Set up andmaintenance of green areas in "extreme" conditions

Slopes, as well as roofs and walls of urban buildings, can be covered with vegetation for decorative and functional purposes. The vegetation covers techniques are very varied today, having to adapt to different needs. There is a very wide range of substrates, support structures, sowing and maintenance systems

The extreme conditions in which set up green, discussed in this article, concern two realities with different end aims. The first refers to sloping land, such as road swamps, mountain slopes, river banks, where the primary objectives are the reduction of erosion, and the soil consolidation. The second reality considered, is the urban one, with possible vertical green and hanging gardens. In this case the main purposes are to increase the urban green, improve the air quality and the comfort of homes. Of course, setting up green in these two extreme realities also get to the achievement of common goals, such as support eco-sustainability and biodiversity. Green on slopes and in mountainous areas It is increasingly prevalent, to set up green on the slopes using naturalistic engineering, that is to say, the set of techniques, to be used individually or even in combination, aimed at reducing erosion and consolidating the soil without resorting to cementing works. They are techniques that envisage the use of natural elements such as wood, soil, stone, as well as the use of biodegradable artificial materials or non-biodegradable nets. Particular attention must be paid to the type of vegetation to be set up, as it is necessary to consider some general principles such as the respect for the ecosystem of the area concerned, and the fact that the level of maintenance must necessarily be kept low. The area considered may be a river or lake bank, a road or rail slope, a slippery slope, a ski slope, or even a burned-out mountainous area. Therefore, very different conditions all affected by climate, exposure, gradient, soil type, etc. When choosing the plants to be set up, consideration should be given to the native flora, and check if it is available on the market. The formulation of floral mixtures requires repeated detections of the major plant associations throughout the entire area of the site of intervention. Preference should be given to the so-called "pioneer" plants, that is to say, able to colonize the territory; plants with specific biotechnical characteristics such as: the radical structure capable of retaining soil, low demand of water and fertilizer, adaptation to specific soil and climatic conditions. All this because we need to combine erosion reduction and soil consolidation, with the need to close the gap between the site of intervention and the surrounding natural landscape to preserve the ecosystem. Focusing only on the regeneration and installation of a stand of grass, the techniques that can be adopted include the use of: turf rolls, pre-sown bio turfs, hydroseeding. The rolling lawn is a prompt action on slopes with low gradient. The turf rolls are rolled from top to bottom using, in the most sloping tracts, pickets to better fix them to the ground. However, the substrate must, first, be coated with a layer of vegetal soil, even with reduced thickness. After laying the turfs, a rolling action must be carried out to ensure a better grip to the soil. The technique of the pre-sown bio turfs is quite similar. The soil, as for the rolling lawn, is immediately protected from erosion and, both seeds and fertilizers, are not exposed to run-off water. It is a flexible, easyto- apply material that must be well attached to the ground. After the installation, it is necessary to irrigate to facilitate the birth of the grass, while over time, the degradation of the bio turfs, will provide a supply of fertilizing elements. Hydroseeding is a naturalistic engineering technique involving the use of water to distribute the appropriate seeds to the lands to be revegetate, as well as other elements mixed in the water. To facilitate both installation and growth of the carpet, it is possible to use seeds covered with a film that enables the incorporation of bio stimulants and mycorrhiza. The techniques used can be summarized as follows: standard hydroseeding, hydroseeding on jute nets, hydro mulching, heavy hydroseeding, hydroseeding with bonded fiber matrix, hydroseeding on hardened grounds. Standard hydroseeding applies when there are no special problems such as excessive slope and inadequate soil structure. The mixture to be distributed consists of water (80-85%), seed mixture (4-5%), fertilizers (5-10%), cellulose fiber (2-4%), glues (1-2%). Jute nets need to reinforce the slopes on higher gradient and at high risk of soil erosion. The net must be secured with at least one picket every 3 m2. Hydro mulching is thought for sloping slopes with critical substrate conditions. Compared with standard hydroseeding, it provides a higher dose of seed mixture, and, cellulose blend (30-50 g / m2) and organic soil improvers (150-250 g / m2) are added toglues and fertilizers. The operation is made of two steps: in the first, the mixture of seeds, fertilizers and adhesives is delivered in a dose of approximately 70% of the total; in the second one the remaining 30% is distributed with the addition, in the blend, of vegetable, cellulose, and fertilizer fiber mulch that will cover the seeds and protect them from runoff waters, as well as foster their germination. In thick seeding, in addition to the mulching described above, the organic fertilizer dose is increased (350-450 g / m2). Two or more steps are required. Hydroseeding with bonded fiber matrix is a version of the mulching one. The mixture of vegetable fibres of different kinds, with biodegradable synthetic fibres and glues is spread along with the mixture of seeds and or ganic soil improvers. This mixture has a high water retention capacity, and can fasten to the ground for over a year. Hydroseeding on hardened grounds is used on very steep slopes, that require primarily a frame to protect the soil. The procedure is carried out in two or more steps, by spreading a mixture like the one described above. Hydroseeding machines are often mounted on a sledge to allow easy transportation by means of different machines according to the size, that is to say made up of off-road vehicles, transporter trucks, trailers, tractors etc. The machine components are: stainless steel or polyethylene tank. The capacity ranges from 500 to 4000 litres and beyond; the homogeneity of the mixture is maintained by one or more mechanical stirrers, or by the internal recirculation of the mixture, or by both systems together; petrol or diesel engine with power ranging from 5 to 40 kW for pump operation. Alternatively, the pump can be actuated by the cardan joint of a tractor or of a transporter; self-priming centrifugal pump with a flow rate ranging from 100 to 1000 l / min; several meters long dispensing hose ending with a spear. Alternatively, a rotating distributor like a fire-retardant cannon. The tank opening for loading is equipped with a grid to complete the crushing of the material while loading the tank. The mechanical agitator normally has variable blades connected to a hydraulic system that enables to vary the rotation speed, and reverse the direction to optimize the mixing. The pump has a maximum pressure of 6 bar and allows the passage of solid bodies up to 2 cm. The throw can reach 30-50 m. Hydroseeding with helicopters is used for revegetating (e.g after fires) difficult- to-access mountainous areas. The intervention is justified on areas not less than 5,000 m2, although the best size is estimated around 100,000 m2, which represents, in normal conditions, (low variability of the areas to be treated) the working area in one day of the entire yard. Its limit is the high cost of the yard requiring a fairly complex organization based on the correct choice of tank loading area brought by the helicopter (600- 800 litres capacity). The maintenance of the green on the slopes, regardless of the installation technique, is minimized and is essentially grass cutting. It can be performed with tractor-mounted articulated arms, and equipped with flail-type cutting attachments. Robotic or radio-controlled lawnmowers with low center of gravity can also be used. On small areas, air cushion mowers are also used, dropped down with ropes. Extreme green in the urban environment As we know, urban greenery has not only aesthetic and ornamental functions, but also, increasingly, the function of reducing environmental pollution by thin dust, as well as reducing noise and electromagnetic emissions, and improving the cities climate and microclimate. It also dampens runoff peaks during rains that have become increasingly violent. The use of green rooftop gardens, green roofs and vertical green, besides enhancing these advantages, provides the buildings with a better thermal insulation, thus saving energy both in summer and winter. The function of noise and electromagnetic protection should not be neglected either. With all these advantages, the building gains more market value. Accordingly, we can talk of bioclimatic, aesthetic, naturalistic and even economic benefits arising from interventions and works carried out in compliance with both national and Community building legislation. The green roof covers the flat roofs of buildings, roofs, terraces, and outside floor areas. Hanging gardens are certainly not new. Just think of the hanging gardens of Babylon, one of the seven wonders of the ancient world, and those of the ancient Romans villas. Coming to modernity, the impetus for the creation of green roofs dates back to the middle of the last century following the development of a urban sprawl with little respect for nature. For this reason, and because of repeated heavy rains, also called "water bombs", the green roof is also seen as an element that helps to regulating rainwater outflow. Roofs account for 15-35% of the total surface area of a city, therefore the planting greenery on these surfaces becomes a buffer solution that mitigates the impact of rough rainfalls concentrated in short periods. When constructing a hanging garden, it is essential to maintain a good wan