We wanted to study some of the ecosystem indicators of greenery in the cities of Rome, Florence and Milan with a focus on the absorption capacity from CO2 and the ability to mitigate temperature in summer and winter.
THE TYPES.
TREE SPECIES CENSUS
CO2 QUOTATION
ROME
FLORENCE
MILAN
The Green of the Municipality of Rome
The Green of the Municipality of Rome consists of all the Green Areas that fall within the municipal territory, appropriately surveyed. Subsequently, this figure was related to the Green IN the Municipality of Rome, i.e., all the Green Areas (including those not surveyed) that insist on the municipal territory.
The Census of Tree Species
We selected 15 of the most representative tree species surveyed by the City of Rome in 2016. In addition to identifying the most numerous plants, we were able to indicate which are the most efficient and the most useful. A species is the more efficient the more it is able, on its own, to absorb carbon dioxide; on the other hand, it is useful when it is able to absorb more CO2 than other plants.
| Tree | Numerosity | % | Unit absorption Kg/year CO2 | Total absorption Kg/year CO2 |
| Pinus | 51.212 | 16% | 89 | 4.557.868 |
| Quercus | 38.504 | 12% | 135 | 5.198.040 |
| Robinia | 29.151 | 9% | 111 | 3.235.761 |
| Platanus | 20.853 | 7% | 78 | 1.626.534 |
| Tilia | 15.776 | 5% | 65 | 1.025.440 |
| Ulmus | 14.912 | 5% | 71 | 1.058.752 |
| Acer | 13.352 | 4% | 79 | 1.054.808 |
| Cupressus | 12.752 | 4% | 66 | 841.632 |
| Populus | 8.121 | 3% | 142 | 1.153.182 |
| Eucalyptus | 5.874 | 2% | 150 | 881.100 |
| Cedrus | 3.712 | 1% | 130 | 482.560 |
| Ailanthus | 3.420 | 1% | 99 | 338.580 |
| Olea | 2.563 | 1% | 101 | 258.863 |
| Magnolia | 2.549 | 1% | 54 | 137.646 |
| Celtis | 2.292 | 1% | 66 | 151.272 |
| Total | 225.043 | 72,0% | 1436 | 22.002.038 |
* The remaining 28% are tree species that have an average CO2 uptake rate that is considered insignificant.
MOST USEFUL
IN ROME: OAK
24%
MOST EFFICIENT: EUCALYPTUS
10%
MOST NUMEROUS: PINE
23%
Oak is the most useful plant in Rome because, considering its numbers, it is the one that absorbs the most CO2.
Eucalyptus is the most efficient species because among all plants it is the one that absorbs the most CO2.
Pine is the most numerous species of urban greenery in Rome.
CO2 Quotation.
CO2 is quoted in a similar way as a stock on the stock exchange.
The European Union has adopted the Emission Trading Scheme (ETS) Directive 2003/87/EC, which establishes an EU-wide system for trading CO2 emission allowances. Emission allowances are allocated to companies: the most polluting ones must buy more permits if they want to continue emitting CO2. It is a measurable form of environmental taxation, based on the principle of proportionality and correspondence that ‘the dirtier, the more you pay.’ Based on the census of tree species published by the City of Rome, based on the ability of the species themselves to capture it, we have estimated an economic value, dynamic over time, for the Capitoline territory and its municipalities.
The CO2 Quotation
Economic value of Rome’s municipalities – CO2
Thanks to the tree species census, we cross-referenced the following tree information on the municipalities: numerosity of species by municipality, capacity of species to absorb CO2, and price of CO2. In doing so, we obtained an economic value of the town halls: a theoretical value estimated based on the price of CO2. An example: a manicured tree absorbs more CO2 than an unmanicured tree. If all trees were cared for equally they would be able to absorb more CO2.
Summer and winter
Trees also help to substantially reduce the pollution produced by our heating and cooling systems.
Building on this discussion, using the price of m^3 gas and kWh and cross-referencing it with the ability of each of the tree species considered to reduce pollution, we estimated an additional economic value for winter and one for summer.
WINTER
SUMMER
Green in the Municipality of Rome
The Municipality of Rome manages only part of the tree species in the municipal area. Thanks to satellite data, we analyzed the totality of the trees in the municipality.
The green IN the Municipality of Rome represents the green spaces and trees that the Municipality manages, while the one shown IN the Municipality is the totality of the green on the municipal territory, obtained from satellite images through the analysis of the IZILab tool.
By then aggregating the information on a municipal basis, CO2 absorption was estimated.
Green of the municipality
Green IN the municipality
Trees
Absorption Kg/year CO2
Trees
Absorption Kg/year CO2
Green of the municipality
Trees
Absorption Kg/year CO2
Green IN the municipality
Trees
Absorption Kg/year CO2
The City of Florence
The same analysis conducted on the territory of Rome was carried out for the city of Florence. Focused on the municipal soil and then on the entire provincial area of Florence. The municipal tree density, obtained as the ratio of the area “occupied” by tree crowns to the municipal area, is 20.66% . The lack of tree area within the historic center heavily affects this figure with a reduced level of CO2 uptake.
Average tree density
Municipal management trees
Kg CO2 per inhabitant absorbed per year
The Green in the Municipality of Florence
The City of Florence manages only part of the tree species in the territory.
Thanks to satellite data, we analyzed the totality of the trees in the municipality.
Different is the trend when aggregating the provincial data.
The presence of forests in the eastern part of the province of Florence means that the tree density of the area is almost 50%, resulting in a better CO2 absorption capacity. -Average tree density
Average tree density
Trees for resident
Tg CO2 per resident absorbed per year
The City of Milan
An analysis was also carried out for the municipal territory of Milan thanks to georeferenced images, with the aim of estimating the amount of trees in the area. In the maps depicted we see the distribution of greenery in the center of Milan and the distribution of greenery in the entire municipal area. Milan was one of the first cities, in 2007, to equip itself with a data model to be used for the survey and management of urban greenery in the city of Milan; a model developed by the Polytechnic University of Milan and which has become the de facto standard for the census of greenery.
The Green in the Municipality of Milan
The City of Milan manages only part of the tree species within the municipal area.
With the help of georeferenced satellite images, we analyzed the totality of the trees in the municipality.
Note
methodological
To estimate the amount of trees on the provincial soil, we started from the “Hight Resolution Tree Cover Density 2018” satellite survey of the European project Copernicus, which on a scale from 0 to 100 represents tree canopy density in relation to area with a per-pixel detail of 20 m per side.
A spatial statistic was applied to the georeferenced image preparatory to data modeling by transforming the image into a shapefile. The information was then aggregated by surface-weighted averaging over a hexagonal overlay (of radius 300 m) of the studied area.
Using an estimate based on the tree sampling carried out by the City of Florence on the municipal soil, it was possible to approximate the maximum number of trees present in each hexagon. Starting from the scientific literature regarding the distribution of tree species in the territories studied, the average CO2 uptake per tree was determined.