the aesthetic and ornamental aspects, we need to identify the functions of green spaces and the services they produce, also in the context of combating climate change. This approach also determines the management to be implemented and the resulting form of maintenance.
The function of green spaces
The link between sustainable development and green spaces is given by the functions of green spaces and the services they provide, i.e. services: environmental, socio-cultural and economic.
Especially in heavily populated and urbanized areas such as those of large cities, the functions of green spaces should be considered with an ecosystemic approach, so as not to affect the relationship between people and nature; a relationship that is increasingly felt and demanded by the population. A recent survey conducted in France on metropolitan cities (UNEP-IPSOS) shows that 90% of French people need a daily relationship with vegetation and 70% try to settle in or near green spaces.
This is because people, and especially those living in the city, have become aware of the multifunctionality of green spaces and the services they can provide. These environmental services range from climate mitigation, improved air quality, water regimenting and maintaining biodiversity, both plant and animal. Socio-cultural services, such as physical and mental health, socialization, recreation and sport. Economic services, which include avoided costs for health and pollution removal, in addition to the economic benefit from the favourable effects on the housing market, tourism and energy savings. Credit for these services basically goes to urban and peri-urban parks.
Generally, in urban parks, most of the surface is occupied by lawns; however, there are also plenty of shrub and tree species acclimated to the planting area. They are often characterized by the subdivision into areas with different functions such as rest, play, sports and recreational activities, which benefit public health. We should not forget that especially among young people, the collective practice of sports activities in open public parks is becoming more and more common. This is why areas are set up for fitness, to practice activities to strengthen muscles, stretch, and so on. To equip an outdoor area of 100-120 m2 dedicated to fitness requires an investment of roughly 25,000-35,000 euros. Such a surface generally includes an area equipped for stretching and one for cardio training. This equipment, which does not involve artificial energy consumption, is usually fixed on a flexible substrate or on a lawn. However, it requires continuous checks and maintenance to ensure the users’ safety.
Generally there are also children’s play areas, a sector where there is a constant evolution in furnishings and equipment that can stimulate the interest of kids to engage in different games and activities with varying levels of difficulty. Again, safety checks must be thorough and ongoing.
The green spaces of peri-urban parks are less frequented and can also play a role in the integration of the surrounding agricultural and forestry systems, as well as a connection between city and countryside.
Management
Public green space management must reconcile two needs: ensuring the quality of the vegetation and services that can satisfy the citizens; contain the costs that result from it. For this reason, what is known as differentiated management is increasingly adopted. This is a management that schedules a maintenance level linked to a varying frequency of the actions carried out with different types of machines, as well as the services offered by green spaces and the way they are used. The services that are managed by the relevant public department generally include maintenance of green spaces and the production of plants and flowers, the design of flowerbeds, roundabouts and other key sites, floral decorations in parks, gardens and places of particular value, as well as the furnishing of specific areas.
As far as maintenance management is concerned, despite the differences due to the use of the green spaces, some general principles apply, such as: non-use or reduction of pesticides; water conservation, since climate change has made water a very precious asset that cannot be wasted; the reduction, especially in the centre of towns, of the atmospheric and acoustic pollution emitted by the tools being used. The maintenance can be entrusted totally to the relevant public department, or partly to the department (usually the most valuable areas) and partly assigned to third parties through tenders. In more peripheral areas, lawn maintenance can also be pastoral.
Of course, the costs have to be kept under control by means of careful analytical accounting, in order to know the operating costs of the activities carried out by the department and those assigned to third parties. All the elements for each sector of activity need to be gathered to achieve this. For example, maintenance will require being familiar with the green space, and knowing the working time of the workforce and that of the machines used in the various jobs.
Maintenance
In general terms, it can be said that in order to comply with the general principles of management mentioned above, electric tools and machines are preferred for carrying out the maintenance. Modern batteries enable machines such as chainsaws, brushcutters, hedge trimmers, blowers, etc. to provide the same performance as those powered by combustion engines. In order to reduce air pollution, instead of employing traditional fuel for combustion engines, alkylate fuel can be used. This is a much less polluting fuel, but it has high costs.
We will limit ourselves to covering the most important actions.
Due to the large surfaces concerned, public park lawns are usually mowed using riding lawn mowers with front engine (tractors) or, more often, with rear engine (rider). The cutting apparatus is usually rotary on a vertical axis. This often involves direct grass collection in a basket. The working widths are between 80 cm and 180 cm or more, with engine powers exceeding 30 kW.
From an environmental point of view, it should be said that new lawn mowers are much less polluting than in the past. According to some studies and analyses conducted in France (Horticulture et Paysage), modern lawn mowers with combustion engines have a lower environmental impact compared with those of the past, and it can be broken down as follows: 9% during the production phase; 1% during the distribution phase; 85% during the usage phase; 5% during the end-of-life phase.
The greatest effort by the manufacturers has therefore been focused on reducing impact during use, by reducing both the emission of pollutants and the sound level of the machines. Another path followed by the manufacturers, which is yet to have any significant impact on the market, is the production of riding lawn mowers with hybrid or fully electric engines.
The use of lawn mowers mounted behind a tractor is also widespread. In this case, the grass is not collected directly and the working width can reach up to 3 metres. Especially in suburban parks, instead of being mowed, the lawn is scythed and the activity is limited to 2 or 3 times a year. Another solution is the use of a flock of sheep, or less frequently, a herd of cattle.
A widespread activity is the cleaning of lawns and roads pertaining to the park. This activity is primarily aimed at gathering leaves, mostly concentrated from the beginning of autumn. Blowers are the main machines for this operation, using a strong air flow to gather the leaves into heaps or swaths to facilitate their subsequent collection. For medium and large surfaces, the blower can be carried by a lawn mower or tractor. It is driven by a mechanical or hydraulic power outlet. The powers involved for these machines vary in range from 5-10 kW for models mounted on lawn mowers with driver on the ground (operating with air flows of 50-80 m3/min), reaching 12-18 kW for models applied to self-propelled machines (operating at higher capacity, up to 250 m3/min).
The collection is carried out with vacuum cleaners that usually operate on the swaths created with the blowers. The machines used on large surfaces, for which the volumes are high, carry out the suction of the leaves and then convey them into a closed container mounted on a trailer. The operator generally operates the intake hose, while the turbine motor assembly is mounted on the trailer. Some models carry out the collection directly through suction holes with working widths of 1.5 to 3 metres. The suction rates can exceed 300 m3/min. Another solution, especially for cleaning streets and squares, is the use of brushing-collecting machines. The working parts consists of rotating brushes that collect leaves and other debris and, utilizing the rotational speed, they convey them into a closed container with mechanical or hydraulic unloading. The brushing-collecting machines are made both in self-propelled and in towed versions.
As far as pesticides are concerned, it is necessary to limit them to a minimum and to comply with the usage thresholds established by the national, regional and municipal regulations. National and regional legislation limits the use of pesticides to those in a low toxicological class, while some municipalities impose a ban on the use of pesticides unless there is a specific permit. When the pesticide treatment is applied to adult trees, pneumatic spraying machines are used, and the risk of drift is very high. It is therefore important to operate under low wind conditions.
For vertical greenery, and in particular for adult trees, ordinary maintenance work essentially concerns stability assessments and pruning, which must be carried out at well-defined intervals. There are several methods for assessing stability. The most widespread method, which has been practiced for a long time, is the Visual Tree Assessment (VTA). It is performed with an initial visual analysis and, if necessary, with subsequent instrumental analyses. These are performed with special instruments such as the sonic tomograph, based on recording the propagation of sonic waves through the wood, and the resistograph, which measures and records the mechanical strength of the wood. The current trend in pruning adult trees is to avoid drastic cuts removing large branches, but rather to carry out “gentle” pruning that maintains the harmony of the branch structure. The operation is easier in a park than it is when pruning along tree-lined streets. The worksite is normally made up of: a special aerial platform, an operator with a chainsaw, a lorry with a bed and a driver tasked with loading, and a wood chipper.
Parks 2.0
In the short and medium term, public parks and gardens will transition to a “digitized” maintenance. This will be achieved by installing various sensors and using drones that will gather in real time information about the state of the vegetation, namely: growth, water stress, parasitic attacks, and so on. This will enable timely and targeted interventions using robotic machines and drones with a low environmental impact, activated by computers, tablets or smartphones. Based on this outlook, amongst the manufacturers of green machinery there are those who think and work, for example, on creating a fleet of automower robots, which can be geo-located with GPS and GSM, distributed around the park and linked to a centralized computer application. This allows the fleet of robots to be controlled simultaneously and remotely, following their work on a Google Map. In addition, each robot can be equipped with sensors for measuring air quality, noise and radiation (UV). It will also be possible to measure telemetrically the level of human use of the different areas of the park and to plan and implement in a timely fashion actions aimed at increasing safety conditions in those areas where the population density is higher.
